87  fs pulse generation in a diode-pumped semiconductor saturable absorber mirror mode-locked Yb:YLF laser

Pirzio, Federico; Fregnani, Luigi; Volpi, Azzurra; Lieto, A. Di; Tonelli, M.; Agnesi, Antonio

doi:10.1364/ao.55.004414

Cited by 24 publications

(15 citation statements)

References 12 publications

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“…These novel laser architectures already enabled kW level power levels from Yb:YAG laser/amplifier systems operating at room temperature. The thermo-opto-mechanical properties of Yb:YAG improves further once the material is cooled to cryogenic temperatures [12,13], as summarized in Table 1 [1,[14][15][16][17][18][19][20][21][22][23][24][25][26]. The main advantages in going to cryogenic temperatures are: (i) transition from a quasi-3-level to a four-level laser structure which minimizes self-absorption losses and lasing thresholds, (ii) improved thermo-optic effects, and (iii) increased emission cross section value.…”

Section: Introductionmentioning

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: Introductionmentioning

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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“…The results also highlight the presence of thermal effects and its role in lowering system efficiency. We have also seen that, for this specific system, due to the limited cooling efficiency of the liquid nitrogen boundary, the absorbed pump power applied to the system is limited to about 500 W. We refer the reader to the literature for more detailed discussions of lasing performance of Yb:YLF lasers in the cw [13,[24][25][26][27][28][29], quasi-cw [30][31][32][33][34], Q-switched [14,29] and cw mode-locked [35,36] regimes.…”

Section: Continuous-wave and Quasi Continuous-wave Lasing Resultsmentioning

confidence: 98%

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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“…Yb:YLF (Yb:LiYF4) is an interesting material that attracts the attention of optics community, not only as a broadband near infrared laser/amplifier gain medium [1][2][3][4][5][6][7][8][9][10][11], but also as a solid-state optical refrigerating medium [12][13][14][15][16][17][18]. From the laser scientist point of view, operating Yb:YLF at cryogenic temperatures enables increased gain and better thermal management, and provides laser sources with 2-3 orders of magnitude higher average power in comparison with roomtemperature operation [19][20][21][22][23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

Temperature and doping dependence of fluorescence lifetime in Yb:YLF (role of impurities)

et al. 2021

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We have investigated temperature and doping dependence of fluorescence lifetime in Yb:YLF crystals in the 78-300 K range, for samples with Yb-doping levels of 0.5%, 1 % and 25%. Radiation-trapping prolonged fluorescence lifetimes are first measured to understand the pros and cons of this inevitable process on fractional thermal load and laser gain. Later, pinhole method was used to acquire ideally trapping free fluoresce lifetimes. For the lowly Yb-doped samples, fluorescence lifetime was measured to be 1.97 ms and 2.1 ms at 78 K and 300 K, respectively. For the 25% Yb-doped sample, strong upconversion emission due to the presence of Er, Tm and Ho impurities were observed. A doubleexponential decay behavior, combined with excitation intensity dependent decay profile was also revealed for this highly doped sample. Even with the pinhole method, the 300 K fluorescence lifetimes was measured as 4.5 ms, showing the difficulty to acquire radiation-trapping free signals at high doping levels. Time dynamics of upconverted emission in different spectral regions were also recorded, which provides hints on the energy transfer mechanisms between the Yb ion and the other rare-earth impurities.

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87 fs pulse generation in a diode-pumped semiconductor saturable absorber mirror mode-locked Yb:YLF laser

Cited by 24 publications

References 12 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

Temperature and doping dependence of fluorescence lifetime in Yb:YLF (role of impurities)

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