Publications
363 results found
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.
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.
Thomas GM, Minassian A, Damzen MJ, 2019, Directly diode-side-pumped alexandrite slab lasers in the bounce geometry and optical vortex generation
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Arbabzadah EA, Kerridge-Johns W, Thomas GM, et al., 2019, High efficiency TEM <inf>00</inf> diode end-pumped Alexandrite laser
Tawy G, Damzen MJ, 2019, Tunable and dual wavelength alexandrite laser using the crystal birefringence
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.
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
Tawy G, Wang J, Damzen MJ, 2019, Population lensing in alexandrite lasers
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.
Sathian J, Lian W, Minassian A, et al., 2019, Brightness-enhanced solid-state light sources: From kaleidoscope effect to uniform illumination
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.
Sathian J, Minassian A, Alford NM, et al., 2019, Enhancing performance of Ce:YAG luminescent concentrators for high power applications
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.
Sathian J, Tawy G, Sheng X, et al., 2019, Compact non-astigmatic alexandrite ring laser with unidirectional single-longitudinal-mode operation
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.
Sathian J, Lian W, Minassian A, et al., 2019, Brightness-Enhanced Solid-State Light Sources: From Kaleidoscope Effect to Uniform Illumination, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Sathian J, Minassian A, Alford NM, et al., 2019, Enhancing Performance of Ce:YAG Luminescent Concentrators for High Power Applications, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Tawy G, Damzen MJ, 2019, Tunable and Dual Wavelength Alexandrite Laser Using the Crystal Birefringence, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Tawy G, Wang J, Damzen MJ, 2019, Population Lensing in Alexandrite Lasers, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Sathian J, Tawy G, Shen X, et al., 2019, Compact Non-Astigmatic Alexandrite Ring Laser with Unidirectional Single-Longitudinal-Mode operation, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
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.
Sheng X, Tawy G, Sathian J, et 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.
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.
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.
Coney AT, Minassian A, Damzen MJ, 2018, High-energy diode-pumped alexandrite oscillator and amplifier development for satellite-based LiDAR
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.
Kerridge-Johns WR, Geberbauer JW, Volpini A, et al., 2018, Vortex laser output with a fundamental Gaussian internal mode using a sagnac interferometer
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.
Parali U, Sheng X, Minassian A, et al., 2017, Diode-pumped Alexandrite laser with passive SESAM Q-switching and wavelength tunability, Optics Communications, Vol: 410, Pages: 970-976, ISSN: 0030-4018
We report the first experimental demonstration of a wavelength tunable passively Q-switched red-diode-endpumped Alexandrite laser using a semiconductor saturable absorber mirror (SESAM). We present the results ofthe study of passive SESAM Q-switching and wavelength-tuning in continuous diode-pumped Alexandritelasers in both linear cavity and X-cavity configurations. In the linear cavity configuration, pulsed operation upto 27 kHz repetition rate in fundamental TEM00 mode was achieved and maximum average power was 41 mW.The shortest pulse generated was 550 ns (FWHM) and the Q-switched wavelength tuning band spanned wasbetween 740 nm and 755 nm. In the X-cavity configuration, a higher average power up to 73 mW, and obtainedwith higher pulse energy 6.5 J at 11.2 kHz repetition rate, in fundamental TEM00 mode with excellent spatialquality M2 < 1.1. The Q-switched wavelength tuning band spanned was between 775 nm and 781 nm.
Sheng X, Parali U, Thomas GM, et al., 2017, Passively SESAM Q-switched Red-Diode-Pumped Alexandrite Laser, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Kerridge-Johns WR, Damzen MJ, 2017, Tunable CW Alexandrite Lasers and Fundamental Limits of Efficiency, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Coney AT, Thomas GM, Minassian A, et al., 2017, High-Energy Diode-Pumped Alexandrite Laser Development for Remote Sensing, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Thomas GM, Minassian A, Kerridge-Johns W, et al., 2017, High power and high energy diode-pumped Alexandrite lasers, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Kerridge-Johns WR, Damzen MJ, 2017, Anti-Resonant Ring Laser Cavities, Conference on Lasers and Electro-Optics Europe / European Quantum Electronics Conference (CLEO/Europe-EQEC), Publisher: IEEE
Damzen MJ, Thomas GM, Minassian A, 2017, Diode-side-pumped Alexandrite slab lasers, Optics Express, Vol: 25, Pages: 11622-11636, ISSN: 1094-4087
We present the investigation of diode-side-pumping of Alexandrite slab lasers in a range of designs using linear cavity and grazing-incidence bounce cavity configurations. An Alexandrite slab laser cavity with double-pass side pumping produces 23.4 mJ free-running energy at 100 Hz rate with slope efficiency ~40% with respect to absorbed pump energy. In a slab laser with single-bounce geometry output power of 12.2 W is produced, and in a double-bounce configuration 6.5 W multimode and 4.5 W output in TEM00 mode is produced. These first results of slab laser and amplifier designs in this paper highlight some of the potential strategies for power and energy scaling of Alexandrite using diode-side-pumped Alexandrite slab architectures with future availability of higher power red diode pumping.
Kerridge-Johns WR, Damzen MJ, 2017, Vortex mode generation from coupled anti-resonant ring lasers
Vortex modes with controllable handedness were generated by coupling two laser cavities through a common Nd:YVO4 gain medium inside an anti-resonant ring. This design is applicable to both isotropic and anisotropic gain media.
Parali U, Thomas GM, Minassian A, et al., 2017, Wavelength tunable passively Q-switched Alexandrite laser with direct diode-pumping at 635 nm, 5th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS), Publisher: SCITEPRESS, Pages: 82-89
We report on a wavelength tunable passively Q-switched Alexandrite laser directly red-diode-pumped at 635 nm. Passive Q-switching was achieved with a semiconductor saturable absorber mirror (SESAM) and wavelength tuning with a birefringent tuner. The pulse repetiton rate was variable on the pump power and wavelength and a maximum 27 kHz rate was achieved in fundamental TEM00 mode. The maximum average output power obtained was 41 mW. The Q-switched wavelength tuning band was studied between 740 nm and 755 nm. To the best of our knowledge, this is the first time that tunable TEM00 passive Q-switched operation of a diode-pumped Alexandrite laser has been achieved. The results obtained in this study can be significantly further optimised for performance. A new cavity configuration for this optimisation is described. Future work is expected to lead to the development of higher power, more efficient tunable passive Q-switched (and potentially passive mode-locked) diode-pumped Alexandrite la (More)
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