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Engholm, Magnus
Publications (10 of 42) Show all publications
Knall, J. M., Vigneron, P.-B. -., Engholm, M., Dragic, P. D., Yu, N., Ballato, J., . . . Digonnet, M. (2020). Experimental observation of cooling in Yb-doped silica fibers. In: Proceedings of SPIE - The International Society for Optical Engineering: . Paper presented at Photonic Heat Engines: Science and Applications II 2020; San Francisco; United States; 5 February 2020 through 6 February 2020. SPIE - International Society for Optical Engineering
Open this publication in new window or tab >>Experimental observation of cooling in Yb-doped silica fibers
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2020 (English)In: Proceedings of SPIE - The International Society for Optical Engineering, SPIE - International Society for Optical Engineering, 2020Conference paper, Published paper (Refereed)
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. 

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2020
Keywords
Anti-Stokes fluorescence, Laser cooling, Optical refrigeration, Rare-earth doped fibers, Silica fibers
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:miun:diva-38962 (URN)10.1117/12.2548506 (DOI)2-s2.0-85083305647 (Scopus ID)9781510633599 (ISBN)
Conference
Photonic Heat Engines: Science and Applications II 2020; San Francisco; United States; 5 February 2020 through 6 February 2020
Available from: 2020-04-29 Created: 2020-04-29 Last updated: 2020-04-29Bibliographically approved
Knall, J., Vigneron, P.-B., Engholm, M., Dragic, P. D., Yu, N., Ballato, J., . . . Digonnet, M. J. F. (2020). Laser cooling in a silica optical fiber at atmospheric pressure. Optics Letters, 45(5), 1092-1095
Open this publication in new window or tab >>Laser cooling in a silica optical fiber at atmospheric pressure
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2020 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 45, no 5, p. 1092-1095Article in journal (Refereed) Published
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. 

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-38655 (URN)10.1364/OL.384658 (DOI)000522833500013 ()2-s2.0-85080105843 (Scopus ID)
Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-04-16Bibliographically approved
Engholm, M., Hammarling, K., Andersson, H., Sandberg, M. & Nilsson, H.-E. (2019). A Bio-Compatible Fiber Optic pH Sensor Based on a Thin Core Interferometric Technique. Photonics, 6(1), Article ID 11.
Open this publication in new window or tab >>A Bio-Compatible Fiber Optic pH Sensor Based on a Thin Core Interferometric Technique
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2019 (English)In: Photonics, ISSN 2304-6732, Vol. 6, no 1, article id 11Article in journal (Refereed) Published
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.

Keywords
interferometric, Mach-Zehnder, pH, sensor, hydrogel, simulation
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-35646 (URN)10.3390/photonics6010011 (DOI)000464341200003 ()2-s2.0-85063143389 (Scopus ID)
Note

MDPI Photonics Special Issue "Advanced Optical Materials and Devices"

Available from: 2019-02-14 Created: 2019-02-14 Last updated: 2020-01-17Bibliographically approved
Balliu, E., Engholm, M. & Nilsson, H.-E. (2019). A compact, single-frequency, high-power, SBS-free, Yb-doped single-stage fiber amplifier. In: W. Andrew Clarkson and Ramesh K. Shori (Ed.), Proceedings of SPIE - The International Society for Optical Engineering: . Paper presented at Solid State Lasers XXVIII: Technology and Devices 2019, San Francisco, California, United States, 5-7 February, 2019 (pp. 6pp). SPIE - International Society for Optical Engineering, 10896, Article ID 1089618.
Open this publication in new window or tab >>A compact, single-frequency, high-power, SBS-free, Yb-doped single-stage fiber amplifier
2019 (English)In: 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, p. 6pp-, article id 1089618Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2019
Keywords
Single-frequency laser, Ytterbium-doped fiber amplifier, stimulated Brillouin scattering, high-power fiber amplifier, compact fiber amplifier
National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-36042 (URN)10.1117/12.2511049 (DOI)000483062600028 ()2-s2.0-85068317380 (Scopus ID)
Conference
Solid State Lasers XXVIII: Technology and Devices 2019, San Francisco, California, United States, 5-7 February, 2019
Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2019-11-26Bibliographically approved
Andersson, H., Šuly, P., Thungström, G., Engholm, M., Zhang, R., Mašlík, J. & Olin, H. (2019). PEDOT: PSS thermoelectric generators printed on paper substrates. Journal of Low Power Electronics and Applications, 9(2)
Open this publication in new window or tab >>PEDOT: PSS thermoelectric generators printed on paper substrates
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2019 (English)In: Journal of Low Power Electronics and Applications, ISSN 2079-9268, Vol. 9, no 2Article in journal (Refereed) Published
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. 

Keywords
Paper substrates, PEDOT:PSS, Seebeck coefficient, Stencil print, Thermoelectric generator
Identifiers
urn:nbn:se:miun:diva-36667 (URN)10.3390/jlpea9020014 (DOI)2-s2.0-85065493304 (Scopus ID)
Available from: 2019-07-09 Created: 2019-07-09 Last updated: 2019-07-09Bibliographically approved
Zhang, R., Hummelgård, M., Örtegren, J., Yang, Y., Andersson, H., Balliu, E., . . . Olin, H. (2019). Sensing body motions based on charges generated on the body. Nano Energy, 63, Article ID 103842.
Open this publication in new window or tab >>Sensing body motions based on charges generated on the body
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2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 63, article id 103842Article in journal (Refereed) Published
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.

Keywords
Body motions, Sensors, Charges, Contact electrification, Electrical induction, Healthcare
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-36826 (URN)10.1016/j.nanoen.2019.06.038 (DOI)000480422400034 ()2-s2.0-85068234493 (Scopus ID)
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-10-16Bibliographically approved
Hammarling, K., Muri, H. I., Wahl, M. S., Engholm, M. & Hjelme, D. R. (2018). A combined glucose and pH sensor on a single optical fiber for continuous point-of-care testing. In: SPIE BIOS, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII: . Paper presented at Proc. SPIE BIOS 10488, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII, 104880A (14 March 2018). SPIE - International Society for Optical Engineering
Open this publication in new window or tab >>A combined glucose and pH sensor on a single optical fiber for continuous point-of-care testing
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2018 (English)In: SPIE BIOS, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII, SPIE - International Society for Optical Engineering, 2018Conference paper, Oral presentation with published abstract (Other academic)
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.

Place, publisher, year, edition, pages
SPIE - International Society for Optical Engineering, 2018
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:miun:diva-37855 (URN)10.1117/12.2290055 (DOI)
Conference
Proc. SPIE BIOS 10488, Optical Fibers and Sensors for Medical Diagnostics and Treatment Applications XVIII, 104880A (14 March 2018)
Available from: 2019-12-03 Created: 2019-12-03 Last updated: 2019-12-06Bibliographically approved
Hammarling, K., Engholm, M., Andersson, H., Sandberg, M. & Nilsson, H.-E. (2018). Broad-Range Hydrogel-Based pH Sensor with Capacitive Readout Manufactured on a Flexible Substrate. Chemosensors, 6(3), Article ID 30.
Open this publication in new window or tab >>Broad-Range Hydrogel-Based pH Sensor with Capacitive Readout Manufactured on a Flexible Substrate
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2018 (English)In: Chemosensors, ISSN 2227-9040, Vol. 6, no 3, p. 15article id 30Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Basel, Switzerland: MDPI, 2018. p. 15
Keywords
interdigital, hydrogel, penetration depth, pH, sensor, coating, thin film, laser ablation, oligo (β-amino esters)
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-34203 (URN)10.3390/chemosensors6030030 (DOI)000448395400006 ()2-s2.0-85052627188 (Scopus ID)
Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2020-05-19Bibliographically approved
Muri, H. I., Hammarling, K., Wahl, M., Engholm, M. & Hjelme, D. R. (2018). Combining interferometric sensors for dual parameter fiber optic chemical sensing. In: Optics InfoBase Conference Papers: . Paper presented at 26th International Conference on Optical Fiber Sensors, OFS 2018, Lausanne, Switzerland, 24 September 2018 through 28 September 2018. OSA - The Optical Society, Article ID WF80.
Open this publication in new window or tab >>Combining interferometric sensors for dual parameter fiber optic chemical sensing
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2018 (English)In: Optics InfoBase Conference Papers, OSA - The Optical Society , 2018, article id WF80Conference paper, Published paper (Refereed)
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.

Place, publisher, year, edition, pages
OSA - The Optical Society, 2018
National Category
Physical Sciences
Identifiers
urn:nbn:se:miun:diva-35437 (URN)10.1364/OFS.2018.WF80 (DOI)2-s2.0-85059485004 (Scopus ID)9781557528209 (ISBN)
Conference
26th International Conference on Optical Fiber Sensors, OFS 2018, Lausanne, Switzerland, 24 September 2018 through 28 September 2018
Available from: 2019-01-14 Created: 2019-01-14 Last updated: 2019-01-14Bibliographically approved
Zhang, R., Engholm, M., Hummelgård, M., Andersson, H., Örtegren, J. & Olin, H. (2018). High-performance transparent and flexible electrodes made by flash-light sintering of gold nanoparticles. ACS Applied Energy Materials, 1(12), 7191-7198
Open this publication in new window or tab >>High-performance transparent and flexible electrodes made by flash-light sintering of gold nanoparticles
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2018 (English)In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 1, no 12, p. 7191-7198Article in journal (Refereed) Published
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.

Keywords
transparent electrode, flexible electrode, gold nanoparticles, flash-light sintering, high performance
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:miun:diva-35380 (URN)10.1021/acsaem.8b01649 (DOI)000458706800063 ()2-s2.0-85064752503 (Scopus ID)
Available from: 2019-01-03 Created: 2019-01-03 Last updated: 2019-07-08Bibliographically approved
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