Green sub-ps laser exceeding 400 W of average power

Abstract

We present the world's first laser at 515 nm with sub-picosecond pulses and an average power of 445 W. To realize this beam source we utilize an Yb:YAG-based infrared laser consisting of a fiber MOPA system as a seed source, a rod-type pre-amplifier and two Innoslab power amplifier stages. The infrared system delivers up to 930 W of average power at repetition rates between 10 and 50 MHz and with pulse durations around 800 fs. The beam quality in the infrared is M-2 = 1.1 and 1.5 in fast and slow axis. As a frequency doubler we chose a Type-I critically phase-matched Lithium Triborate (LBO) crystal in a single-pass configuration. To preserve the infrared beam quality and pulse duration, the conversion was carefully modeled using numerical calculations. These take dispersion-related and thermal effects into account, thus enabling us to provide precise predictions of the properties of the frequency-doubled beam. To be able to model the influence of thermal dephasing correctly and to choose appropriate crystals accordingly, we performed extensive absorption measurements of all crystals used for conversion experiments. These measurements provide the input data for the thermal FEM analysis and calculation. We used a Photothermal Commonpath Interferometer (PCI) to obtain space-resolved absorption data in the bulk and at the surfaces of the LBO crystals. The absorption was measured at 1030 nm as well as at 515 nm in order to take into account the different absorption behavior at both occurring wavelengths

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

“…This suggests that one reason for the aberrations can be a slight misalignment or shift of the infrared beam which leads to diffraction at the aperture. Additionally, we believe that is caused by thermally induced phase mismatches in the LBO crystal [23] or conversion saturation effects also contribute to the deterioration in beam quality. This will be subject to future investigations.…”

“…Additionally, more than 500 W with less than 20 ns of pulse duration at a wavelength of 343 nm were demonstrated in the same work. Frequency-doubling of sup-ps pulses recently led to the demonstration of a green average power of 445 W at pulse repetition rate of 20 MHz [23]. In the UV spectral range, 39.1 W of output power and 39.1 µJ of pulse energy were demonstrated for 12 ps long infrared pulses [24].…”

First experimental results towards a 100 W wavelength tunable femtosecond OPCPA

“…Additionally, crystal growth and handling methods have improved. In a recent work, 18 up-to-date measurements of the absorption coefficients at 515 nm using the photothermal common-path interferometry (PCI) method 22,23 have been presented. It is not so easy to assign a single material value to the linear absorption.…”

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

“…Additionally, more than 500 W with less than 20 ns pulse duration at 343 nm wavelength were demonstrated in the same work. In the ultrafast regime, 445 W of green average power at a repetition rate of 20 MHz (22.5 µJ) were recently reported [19].…”