Whilst many techniques exist for generation of an optical vortex, there remains a need for new de... more 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 with higher powers, greater flexibility of wavelength, and generation beyond the lowest-order Laguerre–Gaussian L G 01 mode to address a broader range of practical applications. This work reveals how an all-mirror based interferometric mode transformation system can provide these properties including revealing, for the first time, the generation of a much richer set of vortex mode patterns than might have been thought possible previously. A new developed theoretical formulation, confirmed with excellent agreement by experimental demonstrations in an imbalanced Sagnac interferometer, shows interferometric transformation is possible for all orders of Laguerre–Gaussian L G 0 l modes into a rich set of high quality higher-order vortex and vortex superposition. The interferometric approach is shown to be configurable to increase or dec...
This work presents a study of a fully non-astigmatic design of a singlelongitudinal-mode, wavelen... more This work presents a study of a fully non-astigmatic design of a singlelongitudinal-mode, wavelength-tunable, unidirectional Alexandrite ring laser cavity and assessment of its performance compared to more complex laser design requiring astigmatism compensation. A "displaced mode" non-astigmatic laser cavity design eliminating astigmatic cavity elements is developed around an Alexandrite crystal end-pumped by a low brightness high power red diode laser pump system. Single-longitudinal-mode, continuous-wave operation is demonstrated with output power 700 mW with an excellent TEM00 mode (M 2 <1.1) across a wide pump power range. Wavelength tuning from 748-773 nm is produced using a birefringent filter plate. The non-astigmatic Alexandrite laser design achieves better spatial quality and resilience to maintain TEM 00 operation across wide variation in pumpinduced lensing compared to the astigmatic design. To the best of our knowledge, this is the first wavelength-tunable, single-longitudinal-mode operation of a unidirectional Alexandrite ring system in a fully non-astigmatic cavity regime.
Journal of Optics A: Pure and Applied Optics, 2003
This special issue of Journal of Optics A: Pure and Applied Optics is devoted to a mature field o... more This special issue of Journal of Optics A: Pure and Applied Optics is devoted to a mature field of nonlinear optics: photorefractive materials and effects for photonics. Photorefractivity was discovered long time ago by A Ashkin et al in 1966 and since then much work has been performed to characterize the phenomenon and to apply it. Nevertheless, research in this field remain very active and productive, in both basic and applied directions. Some leading groups worldwide present their most up-to-date investigations of photorefractive materials and effects, as well as their applications in photonics. Thus, the papers in this issue report new results in three directions: photorefractive material researches, wave propagation (particularly solitons) through these nonlinear optical materials, and various applications and devices using photorefractive effects. The challenging goal of photorefractive material research is to find sensitive and fast materials for information transmission and processing. P M Johansen studies the fundamental problem of space--charge field formation in photorefractives. V Marinova et al show that light-induced properties of Ru-doped Bi12TiO20 (BTO) crystals has an extended sensitivity in the near infrared region. H A Al-Attar and O Taqatqa introduce a new photorefractive polymer composite for their interesting properties for optical data storage. R Ramos-Garcia et al perform measurements of absorption coefficient and refractive index changes in photorefractive quantum wells of GaAs. A Radoua et al characterize by two-wave mixing the photorefractive Ba0.77Ca0.23TiO3:Rh crystals (BCT) at 1.06 μm, and M K Balakirev et al study the photorefractive effect upon all optical poling of glass. Wave propagation and solitons are intensively studied in photorefractive crystals due to the possibility of obtaining steady-state spatial solitons, dynamic waveguiding and soliton interactions at low laser intensity. W Ramadan et al introduce a new procedure to obtain stationary self-confined beams at non-absorbed wavelengths in Bi12SiO20 (BSO). Two groups, C Weilnau and C Denz and Z Chen et al, investigate photorefractive solitons using partially coherent light beams. Waveguiding and interactions in photorefractive soliton arrays are demonstrated by R Delgado Macuil and M D Iturbe Castillo and by D Trager et al. V Matusevich et al show some aspects of fanning, self-focusing and self-defocusing in a photorefractive BCT crystal. Applications and devices are developing in hologram recording and storage, image processing, interferometry and optical phase conjugation in photorefractive materials. G Berger et al record non-volatile volume holograms in bismuth tellurite crystals. I de Oliveira and J Frejlich perform diffraction efficiency measurement in photorefractive thick volume holograms. Holography with photorefractive multiple quantum well devices is used by C Dunsby et al in high-speed wide-field coherence-gated imaging. A photorefractive fringe-locked running hologram is analysed by M C Barbosa and J Frejlich in three-dimensional space. Detection of small in-plane vibrations using the polarization self-modulation effect in GaP is performed by Y Iida et al. E Weidner et al design an interferometric camera with a wavefront buffer memory using a photorefractive crystal as the active medium. R Nicolaus et al investigate and optimize a pulsed ultraviolet image amplifier within a micro-marking system. C Gu et al apply unconventional photorefractive materials in fibre optic devices. Photorefractive phase conjugate mirrors are used by T Omatsu et al to obtain multi-watt picosecond pulses from a diode-pumped Nd:YVO4 amplifier with a diffraction-limited spatial profile, and V M Petrov et al design optical on-line controllable filters based on photorefractive crystals. We hope that this special issue of Journal of Optics A: Pure and Applied Optics will reflect the intense activity in the field of photorefractivity and will demonstrate to readers some of the actual directions of research in these topics. We express our full appreciation to the authors and we would like to thank the paper reviewers for their important role in the paper selection process. We acknowledge the Publisher, Claire Bedrock, and the technical staff of the journal for their support, dedication and energy, which made feasible this special issue.
This volume presents results from fundamental research on the phenomenon of phase conjugation of ... more This volume presents results from fundamental research on the phenomenon of phase conjugation of laser emission discovered at the Physics Institute of the Academy of Sciences during stimulated scattering in hypersound, and with four-wave interaction in a wavelength range from the visible through the mid-infrared. Fundamentally new optical designs and methods of controlling laser emission are proposed and tested experimentally on the basis of this effect.
distributed feedback laser [12] or filtering at the laser output may be more effective. 4) The do... more distributed feedback laser [12] or filtering at the laser output may be more effective. 4) The dominant frequency of emission from a high-power D 2 0 laser oscillator is at the Raman frequency expected for small signal pump and FIR emission fields. No ac Stark shifting or strong FIR field pulling has been observed.
Efficient, wavelength-tunable diode-pumped alexandrite laser systems offer the potential for a mo... more Efficient, wavelength-tunable diode-pumped alexandrite laser systems offer the potential for a more versatile, satellite-based lidar source compared to fixed wavelength Nd:YAG systems and non-space compliant lamp-pumped alexandrite. In this paper, we develop a strategy to enable the high-energy operation required for atmospheric lidar based on an efficient diode-pumped master oscillator power amplifier (MOPA) system design. A novel multipass “diamond” slab amplifier geometry is introduced alongside the experimental results of the world’s first diode-pumped alexandrite amplifier producing a gain of 2.13 in a demonstration system. A diode-pumpedQ-switched alexandrite oscillator is presented with a record-highest pulse energy of 3.80 mJ. Detailed optimization of a two-stage amplifier design is studied numerically and maximized with temperature, wavelength, and pump pulse duration to produce 50 mJ pulse energy. This forms part of an optimized alexandrite MOPA design capable of high pulse energy, showing the future potential of diode-pumped alexandrite for satellite-based atmospheric lidar.
We experimentally demonstrate and theoretically analyze practical aspects of using a laser-pumped... more We experimentally demonstrate and theoretically analyze practical aspects of using a laser-pumped dye medium as an ultrafast (10-ps) optically addressed spatial light modulator for application with high-power radiation. Optical modulation of the absorption of a high-power pump beam is produced by a relatively weak (control) beam that is experiencing stimulated emission. The intensity of the control beam required for strong switching of the pump-beam transmission is determined by the gain that is due to stimulated emission at the control-beam frequency. A practical limitation on the gain that is due to excited-state absorption of the pump frequency is described. We demonstrate the application of the dye medium spatial light modulator for high-resolution image transfer and determine the resolution limit of the transfer process. Experimental demonstration is made of optical image processing (edge enhancement). The control beam can also be generated by self-lasing in feedback geometries, and pump transmission can be controlled by the strength of the feedback.
The acoustic decay time of hypersound generated by stimulated Brillouin scattering (SBS) has been... more The acoustic decay time of hypersound generated by stimulated Brillouin scattering (SBS) has been measured in several heavy gases (Xe, SF 6 , CCIF 3 , C 2 F 6 ) over a range of pressures. A straightforward optical probing technique is used whereby the decay time can be measured directly with high precision. A theoretical formulation of the decay mechanisms in a polyatomic gas is presented, and it is shown both theoretically and experimentally that vibrational relaxation can become the major decay process at high gas density. The Brillouin gain coefficient and acoustic frequency are also experimentally determined or calculated for the gases investigated. Two Brillouin-active gases (CCIF 3 and C 2 F 6 ) with high Brillouin gains, which have not been studied previously, have been characterized. A study of the gas C 2 F 6 near its critical point showed a large variation of the acoustic velocity which reaches a minimum value in the vicinity of its critical density.
It is essential to understand the pump-induced lensing and aberration effects in solidstate laser... more It is essential to understand the pump-induced lensing and aberration effects in solidstate lasers, such as Alexandrite, since these set limits on laser power scaling whilst maintaining high spatial TEM 00 beam quality. In this work, we present direct wavefront measurements of pump-induced lensing and spherical aberration using a Shack-Hartmann wavefront sensor, for the first 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 pump power, and under lasing, the lensing power is observed to decrease to 60 % of its non-lasing value. The results are inconsistent with a thermal lens model but a fuller theoretical formulation is made of a combined thermal and population lens model giving good quantitative agreement to the observed pump power dependence of the induced-lensing under non-lasing conditions and the reduced lensing under lasing conditions. The deduced value for the difference in excited to ground state polarizability is consistent with prior measurement estimates for other chromium-doped gain media. The finding of this paper provide new insight into pump-induced lensing in Alexandrite and also provides a basis for a fast saturable population lens mechanism to account for self-Q-switching observed recently in Alexandrite laser systems.
We present a red-diode-pumped Alexandrite laser with continuous wavelength tunability, dual wavel... more 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. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Optical vortex Laguerre-Gaussian (LG 0l) modes have wide-ranging applications due to their annula... more Optical vortex Laguerre-Gaussian (LG 0l) 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 LG 0l 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:YVO 4 gain medium. From 24 W of pump power, 8.9 W LG 01 and 4.3 W LG 02 modes were generated, all with high mode purity and pure handedness. The LG 01 mode handedness was controlled with a new technique. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Diode pumped Alexandrite is a promising route to high power, efficient and inexpensive lasers wit... more 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. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
We report the first experimental demonstration of a wavelength tunable passively Q-switched red-d... more We report the first experimental demonstration of a wavelength tunable passively Q-switched red-diode-end pumped Alexandrite laser using a semiconductor saturable absorber mirror (SESAM). We present the results of the study of passive SESAM Q-switching and wavelength-tuning in continuous diode-pumped Alexandrite lasers in both linear cavity and X-cavity configurations. In the linear cavity configuration, pulsed operation up to 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 was between 740 nm and 755 nm. In the X-cavity configuration, a higher average power up to 73 mW, and obtained with higher pulse energy 6.5 J at 11.2 kHz repetition rate, in fundamental TEM00 mode with excellent spatial quality M 2 < 1.1. The Q-switched wavelength tuning band spanned was between 775 nm and 781 nm.
An analytical model is formulated to support understanding and underpin experimental development ... more An analytical model is formulated to support understanding and underpin experimental development of laser action in the promising diode end-pumped Alexandrite system. Closed form solutions are found for output power, threshold and slope efficiency that for the first time incorporate the combined effects of laser ground state absorption (GSA) and excited state absorption (laser ESA), along with pump excited state absorption (pump ESA), in the case of an end-pumping geometry. Comparison is made between model predictions and experimental results from a fibre-delivered diode end-pumped Alexandrite laser system, showing the impact of wavelength tuning, crystal temperature, laser output coupling, and intracavity loss. The model is broadly applicable to other quasi-three-level lasers with combined laser and pump ESA. A condition for bistable operation is also formulated.
A diode-pumped Nd:YVO4 laser is demonstrated that has a reciprocal self-intersecting loop cavity ... more A diode-pumped Nd:YVO4 laser is demonstrated that has a reciprocal self-intersecting loop cavity with self-organization by formation of a dynamic holographic grating induced by the generating beam. Continuous-wave high spatial quality generation (M2 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 1.2) with 9.6 W of power and 32% optical efficiency is obtained. Spectral compositions and temporal dynamics are investigated as functions of diode-pumping power.
We present a novel way of Q-switching a flashlamp-pumped, 2.8 m Er,Cr:YSGG laser, wherein a ... more We present a novel way of Q-switching a flashlamp-pumped, 2.8 m Er,Cr:YSGG laser, wherein a rotating polygon is used as an optical chopper. Single pulse energies of ~3.8 mJ were achieved with pulsewidths of ~305 ns. The scheme benefits from the simplicity of design, and, compared with other Q-switching methods, a reduction in losses and laser damage problems from intracavity components. We also investigate the optimisation of the laser output through purging of the laser with nitrogen, and find a 29% increase in peak output energy.
We demonstrate, for the first time to our knowledge, a spatially adaptive holographic solid-state... more We demonstrate, for the first time to our knowledge, a spatially adaptive holographic solid-state dye laser using a self-intersecting loop geometry. The gain medium was a solid matrix of polymethyl methacrylate (PMMA) doped with pyrromethene 650 (P650) and inverted by 532 nm radiation. A diffractive gain hologram was induced by self-intersection in the gain medium with an injected signal beam at 616 nm. The holographic laser attained threshold for an injected signal energy of 0.63 nJ and produced TEM00 output with adaptive correction of thermally induced aberration. A phase conjugate reflectivity greater than 37,000% was achieved.
We present a study of vector phase conjugation based on degenerate four-wave mixing in inverted N... more We present a study of vector phase conjugation based on degenerate four-wave mixing in inverted Nd:YAG. The results demonstrate polarization correction for weak probe strength, with near-unity fidelity for polarization compensation of the returning conjugate. As the probe strength is increased, the fidelity of the polarization state of the conjugate is seen to deteriorate to an average value of 92% when the probe is strongly saturating and is several times stronger than the pump beams. We also show that, for strong probe strengths, an individual transmission grating or reflection grating is more efficient than when both gratings are present.
Whilst many techniques exist for generation of an optical vortex, there remains a need for new de... more 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 with higher powers, greater flexibility of wavelength, and generation beyond the lowest-order Laguerre–Gaussian L G 01 mode to address a broader range of practical applications. This work reveals how an all-mirror based interferometric mode transformation system can provide these properties including revealing, for the first time, the generation of a much richer set of vortex mode patterns than might have been thought possible previously. A new developed theoretical formulation, confirmed with excellent agreement by experimental demonstrations in an imbalanced Sagnac interferometer, shows interferometric transformation is possible for all orders of Laguerre–Gaussian L G 0 l modes into a rich set of high quality higher-order vortex and vortex superposition. The interferometric approach is shown to be configurable to increase or dec...
This work presents a study of a fully non-astigmatic design of a singlelongitudinal-mode, wavelen... more This work presents a study of a fully non-astigmatic design of a singlelongitudinal-mode, wavelength-tunable, unidirectional Alexandrite ring laser cavity and assessment of its performance compared to more complex laser design requiring astigmatism compensation. A "displaced mode" non-astigmatic laser cavity design eliminating astigmatic cavity elements is developed around an Alexandrite crystal end-pumped by a low brightness high power red diode laser pump system. Single-longitudinal-mode, continuous-wave operation is demonstrated with output power 700 mW with an excellent TEM00 mode (M 2 <1.1) across a wide pump power range. Wavelength tuning from 748-773 nm is produced using a birefringent filter plate. The non-astigmatic Alexandrite laser design achieves better spatial quality and resilience to maintain TEM 00 operation across wide variation in pumpinduced lensing compared to the astigmatic design. To the best of our knowledge, this is the first wavelength-tunable, single-longitudinal-mode operation of a unidirectional Alexandrite ring system in a fully non-astigmatic cavity regime.
Journal of Optics A: Pure and Applied Optics, 2003
This special issue of Journal of Optics A: Pure and Applied Optics is devoted to a mature field o... more This special issue of Journal of Optics A: Pure and Applied Optics is devoted to a mature field of nonlinear optics: photorefractive materials and effects for photonics. Photorefractivity was discovered long time ago by A Ashkin et al in 1966 and since then much work has been performed to characterize the phenomenon and to apply it. Nevertheless, research in this field remain very active and productive, in both basic and applied directions. Some leading groups worldwide present their most up-to-date investigations of photorefractive materials and effects, as well as their applications in photonics. Thus, the papers in this issue report new results in three directions: photorefractive material researches, wave propagation (particularly solitons) through these nonlinear optical materials, and various applications and devices using photorefractive effects. The challenging goal of photorefractive material research is to find sensitive and fast materials for information transmission and processing. P M Johansen studies the fundamental problem of space--charge field formation in photorefractives. V Marinova et al show that light-induced properties of Ru-doped Bi12TiO20 (BTO) crystals has an extended sensitivity in the near infrared region. H A Al-Attar and O Taqatqa introduce a new photorefractive polymer composite for their interesting properties for optical data storage. R Ramos-Garcia et al perform measurements of absorption coefficient and refractive index changes in photorefractive quantum wells of GaAs. A Radoua et al characterize by two-wave mixing the photorefractive Ba0.77Ca0.23TiO3:Rh crystals (BCT) at 1.06 μm, and M K Balakirev et al study the photorefractive effect upon all optical poling of glass. Wave propagation and solitons are intensively studied in photorefractive crystals due to the possibility of obtaining steady-state spatial solitons, dynamic waveguiding and soliton interactions at low laser intensity. W Ramadan et al introduce a new procedure to obtain stationary self-confined beams at non-absorbed wavelengths in Bi12SiO20 (BSO). Two groups, C Weilnau and C Denz and Z Chen et al, investigate photorefractive solitons using partially coherent light beams. Waveguiding and interactions in photorefractive soliton arrays are demonstrated by R Delgado Macuil and M D Iturbe Castillo and by D Trager et al. V Matusevich et al show some aspects of fanning, self-focusing and self-defocusing in a photorefractive BCT crystal. Applications and devices are developing in hologram recording and storage, image processing, interferometry and optical phase conjugation in photorefractive materials. G Berger et al record non-volatile volume holograms in bismuth tellurite crystals. I de Oliveira and J Frejlich perform diffraction efficiency measurement in photorefractive thick volume holograms. Holography with photorefractive multiple quantum well devices is used by C Dunsby et al in high-speed wide-field coherence-gated imaging. A photorefractive fringe-locked running hologram is analysed by M C Barbosa and J Frejlich in three-dimensional space. Detection of small in-plane vibrations using the polarization self-modulation effect in GaP is performed by Y Iida et al. E Weidner et al design an interferometric camera with a wavefront buffer memory using a photorefractive crystal as the active medium. R Nicolaus et al investigate and optimize a pulsed ultraviolet image amplifier within a micro-marking system. C Gu et al apply unconventional photorefractive materials in fibre optic devices. Photorefractive phase conjugate mirrors are used by T Omatsu et al to obtain multi-watt picosecond pulses from a diode-pumped Nd:YVO4 amplifier with a diffraction-limited spatial profile, and V M Petrov et al design optical on-line controllable filters based on photorefractive crystals. We hope that this special issue of Journal of Optics A: Pure and Applied Optics will reflect the intense activity in the field of photorefractivity and will demonstrate to readers some of the actual directions of research in these topics. We express our full appreciation to the authors and we would like to thank the paper reviewers for their important role in the paper selection process. We acknowledge the Publisher, Claire Bedrock, and the technical staff of the journal for their support, dedication and energy, which made feasible this special issue.
This volume presents results from fundamental research on the phenomenon of phase conjugation of ... more This volume presents results from fundamental research on the phenomenon of phase conjugation of laser emission discovered at the Physics Institute of the Academy of Sciences during stimulated scattering in hypersound, and with four-wave interaction in a wavelength range from the visible through the mid-infrared. Fundamentally new optical designs and methods of controlling laser emission are proposed and tested experimentally on the basis of this effect.
distributed feedback laser [12] or filtering at the laser output may be more effective. 4) The do... more distributed feedback laser [12] or filtering at the laser output may be more effective. 4) The dominant frequency of emission from a high-power D 2 0 laser oscillator is at the Raman frequency expected for small signal pump and FIR emission fields. No ac Stark shifting or strong FIR field pulling has been observed.
Efficient, wavelength-tunable diode-pumped alexandrite laser systems offer the potential for a mo... more Efficient, wavelength-tunable diode-pumped alexandrite laser systems offer the potential for a more versatile, satellite-based lidar source compared to fixed wavelength Nd:YAG systems and non-space compliant lamp-pumped alexandrite. In this paper, we develop a strategy to enable the high-energy operation required for atmospheric lidar based on an efficient diode-pumped master oscillator power amplifier (MOPA) system design. A novel multipass “diamond” slab amplifier geometry is introduced alongside the experimental results of the world’s first diode-pumped alexandrite amplifier producing a gain of 2.13 in a demonstration system. A diode-pumpedQ-switched alexandrite oscillator is presented with a record-highest pulse energy of 3.80 mJ. Detailed optimization of a two-stage amplifier design is studied numerically and maximized with temperature, wavelength, and pump pulse duration to produce 50 mJ pulse energy. This forms part of an optimized alexandrite MOPA design capable of high pulse energy, showing the future potential of diode-pumped alexandrite for satellite-based atmospheric lidar.
We experimentally demonstrate and theoretically analyze practical aspects of using a laser-pumped... more We experimentally demonstrate and theoretically analyze practical aspects of using a laser-pumped dye medium as an ultrafast (10-ps) optically addressed spatial light modulator for application with high-power radiation. Optical modulation of the absorption of a high-power pump beam is produced by a relatively weak (control) beam that is experiencing stimulated emission. The intensity of the control beam required for strong switching of the pump-beam transmission is determined by the gain that is due to stimulated emission at the control-beam frequency. A practical limitation on the gain that is due to excited-state absorption of the pump frequency is described. We demonstrate the application of the dye medium spatial light modulator for high-resolution image transfer and determine the resolution limit of the transfer process. Experimental demonstration is made of optical image processing (edge enhancement). The control beam can also be generated by self-lasing in feedback geometries, and pump transmission can be controlled by the strength of the feedback.
The acoustic decay time of hypersound generated by stimulated Brillouin scattering (SBS) has been... more The acoustic decay time of hypersound generated by stimulated Brillouin scattering (SBS) has been measured in several heavy gases (Xe, SF 6 , CCIF 3 , C 2 F 6 ) over a range of pressures. A straightforward optical probing technique is used whereby the decay time can be measured directly with high precision. A theoretical formulation of the decay mechanisms in a polyatomic gas is presented, and it is shown both theoretically and experimentally that vibrational relaxation can become the major decay process at high gas density. The Brillouin gain coefficient and acoustic frequency are also experimentally determined or calculated for the gases investigated. Two Brillouin-active gases (CCIF 3 and C 2 F 6 ) with high Brillouin gains, which have not been studied previously, have been characterized. A study of the gas C 2 F 6 near its critical point showed a large variation of the acoustic velocity which reaches a minimum value in the vicinity of its critical density.
It is essential to understand the pump-induced lensing and aberration effects in solidstate laser... more It is essential to understand the pump-induced lensing and aberration effects in solidstate lasers, such as Alexandrite, since these set limits on laser power scaling whilst maintaining high spatial TEM 00 beam quality. In this work, we present direct wavefront measurements of pump-induced lensing and spherical aberration using a Shack-Hartmann wavefront sensor, for the first 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 pump power, and under lasing, the lensing power is observed to decrease to 60 % of its non-lasing value. The results are inconsistent with a thermal lens model but a fuller theoretical formulation is made of a combined thermal and population lens model giving good quantitative agreement to the observed pump power dependence of the induced-lensing under non-lasing conditions and the reduced lensing under lasing conditions. The deduced value for the difference in excited to ground state polarizability is consistent with prior measurement estimates for other chromium-doped gain media. The finding of this paper provide new insight into pump-induced lensing in Alexandrite and also provides a basis for a fast saturable population lens mechanism to account for self-Q-switching observed recently in Alexandrite laser systems.
We present a red-diode-pumped Alexandrite laser with continuous wavelength tunability, dual wavel... more 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. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Optical vortex Laguerre-Gaussian (LG 0l) modes have wide-ranging applications due to their annula... more Optical vortex Laguerre-Gaussian (LG 0l) 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 LG 0l 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:YVO 4 gain medium. From 24 W of pump power, 8.9 W LG 01 and 4.3 W LG 02 modes were generated, all with high mode purity and pure handedness. The LG 01 mode handedness was controlled with a new technique. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Diode pumped Alexandrite is a promising route to high power, efficient and inexpensive lasers wit... more 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. Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
We report the first experimental demonstration of a wavelength tunable passively Q-switched red-d... more We report the first experimental demonstration of a wavelength tunable passively Q-switched red-diode-end pumped Alexandrite laser using a semiconductor saturable absorber mirror (SESAM). We present the results of the study of passive SESAM Q-switching and wavelength-tuning in continuous diode-pumped Alexandrite lasers in both linear cavity and X-cavity configurations. In the linear cavity configuration, pulsed operation up to 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 was between 740 nm and 755 nm. In the X-cavity configuration, a higher average power up to 73 mW, and obtained with higher pulse energy 6.5 J at 11.2 kHz repetition rate, in fundamental TEM00 mode with excellent spatial quality M 2 < 1.1. The Q-switched wavelength tuning band spanned was between 775 nm and 781 nm.
An analytical model is formulated to support understanding and underpin experimental development ... more An analytical model is formulated to support understanding and underpin experimental development of laser action in the promising diode end-pumped Alexandrite system. Closed form solutions are found for output power, threshold and slope efficiency that for the first time incorporate the combined effects of laser ground state absorption (GSA) and excited state absorption (laser ESA), along with pump excited state absorption (pump ESA), in the case of an end-pumping geometry. Comparison is made between model predictions and experimental results from a fibre-delivered diode end-pumped Alexandrite laser system, showing the impact of wavelength tuning, crystal temperature, laser output coupling, and intracavity loss. The model is broadly applicable to other quasi-three-level lasers with combined laser and pump ESA. A condition for bistable operation is also formulated.
A diode-pumped Nd:YVO4 laser is demonstrated that has a reciprocal self-intersecting loop cavity ... more A diode-pumped Nd:YVO4 laser is demonstrated that has a reciprocal self-intersecting loop cavity with self-organization by formation of a dynamic holographic grating induced by the generating beam. Continuous-wave high spatial quality generation (M2 &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 1.2) with 9.6 W of power and 32% optical efficiency is obtained. Spectral compositions and temporal dynamics are investigated as functions of diode-pumping power.
We present a novel way of Q-switching a flashlamp-pumped, 2.8 m Er,Cr:YSGG laser, wherein a ... more We present a novel way of Q-switching a flashlamp-pumped, 2.8 m Er,Cr:YSGG laser, wherein a rotating polygon is used as an optical chopper. Single pulse energies of ~3.8 mJ were achieved with pulsewidths of ~305 ns. The scheme benefits from the simplicity of design, and, compared with other Q-switching methods, a reduction in losses and laser damage problems from intracavity components. We also investigate the optimisation of the laser output through purging of the laser with nitrogen, and find a 29% increase in peak output energy.
We demonstrate, for the first time to our knowledge, a spatially adaptive holographic solid-state... more We demonstrate, for the first time to our knowledge, a spatially adaptive holographic solid-state dye laser using a self-intersecting loop geometry. The gain medium was a solid matrix of polymethyl methacrylate (PMMA) doped with pyrromethene 650 (P650) and inverted by 532 nm radiation. A diffractive gain hologram was induced by self-intersection in the gain medium with an injected signal beam at 616 nm. The holographic laser attained threshold for an injected signal energy of 0.63 nJ and produced TEM00 output with adaptive correction of thermally induced aberration. A phase conjugate reflectivity greater than 37,000% was achieved.
We present a study of vector phase conjugation based on degenerate four-wave mixing in inverted N... more We present a study of vector phase conjugation based on degenerate four-wave mixing in inverted Nd:YAG. The results demonstrate polarization correction for weak probe strength, with near-unity fidelity for polarization compensation of the returning conjugate. As the probe strength is increased, the fidelity of the polarization state of the conjugate is seen to deteriorate to an average value of 92% when the probe is strongly saturating and is several times stronger than the pump beams. We also show that, for strong probe strengths, an individual transmission grating or reflection grating is more efficient than when both gratings are present.
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Papers by M. Damzen