E. Caracciolo

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

A new high-performance Yb:CaAlGdO(4) (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 of pulse energy and 258 MW peak power. The compressed pulses have a time-bandwidth product of 0.69 and could be shortened further with an improved compressor setup.

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.

42 W femtosecond Yb:Lu 2 O 3 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.

Performance of Yb:Sc 2 SiO 5 crystal in diode-pumped femtosecond oscillator and regenerative amplifier

Yb:Sc2SiO5 has been investigated in a low-power laser femtosecond oscillator pumped by 400-mW single-mode fiber-coupled diode at 976 nm. Pulses as short as 71 fs were achieved. The same crystal was later employed in a regenerative amplifier, with an output power as high as 4.7 W at 500 kHz and sub-300-fs pulses.

High power Yb:CALGO ultrafast regenerative amplifier for industrial application

We present a high-power, single-crystal based, Yb:CALGO regenerative amplifier. The system delivers more than 50 W output power in continuous-wave regime, with diffraction limited beam quality. In Q-switching regime the spectrum is centered at 1043 nm and is 11 nm wide. In regenerative amplification experiments we achieved 34 W at 500 kHz with 12.7 nm FWHM wide spectra centered at 1044 nm seeding with a broadly tunable, single-prism SESAM mode-locked Yb:CALGO laser providing 9 nm wide spectra at 1049 nm. Pulse duration after compression was 140 fs, with excellent beam quality (M2 < 1.25).

High-energy multiwatt femtosecond diode-pumped Yb:CaAlGdO4 and Yb:CaF2 regenerative 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. These laser sources are extremely interesting for industrial applications where high pulse energies at relative high repetition rates allow to considerably reduce the manufacturing throughput time.

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 ≈ 110 ps) with a maximum energy of 205 μJ 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 μJ 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.

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.