High-energy multiwatt femtosecond diode-pumped Yb:CaAlGdO4and Yb:CaF2regenerative amplifiers

We study and compare the performance of Yb:CaAlGdO4- and Yb:CaF2-based regenerative amplifiers at low (5 to 10 kHz) and high (up to 500 kHz) repetition rates. Both materials allow for pulse energies of <1 mJ with sub-400-fs at low repetition rates and up to 9.4 W of average output power at 500 kHz. Thanks to the good thermal properties of Yb:CaF2 and Yb:CALGO, the extracted energy has the potential to be significantly increased with further pump power scaling. Shorter pulses are also potentially achievable by optimizing the design of stretcher and compressor in order to better compensate higher-order dispersion and reduce nonlinear effects

High pulse energy multiwatt Yb:CaAlGdO4 and Yb:CaF2 regenerative amplifiers

We investigated and compared Yb:CaAlGdO4 and Yb:CaF2 regenerative amplifiers at repetition rates 5-10 kHz, a frequency range interesting for industrial applications requiring relatively high pulse energy. Both materials allow for pulse energies close to 1 mJ with sub-400-fs pulses. The two laser materials offer comparable performance in the pump power range investigated. The same regenerative amplifiers can be run up to 500 kHz for much faster material processing, with maximum output power of up to 9.4 W

28 W, 217-fs regenerative bulk amplifier based on Yb:CAlGdO4

Yb:CaAlGdO4 (Yb:CALGO) is a very promising material for high power ultrashort pulse generation, due to its broad emission bandwidth and good thermal properties. Here we report, to the best of our knowledge, the highest power and shorter pulses ever demonstrated from a Yb:CALGO-based regenerative amplifier. The system layout consists of a Yb:CALGO oscillator seeding a Yb:CALGO regenerative amplifier followed by a folded grating compressor. The Yb:CALGO oscillator provides approximately 650 mW output power in a 63 MHz repetition rate pulse train of 92-fs long pulses. The related spectrum is 12.5 nm wide (FWHM) and centered around 1050 nm. Average output powers as high as 36 W at 500 kHz are achieved out of the regenerative amplifier while pumping with 116 W at approximately 980 nm. A small roll-over in the regenerative output power is observed at maximum pump power. This is mostly due to a drift of the pump wavelength away from the maximum crystal absorption peak with increasing pump current. After compression, we obtained 28 W in a train of 217-fs long pulses, corresponding to a pulse energy higher than 50 µJ per pulse and a peak power above 0.25 GW. The pulse spectrum is centered at 1046 nm and is approximately 11 nm wide, corresponding to a time bandwidth product of 0.69. The beam quality factor stays below M2=1.15 up to the maximum output power level, confirming the outstanding thermal performances of the Yb:CALGO material. Experiments on further power up-scaling are in progress

Performance of the Yb:Lu2O3 laser crystal in diode-pumped femtosecond oscillators and high-power regenerative amplifiers

We investigated the performance of the laser gain medium Yb:Lu2O3 in a low-power oscillator and a high-power regenerative amplifier. Almost Fourier transform limited 78-fs pulses were demonstrated in the low-power, SESAM mode-locked oscillator pumped with a single-mode fiber-coupled laser diode. Exploiting the excellent thermomechanical properties of Yb:Lu2O3, we were able to achieve up to 22.2 W of average output power at a repetition rate of 500 kHz and 670-fs long pulses with the regenerative bulk amplifier. Experiments on further power up-scaling and pulse duration shortening are in progress. Up to 65 W were already proved in preliminary tests in cw regime

Multi-kHz, High Energy, Femtosecond Diode-Pumped Yb:CaF2 Regenerative Amplifier

We report an efficient, high-energy, diode-pumped Yb:CaF2 regenerative amplifier. Energies up to 1.02 mJ at 1045-nm and 5 kHz-repetition rate in 324 fs-long pulses have been obtained with a beam quality factor of M2 =1.1

28-W, 217-fs solid-state Yb:CAlGdO4 regenerative amplifier

A new high-perfomance Yb:CaAlGdO4 (Yb:CALGO) regenerative amplifier is demonstrated. Pumped by 116 W at ≈ 980 nm and seeded by means of a 92-fs oscillator, it generates as much as 36-W of average output power with chirped pulses, and 28-W with 217-fs compressed pulses at 500-kHz repetition rate. This corresponds to 56-μJ pulse energy and 258-MW peak power. The compressed pulses have a time-bandwidth product of 0.69 and could be further shortened with an improved compressor setup

42 W femtosecond Yb:Lu₂O₃ regenerative amplifier

We report on a femtosecond high-power regenerative amplifier based on Yb:Lu₂O₃. Exploiting the excellent thermo-mechanical properties of this material, we were able to achieve up to 64.5 W in continuous-wave regime, limited only by the available pump power. In pulsed operation, 42 W of average output power at a repetition rate of 500 kHz with 780 fs long pulses could be demonstrated, resulting in a pulse peak power of ∼100  MW. The spectrum was centered at 1034 nm with an FWHM of 2.4 nm, potentially allowing for even shorter pulses. At the maximum output power the beam was nearly TEM₀₀, with an M² value of 1.2 in both axes

Single grating mirror intracavity stretcher design for chirped pulse regenerative amplification

We demonstrated for the first time, to the best of our knowledge a new intracavity pulse stretching design, employing a single grating-mirror based on a leaky-mode grating-waveguide design. The extremely compact and flexible layout allows for femtosecond pulses to be easily stretched up to nanosecond durations. The stretcher was implemented in a diode-pumped Yb:CALGO regenerative amplifier followed by a standard transmission grating compressor. We demonstrated sub-200 fs long pulses (stretched pulses approximate to 110 ps) with a maximum energy of 205 mu J at 20 kHz repetition rate. As a proof of the robustness and potential energy scaling of leaky-mode grating- waveguide intracavity stretcher, energies up to 700 mu J and 400 ps long pulses before compression at a lower repetition rate of 10 kHz, have been achieved. A simple model is proposed to investigate the cavity behavior in presence of induced spatial chirp