Compact gigawatt-class sub-picosecond Yb:YAG thin-disk regenerative chirped-pulse amplifier with high average power at up to 800 kHz

Abstract

Ultrashort pulses are capable of processing practically any material with a negligible heat affected zone [1]. For productive industrial applications a pulse duration of about 5 ps is a well established compromise between being faster than the electron-phonon interaction time of the material and being long enough to suppress detrimental effects such as nonlinear interaction with the ablated plasma plume. The scalable disk technology applied to high peak power lasers has resulted in today's most powerful ultrafast systems for high precision industrial micro processing [2]. However, sub-picosecond pulses can further increase the ablation efficiency for certain materials, depending on the available average power and peak fluence as well as the desired feature size. On the one hand, for practical situations the efficiency generally changes little from 1 ps to 500 fs [3,4]. On the other hand, the situation may be different at harmonic wavelengths, where a careful optimization at high average power is challenging, in particular as frequency conversion is typically optimized for certain pulse durations and energies.Here, we report on a sub-picosecond amplifier similar to that described in [5], reaching gigawatt intensities and up to 160 W average power with a simplified and much more compact laser system (laser head dimensions 100 cm x 60 cm). A commercially available TruMicro 5070 [6], based on a single-disk regenerative amplifier operating at 1030 nm, was modified replacing the picosecond seed by a femtosecond fiber laser with reduced stretching compared to [5] and replacing the optional frequency conversion module by a very compact pulse compressor: In contrast to the large 3.5 m grating separation used in [5] we employ a single-pass transmission grating compressor with below 2 cm grating separation. Our compressor design offers higher efficiencies beyond 90 % at a small footprint and maintains the high beam quality of the laser. Figure 1 shows the output power versus pump power, the optical spectrum, and the autocorrelation trace for high average power at 800 kHz as well as at high peak power at 100 kHz. At 800 kHz, 750 fs pulses were obtained with a beam quality M 2 < 1.2 and an average compressed output power of 160 W, only limited by installed pump power. At 100 kHz, 650 fs pulses were obtained with an average output power of 85 W. The compressed pulse energy was limited to 850 μJ by the onset of self-phase modulation which is clearly apparent in the optical spectrum and the pedestal to the autocorrelation trace. Peak power scaling would be straight forward using a somewhat larger stretching. Gigawatt sub-picosecond pulses can thus be obtained from a compact industrial laser system.

The amazing progress of high-power ultrafast thin-disk lasers

“…Since their introduction as the world's first high average power industrial ultrafast lasers with 50 W of average power back in 2007 they have become the most successful commercial ultrafast lasers for direct micromachining [20]. The first high power industrial femtosecond lasers exceeding 100 W, demonstrated in 2013, were based on a CPA thin-disk regenerative amplifier, and obtained gigawatt peak powers [21]. Such peak powers are even possible in CPA-free systems using cm-size Pockels cells [22].…”

Yb:CALYO-based femtosecond chirped pulse regenerative amplifier for temporally resolved pump-probe spectroscopy

“…Up to now, the highest average power RA systems are presented by thin-disk concept RAs. For example, up to 160 W average output power at 800 kHz PRF with 750 fs pulse duration were achieved in [4]. Up to 100 W average power at 400 kHz PRF with 800 fs pulse duration were reached in [5] employing Yb:YAG thin-disk active element.…”

28-W, 217 fs solid-state Yb:CAlGdO_4 regenerative amplifiers

“…An Yb:YAG TDL RA yielded as much as 160 W at 800 kHz, although with significantly longer 750 fs pulses [7].…”