160-mJ Cryogenically-Cooled Yb:YLF Amplifier System at 1019 nm

Çankaya, Hüseyin; Demibas, Umit; Pergament, Mikhail; Hemmer, Michaël; Hua, Yi; Zapata, Luis E.; Kärtner, Franz X.

doi:10.1109/cleoe-eqec.2019.8872579

Cited by 2 publications

(2 citation statements)

References 16 publications

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“…5(b)). Here a 5 ms long pump pulsewidth is chosen in purpose, since in our earlier multipass with Yb:YLF amplifiers, we have seen that this pump pulsewidth is a reasonable value for pumping the Yb:YLF gain media (2.5 times longer than the 2 ms fluorescence lifetime of Yb:YLF) [51]. So, one can see this experiment as the investigation of repetition rate scaling potential of cryogenic Yb:YLF multipass amplifiers, but of course the lasing physics observed here is quite different than the mechanism that will be observed in a seeded amplifier with limited number of passes through the gain media.…”

Section: Quasi-continuous-wave (Long-pulse) Lasing Resultsmentioning

confidence: 99%

Efficient, diode-pumped, high-power (>300W) cryogenic Yb:YLF laser with broad-tunability (995-10205 nm): investigation of E//a-axis for lasing

et al. 2019

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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.

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Section: Quasi-continuous-wave (Long-pulse) Lasing Resultsmentioning

confidence: 99%

Efficient, diode-pumped, high-power (>300W) cryogenic Yb:YLF laser with broad-tunability (995-10205 nm): investigation of E//a-axis for lasing

et al. 2019

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“…However, due to the flat gain profile, the FWHM of the amplified pulses still had a width of 2.1 nm. The corresponding transform-limited pulse duration for such a spectrum is around 700-fs, and we have measured a sub-ps pulse duration earlier from a lower repetition rate version of this system [37,38]. On the other hand, it is clear from Fig.…”

Section: Regenerative Amplification Resultsmentioning

confidence: 82%

20-mJ, sub-ps pulses at up to 70 W average power from a cryogenic Yb:YLF regenerative amplifier

et al. 2020

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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 beam maintained a TEM 00 beam profile at all power levels, and possesses a beam quality factor better than 1.05 in both axis. The relatively narrow bandwidth of the current seed source and the moderate gain available from the single Yb:YLF crystal was the main limiting factor in this initial study. a gain bandwidth of 10 nm for the E//a axis at cryogenic temperatures [1]. Moreover, unlike Yb:YAG, the emission profile is rather smooth, which minimizes gain-narrowing effects, that could potentially enable amplification of sub-250 fs long pulses. At the same time, parameters of Yb:YLF such as thermal conductivity, thermal expansion coefficient, thermo-optic coefficient (dn/dT) are better than for RT Yb:YAG. On the other hand, the emission cross section of Yb:YLF at 80 K is only around 0.7 × 10 −20 cm 2 for the E//a axis, which is around 3 times lower than RT-Yb:YAG and 14 times lower when compared to cryogenic Yb:YAG. However, the longer fluorescence lifetime, τ=1990 µs [17], partly balances for the reduced gain, resulting in a σ em τ-product of 1.4 x10 −23 cm 2 s in comparison with 2 × 10 −23 cm 2 s and 9.4 × 10 −23 cm 2 s of RT and cryogenic Yb:YAG, respectively. As a result of the low emission cross section, one also suffers from a rather high saturation fluence (14 J/cm 2 ) in Yb:YLF, which creates challenges in optimizing extraction from amplifiers. As an example, for a stretched pulsewidth of 1 ns, the cavity optics has an estimated laser induced damage threshold (LIDT) of around 6.3 J/cm 2 , and long-term damage free operation usually requires operating the amplifier at a lower/safer value of ∼3 J/cm 2 or below. Operating the amplifier at a fluence value much lower than the saturation fluence: (i) reduces the extraction efficiency of the circulating amplified pulse, (ii) increases output energy fluctuations upon undesired perturbations, and (iii) results in circulation of a Gaussian beam profile in the amplifier (which is known to have 2 times higher fluence compared to flattop beams). Note that, despite these disadvantages, if the am...

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160-mJ Cryogenically-Cooled Yb:YLF Amplifier System at 1019 nm

Cited by 2 publications

References 16 publications

Efficient, diode-pumped, high-power (>300W) cryogenic Yb:YLF laser with broad-tunability (995-10205 nm): investigation of E//a-axis for lasing

Efficient, diode-pumped, high-power (>300W) cryogenic Yb:YLF laser with broad-tunability (995-10205 nm): investigation of E//a-axis for lasing

20-mJ, sub-ps pulses at up to 70 W average power from a cryogenic Yb:YLF regenerative amplifier

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