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

Abstract

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.

Ultrafast thin-disk multipass laser amplifier delivering 14 kW (47 mJ, 1030 nm) average power converted to 820 W at 515 nm and 234 W at 343 nm

“…The seed laser generates pulses with a duration of 6.5 ps at an average output power of 115 W. In comparison to the previous investigations with 800 kHz [20] the repetition rate was now reduced to 300 kHz [27] to further explore the capability of energy scaling with the multipass thin-disk laser amplifier. Figure 1 shows the setup of the multipass amplifier, which is identical to the one described in [20,27].…”

“…8. At a maximum fundamental input power of 1170 W the output power at 515 nm was measured to be 820 W, corresponding to 2.7 mJ of energy per pulse [27]. To the best of our knowledge this is the highest average output power reported for an ultrafast laser at this wavelength and corresponds to a conversion efficiency of 70%.…”

“…Figure 1 shows the setup of the multipass amplifier, which is identical to the one described in [20,27]. The amplifier medium consists of an anti-reflection coated, planeparallel Yb:YAG thin-disk (with a diameter of 17 mm, a radius of curvature of 20.5 m, a thickness of 130 µm, and 10-11% of doping concentration) mounted on a diamond heat sink by TRUMPF.…”

High-power and high-efficiency frequency-doubled fundamental-mode thin-disk laser

“…This problem can be circumvented for instance by using laser radiation in the green regime, as with about 40% at room temperature, the absorption for this wavelength regime is significantly higher in copper [1], so that at this point, a high-power, high-brightness green laser source could lead to a new level of high quality and high reliability copper welding technology. Whereas for pulsed systems, high average powers have been demonstrated in the green regime both for intra-cavity [2] (1,8 kW average output power, pulse duration between 100 ns and 300 ns) and extra-cavity frequency doubling [3] (820 W average output power at 70% efficiency), efficient high-power fundamental-mode cw operation using intra-cavity frequency conversion is still limited by losses and thermal lensing issues induced by the additional intra-cavity elements needed for wavelength and polarization stabilization such as etalons and thin-film polarizers. The highest output power demonstrated to date is 255 W with an optical efficiency of 30% [4] and 470 W in multimode operation [5].…”