Umit Demirbas - Academia.edu (original) (raw)

Papers by Umit Demirbas

2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021

Yb:YLF is a broadly tunable (996-1076 nm) continuous-wave (cw) laser that allows generation of su... more Yb:YLF is a broadly tunable (996-1076 nm) continuous-wave (cw) laser that allows generation of sub-100-fs long pulses upon mode-locking at room temperature [1] - [4] . Unfortunately, the power handling limitations of the thermo-mechanically weak YLF host at room temperature limited the average mode-locked output power to the 100 mW level in earlier studies. The advantages of cryogenic operation with respect to power scaling is well-known and ample explored in cw, q-switched and amplifier geometries in Yb:YLF systems and output power above 300 W has been achieved [5] - [8] . Interestingly, unlike other media like Yb:YAG, Yb:YLF possess a relatively broad gain bandwidth even at cryogenic temperatures (FWHM: ~10 nm in E//a axis). Despite that, to our knowledge, till this study [9] , mode-locking of Yb:YLF was not explored at cryogenic temperatures.

OSA Continuum, 2020

We report record output pulse energies from a cryogenic 8-pass Yb:YLF amplifier system operating ... more We report record output pulse energies from a cryogenic 8-pass Yb:YLF amplifier system operating at 10 Hz repetition rate. When seeded with 20-mJ, 1-ns stretched pulses, the amplifier produced output pulses with 305 mJ of energy at 1018.5 nm with a spectral width supporting sub-ps pulse-duration. The output beam profile was quite symmetric and had a measured beam quality factor (M2) of ∼1.45. To achieve this performance, the diameter of the beam inside the gain element is gradually increased via an adjustable telescope from around 4.6 mm to 6.2 mm. This enables adjustment of the fluence to a moderate value in subsequent passes: high enough for efficient extraction and low enough to prevent laser induced damage. To our knowledge, this is the highest pulse energy reported from cryogenically cooled Yb:YLF amplifiers to date. Further scaling in peak power and repetition rate is anticipated in future work.

Optics Express, 2020

We report, what is to our knowledge, the highest average power obtained directly from a Yb:YLF re... more We report, what is to our knowledge, the highest average power obtained directly from a Yb:YLF regenerative amplifier to date. A fiber front-end provided seed pulses with an energy of 10 nJ and stretched pulsewidth of around 1 ns. The bow-tie type Yb:YLF ring amplifier was pulse pumped by a kW power 960 nm fiber coupled diode-module. By employing a pump spot diameter of 2.1 mm, we could generate 20-mJ pulses at repetition rates between 1 Hz and 3.5 kHz, 10 mJ pulses at 5 kHz, 6.5 mJ pulses at 7.5 kHz and 5 mJ pulses at 10 kHz. The highest average power (70 W) was obtained at 3.5 kHz operation, at an absorbed pump power level of 460 W, corresponding to a conversion efficiency of 15.2%. Despite operating in the unsaturated regime, usage of a very stable seed source limited the power fluctuations below 2% rms in a 5 minute time interval. The output pulses were centered around 1018.6 nm with a FWHM bandwidth of 2.1 nm, and could be compressed to below 1-ps pulse duration. The output bea...

OSA Continuum, 2019

We report 190-mJ pulses with spectral content supporting sub-ps pulse-duration at a 10 Hz repetit... more We report 190-mJ pulses with spectral content supporting sub-ps pulse-duration at a 10 Hz repetition rate generated by a cryogenically-cooled, bulk Yb:YLF laser amplifier system. The amplifier system relies on a chirped pulse amplification architecture and consists of a fiber front-end, a regenerative amplifier, and two 4-pass amplifiers. The fiber front-end delivers 15-nJ, 1-ns stretched seed pulses, which are first amplified to 13-mJ pulse energy inside a Yb:YLF regenerative amplifier. Then the pulses are boosted further to 115 mJ and 190 mJ in two consecutive 4-pass amplifiers. To our knowledge, these are the highest pulse energies reported from Yb:YLF based amplifiers to date. We foresee shortening the pulsewidths to sub-400-fs range in future studies.

Optics Express, 2017

In this study, we numerically and experimentally investigate application of birefringent filters ... more In this study, we numerically and experimentally investigate application of birefringent filters (BRFs) as frequency selective elements in multicolor lasers. A BRF plate made out of crystalline quartz with an arbitrarily oriented optical axis has been explored. Simulation results have shown that compared to regular BRFs where the optical axis lies in the plane of the plates surface, a BRF with an optical axis pointing out of its surface enables design flexibility in filter parameters, providing access to a wider set of free spectral range and bandwidth values. As a result, multicolor operation could be obtained in many wavelength pairs using a single BRF plate. In the experiments a 3-mm thick quartz BRF with an optical axis 45° to the surface plane has been used. With Cr:Nd:GSGG as a laser medium two-color and three-color cw laser operation has been demonstrated in 11 and 3 different transition combinations, respectively. Moreover, two-color laser operation has been demonstrated in 10 different wavelength pairs in Cr:LiSAF. To our knowledge, this study is the first detailed investigation and experimental demonstration of BRFs with tilted optical axis for multicolor operation of solid-state lasers. Compared to other methods, BRFs enable a rich selection of transition pairs and also the ratio of the power in each line could be regulated by fine adjustment of the rotation angle. Implementation of tilted-axis BRFs should boost development of efficient and low-cost multicolor lasers in other gain media as well.

Laser Congress 2019 (ASSL, LAC, LS&C), 2019

We report, to the best of our knowledge, direct generation of the shortest pulses from a single-w... more We report, to the best of our knowledge, direct generation of the shortest pulses from a single-walled carbon nanotube mode-locked solid-state laser with a Cr:LiSAF gain medium, yielding 23-fs, nearly transform-limited pulses at 850 nm.

Optics Letters, 2021

We report an efficient diode-pumped high-power cryogenic regenerative amplifier operating at 1019... more We report an efficient diode-pumped high-power cryogenic regenerative amplifier operating at 1019 nm employing the c-axis of Yb:YLF. Compared to the usually selected 1017 nm transition of a-axis, the c-axis 1019 nm line has 3-fold higher emission cross section and still possess a full-width-half-maximum (FWHM) of 6.5 nm at 125 K. The chirped-pulse amplifier system is seeded by a fiber front-end with an energy of 30 nJ and stretched pulsewidth of 2 ns. In regenerative amplification studies, using the advantage of higher gain in the c-axis, we have achieved record average powers up to 370 W, with an extraction efficiency of 78% at 50 kHz repetition rate. The output pulses were centered around 1019.15 nm with a FWHM bandwidth of 1.25 nm, which supports sub-1.5 ps pulse durations. The output beam maintained a TEM00 beam profile at output power levels below 250 W with an M 2 below 1.2. Above this power level the thermally induced lensing in Yb:YLF created a multimode output beam. The thermal lens was rather dynamic and deteriorated the system stability above 250 W average power level.

Applied Physics B, 2021

We present detailed experimental results with cryogenic Yb:YLF gain media in rod-geometry. We hav... more We present detailed experimental results with cryogenic Yb:YLF gain media in rod-geometry. We have comparatively investigated continuous-wave (cw) lasing and regenerative amplification performance under different experimental conditions. In the cw lasing experiments effect of crystal doping, cw laser cavity geometry and pump wavelength on lasing performance were explored. Regenerative amplification behavior was analyzed and the role of depolarization losses on performance was investigated. A recently developed temperature estimation method was also employed for the first time in estimating average crystal temperature under lasing conditions. It is shown that the thermal lens induced by transverse temperature gradients is the main limiting factor and strategies for future improvements are discussed. To the best of our knowledge, the achieved results in this study (375 W in cw, and 90 W in regenerative amplification) are the highest average powers ever obtained from this system via em...

OSA High-brightness Sources and Light-driven Interactions Congress 2020 (EUVXRAY, HILAS, MICS), 2020

We demonstrate a cryogenically-cooled Yb:YLF regenerative amplifier delivering 20-mJ pulses at 3.... more We demonstrate a cryogenically-cooled Yb:YLF regenerative amplifier delivering 20-mJ pulses at 3.5 kHz corresponding to 70 W average power. The pulses possess 2.1 nm spectral bandwidth centered at 1019 nm supporting sub-ps pulses.

2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021

Nowadays the compact high power and high energy laser sources could be used for a variety of scie... more Nowadays the compact high power and high energy laser sources could be used for a variety of scientific and industrial applications as high harmonic generation, electron acceleration and material processing [1] . Although the room-temperature laser systems can provide millijoule energy at high average powers of hundreds of watts with pulse widths in the 0.5-5 ps, yet that requires to a complicated laser architecture [2] , [3] . The lasers operating at cryogenic temperatures exhibit simpler optical design together with a pristine beam quality [4] . In this work we propose as an attractive crystal choice of Yb:YLF (Yb:LiYF 4 ) for cryogenic regenerative amplifiers. Yb:YLF crystal combine adequate thermomechanical strength with a relatively broad gain bandwidth that could ideally support amplification of sub-250-fs pulses [4] .

Applied Optics, 2021

We report, to the best of our knowledge, the first mode-locking results of a Cr:LiSAF laser near ... more We report, to the best of our knowledge, the first mode-locking results of a Cr:LiSAF laser near the 1 µm region. The system is pumped only by a single 1.1 W high-brightness tapered diode laser at 675 nm. A semiconductor saturable absorber mirror (SESAM) with a modulation depth of 1.5% and non-saturable losses below 0.5% was used for mode-locking. Once mode-locked, the Cr:LiSAF laser produced almost-transform-limited sub-200-fs pulses with up to 12.5 mW of average power at a repetition rate of 150 MHz. Using an intracavity birefringent filter, the central wavelength of the pulses could be smoothly tuned in the 1000–1020 nm range. Via careful dispersion optimization, pulse widths could be reduced down to the 110-fs level. The performance in this initial study was limited by the design parameters of the SESAM used, especially its passive losses and could be improved with an optimized SESAM design.

Optics Express, 2019

We present, what is to our knowledge, the first detailed lasing investigation of cryogenic Yb:YLF... more We present, what is to our knowledge, the first detailed lasing investigation of cryogenic Yb:YLF gain media in the E//a-axis. Compared to the usually employed E//c-axis, the a-axis of Yb:YLF provides a much broader and smooth gain profile, but this comes at the expense of reduced gain product. We have shown that, despite the lower gain, which (i) increases susceptibility to cavity losses, (ii) raises lasing threshold, and (iii) inflates thermal load, efficient and high-power lasing could be achieved in the E//a axis as well. A record continuous-wave (cw) powers above 300 W, cw slope efficiencies of 73%, and a tuning range covering the 995-1020.5 nm region were demonstrated. In quasi-cw lasing experiments, via minimization of thermal effects, slope efficiencies can be scaled up to 85%. In gain-switched operation, sub-50-µs long pulses with a peak power exceeding 2.5 kW at multi-kHz repetition rate were attained. We measured a beam quality factor below 1.5 for laser average powers up to 100 W and below 3 for laser average powers up to 300 W. Power scaling limits due to thermal effects, laser dynamics in pulsed pumping, and multicolor lasing operation potential were also investigated. The detailed results presented in this manuscript will pave the way towards development of high-power and high-energy Yb:YLF oscillators and amplifiers with sub-500-fs pulse duration.

Optical Materials Express, 2019

We present detailed measurements of effective emission cross section spectra of the Alexandrite g... more We present detailed measurements of effective emission cross section spectra of the Alexandrite gain medium in the 25-450°C temperature range and provide analytic formulas that can be used to match the measured spectra. The measurement results have been used to investigate the wavelength and temperature dependence of small signal gain, as well as gain bandwidth relevant for ultrafast pulse generation/amplification. We show that the estimated laser performance based on the measured spectroscopic data provides a good fit to the results in the literature. We further discuss the need for a detailed measurement of excited-state absorption cross section in future studies.

Optics Letters, 2018

We report, to the best of our knowledge, the shortest femtosecond pulses generated from a Kerr-le... more We report, to the best of our knowledge, the shortest femtosecond pulses generated from a Kerr-lens mode-locked (KLM) Alexandrite laser operating near 750 nm. The Alexandrite gain medium was pumped with a continuous-wave (cw), 532 nm laser, and the performance of both the short and extended resonators was investigated. The use of an extended cavity eliminated the multi-wavelength spectral instabilities observed during the cw operation of the short cavity. Furthermore, since the repetition rate of the Alexandrite laser was reduced from 107 to 5.6 MHz, the resulting increase in the intracavity pulse energy provided enhanced Kerr nonlinearity and eliminated the Q-switching instabilities during mode-locked operation. The KLM MPC Alexandrite laser produced nearly transform-limited, 70 fs pulses at a pulse repetition rate of 5.6 MHz with only 1 W of pump power. The time-bandwidth product was further measured to be 0.331.

Applied Optics, 2019

In this paper, we present highly-efficient continuous-wave (cw) laser operation of Tm:YAG and Tm:... more In this paper, we present highly-efficient continuous-wave (cw) laser operation of Tm:YAG and Tm:LuAG lasers pumped by high-brightness red tapered diodes. The single-emitter tapered diode lasers (TDLs) provide up to 1-W of pump power around 680 nm. By adjusting the operation temperature of the TDL, the pump central wavelength could be matched to the strong absorption peak of Tm 3+ ions in this region (3 H6→ 3 F3 excitation). This absorption peak is around 3-fold stronger than the usually employed 785 nm transition (3 H6→ 3 H4). In the cw laser experiments, we have achieved slope efficiencies exceeding 55% at room temperature, which is far above the stokes limited slope efficiency (34%), indicating presence of strong two-for-one cross-relaxation process. Pumping with high-brightness tapered diode lasers further facilitated usage of smaller pump spots (enabling quite low lasing thresholds) and generation of near-diffraction limited output beam profiles from standard z-type cavities. To the best of our knowledge, this is the first report of diode pumping of Tm-doped solid-state lasers around 680 nm, as well as the first usage of TDLs as pump sources in Tm-doped laser systems.

2009 IEEE LEOS Annual Meeting Conference Proceedings, 2009

We summarize recent progress in low-cost and highly-efficient Cr:Colquiriite laser technology. Pu... more We summarize recent progress in low-cost and highly-efficient Cr:Colquiriite laser technology. Pumping with inexpensive single-mode diodes, 270-mW of output power and a total tunability from 754 to 1042 nm were demonstrated in continuous-wave operation. In mode-locked operation, 100-fs pulses with 50-nJ pulse energy were demonstrated. TuEE4 16.30-16.45

Optics Letters

We report, to the best of our knowledge, the first mode-locked operation of Yb:YLF gain media at ... more We report, to the best of our knowledge, the first mode-locked operation of Yb:YLF gain media at cryogenic temperatures. A saturable Bragg reflector was used for initiating and sustaining mode locking. Once aligned, the system was self-starting and quite robust. Using output couplers in the 10-40% range, 3-5 ps long pulses with an average power as high as 28 W were achieved. The repetition rate was 46.45 MHz, and the corresponding pulse energy and peak power were as high as 602 nJ and 126.5 kW, respectively. The central wavelength of the mode-locked pulses could be tuned in the 1013.5-1019 nm range using an intracavity birefringent filter. The achieved output power performance is two to three orders of magnitude higher than previous room-temperature Yb:YLF systems.

2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2017

Dual-wavelength and tri-wavelength operation of solid-state lasers has been attracting a great de... more Dual-wavelength and tri-wavelength operation of solid-state lasers has been attracting a great deal of attention, due to the need for such sources in applications like coherent terahertz generation [1]. Multicolor laser operation has been shown in many solid-state laser gain media including Nd:YAG, Yb:KGW, Tm:YAP, Cr:LiSAF, Alexandrite, Tm:CaYAlO4, and Ti:Sapphire. Most of the earlier studies report dual/triple wavelength operation in a few pairs of lines. Furthermore, the ratio of the power in each line varies with external factors such as pump power, and could not be controlled easily. These disadvantages are due to the method used for frequency selection, where operating in a multi-wavelength regime requires specially coated cavity optics and/or coupled cavities, which can usually be optimized for a single transition pair at a fixed output coupling and pump power.

2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021

Yb:YLF is a broadly tunable (996-1076 nm) continuous-wave (cw) laser that allows generation of su... more Yb:YLF is a broadly tunable (996-1076 nm) continuous-wave (cw) laser that allows generation of sub-100-fs long pulses upon mode-locking at room temperature [1] - [4] . Unfortunately, the power handling limitations of the thermo-mechanically weak YLF host at room temperature limited the average mode-locked output power to the 100 mW level in earlier studies. The advantages of cryogenic operation with respect to power scaling is well-known and ample explored in cw, q-switched and amplifier geometries in Yb:YLF systems and output power above 300 W has been achieved [5] - [8] . Interestingly, unlike other media like Yb:YAG, Yb:YLF possess a relatively broad gain bandwidth even at cryogenic temperatures (FWHM: ~10 nm in E//a axis). Despite that, to our knowledge, till this study [9] , mode-locking of Yb:YLF was not explored at cryogenic temperatures.

OSA Continuum, 2020

We report record output pulse energies from a cryogenic 8-pass Yb:YLF amplifier system operating ... more We report record output pulse energies from a cryogenic 8-pass Yb:YLF amplifier system operating at 10 Hz repetition rate. When seeded with 20-mJ, 1-ns stretched pulses, the amplifier produced output pulses with 305 mJ of energy at 1018.5 nm with a spectral width supporting sub-ps pulse-duration. The output beam profile was quite symmetric and had a measured beam quality factor (M2) of ∼1.45. To achieve this performance, the diameter of the beam inside the gain element is gradually increased via an adjustable telescope from around 4.6 mm to 6.2 mm. This enables adjustment of the fluence to a moderate value in subsequent passes: high enough for efficient extraction and low enough to prevent laser induced damage. To our knowledge, this is the highest pulse energy reported from cryogenically cooled Yb:YLF amplifiers to date. Further scaling in peak power and repetition rate is anticipated in future work.

Optics Express, 2020

We report, what is to our knowledge, the highest average power obtained directly from a Yb:YLF re... more We report, what is to our knowledge, the highest average power obtained directly from a Yb:YLF regenerative amplifier to date. A fiber front-end provided seed pulses with an energy of 10 nJ and stretched pulsewidth of around 1 ns. The bow-tie type Yb:YLF ring amplifier was pulse pumped by a kW power 960 nm fiber coupled diode-module. By employing a pump spot diameter of 2.1 mm, we could generate 20-mJ pulses at repetition rates between 1 Hz and 3.5 kHz, 10 mJ pulses at 5 kHz, 6.5 mJ pulses at 7.5 kHz and 5 mJ pulses at 10 kHz. The highest average power (70 W) was obtained at 3.5 kHz operation, at an absorbed pump power level of 460 W, corresponding to a conversion efficiency of 15.2%. Despite operating in the unsaturated regime, usage of a very stable seed source limited the power fluctuations below 2% rms in a 5 minute time interval. The output pulses were centered around 1018.6 nm with a FWHM bandwidth of 2.1 nm, and could be compressed to below 1-ps pulse duration. The output bea...

OSA Continuum, 2019

We report 190-mJ pulses with spectral content supporting sub-ps pulse-duration at a 10 Hz repetit... more We report 190-mJ pulses with spectral content supporting sub-ps pulse-duration at a 10 Hz repetition rate generated by a cryogenically-cooled, bulk Yb:YLF laser amplifier system. The amplifier system relies on a chirped pulse amplification architecture and consists of a fiber front-end, a regenerative amplifier, and two 4-pass amplifiers. The fiber front-end delivers 15-nJ, 1-ns stretched seed pulses, which are first amplified to 13-mJ pulse energy inside a Yb:YLF regenerative amplifier. Then the pulses are boosted further to 115 mJ and 190 mJ in two consecutive 4-pass amplifiers. To our knowledge, these are the highest pulse energies reported from Yb:YLF based amplifiers to date. We foresee shortening the pulsewidths to sub-400-fs range in future studies.

Optics Express, 2017

In this study, we numerically and experimentally investigate application of birefringent filters ... more In this study, we numerically and experimentally investigate application of birefringent filters (BRFs) as frequency selective elements in multicolor lasers. A BRF plate made out of crystalline quartz with an arbitrarily oriented optical axis has been explored. Simulation results have shown that compared to regular BRFs where the optical axis lies in the plane of the plates surface, a BRF with an optical axis pointing out of its surface enables design flexibility in filter parameters, providing access to a wider set of free spectral range and bandwidth values. As a result, multicolor operation could be obtained in many wavelength pairs using a single BRF plate. In the experiments a 3-mm thick quartz BRF with an optical axis 45° to the surface plane has been used. With Cr:Nd:GSGG as a laser medium two-color and three-color cw laser operation has been demonstrated in 11 and 3 different transition combinations, respectively. Moreover, two-color laser operation has been demonstrated in 10 different wavelength pairs in Cr:LiSAF. To our knowledge, this study is the first detailed investigation and experimental demonstration of BRFs with tilted optical axis for multicolor operation of solid-state lasers. Compared to other methods, BRFs enable a rich selection of transition pairs and also the ratio of the power in each line could be regulated by fine adjustment of the rotation angle. Implementation of tilted-axis BRFs should boost development of efficient and low-cost multicolor lasers in other gain media as well.

Laser Congress 2019 (ASSL, LAC, LS&C), 2019

We report, to the best of our knowledge, direct generation of the shortest pulses from a single-w... more We report, to the best of our knowledge, direct generation of the shortest pulses from a single-walled carbon nanotube mode-locked solid-state laser with a Cr:LiSAF gain medium, yielding 23-fs, nearly transform-limited pulses at 850 nm.

Optics Letters, 2021

We report an efficient diode-pumped high-power cryogenic regenerative amplifier operating at 1019... more We report an efficient diode-pumped high-power cryogenic regenerative amplifier operating at 1019 nm employing the c-axis of Yb:YLF. Compared to the usually selected 1017 nm transition of a-axis, the c-axis 1019 nm line has 3-fold higher emission cross section and still possess a full-width-half-maximum (FWHM) of 6.5 nm at 125 K. The chirped-pulse amplifier system is seeded by a fiber front-end with an energy of 30 nJ and stretched pulsewidth of 2 ns. In regenerative amplification studies, using the advantage of higher gain in the c-axis, we have achieved record average powers up to 370 W, with an extraction efficiency of 78% at 50 kHz repetition rate. The output pulses were centered around 1019.15 nm with a FWHM bandwidth of 1.25 nm, which supports sub-1.5 ps pulse durations. The output beam maintained a TEM00 beam profile at output power levels below 250 W with an M 2 below 1.2. Above this power level the thermally induced lensing in Yb:YLF created a multimode output beam. The thermal lens was rather dynamic and deteriorated the system stability above 250 W average power level.

Applied Physics B, 2021

We present detailed experimental results with cryogenic Yb:YLF gain media in rod-geometry. We hav... more We present detailed experimental results with cryogenic Yb:YLF gain media in rod-geometry. We have comparatively investigated continuous-wave (cw) lasing and regenerative amplification performance under different experimental conditions. In the cw lasing experiments effect of crystal doping, cw laser cavity geometry and pump wavelength on lasing performance were explored. Regenerative amplification behavior was analyzed and the role of depolarization losses on performance was investigated. A recently developed temperature estimation method was also employed for the first time in estimating average crystal temperature under lasing conditions. It is shown that the thermal lens induced by transverse temperature gradients is the main limiting factor and strategies for future improvements are discussed. To the best of our knowledge, the achieved results in this study (375 W in cw, and 90 W in regenerative amplification) are the highest average powers ever obtained from this system via em...

OSA High-brightness Sources and Light-driven Interactions Congress 2020 (EUVXRAY, HILAS, MICS), 2020

We demonstrate a cryogenically-cooled Yb:YLF regenerative amplifier delivering 20-mJ pulses at 3.... more We demonstrate a cryogenically-cooled Yb:YLF regenerative amplifier delivering 20-mJ pulses at 3.5 kHz corresponding to 70 W average power. The pulses possess 2.1 nm spectral bandwidth centered at 1019 nm supporting sub-ps pulses.

2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021

Nowadays the compact high power and high energy laser sources could be used for a variety of scie... more Nowadays the compact high power and high energy laser sources could be used for a variety of scientific and industrial applications as high harmonic generation, electron acceleration and material processing [1] . Although the room-temperature laser systems can provide millijoule energy at high average powers of hundreds of watts with pulse widths in the 0.5-5 ps, yet that requires to a complicated laser architecture [2] , [3] . The lasers operating at cryogenic temperatures exhibit simpler optical design together with a pristine beam quality [4] . In this work we propose as an attractive crystal choice of Yb:YLF (Yb:LiYF 4 ) for cryogenic regenerative amplifiers. Yb:YLF crystal combine adequate thermomechanical strength with a relatively broad gain bandwidth that could ideally support amplification of sub-250-fs pulses [4] .

Applied Optics, 2021

We report, to the best of our knowledge, the first mode-locking results of a Cr:LiSAF laser near ... more We report, to the best of our knowledge, the first mode-locking results of a Cr:LiSAF laser near the 1 µm region. The system is pumped only by a single 1.1 W high-brightness tapered diode laser at 675 nm. A semiconductor saturable absorber mirror (SESAM) with a modulation depth of 1.5% and non-saturable losses below 0.5% was used for mode-locking. Once mode-locked, the Cr:LiSAF laser produced almost-transform-limited sub-200-fs pulses with up to 12.5 mW of average power at a repetition rate of 150 MHz. Using an intracavity birefringent filter, the central wavelength of the pulses could be smoothly tuned in the 1000–1020 nm range. Via careful dispersion optimization, pulse widths could be reduced down to the 110-fs level. The performance in this initial study was limited by the design parameters of the SESAM used, especially its passive losses and could be improved with an optimized SESAM design.

Optics Express, 2019

We present, what is to our knowledge, the first detailed lasing investigation of cryogenic Yb:YLF... more We present, what is to our knowledge, the first detailed lasing investigation of cryogenic Yb:YLF gain media in the E//a-axis. Compared to the usually employed E//c-axis, the a-axis of Yb:YLF provides a much broader and smooth gain profile, but this comes at the expense of reduced gain product. We have shown that, despite the lower gain, which (i) increases susceptibility to cavity losses, (ii) raises lasing threshold, and (iii) inflates thermal load, efficient and high-power lasing could be achieved in the E//a axis as well. A record continuous-wave (cw) powers above 300 W, cw slope efficiencies of 73%, and a tuning range covering the 995-1020.5 nm region were demonstrated. In quasi-cw lasing experiments, via minimization of thermal effects, slope efficiencies can be scaled up to 85%. In gain-switched operation, sub-50-µs long pulses with a peak power exceeding 2.5 kW at multi-kHz repetition rate were attained. We measured a beam quality factor below 1.5 for laser average powers up to 100 W and below 3 for laser average powers up to 300 W. Power scaling limits due to thermal effects, laser dynamics in pulsed pumping, and multicolor lasing operation potential were also investigated. The detailed results presented in this manuscript will pave the way towards development of high-power and high-energy Yb:YLF oscillators and amplifiers with sub-500-fs pulse duration.

Optical Materials Express, 2019

We present detailed measurements of effective emission cross section spectra of the Alexandrite g... more We present detailed measurements of effective emission cross section spectra of the Alexandrite gain medium in the 25-450°C temperature range and provide analytic formulas that can be used to match the measured spectra. The measurement results have been used to investigate the wavelength and temperature dependence of small signal gain, as well as gain bandwidth relevant for ultrafast pulse generation/amplification. We show that the estimated laser performance based on the measured spectroscopic data provides a good fit to the results in the literature. We further discuss the need for a detailed measurement of excited-state absorption cross section in future studies.

Optics Letters, 2018

We report, to the best of our knowledge, the shortest femtosecond pulses generated from a Kerr-le... more We report, to the best of our knowledge, the shortest femtosecond pulses generated from a Kerr-lens mode-locked (KLM) Alexandrite laser operating near 750 nm. The Alexandrite gain medium was pumped with a continuous-wave (cw), 532 nm laser, and the performance of both the short and extended resonators was investigated. The use of an extended cavity eliminated the multi-wavelength spectral instabilities observed during the cw operation of the short cavity. Furthermore, since the repetition rate of the Alexandrite laser was reduced from 107 to 5.6 MHz, the resulting increase in the intracavity pulse energy provided enhanced Kerr nonlinearity and eliminated the Q-switching instabilities during mode-locked operation. The KLM MPC Alexandrite laser produced nearly transform-limited, 70 fs pulses at a pulse repetition rate of 5.6 MHz with only 1 W of pump power. The time-bandwidth product was further measured to be 0.331.

Applied Optics, 2019

In this paper, we present highly-efficient continuous-wave (cw) laser operation of Tm:YAG and Tm:... more In this paper, we present highly-efficient continuous-wave (cw) laser operation of Tm:YAG and Tm:LuAG lasers pumped by high-brightness red tapered diodes. The single-emitter tapered diode lasers (TDLs) provide up to 1-W of pump power around 680 nm. By adjusting the operation temperature of the TDL, the pump central wavelength could be matched to the strong absorption peak of Tm 3+ ions in this region (3 H6→ 3 F3 excitation). This absorption peak is around 3-fold stronger than the usually employed 785 nm transition (3 H6→ 3 H4). In the cw laser experiments, we have achieved slope efficiencies exceeding 55% at room temperature, which is far above the stokes limited slope efficiency (34%), indicating presence of strong two-for-one cross-relaxation process. Pumping with high-brightness tapered diode lasers further facilitated usage of smaller pump spots (enabling quite low lasing thresholds) and generation of near-diffraction limited output beam profiles from standard z-type cavities. To the best of our knowledge, this is the first report of diode pumping of Tm-doped solid-state lasers around 680 nm, as well as the first usage of TDLs as pump sources in Tm-doped laser systems.

2009 IEEE LEOS Annual Meeting Conference Proceedings, 2009

We summarize recent progress in low-cost and highly-efficient Cr:Colquiriite laser technology. Pu... more We summarize recent progress in low-cost and highly-efficient Cr:Colquiriite laser technology. Pumping with inexpensive single-mode diodes, 270-mW of output power and a total tunability from 754 to 1042 nm were demonstrated in continuous-wave operation. In mode-locked operation, 100-fs pulses with 50-nJ pulse energy were demonstrated. TuEE4 16.30-16.45

Optics Letters

We report, to the best of our knowledge, the first mode-locked operation of Yb:YLF gain media at ... more We report, to the best of our knowledge, the first mode-locked operation of Yb:YLF gain media at cryogenic temperatures. A saturable Bragg reflector was used for initiating and sustaining mode locking. Once aligned, the system was self-starting and quite robust. Using output couplers in the 10-40% range, 3-5 ps long pulses with an average power as high as 28 W were achieved. The repetition rate was 46.45 MHz, and the corresponding pulse energy and peak power were as high as 602 nJ and 126.5 kW, respectively. The central wavelength of the mode-locked pulses could be tuned in the 1013.5-1019 nm range using an intracavity birefringent filter. The achieved output power performance is two to three orders of magnitude higher than previous room-temperature Yb:YLF systems.

2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2017

Dual-wavelength and tri-wavelength operation of solid-state lasers has been attracting a great de... more Dual-wavelength and tri-wavelength operation of solid-state lasers has been attracting a great deal of attention, due to the need for such sources in applications like coherent terahertz generation [1]. Multicolor laser operation has been shown in many solid-state laser gain media including Nd:YAG, Yb:KGW, Tm:YAP, Cr:LiSAF, Alexandrite, Tm:CaYAlO4, and Ti:Sapphire. Most of the earlier studies report dual/triple wavelength operation in a few pairs of lines. Furthermore, the ratio of the power in each line varies with external factors such as pump power, and could not be controlled easily. These disadvantages are due to the method used for frequency selection, where operating in a multi-wavelength regime requires specially coated cavity optics and/or coupled cavities, which can usually be optimized for a single transition pair at a fixed output coupling and pump power.