André Loescher

Ultrafast thin-disk multipass laser amplifier delivering 1.4 kW (4.7 mJ, 1030 nm) average power converted to 820 W at 515 nm and 234 W at 343 nm

We report on an Yb:YAG thin-disk multipass laser amplifier delivering sub-8 ps pulses at a wavelength of 1030 nm with 1420 W of average output power and 4.7 mJ of pulse energy. The amplifier is seeded by a regenerative amplifier delivering 6.5 ps pulses with 300 kHz of repetition rate and an average power of 115 W. The optical efficiency of the multipass amplifier was measured to be 48% and the beam quality factor was better than M2 = 1.4. Furthermore we report on the external second harmonic generation from 1030 nm to 515 nm using an LBO crystal leading to an output power of 820 W with 2.7 mJ of energy per pulse. This corresponds to a conversion efficiency of 70%. Additionally, 234 W of average power were obtained at the third harmonic with a wavelength of 343 nm.

High power Yb:YAG single-crystal fiber amplifiers for femtosecond lasers

We describe a multi-stages single crystal fiber (SCF) amplifier for the amplification of femtosecond pulses with radial or azimuthal polarization in view of high speed material processing (surface structuring, drilling). We demonstrate a three stages diode-pumped Yb:YAG single crystal fiber amplifier to achieve femtosecond pulses at an average power of 85W at 20 MHz in radial and azimuthal polarization.

Ultrafast thin-disk multipass amplifier with 1.4 kW average power and 4.7 mJ pulse energy at 1030 nm converted to 820 W and 2.7 mJ at 515 nm

In recent years, there has been a growing interest in increasing the output power of ultrafast lasers to the kW-range. This allows higher productivity for laser material processing, e.g. for cutting of carbon-fiber reinforced plastics (CFRP) or for micro-machining. We developed an Yb:YAG thin-disk multipass amplifier delivering sub-8 ps pulses with 1.4 kW average power which is – to the best of our knowledge – the highest output power reported for a sub-100 ps ultrafast laser system so far. The amplifier is seeded by a regenerative amplifier with 6.5 ps pulses and 115 W of average power at a repetition rate of 300 kHz. Taking this repetition rate into account, the energy of the amplified pulses is as high as 4.7 mJ. This was achieved using a scheme with 40 mirrors in an array to geometrically fold the seed beam 40 times over the thin-disk. The beam quality was measured to be better than M2=1.4. This system was used in first experiments to cut CFRP with very good quality and with unprecedented efficiency. Additionally, the output beam of the amplifier was frequency-doubled in an LBO crystal to 820 W (70 % conversion efficiency) output power at the second harmonic wavelength (515 nm) and 106 W (26.5 % conversion efficiency) at the third harmonic wavelength (343 nm). Both results are record output powers for ultrafast laser systems at the respective wavelengths. In the presentation, we will show concepts on further power scaling of the system.

Ultra-Short pulse laser processing of CFRP with kilowatt average power

For laser processing of carbon fiber reinforced plastics (CFRP), high intensities over 108 W/cm² are necessary to process the material with a thermal damage smaller than 10 µm. Today such high intensities are preferably achieved with ultra-short pulse laser systems. However, the average laser power of such laser systems is usually too low for productive cutting processes. The IFSW thin-disk multipass amplifier yielding a maximum average output power of 1400 W at a pulse repetition rate of 300 kHz, a pulse duration of 8 ps, and a pulse energy of about 4.7 mJ allowed for the first time to process CFRP at this average power and pulse energy level. In the presented experiments, the average laser power was limited to 1.1 kW and the pulse energy to 3.7 mJ.With this unique laser system CFRP with a thickness of 2 mm was cut by deflecting the laser beam multiple times over the same trajectory with a fast scanner system. By avoiding heat accumulation effects it was possible to minimize the extent of the thermal damage to below 10 µm. The effective average cutting speed was 0.9 m/min.For laser processing of carbon fiber reinforced plastics (CFRP), high intensities over 108 W/cm² are necessary to process the material with a thermal damage smaller than 10 µm. Today such high intensities are preferably achieved with ultra-short pulse laser systems. However, the average laser power of such laser systems is usually too low for productive cutting processes. The IFSW thin-disk multipass amplifier yielding a maximum average output power of 1400 W at a pulse repetition rate of 300 kHz, a pulse duration of 8 ps, and a pulse energy of about 4.7 mJ allowed for the first time to process CFRP at this average power and pulse energy level. In the presented experiments, the average laser power was limited to 1.1 kW and the pulse energy to 3.7 mJ.With this unique laser system CFRP with a thickness of 2 mm was cut by deflecting the laser beam multiple times over the same trajectory with a fast scanner system. By avoiding heat accumulation effects it was possible to minimize the extent of the thermal dam...

Recent Progress in Thin-disk Lasers Based on Various Yb-doped Materials

We will give an overview about the current status of thin-disk laser development in the cw and ultrafast regime (oscillators and amplifiers) with a special emphasis on our group’s activities.

Thin-disk multipass amplifier delivering 10 GW of peak power

Recent development of thin-disk multipass amplifiers has resulted in several breakthroughs in average power and pulse energy of both ps- and fs-amplifiers [1-3]. These results confirm the suitability of this laser architecture for amplification of ultrafast pulses with high energy and at high average powers thanks to low nonlinearities in the thin-disk and to an efficient cooling scheme. However, as peak powers are reaching or exceeding the GW, even nonlinearities induced by propagation in air become relevant in terms of spectral broadening due to self-phase modulation (SPM).

Thin-disk multipass amplifier emitting radially polarized beam with 635 W of average power and 2.1 mJ of pulse energy

We present our latest achievements on the amplification of ultrafast beams with radial polarization using a thin-disk multipass amplifier. Starting with a seed laser (TruMikro5050 provided by the company TRUMPF laser GmbH) delivering a linearly polarized beam with 115 W of average output power, 6.5 ps pulse duration at a repetition rate of 300 kHz, we could extract radially polarized laser pulses with an average output power of 635 W and a pulse energy of 2.1 mJ. The radial polarization was obtained by using a segmented wave-plate placed in front of the amplifier. This is, to the best of our knowledge, the highest average output power and pulse energy reported so far for radially polarized ultrafast lasers. A scheme for direct amplification of such ring-shaped radially polarized laser beams is presented together with a possible solution to compensate for the depolarizing phase shift introduced by the optical components in the amplifier.