Imperial College London

ProfessorMichaelDamzen

Faculty of Natural SciencesDepartment of Physics

Professor of Experimental Laser Physics
 
 
 
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Contact

 

+44 (0)20 7594 7783m.damzen Website

 
 
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Location

 

610Blackett LaboratorySouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

326 results found

Damzen M, Sathian J, Tawy G, Sheng X, Minassian Aet al., Non-astigmatic Alexandrite ring laser design with wavelength-tunable single-longitudinal-mode operation, Journal of the Optical Society of America B: Optical Physics, ISSN: 0740-3224

Journal article

Damzen M, Tawy G, Minassian A, High-power 7.4W TEM00 and wavelength-tunable Alexandrite laser with novel cavity design and efficient fibre-coupled diode-pumping, OSA Continuum

Journal article

Geberbauer J, Kerridge-Johns WR, Damzen MJ, 2020, Q-switched laser with self-mode-filtering interferometric vortex output coupler, OSA Continuum, Vol: 3, Pages: 204-213, ISSN: 2578-7519

Vortex lasers are an attractive prospect for efficient generation of high-quality beams in compact, environmentally robust, and turnkey systems. We demonstrate conversion of a Q-switched, diode-pumped Nd:YVO4, TEM00 Gaussian laser into a vortex laser source by replacing the output coupling mirror by a vortex output coupler (VOC) based on an imbalanced Sagnac interferometer. The Q-switched VOC laser generated a vortex output with 5.1 W average power, slope efficiency of 46% at 150 kHz pulse repetition rate, only marginally lower than the 5.4W and 49% slope efficiency of the plane mirror laser. Vortex handedness was switchable with a single VOC control without loss of vortex power. In both handedness cases, the vortex mode quality was assessed to be excellent by detailed analysis of the vortex phase profile and propagation characteristics and comparison to an ideal vortex. Further investigation verified the ability for the VOC laser to self-mode-filter the intracavity mode, showing maintenance of high TEM00 quality even after introducing deliberate mode to pump size mismatch, when the equivalent plane mirror laser becomes multimode. This work highlights the potential of the VOC as a simple route to high powered structured light sources using just standard high-power handling mirror components and its self-mode-filtering property to compensate intra-cavity spatial mode degradation when power-scaling.

Journal article

Tawy G, Damzen MJ, 2020, Ultra-compact >100kHz Q-switched Alexandrite lasers, ISSN: 0277-786X

© 2020 SPIE. We report <100 kHz continuous wave diode pumping of Alexandrite lasers in self-Q-switched (SQS) operation using an ultra-compact system. The laser had up to 1:46W of average power with slope efficiency of 49% and M2 ≤ 1.2. A pulse duration of 657 ns at 138 kHz is obtained, with a corresponding pulse energy and peak power of 9.6 μJ and 14.6 W, respectively. Detailed results related to the laser power, spectrum and temporal profile are provided. A description of the pulse stability with respect to pump power and crystal temperature is also shown. The SQS mechanism is attributed to a time-dependent variation in the refractive index of the population inversion density giving rise to a time-dependent population lens. In a separate study we obtain the value for the variation in polarizability of the excited and ground state that gives rise to the refractive index variation. It is found to be in good agreement with a prior measurement for Alexandrite and in the range measured for other Chromium-doped gain media for which SQS has also been observed.

Conference paper

Tawy G, Damzen MJ, 2020, Narrow linewidth tunable and dual wavelength compact Alexandrite laser, ISSN: 0277-786X

© 2020 SPIE. In this work we present a novel compact Alexandrite laser with continuous wavelength tuning and dual wavelength operation. Wavelength tuning is achieved by tilting a Brewster-cut Alexandrite crystal to change the path length and birefringence in a plane-plane cavity. Fiber-coupled diode pumping provides a small footprint stable system with <1W of output power in TEM00 mode. Results are shown for two laser crystals with the broadest tuning of 746-768nm demonstrated with 15 GHz linewidth. Wavelength tuning at a rate of -0.07nmK-1 is also demonstrated by varying the crystal temperature. Stable dual wavelength operation with 12-13nm peak-to- peak separation is shown in addition. A theoretical model for wavelength tuning based on the change in geometrical path length and refractive index is found to be in excellent agreement with the experimental results. Power scaling of the system is also investigated with a second compact cavity design. A total tuning range of 754-769nm and dual wavelength operation is demonstrated with a maximum power of 3.2W and beam quality M2 = 1.8.

Conference paper

Tawy G, Wang J, Damzen MJ, 2020, Thermal and population induced lensing in Alexandrite lasers, ISSN: 0277-786X

© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. We present an overview of pump-induced lensing effects in end-pumped Alexandrite lasers. The dioptric lens power is measured for a diode pumped Alexandrite laser using a Shack-Hartmann wavefront sensor under both non-lasing and lasing conditions. Under non-lasing conditions, the lens dioptric power is measured for two pump sizes and in both cases is found to be nearly linear with respect to the absorbed pump power. Under lasing conditions the lens dioptric power is up to 60% weaker. Good agreement is found between the non lasing and lasing experimental results using a model based on a combined lens consisting of a thermal lens, and a population lens arising from the electronic component of the refractive index. Fitting parameters using an analytical model for the two pump sizes are also found to be consistent. Values for the difference in excited to ground state polarizability are obtained and found to be consistent with prior measurements for Alexandrite and other Chromium-doped gain media.

Conference paper

Geberbauer JWT, Kerridge-Johns WR, Damzen MJ, 2020, Q-switched vortex laser using a Sagnac interferometer as an output coupler, ISSN: 0277-786X

© 2020 SPIE. Vortex lasers are an attractive prospect for efficient generation of high-quality beams in compact, environmentally robust, and turnkey systems. We demonstrate conversion of a Q-switched, diode-pumped Nd:YVO4, TEM00 Gaussian laser into a vortex laser source by replacing the output coupling mirror by a vortex output coupler (VOC) based on an imbalanced Sagnac interferometer. The Q-switched VOC laser generated a vortex output with 5.1 W average power, slope efficiency of 46% at 150 kHz pulse repetition rate, only marginally lower than the 5.4 W and 49% slope efficiency of the plane mirror laser. Vortex handedness was switchable with a single VOC control without loss of vortex power. In both handedness cases the vortex mode quality was assessed to be excellent by detailed analysis of vortex phase profile and propagation characteristics and comparison to an ideal vortex. The power scaling potential of the VOC was demonstrated in a higher power cavity, achieving a vortex output power of 14.3 W and a slope efficiency of 55%. Further investigation verified the ability for the VOC laser to self-mode-filter the intracavity mode, showing maintenance of high TEM00 quality even after introducing deliberate mode to pump size mismatch, when the equivalent plane mirror laser becomes multimode. This work highlights the potential of the VOC as a simple route to high powered structured light sources using just standard high-power handling mirror components and its self-mode-filtering property to compensate intra-cavity spatial mode degradation when power-scaling.

Conference paper

Damzen M, Kerridge-Johns W, Geberbauer J, 2019, Vortex mode transformation interferometry, Journal of Optics, Vol: 22, Pages: 1-9, ISSN: 1464-4258

Whilst many techniques exist for generation of an optical vortex, there remains a need for new devices and methods that can also provide vortex generation withhigher powers, greater flexibility of wavelength, and generation beyondthe lowest-order Laguerre-Gaussian ๐ฟ๐บ01modeto address a broader range of practical applications.This work revealshow an all-mirror based interferometricmode transformation system can provide these propertiesincludingrevealing, for the first time,the generation ofa much richer set of vortex mode patterns than might have been thought possible previously.Anew developed theoreticalformulation, confirmed with excellent agreement by experimental demonstrationsin an imbalanced Sagnac interferometer,showsinterferometric transformation is possible for all orders of Laguerre-Gaussian ๐ฟ๐บ0๐‘™modes into a rich set of high quality higher-order vortex and vortex superposition. The interferometric approachis shown to be configurabletoincrease or decrease vorticity. The new mathematical formulation provides the ability to perform a fullmodal power analysis of both the mode-transformed transmitted vortex and the complementary reflected beam at the Sagnac beamsplitter port.A discussion is made on the origin of the orbital angular momentum transferred to the vortex output from the Sagnac beamsplitter.

Journal article

Tawy G, Wang J, Damzen M, 2019, Pump-induced lensing effects in diode pumped Alexandrite lasers, Optics Express, Vol: 27, Pages: 35865-35883, ISSN: 1094-4087

It is essential to understand the pump-induced lensing and aberration effects in solid-state lasers, such as Alexandrite, since these set limits on laser power scaling whilst maintaininghigh spatial TEM00beam quality. In this work, we present direct wavefront measurements ofpump-induced lensing and spherical aberration using a Shack-Hartmann wavefront sensor, for thefirst time, in a diode-pumped Alexandrite laser, and under both non-lasing and lasing conditions.The lens dioptric power is found to be weakly sub-linear with respect to the absorbed pumppower, and under lasing, the lensing power is observed to decrease to60 %of its non-lasingvalue. The results are inconsistent with a thermal lens model but a fuller theoretical formulationis made of a combined thermal and population lens model giving good quantitative agreementto the observed pump power dependence of the induced-lensing under non-lasing conditionsand the reduced lensing under lasing conditions. The deduced value for the difference inexcited to ground state polarizability is consistent with prior measurement estimates for otherchromium-doped gain media. The finding of this paper provide new insight into pump-inducedlensing in Alexandrite and also provides a basis for a fast saturable population lens mechanism toaccount for self-Q-switching observed recently in Alexandrite laser systems.

Journal article

Tawy G, Damzen M, 2019, Tunable, dual wavelength and self-Q-switched Alexandrite laser using crystal birefringence control, Optics Express, Vol: 27, Pages: 17507-17520, ISSN: 1094-4087

We present a red-diode-pumped Alexandrite laser with continuous wavelength tunability, dual wavelength and self-Q-switching in an ultra-compact resonator containing only the gain medium. Wavelength tuning is obtained by varying the geometrical path length and birefringence by tilting a Brewster-cut Alexandrite crystal. Two crystals from independent suppliers are used to demonstrate and compare the performance. Wavelength tuning between 750 and 764 nm is demonstrated in the first crystal and between 747 and 768 nm in the second crystal. Stable dual wavelength operation is also obtained in both crystals with wavelength separation determined by the crystal free spectral range. Temperature tuning was also demonstrated to provide finer wavelength tuning at a rate of −0.07 nm K −1. Over a narrow tuning range, stable self-Q-switching is observed with a pulse duration of 660 ns at 135 kHz, which we believe is the highest Q-switched pulse rate in Alexandrite to date. Theoretical modelling is performed showing good agreement with the wavelength tuning and dual wavelength results.

Journal article

Tawy G, Wang J, Damzen MJ, 2019, Population lensing in alexandrite lasers

© 2019 IEEE. Alexandrite (Cr3+:BeAl2O4) is a vibronic laser at 701-858 nm. Its excellent thermo-mechanical properties and high energy storage make it an ideal high power and high energy Q-switched source with recent development in mJ-level red-diode-pumped Alexandrite oscillators and amplifiers [1-3]. Further power scaling of these systems is limited by thermal lensing which has yet to be addressed in great detail. In this work we present experimental and finite element analysis (FEA) results on the investigation of thermal lensing in a red-diode-pumped Alexandrite laser. Differences in the thermal lensing power for non-lasing and lasing conditions are attributed to a 'population lens' effect. In a separate study stable self-Q-switching (SQS) is observed in an Alexandrite laser cavity containing only the gain medium where the SQS loss mechanism is attributed to the population lens.

Conference paper

Sathian J, Minassian A, Alford NM, Damzen MJet al., 2019, Enhancing performance of Ce:YAG luminescent concentrators for high power applications

© 2019 IEEE. High power scaling of an LED pumped luminescent concentrator (LC) can address significant excitation and illumination applications, including laser pumping and medical light therapy [1-3]. However, heat deposited into the luminescent material is critical and was already a serious issue in our prior systems [3] where forced air cooling of the Ce:YAG LC light-guide was employed but limited power and/or duration of operation. Here we report the successful demonstration of a temperature controlled Ce:YAG LC pumped with blue InGaN LEDs.

Conference paper

Tawy G, Damzen MJ, 2019, Tunable and dual wavelength alexandrite laser using the crystal birefringence

© 2019 IEEE. Red-diode-pumped Alexandrite lasers has proven to be an efficient method of generating light in the near infrared with broad tunability from 714 to 818 nm recently demonstrated [1]. Conventionally, tunable Alexandrite lasers have used wavelength selective elements such as birefringent filters or external gratings [1, 2]. In this work wavelength tuning is obtained by exploiting the birefringence of the crystal to use the crystal itself as the wavelength selective element, greatly simplifying the cavity and reducing innecessary loss components.

Conference paper

Sathian J, Tawy G, Sheng X, Minassian A, Damzen MJet al., 2019, Compact non-astigmatic alexandrite ring laser with unidirectional single-longitudinal-mode operation

© 2019 IEEE. Progress in single frequency and precise wavelength tunable lasers are essential to address future demands in high resolution spectroscopy, metrology and quantum technology systems. Alexandrite lasers with wide tunability in near-IR spectral region when pumped by low cost red diodes provide a good prospect as a cost effective precision laser source. This was demonstrated in our earlier work [1] using a tunable single-frequency bow-tie cavity with Brewster-cut Alexandrite crystal. The astigmatism of the Brewster cut gain medium and need for angled curved mirrors for astigmatic compensation, whilst being well established [2,3] also places some complexity on the design and can be compromised by astigmatic thermal lensing [1]. Here we report the investigation and successful operation of a non-astigmatic compact design of a unidirectional wavelength tunable Alexandrite ring laser with single frequency operation.

Conference paper

Sathian J, Lian W, Minassian A, Damzen MJet al., 2019, Brightness-enhanced solid-state light sources: From kaleidoscope effect to uniform illumination

© 2019 IEEE. Luminescent concentrators (LCs) are systems that can increase the brightness of lambertian light sources such as an LED. Applications considered for LED-pumped LCs include laser pumping, general lighting and medical illumination [1-3]. Most studies consider the output power, spectrum and efficiency of the LC system. Here we explore the spatial nature of the output of the LCs under both laser and LED illumination.

Conference paper

Kerridge-Johns W, Geberbauer JWT, Damzen M, 2019, Vortex laser by transforming Gaussian mode with an interferometric output coupler, Optics Express, Vol: 27, Pages: 11642-11650, ISSN: 1094-4087

Generation of vortex beams directly from the laser source can be limited in power and efficiency, or to specific pump sources and gain media. Here, we propose a new high power and high efficiency vortex laser methodology with interferometric mode transformation as output coupling, which uses high power handling and low loss optics that have wavelength versatility. Experimental demonstration is made in a diode-pumped Nd:YVO4 laser using an imbalanced Sagnac interferometer as output coupler producing high quality vortex output beams (M2 = 2.07) with fully selectable control of handedness whilst the intracavity mode is maintained as a fundamental Gaussian. Vortex output power >3W is produced with only small reduction in efficiency compared to the equivalent TEM00 laser. Continuous variation of vortex output coupling transmission and the quality of the vortex is investigated experimentally showing good agreement with theory. This work reveals a new approach to high power structured laser radiation direct from the source through interferometric spatial mode transformations.

Journal article

Tawy G, Wang J, Damzen MJ, 2019, Population lensing in alexandrite lasers

© 2019 IEEE Alexandrite (Cr3+:BeAl2O4) is a vibronic laser at 701-858 nm. Its excellent thermo-mechanical properties and high energy storage make it an ideal high power and high energy Q-switched source with recent development in mJ-level red-diode-pumped Alexandrite oscillators and amplifiers [1-3]. Further power scaling of these systems is limited by thermal lensing which has yet to be addressed in great detail. In this work we present experimental and finite element analysis (FEA) results on the investigation of thermal lensing in a red-diode-pumped Alexandrite laser. Differences in the thermal lensing power for non-lasing and lasing conditions are attributed to a 'population lens' effect. In a separate study stable self-Q-switching (SQS) is observed in an Alexandrite laser cavity containing only the gain medium where the SQS loss mechanism is attributed to the population lens.

Conference paper

Sathian J, Lian W, Minassian A, Damzen MJet al., 2019, Brightness-enhanced solid-state light sources: From kaleidoscope effect to uniform illumination

© 2019 IEEE Luminescent concentrators (LCs) are systems that can increase the brightness of lambertian light sources such as an LED. Applications considered for LED-pumped LCs include laser pumping, general lighting and medical illumination [1-3]. Most studies consider the output power, spectrum and efficiency of the LC system. Here we explore the spatial nature of the output of the LCs under both laser and LED illumination.

Conference paper

Sathian J, Minassian A, Alford NM, Damzen MJet al., 2019, Enhancing performance of Ce:YAG luminescent concentrators for high power applications

© 2019 IEEE High power scaling of an LED pumped luminescent concentrator (LC) can address significant excitation and illumination applications, including laser pumping and medical light therapy [1-3]. However, heat deposited into the luminescent material is critical and was already a serious issue in our prior systems [3] where forced air cooling of the Ce:YAG LC light-guide was employed but limited power and/or duration of operation. Here we report the successful demonstration of a temperature controlled Ce:YAG LC pumped with blue InGaN LEDs.

Conference paper

Sathian J, Tawy G, Sheng X, Minassian A, Damzen MJet al., 2019, Compact non-astigmatic alexandrite ring laser with unidirectional single-longitudinal-mode operation

© 2019 IEEE Progress in single frequency and precise wavelength tunable lasers are essential to address future demands in high resolution spectroscopy, metrology and quantum technology systems. Alexandrite lasers with wide tunability in near-IR spectral region when pumped by low cost red diodes provide a good prospect as a cost effective precision laser source. This was demonstrated in our earlier work [1] using a tunable single-frequency bow-tie cavity with Brewster-cut Alexandrite crystal. The astigmatism of the Brewster cut gain medium and need for angled curved mirrors for astigmatic compensation, whilst being well established [2,3] also places some complexity on the design and can be compromised by astigmatic thermal lensing [1]. Here we report the investigation and successful operation of a non-astigmatic compact design of a unidirectional wavelength tunable Alexandrite ring laser with single frequency operation.

Conference paper

Thomas GM, Minassian A, Damzen MJ, 2019, Directly diode-side-pumped alexandrite slab lasers in the bounce geometry and optical vortex generation

Conference paper

Arbabzadah EA, Kerridge-Johns W, Thomas GM, Minassian A, Damzen MJet al., 2019, High efficiency TEM <inf>00</inf> diode end-pumped Alexandrite laser

Conference paper

Tawy G, Damzen MJ, 2019, Tunable and dual wavelength alexandrite laser using the crystal birefringence

© 2019 IEEE Red-diode-pumped Alexandrite lasers has proven to be an efficient method of generating light in the near infrared with broad tunability from 714 to 818 nm recently demonstrated [1]. Conventionally, tunable Alexandrite lasers have used wavelength selective elements such as birefringent filters or external gratings [1, 2]. In this work wavelength tuning is obtained by exploiting the birefringence of the crystal to use the crystal itself as the wavelength selective element, greatly simplifying the cavity and reducing innecessary loss components.

Conference paper

Teppitaksak A, Thomas GM, Damzen MJ, 2019, Gain-switched diode laser seeding of ultra-high-gain Nd: YVO <inf>4</inf> bounce amplifier system as a versatile pulsed laser source

Conference paper

Kerridge-Johns W, Damzen MJ, 2018, Vortex laser from anti-resonant ring coupled cavities, Optics Express, Vol: 26, Pages: 32839-32846, ISSN: 1094-4087

Optical vortex Laguerre-Gaussian (LG0l) modes have wide-ranging applications due to their annular spatial form and orbital angular momentum. Their direct generation from a laser is attractive, due to the pure and high-power modes possible; however, previous demonstrations have had limited ranges of applicability. Here, we propose and implement direct LG0l vortex mode generation with an anti-resonant ring (ARR) coupled laser cavity geometry, where the gain medium inside the ARR is shared between two laser cavities. This generation uses standard wavelength-insensitive optical components, is suitable for high peak and average power levels, and could be applied to any bulk gain medium in pulsed or continuous wave regimes. This work demonstrates the technique with a diode end-pumped Nd:YVO4 gain medium. From 24 W of pump power, 8.9 W LG01 and 4.3 W LG02 modes were generated, all with high mode purity and pure handedness. The LG01 mode handedness was controlled with a new technique.

Journal article

Sheng X, Tawy G, Sathian J, Minassian A, Damzen Met al., 2018, Unidirectional single-frequency operation of a continuous-wave Alexandrite ring laser with wavelength tunability, Optics Express, Vol: 26, Pages: 31129-31136, ISSN: 1094-4087

High resolution spectroscopy, metrology and quantum technologies (e.g. trapping and cooling) require precision laser sources with narrow linewidth and wavelength tunability. The widespread use of these lasers will be promoted if they are cost-effective, compact and efficient. Alexandrite lasers with a broad tuning band pumped efficiently by low-cost red diodes are a potential candidate, but full performance as a precision light source has not been fully achieved. We present in this work the first continuous-wave (CW) and single-frequency operation of a unidirectional diode-end-pumped Alexandrite ring laser with wavelength tunability. An ultra-compact bow-tie ring cavity is developed with astigmatic compensation and a novel ‘displaced mode’ design producing CW output power > 1 W in excellent TEM00 mode (M2 < 1.2) when using a low brightness pump (M2 ≥ 30). Wavelength tuning from 727 - 792 nm is demonstrated using a birefringent filter plate. This successful operation opens the prospects of precision light source applications.

Journal article

Kerridge-Johns WR, Damzen MJ, 2018, Temperature effects on tunable CW Alexandrite lasers under diode end-pumping, Optics Express, Vol: 26, Pages: 7771-7785, ISSN: 1094-4087

Diode pumped Alexandrite is a promising route to high power, efficient and inexpensive lasers with a broad (701 nm to 858 nm) gain bandwidth; however, there are challenges with its complex laser dynamics. We present an analytical model applied to experimental red diode end-pumped Alexandrite lasers, which enabled a record 54 % slope efficiency with an output power of 1.2 W. A record lowest lasing wavelength (714 nm) and record tuning range (104 nm) was obtained by optimising the crystal temperature between 8 °C and 105 °C in the vibronic mode. The properties of Alexandrite and the analytical model were examined to understand and give general rules in optimising Alexandrite lasers, along with their fundamental efficiency limits. It was found that the lowest threshold laser wavelength was not necessarily the most efficient, and that higher and lower temperatures were optimal for longer and shorter laser wavelengths, respectively. The pump excited to ground state absorption ratio was measured to decrease from 0.8 to 0.7 by changing the crystal temperature from 10 °C to 90 °C.

Journal article

Thomas G, Minassian A, Damzen MJ, 2018, Optical vortex generation from a diode-pumped alexandrite laser, Laser Physics Letters, Vol: 15, ISSN: 1612-2011

We present the demonstration of an optical vortex mode directly generated from a diode-pumped alexandrite slab laser, operating in the bounce geometry. This is the first demonstration of an optical vortex mode generated from an alexandrite laser or from any other vibronic laser. An output power of 2 W for a vortex mode with a 'topological charge' of 1 was achieved and the laser was made to oscillate with both left- and right-handed vorticity. The laser operated at two distinct wavelengths simultaneously, 755 and 759 nm, due to birefringent filtering in the alexandrite gain medium. The result offers the prospect of broadly wavelength tunable vortex generation directly from a laser.

Journal article

Coney AT, Minassian A, Damzen MJ, 2018, High-energy diode-pumped alexandrite oscillator and amplifier development for satellite-based LiDAR

© OSA 2018. Development of a Q-switched diode-pumped Alexandrite oscillator producing 3.8mJ pulse energy is described with wavelength and temperature optimisation of a diode-pumped Alexandrite slab amplifier as part of a future Alexandrite design for satellite-based lidar.

Conference paper

Kerridge-Johns WR, Geberbauer JW, Volpini A, Damzen MJet al., 2018, Vortex laser output with a fundamental Gaussian internal mode using a sagnac interferometer

© OSA 2018. We experimentally demonstrate a simple technique to convert any linear laser cavity into an optical vortex source using a Sagnac interferometer as an output coupler. No specialist optics are needed, the vortex has controlled handedness.

Conference paper

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