miun.sePublikationer
Ändra sökning
Avgränsa sökresultatet
1 - 42 av 42
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Andersson, Henrik
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Šuly, Pavol
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion. Tomas Bata University in Zlin, Zlin, Czech Republic.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Zhang, Renyun
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Mašlík, Jan
    Tomas Bata University in Zlin, Zlin, Czech Republic.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    PEDOT: PSS thermoelectric generators printed on paper substrates2019Ingår i: Journal of Low Power Electronics and Applications, ISSN 2079-9268, Vol. 9, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Flexible electronics is a field gathering a growing interest among researchers and companies with widely varying applications, such as organic light emitting diodes, transistors as well as many different sensors. If the circuit should be portable or off-grid, the power sources available are batteries, supercapacitors or some type of power generator. Thermoelectric generators produce electrical energy by the diffusion of charge carriers in response to heat flux caused by a temperature gradient between junctions of dissimilar materials. As wearables, flexible electronics and intelligent packaging applications increase, there is a need for low-cost, recyclable and printable power sources. For such applications, printed thermoelectric generators (TEGs) are an interesting power source, which can also be combined with printable energy storage, such as supercapacitors. Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate), or PEDOT:PSS, is a conductive polymer that has gathered interest as a thermoelectric material. Plastic substrates are commonly used for printed electronics, but an interesting and emerging alternative is to use paper. In this article, a printed thermoelectric generator consisting of PEDOT:PSS and silver inks was printed on two common types of paper substrates, which could be used to power electronic circuits on paper. 

    Ladda ner fulltext (pdf)
    fulltext
  • 2.
    Balliu, Enkeleda
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Forsberg, Sven
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Laser-assisted reduction of graphene oxide for paper based large area flexible electronics2016Ingår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2016, Vol. 9736, artikel-id 973610Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this work we present a promising method for fabrication of conductive tracks on paper based substrates by laser assisted reduction of Graphene Oxide (GO). Printed electronics on paper based substrates is be coming more popular due to lower cost and recyclability. Fabrication of conductive tracks is of great importance where metal, carbon and polymer inks are commonly used. An emerging option is reduced graphene oxide (r-GO), which can be a good conductor. Here we have evaluated reduction of GO by using a 532 nm laser source, showing promising results with a decrease of sheet resistance from >100 M Ω/Sqr for unreduced GO down to 126 Ω/Sqr. without any observable damage to the paper substrates.

  • 3.
    Balliu, Enkeleda
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Öhlund, Thomas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Selective laser sintering of inkjet-printed silver nanoparticle inks on paper substrates to achieve highly conductive patterns2018Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, nr 1, artikel-id 10408Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Development of cost-effective and environmentally friendly manufacturing methods will enable important advances for the production of large-scale flexible electronics. Laser processing has shown to be a promising candidate that offers a fast and non-destructive way to produce highly conductive patterns on flexible substrates such as plastics. However, an emerging option with a lower environmental impact is instead the use of cellulose-based flexible substrates, such as paper. In this work we investigate the use of laser sintering of silver nanoparticle inks, which were inkjet-printed on three different types of paper. Patterns with a high conductivity could be manufactured where a special care was taken to prevent the substrates from damage by the intense laser light. We found that the best results was obtained for a photopaper, with a conductivity of 1.63 107 S/m corresponding to nearly 26% of the bulk silver conductivity. In addition, we demonstrate laser sintering to fabricate a fully functional near field communication tag printed on a photopaper. Our results can have an important bearing for the development of cost-effective and environmentally friendly production methods for flexible electronics on a large scale. 

    Ladda ner fulltext (pdf)
    fulltext
  • 4.
    Balliu, Enkeleda
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Hummelgård, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Laser sintering of silver nano-particles inks printed on paper substrates2015Ingår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2015, s. Art. no. 935112-Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this work we have investigated the use of laser sintering of different ink-jet printed nano-particle inks (NPIs) on paper substrates. Laser sintering is shown to offer a fast and non-destructive way to produce paper based printed electronics. A continuous wave fiber laser source at 1064 nm is used and evaluated in combination with a galvo-scanning mirror system. A conductivity in order of 2.16 ∗ 107 S/m is reached for the silver NPI structures corresponding to nearly 35 % conductivity compared to that of bulk silver and this is achieved without any observable damage to the paper substrate. © 2015 SPIE.

  • 5.
    Balliu, Enkeleda
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Hellström, J.
    Cobolt AB, SE-171 54 Solna, Sweden.
    Elgcrona, G.
    Cobolt AB, SE-171 54 Solna, Sweden.
    Karlsson, H.
    Cobolt AB, SE-171 54 Solna, Sweden.
    Compact nanosecond pulsed single stage Yb-doped fiber amplifier2014Ingår i: Proceedings of SPIE - The International Society for Optical Engineering, 2014, s. Art. no. 895910-Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this work we present a compact, nanosecond pulsed, single frequency, single stage Yb-doped fiber amplifier by using an overall fiber core diameter of 20 μm. The key component is a custom made, compact, ultra-low noise, single frequency ring-cavity solid state laser (SSL) at 1064 nm used as a master oscillator. The SSL can be designed to provide nanosecond pulses with pulse energies in the sub-mJ range. Our ultimate goal is to develop a compact linearly polarized, single frequency, nanosecond pulsed laser source in an all-fiber format. Short (less than 1m), highly Yb-doped fibers have been used in order to suppress non-linear effects. © 2014 SPIE.

  • 6.
    Balliu, Enkeleda
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    A compact, single-frequency, high-power, SBS-free, Yb-doped single-stage fiber amplifier2019Ingår i: Proceedings of SPIE - The International Society for Optical Engineering / [ed] W. Andrew Clarkson and Ramesh K. Shori, SPIE - International Society for Optical Engineering, 2019, Vol. 10896, s. 6pp-, artikel-id 1089618Konferensbidrag (Refereegranskat)
    Abstract [en]

    Interest in compact, single-frequency fiber amplifier has increased within many scientific and industrial applications. The main challenge is the onset of nonlinear effects, which limit their power scaling. Here we demonstrate a compact, high-power, single-frequency, polarization-maintaining, continous-wave fiber amplifier using only one amplification stage. We developed the fiber amplifier using a master oscillator fiber amplifier architecture, where a low-noise, single-frequency, solid-state laser operating at 1064 nm was used as a seed source. We evaluated the amplifier's performance by using several state-of-the-art, small-core, Ytterbium (yb)-doped fibers, as well as an in-house-made, highly Yb-doped fiber. An output power of 82 W was achieved with no sign of stimulated Brillouin scattering. A good beam quality and a polarization extinction ratio (PER) of > 25 dB were achieved. The compact fiber amplifier can be a competitive alternative to multi stage designed fiber amplifiers.

  • 7.
    Edvardsson, Sverker
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Karlsson, K. G.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Accurate spin axes and solar system dynamics: climatic variations for the Earth and Mars2002Ingår i: Astronomy & Astrophysics, ISSN 0004-6361, Vol. 384, nr 2, s. 689-701Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Celestial mechanical simulations from a purely classical point of view of the solar system, including our Moon and the Mars moons {Phobos and Deimos {are carried out for 2 millions of years before present. Within the classical approximation, the results are derived at a very high level of accuracy. Effects from general relativity for a number of variables are investigated and found to be small. For climatic studies of about 1 Myr, general relativity can safely be ignored. Three different and independent integration schemes are used in order to exclude numerical anomalies. The converged results from all methods are found to be in complete agreement. For verification, a number of properties such as spin axis precession, nutation, and orbit inclination for Earth and Mars have been calculated. Times and positions of equinoxes and solstices are continously monitored. As also observed earlier, the obliquity of the Earth is stabilized by the Moon. On the other hand, the obliquity of Mars shows dramatic variations. Climatic influences due to celestial variables for the Earth and Mars are studied. Instead of using mean insolation as in the usual applications of Milankovitch theory, the present approach focuses on the instantaneous solar radiation power (insolation) at each summer solstice. Solar radiation power is compared to the derivative of the icevolume and these quantities are found to be in excellent agreement. Orbital precessions for the inner planets are studied as well. In the case of Mercury, it is investigated in detail.

  • 8.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Materials optimization for optical fiber amplifiers and fiber lasers2008Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
  • 9.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Hammarling, Krister
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Sandberg, Mats
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion. RISE Acreo.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    A Bio-Compatible Fiber Optic pH Sensor Based on a Thin Core Interferometric Technique2019Ingår i: Photonics, ISSN 2304-6732, Vol. 6, nr 1, artikel-id 11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There is an increasing demand for compact, reliable and versatile sensor concepts for pH-level monitoring within several industrial, chemical as well as bio-medical applications. Many pHsensors concepts have been proposed, however, there is still a need for improved sensor solutionswith respect to reliability, durability and miniaturization but also for multiparameter sensing. Here wepresent a conceptual verification, which includes theoretical simulations as well as experimentalevaluation of a fiber optic pH-sensor based on a bio-compatible pH sensitive material not previouslyused in this context. The fiber optic sensor is based on a Mach-Zehnder interferometric technique,where the pH sensitive material is coated on a short, typically 20-25 mm thin core fiber splicedbetween two standard single mode fibers. The working principle of the sensor is simulated by usingCOMSOL Multiphysics. The simulations are used as a guideline for the construction of the sensorsthat have been experimentally evaluated in different liquids with pH ranging from 1.95 to 11.89. The results are promising, showing the potential for the development of bio-compatible fiber optic pH sensor with short response time, high sensitivity and broad measurement range. The developedsensor concept can find future use in many medical- or bio-chemical applications as well as inenvironmental monitoring of large areas. Challenges encountered during the sensor developmentdue to variation in the design parameters are discussed.

    Ladda ner fulltext (pdf)
    fulltext
  • 10.
    Engholm, Magnus
    et al.
    Fiber Optic Valley AB.
    Jelger, P.
    KTH.
    Laurell, F.
    KTH.
    Norin, L.
    Acreo FiberLab.
    Improved photodarkening resistivity in ytterbium-doped fiber lasers by cerium codoping2009Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, nr 8, s. 1285-1287Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We show that the photodarkening resistivity of ytterbium-doped fiber lasers can be greatly improved by cerium codoping. It is suggested that the coexistence of the redox couple Ce3+⁄Ce4+ in the glass provides means for trapping both hole- and electron-related color centers that are responsible for the induced optical losses in Yb-doped fiber lasers.

  • 11.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Lashgari, K.
    Edvardsson, Sverker
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Westin, G.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Atomically designed precursors in optical fiber amplifiers: The thermal stability of the heteroimetallic ErAl_3(OPri)_12 in a solution-coated silica soot2005Ingår i: Journal of Applied Physics, ISSN 0021-8979, Vol. 97, nr 11, s. 113104-Artikel i tidskrift (Refereegranskat)
  • 12.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Comment on:"Photodarkeningin Yb-doped aluminosilicate fiber induced by 488nm irradiation"2007Ingår i: Optical Letter, ISSN 0146-9592, Vol. 33, nr 11, s. 1216.-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present some strong evidence against the assignment of an ytterbium-related oxygen deficiency center (ODC) near 230 nm in Yb-doped aluminosilicate glass in the Letter by Yoo

  • 13.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Divalent Ytterbium in Ytterbium Doped Aluminosilicate Glass - Aspects on Photodarkening in Fiber Lasers2007Ingår i: 2007 CONFERENCE ON LASERS & ELECTRO-OPTICS/QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE (CLEO/QELS 2007), VOLS 1-5, New York: IEEE conference proceedings, 2007, s. 1902-1903Konferensbidrag (Refereegranskat)
    Abstract [en]

    We show that divalent ytterbium ions are present in ytterbium doped aluminosilicate glass. The presence of Yb^2+-ions may influence the formation of induced color centers in ytterbium doped fiber lasers leading to reduced performance.

  • 14.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Materials optimization for ytterbium-doped high power fiber lasers2008Ingår i: 2008 CONFERENCE ON LASERS AND ELECTRO-OPTICS & QUANTUM ELECTRONICS AND LASER SCIENCE CONFERENCE, VOLS 1-9, New York: IEEE conference proceedings, 2008, s. 232-233Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we will present paths to reduce the extent of photodarkening in ytterbium. doped fiber lasers based on the aluminosilicate glass matrix. This will enable higher powers and longer operating lifetimes.

  • 15.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Preventing Photodarkening in Ytterbium-Doped High Power Fiber Lasers; Correlation to the UV-Transparency of the Core Glass2008Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 16, nr 2, s. 1260-1268Artikel i tidskrift (Refereegranskat)
    Abstract [en]

     

    Photodarkening experiments are performed on ytterbium-doped silicate glass

    samples. A strong charge-transfer (CT) absorption band near 230nm in

    aluminosilicate glass is found to be correlated to the mechanism of induced

    color center formation. Excitation into the CT-absorption band generates

    similar color centers as observed in ytterbium-doped fiber lasers under

    915nm high power diode pumping. The position of the CT-absorption band is

    compositional dependent and is shifted to shorter wavelengths in ytterbium

    doped phosphosilicate glass. Very low levels of photodarkening is observed

    for the ytterbium doped phosphosilicate glass composition under 915nm high

    power diode pumping. Possible excitation routes to reach the CT-absorption

    band under 915nm pumping are discussed.

     

  • 16.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier. Acreo FiberLab, Sweden.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Reduction of photodarkening in Yb/Al-doped fiber lasers2008Ingår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2008, s. U269-U276Konferensbidrag (Refereegranskat)
    Abstract [en]

    A strong charge-transfer band at UV-wavelengths is found to play a major role for the observed induced optical losses (photodarkening) in ytterbium doped high-power fiber lasers. This is correlated to the valence stability of the ytterbium ion in the silicate glass matrix, which we believe is the origin of photodarkening. We have performed UV-irradiation experiments on ytterbium-doped preform samples and accelerated photodarkening experiments on Yb-doped fibers, by using 915nm high power diodes. Our results show that photodarkening can be reduced, to low levels, either by preparing the preform glass in a reducing atmosphere or by hydrogen loading the fiber in a pressure chamber at room temperature.

  • 17.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Strong UV absorption and visible luminescence in ytterbium-doped aluminosilicate glass under UV excitation2007Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 32, nr 22, s. 3352-3354Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A broad visible luminescence band and characteristic IR luminescence of Yb3+ ions are observed under UV excitation in ytterbium-doped aluminosilicate glass. Samples made under both oxidizing and reducing conditions are analyzed. A strong charge-transfer absorption band in the UV range is observed for glass samples containing ytterbium. Additional absorption bands are observed for the sample made under reducing conditions, which are associated with f�d transitions of divalent ytterbium. The visible luminescence band is attributed to 5d�4f emission from Yb2+ ions, and the IR luminescence is concluded to originate from a relaxed charge-transfer transition. The findings are important to explain induced optical losses (photodarkening) in high-power fiber lasers.

  • 18. Engholm, Magnus
    et al.
    Norin, Lars
    Acreo FiberLab AB.
    The role of charge transfer processes for the induced optical lossesin ytterbium doped fiber lasers2009Ingår i: The role of charge transfer processes for the induced optical lossesin ytterbium doped fiber lasers, 2009, Vol. 7195, nr 71950TKonferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present how charge transfer processes influences the induced optical losses (photodarkening) in ytterbium doped fiber lasers. The location of the charge transfer absorption band is strongly composition dependent and is correlated to the valence stability of the ytterbium ion in the silicate glass matrix. An improved photodarkening performance can in general be observed for a charge-transfer band shifted to shorter wavelengths, although other routes are also possible to reduce photodarkening. Other parameters that affect the laser performance, such as absorption and emission cross section, must also be considered.

  • 19.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Edvardsson, Sverker
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Lashgari, K.
    Uppsala University.
    Westin, G.
    Uppsala University.
    A structural investigation of a synthesized precursor for fiber optical applications; the heterobimetallic ErNb_2(OPr^i)_132006Ingår i: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 29, nr 4, s. 386-391Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A structural investigation of a synthesized precursor in a silica glass matrix is performed. Silica soot samples are doped with the heterobimetallic precursor ErNb2(OPri)13 by using a conventional solution doping technique and heat treatments to different temperatures. The precursor has also been introduced into a silica fiber preform by using the modified chemical vapor deposition technique. Analyses are made by using ultraviolet–visible–near infrared absorption spectroscopy, scanning electron microscopy, energy dispersive spectroscopy and powder X-ray diffraction. It is concluded that an immiscible system of ErNbO4 crystallites and Nb2O5 is formed in the silica soot samples at high temperatures. Colloidal particles of ErNbO4 are also formed in the silica glass fiber preform showing interesting features.

  • 20.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Rydberg, Sara
    Hammarling, Krister
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Strong excited state absorption (ESA) in Yb-doped fiber lasers2013Ingår i: FIBER LASERS X: TECHNOLOGY, SYSTEMS, AND APPLICATIONS, SPIE - International Society for Optical Engineering, 2013, s. Art. no. 86010P-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Excited state absorption (ESA) measurements performed on Yb-doped silica bers show the onset of a strong absorption band in the visible range. In this work, we perform experiments to investigate the possibility for ESA to be part of the induced optical losses (photodarkening) observed in Yb-doped ber lasers. Our results indicate that an ESA process, from the 2F5/2 excited state manifold in the Yb3+ ion to the charge-transfer state with absorption bands in the UV range, may constitute a transfer route for pump- and laser photons in the near-infrared range. © 2013 Copyright SPIE.

  • 21.
    Engholm, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Vanin, E
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Characterization of Erbiuim Crystallites Embedded in Silica GlassManuskript (Övrig (populärvetenskap, debatt, mm))
  • 22.
    Forsberg, Viviane
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Zhang, Renyun
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Hummelgård, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Norgren, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för kemiteknik.
    Photodetector of multilayer exfoliated MoS2 deposited on polyimide films2018Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We fabricated a photodetector based on multilayer molybdenum disulfide (MoS2) by micromechanical cleavage of a molybdenite crystal using a polyimide film. We deposited 40 nm of gold by vacuum sputtering and copper tape was used for the contacts.  Without any surface treatment, we achieved high responsivity at different incident optical power. The calculated responsivity was 23 mA/W of incident optical power in the range between 400 and 800 nm. For the responsivity measurement it was estimated that MoS2 have a bandgap of 1.6 eV, which lies between monolayer and multilayer films. The thickness of the MoS2 thin film was determined by Raman spectroscopy evaluating the difference between the in plane  and out of plane  Raman modes. The measurement of IV curves indicated Ohmic contacts in respect to the Au regardless of the incident optical power. Our device fabrication was much simpler than previous reported devices and can be used to test the light absorption and luminescence capabilities of exfoliated MoS2.

  • 23.
    Hammarling, Krister
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Sandberg, Mats
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion. RISE Acreo AB, Bredgatan 33, 601 17 Norrköping, Sweden.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Broad-Range Hydrogel-Based pH Sensor with Capacitive Readout Manufactured on a Flexible Substrate2018Ingår i: Chemosensors, ISSN 2227-9040, Vol. 6, nr 3, s. 15artikel-id 30Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Environmental monitoring of land, water and air, is an area receiving greater attention because of human health and safety concerns. Monitoring the type of pollution and concentration levels is vital, so that appropriate contingency plans can be determined. To effectively monitor the environment, there is a need for new sensors and sensor systems that suits these type of measurements. However, the diversity of sensors suitable for low, battery powered- and large area sensor systems are limited. We have manufactured and characterized a flexible pH sensor using laser processing and blade coating techniques that is able to measure pH between 2.94 and 11.80. The sensor consists of an interdigital capacitance with a pH sensitive hydrogel coating. Thin sensors can reach 95% of their final value value within 3 min, and are stable after 4 min. Good repeatability was achieved in regard to cycling of the sensor with different pH and multiple measurements from dry state. We have also studied the relation between an interdigital capacitance penetration depth and hydrogels expansion. We believe that our passive sensor is suitable to be used in low power and large area sensor networks.

    Ladda ner fulltext (pdf)
    fulltext
  • 24.
    Hammarling, Krister
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Muri, Harald Ian
    NTNU, Trondheim, Norway.
    Wahl, Markus Solberg
    NTNU, Trondheim, Norway.
    Hjelme, Dag Roar
    NTNU, Trondheim, Norway.
    Dual parameter fiber optic sensor combining a Fabry-Perot and a Mach-Zehnder interferometer2017Ingår i: Proceedings of IEEE Sensors, IEEE, 2017, s. 1440-1442Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A new concept for dual parameter fiber optic sensorhas been developed and characterized, both in a two-fiber andsingle-fiber configuration. The liquid sensor measures ethanolconcentration with a stimuli responsive hydrogel whichconstitutes a low finesse Fabry-Perot cavity, and refractive indexwith a Mach-Zehnder type fiber optic interferometer. The two-fiber configuration utilize a fiber optic 1310/1550 nm wavelengthdivision multiplexer to separate the two parameters, while aversatile filtering algorithm extracts and separates the twoparameters in the single-fiber configuration. No cross talk wereobserved for the measured parameters of free spectral range andrefractive index for the two-fiber configurations, while for thesingle fiber configuration cross-talk were observed. The twoconfigurations prove to be versatile dual parametric fiber opticsensor concepts for accurate detection of specific parameters,based on stimuli responsive hydrogels.

  • 25.
    Hammarling, Krister
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Muri, Harald Ian
    NTNU.
    Wahl, Markus Solberg
    NTNU.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Hjelme, Dag Roar
    NTNU.
    A combined glucose and pH sensor on a single optical fiber for continuous point-of-care testing2018Ingår i: SPIE BIOS, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII, SPIE - International Society for Optical Engineering, 2018Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    Stress-induced hyperglycemia is very common for patients in intensive care units, which can become fatal if left uncontrolled. Blood glucose concentrations for patients at the intensive care units should therefore be monitored at all times. To be successful in monitoring the glucose concentrations of patients, the sensor needs to be fast, accurate and able to measure in real time. In addition, the pH level should be monitored, as a diagnostic parameter by itself, or to improve the reliability of the glucose measurement. To address this challenge, a fiber optic sensor for dual parameter measurement of glucose concentration and pH level for use in point-of-care testing has been developed. The sensor utilizes two stimuli responsive hydrogels to create two interferometers combined on one single mode fiber. The sensor is created by splicing a short section of thin-core fiber (SM450) coated with a pH-sensitive polymer, which constitutes a Mach-Zehnder type interferometer. The glucose is measured with a low finesse Fabry-Perot cavity made by polymerizing a glucose sensitive hydrogel hemisphere at the end face of the fiber. A versatile Fourier transform based, low pass filter was developed, which enable evaluation of the two signals independently. Our results show the feasibility of measuring glucose concentration and pH level by using a single fiber. This dual parameter and single point fiber optic biosensor is expected to be of great interest for in vivo measurements in medical applications where pH and glucose, as specific markers are monitored in real time, during or after surgery.

  • 26.
    Hammarling, Krister
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Sandberg, Mats
    RISE Acreo AB, Norrköping.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Synthesis, Curing Behavior and Swell Tests of pH-Responsive Coatings from Acryl-Terminated Oligo(beta-Amino Esters)2018Ingår i: CHEMOSENSORS, ISSN 2227-9040, Vol. 6, nr 1, artikel-id 10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ability of acryl-terminated oligo(beta-amino esters) (AOBAE) to be coated on fibers and printed electronics without solvents and to be cross-linked to a pH-responsive coatings, makes AOBAE-based coatings a potential type of pH-sensor coating. However, there are currently no reports of AOBAEs used as a pH-responsive coating material in sensor applications. Here we present an investigation of the synthesis, curing behavior and swell tests of AOBAEs. AOBAEs were synthesized from reacting an excess of asymmetric diacrylates with piperazine without the use of any solvents. They were then cross-linked to an insoluble network by UV-curing. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the AOBAEs. NMR was used to clarify the irregular structure of the AOBAE. FTIR was used to monitor the effects of UV-curing dose and air exposure on monomer conversion during curing. An interferometric technique was used to monitor the swelling behavior of the coating in response to pH variations. Swell experiments showed that the AOBAE also responded to pH variations after polymerization. Therefore, AOBAE is an interesting class of material with potential use as a pH responsive coating in optical-and printed electronics pH-sensors applications.

    Ladda ner fulltext (pdf)
    fulltext
  • 27. Knall, J. M.
    et al.
    Vigneron, P. -B
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Dragic, P. D.
    Yu, N.
    Ballato, J.
    Bernier, M.
    Digonnet, M.
    Experimental observation of cooling in Yb-doped silica fibers2020Ingår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2020Konferensbidrag (Refereegranskat)
    Abstract [en]

    Anti-Stokes fluorescence cooling in a silica-based fiber is reported for the first time. The fiber had a core with a 20-μm diameter doped with 2.06 wt.% Yb and co-doped with 0.86 wt.% Al and 0.88 wt.% F. Core-pumping the fiber with 1040- nm light, temperature changes as large at -50 mK were measured at atmospheric pressure. Temperature measurements were performed at 12 pump wavelengths, and the measured dependence of the temperature change as a function of pump wavelength was in excellent agreement with a previously reported model. With this model, the absorptive loss in the fiber was inferred to be less than 15 dB/km, and the critical quenching concentration to be ∼15.6 wt.% Yb. This combination of low loss and high quenching concentration (a factor of 16 times higher than the highest reported values for Yb-doped silica) is what allowed the observation of cooling. The temperature measurements were performed at atmospheric pressure using a custom slow-light fiber Bragg grating sensor with an improved thermal contact between the test fiber and the FBG. The improved method involves isopropanol to establish a good thermal contact between the two fibers. This eliminated a source of heating and enabled more accurate measurements of the cooled-fiber temperature. This improved temperaturemeasurement set-up also led to a new cooling record in a multimode Yb-doped ZBLAN fiber at atmospheric pressure. When pumped at 1030 nm, the fiber cooled by -3.5 K, a factor of 5.4 times higher than the previous record. 

  • 28.
    Knall, Jennifer
    et al.
    Stanford University, Stanford, CA, United States.
    Vigneron, Pierre-Baptiste
    Stanford University, Stanford, CA, United States.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Dragic, Peter D.
    University of Illinois at Urbana-Champaign, Urbana, IL, United States.
    Yu, Nanjie
    University of Illinois at Urbana-Champaign, Urbana, IL, United States.
    Ballato, John
    Clemson University, Clemson, SC, United States.
    Bernier, Martin
    Université Laval, Québec, QC, Canada.
    Digonnet, Michel J. F.
    Stanford University, Stanford, CA, United States.
    Laser cooling in a silica optical fiber at atmospheric pressure2020Ingår i: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 45, nr 5, s. 1092-1095Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For the first time, to the best of our knowledge, laser cooling is reported in a silica optical fiber. The fiber has a 21-μm diameter core doped with 2.06 wt.% YbM3+ and co-doped with Al2O3 and F- to increase the critical quenching concentration by a factor of 16 over the largest reported values for the Yb-doped silica. Using a custom slow-light fiber Bragg grating sensor, temperature changes up to -50 mK were measured with 0.33 W/m of absorbed pump power per unit length at 1040 nm. The measured dependencies of the temperature change on the pump power and the pump wavelength are in excellent agreement with predictions from an existing model, and they reflect the fiber's groundbreaking quality for the radiation-balanced fiber lasers. 

  • 29. Lashgari, K
    et al.
    Kritikos, M
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Norin, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Edvardsson, Sverker
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Westin, G
    Sol-gel preparation of Er-doped planar and fibre wave-guides using heterometallic2006Ingår i: SPIE conference, San Diego (2006)., 2006Konferensbidrag (Övrigt vetenskapligt)
  • 30.
    Maslik, Jan
    et al.
    Tomas Bata University in Zlin, Czech Republic.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Forsberg, Viviane
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Zhang, Renyun
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    PEDOT:PSS temperature sensor ink-jet printed on paper substrate2018Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 13, artikel-id C12010Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    In this work we present an ink-jet printed temperature sensor consisting of PEDOT:PSSprinted on paper suitable for packaging, flexible electronics and other printed applications. Thesubstrate showed to have a large influence on both the resistance aswell as the temperature sensitivityof the PEDOT:PSS ink. This effect is most likely due to NaCl content in the photo paper coating,which reacts with the PEDOT:PSS. The temperature coefficient of a prepared device of  α= -0.030 relative to room temperature (22°C) was measured, which is higher than compared to for exampleSilicon α = -0.075.

  • 31.
    Mazlik, Jan
    et al.
    Tomas Bata University.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Forsberg, Viviane
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Zhang, Renyun
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Temperature sensor based on PEDOT: PSS ink-jet printed on paper substrate2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    Printed electronics is rapidly developing, where more and more components are printable. High speed roll-to-roll processesare preferred for low cost production of flexible electronics. Often, the substrates used for printed electronics are some typeof plastic such as PET or Kapton. An alternative to plastic is to use paper substrate that has the benefits of beingenvironmentally friendly, recyclable and renewable. Paper is also the material of choice for packages of various goods.In this work we have developed an ink-jet printable temperature sensor, a thermistor, consisting ofpoly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)( PEDOT:PSS) on paper substrate. The starting material is acommercial PEDOT:PSS ink-jet ink (Orgacon IJ-1005, Agfa). This ink was then modified to increase the thermal sensitivityby addition of the co-solvents Dimethyl sulfoxide (DMSO) and Polyethylene glycol (PEG) in different quantities. DMSO hasbeen shown to increase the conductance by arranging the PEDOT into more conductive pathways and by removing PSS[1] and PEG to increase the carrier density and mobility [2].The sensors consisted of modified PEDOT:PSS lines printed on photo-paper substrate between contacts printed usingsilver nano-particle ink. The line widths were varied from one pixel, corresponding to one pass of one nozzle up-to 20pixels. The linewidths were then measured to be from 45 μm up-to 450 μm. The thickness of the sensor was also varied asone, two or three printed layers. The characterization as a temperature sensor was performed by using a setup consistingof a Peltier cooler and a heating element to step the temperature. As a reference a PT-100 element fixed to the surface ofthe cooler/heater was used.An increase in resistance from 30.5 MΩ to 85 MΩ, corresponding to a change of 2.8 times, were measured when thetemperature were changed from 22 °C to -12 °C as can be seen in the figure. This gives a ΔR/ΔT of 0.093.Such a printed sensor can be used for applications where a low cost, printable solution is needed, such as printed directlyon packages, for environmental monitoring and similar.[1] C.S. Pathak, J.P. Singh, R. Singh, Effect of dimethyl sulfoxide on the electrical properties of PEDOT:PSS/ n-Siheterojunction diodes, Current Applied Physics, 15, (2015), 528-534[2] Yow-Jon Lin, Wei-Shih Ni and Jhe-You Lee, Effect of incorporation of ethylene glycol into PEDOT:PSS on electronphonon coupling and conductivity, Journal of Applied Physics 117, (2015), 215501

  • 32.
    Muri, H. I.
    et al.
    Norwegian University of Science and Technology, Trondheim, Norway.
    Hammarling, Krister
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Wahl, M.
    Norwegian University of Science and Technology, Trondheim, Norway.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Hjelme, D. R.
    Norwegian University of Science and Technology, Trondheim, Norway.
    Combining interferometric sensors for dual parameter fiber optic chemical sensing2018Ingår i: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018, artikel-id WF80Konferensbidrag (Refereegranskat)
    Abstract [en]

    Long and short path length differences interferometric sensing modalities have been combined based on immobilizing hydrogel on thin-core optical fiber end face. Dual parameter sensing of hydrogel swelling and refractive index was demonstrated.

  • 33.
    Norin, L.
    et al.
    Fiber Optics, Acreo Swedish ICT AB, SE-824 42 Hudiksvall, Sweden.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    On the origin of color centers in photodarkened Yb-fibers2013Ingår i: Optics InfoBase Conference Papers, 2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    Photodarkening spectra were studied for Yb-fibers co-doped with Al, Al/Ce or Al with H2-loading and it is proposed that the pump-induced color centers in Yb/Al-doped silica fibers mainly consist of Yb2+ and AlOHC.

  • 34.
    Rydberg, Sara C.
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Photodarkening mechanisms in ytterbium fiber lasers; a comparison of UV-induced losses in glass and crystalline materials2012Ingår i: 2012 Conference on Lasers and Electro-Optics, CLEO 2012, 2012, s. Art. no. 6326558-Konferensbidrag (Refereegranskat)
    Abstract [en]

    UV-induced absorption is investigated for three different ytterbium doped laser materials. It is found that the induced transmission loss originates from the formation of Yb 2+-ions and hole-related defects. 

  • 35.
    Rydberg, Sara
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Charge transfer processes and UV induced absorption in Yb:YAG single crystal laser materials2013Ingår i: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 113, nr 22, s. Art. no. 223510-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Charge transfer (CT) transitions and UV induced color centers in Yb:YAG single crystals have been investigated. A simultaneous pair formation of a stable Yb2+ ion and a hole related (O -) color center (hole polaron) are observed through a CT-process. Slightly different types of hole related color centers are formed in Yb:YAG crystals containing small levels of iron impurities. Furthermore, excitation spectroscopy on the UV irradiated Yb:YAG samples could confirm an energy transfer process between Yb3+ and Yb2+ ions. The findings are important for an increased knowledge of the physical loss mechanisms observed in Yb-doped laser materials, such as the nonlinear decay process in Yb:YAG crystals as well as the photodarkening phenomenon in Yb-doped fiber lasers.

    Ladda ner fulltext (pdf)
    Rydberg_Charge_transfer_processes
  • 36.
    Rydberg, Sara
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Experimental evidence for the formation of divalent Ytterbium in the photodarkening process of Yb-doped fiber lasers2013Ingår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, nr 6, s. 6681-6688Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work we present experimental evidence that the valence instability of the ytterbium ion play a key role for the observed photodarkening mechanism in Yb-doped fiber lasers. Luminescence and excitation spectroscopy performed on UV irradiated Yb/Al doped silica glass preforms and near-infrared diode pumped photodarkened fibers show a concentration increase of Yb2+ ions. A concentration decrease in Yb3+ could also be observed for the UV irradiated preform. The findings contribute to an increased understanding of the kinetic processes related to photodarkening in Yb-doped high power fiber lasers.

    Ladda ner fulltext (pdf)
    Rydberg_Experimental_evidence
  • 37.
    Zeil, P.
    et al.
    Laser Physics, KTH, Royal Institute of Technology, 106 91 Stockholm, Sweden.
    Malmstrom, M.
    Laser Physics, KTH, Royal Institute of Technology, 106 91 Stockholm, Sweden.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Jelger, P.
    Laser Physics, KTH, Royal Institute of Technology, 106 91 Stockholm, Sweden.
    Jacobsson, B.
    Laser Physics, KTH, Royal Institute of Technology, 106 91 Stockholm, Sweden.
    Pasiskevicius, V.
    Laser Physics, KTH, Royal Institute of Technology, 106 91 Stockholm, Sweden.
    Laurell, F.
    Laser Physics, KTH, Royal Institute of Technology, 106 91 Stockholm, Sweden.
    Extended tunability of narrow-linewidth Yb-fiber laser2011Ingår i: 2011 Conference on Lasers and Electro-Optics: Laser Science to Photonic Applications, CLEO 2011, IEEE conference proceedings, 2011, s. Art. no. 5950619-Konferensbidrag (Refereegranskat)
    Abstract [en]

    We report on a tunable ytterbium-doped fiber laser bridging the gap from three-level lasing around 980 nm to true four-level lasing at 1066 nm. Wavelength-locking and -tuning was achieved by an external volume-Bragg grating (VBG). Results are compared with a numerical analysis based on a spectrally resolved rate equation analysis. 

  • 38.
    Zhang, Renyun
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Recent Progress on the Fabrication and Properties of Silver Nanowire-Based Transparent Electrodes2018Ingår i: Nanomaterials, ISSN 2079-4991, Vol. 8, nr 8, artikel-id 628Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transparent electrodes (TEs) made of metallic nanowires, such as Ag, Au, Cu, and Ni, are attracting increasing attention for several reasons: (1) they can act as a substitute for tin oxide-based TEs such as indium-tin oxide (ITO) and fluorine-doped tin oxide (FTO); (2) various methods exist for fabricating such TEs such as filtration, spraying, and Meyer bar coating; (3) greater compatibility with different substrates can be achieved due to the variety of fabrication methods; and (4) extra functions in addition to serving as electrodes, such as catalytic abilities, can be obtained due to the metals of which the TEs are composed. There are a large number of applications for TEs, ranging from electronics and sensors to biomedical devices. This short review is a summary of recent progress, mainly over the past five years, on silver nanowire-based TEs. The focus of the review is on theory development, mechanical, chemical, and thermal stability as well as optical properties. The many applications of TEs are outside the scope of this review.

    Ladda ner fulltext (pdf)
    fulltext
  • 39.
    Zhang, Renyun
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Hummelgård, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Örtegren, Jonas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    High-performance transparent and flexible electrodes made by flash-light sintering of gold nanoparticles2018Ingår i: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 1, nr 12, s. 7191-7198Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Metallic nanowire-based transparent electrodes (TEs) are potential alternatives to indium tin oxide (ITO). To achieve a high performance [sheet resistance (Rs) < 100 Ω/sq, transmittance (T%) > 90%], the nanowires must have a high length-to-diameter (L/D) ratio to minimize the number of wire-to-wire junctions. Attempts to produce TEs with gold nanowires have been made, and the results reveal difficulties in achieving the requirements. A successful strategy involves creating templated gold nanonetworks through multiple procedures. Here, we present a simple and efficient method that uses flash-light sintering of a gold nanonetwork film into gold TEs (Rs: 82.9 Ω/sq, T %: 91.79%) on a thin polycarbonate film (25 μm). The produced gold TEs have excellent mechanical, electrical, optical, and chemical stabilities. Mechanisms of the formation of gold nanonetworks and the effect of flash-light have been analyzed. Our findings provide a scalable process for producing transparent and flexible gold electrodes with a total processing time of less than 8 min without the use of heating, vacuum processing, and organic chemicals and without any material loss. This is possible because all the gold nanoparticles have been aggregated and filtrated on the filter membranes. The area density of gold is 0.094 g/m2 leading low material costs, which is very competitive with the price of commercial TEs.

  • 40.
    Zhang, Renyun
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Hummelgård, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Forsberg, Viviane
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Öhlund, Thomas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olsen, Martin
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Örtegren, Jonas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Photoconductivity of acid exfoliated and flash-light-processed MoS2 films2018Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikel-id 3296Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    MoS2 has been studied intensively during recent years as a semiconducting material in several fields, including optoelectronics, for applications such as solar cells and phototransistors. The photoresponse mechanisms of MoS2 have been discussed but are not fully understood, especially the phenomenon in which the photocurrent slowly increases. Here, we report on a study of the photoresponse flash-light-processed MoS2 films of different thicknesses and areas. The photoresponse of such films under different light intensities and bias voltages was measured, showing significant current changes with a quick response followed by a slow one upon exposure to pulsed light. Our in-depth study suggested that the slow response was due to the photothermal effect that heats the MoS2; this hypothesis was supported by the resistivity change at different temperatures. The results obtained from MoS2 films with various thicknesses indicated that the minority-carrier diffusion length was 1.36 mu m. This study explained the mechanism of the slow response of the MoS2 film and determined the effective thickness of MoS2 for a photoresponse to occur. The method used here for fabricating MoS2 films could be used for fabricating optoelectronic devices due to its simplicity.

    Ladda ner fulltext (pdf)
    fulltext
  • 41.
    Zhang, Renyun
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Hummelgård, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Örtegren, Jonas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Yang, Ya
    Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing, PR China; University of Chinese Academy of Science, Beijing, PR China.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Balliu, Enkeleda
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Blomquist, Nicklas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Olsen, Martin
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Wang, Zhong Lin
    Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing, PR China; University of Chinese Academy of Science, Beijing, PR China; Georgia Institute of Technology, Atlanta, GA, USA.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Sensing body motions based on charges generated on the body2019Ingår i: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 63, artikel-id 103842Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The sensing of body motions is of great importance in areas such as healthcare, rehabilitation, and human-computer interactions. Different methods have been developed based on visual or electrical signals. However, such signals are acquired by external devices and are not intrinsic signals that are created on the body. Here, we report a new universal body motion sensor (UBS) to detect motions based on the intrinsic contact electrification (CE) of the skin or electrical induction (EI) of the body. The CE or EI generates charges on the body, leading to potential differences between the body and ground that can be measured to identify different body motions, such as motions of the head, arms, fingers, waist, legs, feet and toes. Proof-of-concept experiments have demonstrated that the UBS can be used to monitor the conditions of people with Parkinson's disease (PD) and to quantitatively monitor the recovery of those with a leg injury, suggesting great potential for healthcare applications.

  • 42.
    Åberg, Daniel
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Edvardsson, Sverker
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Direct calculation of correlated absorption amplitudes for Nd:LiYF42003Ingår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 68, nr 19, artikel-id 195105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The correlation contribution to the transition amplitudes are investigated in the case of Nd:LiYF4. By using many-body perturbation theory, we derive expressions for an effective dipole operator. The operators considered are Omega(es)((1)dagger)DOmega(cf)((1)), Omega(cf)((1)dagger)DOmega(es)((1)), Omega(es-cf)((2)dagger)D, and DOmega(es-cf)((2)). In contrast to third-order spin-orbit and crystal-field modified amplitudes, inclusion of correlation modifies the standard second-order amplitudes significantly. A model cluster is optimized to experimental energy levels. This approach is then used to compute consistent odd and even crystal-field parameters needed for theoretical absorption spectra. As expected, it is observed that transitions occurring at small wavelengths are quite heavily influenced by correlation. The overall agreement between experimental and theoretical spectra below 600 nm (above 17000 cm(-1)) is greatly improved when correlation is taken into account.

1 - 42 av 42
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf