Balancing the conversion efficiency and beam quality of second harmonic generation of a two-picosecond Yb:YAG thin-disk laser

Abstract

In this work, the optimization of the second harmonic generation in an LiB3O5 crystal of the 1 kHz, 2 ps Yb:YAG laser is being investigated. Depending on the crystal thickness, an optimal intensity exists, above which the back-conversion process negatively affects the beam quality and pulse shape, while decreasing conversion efficiency. For a selected 2 mm thick frequency doubling crystal, the conversion efficiency of 80% at an optimal intensity of 120 GW cm−2 has been achieved, with output pulse duration of 1.3 ps and with beam quality of 1.4 and 1.6 in a horizontal and vertical direction, respectively, which is only slightly worse than the beam quality at a fundamental frequency.

Micromachining of Invar with 784 Beams Using 1.3 ps Laser Source at 515 nm

“…Invar (FeNi36) foils provided by Goodfellow GmbH (Friedberg, Germany) with a thickness of 20 µm and dimensions of 50 × 50 mm were used as received (Ra~0.07 µm). The foils were treated by Perla laser system from HiLASE (Dolni Brezany, Czech Republic), equipped with second harmonic generation module emitting at wavelength of 515 nm, with pulse duration of 1.3 ps, beam quality factor M2 better than 1.5, repetition rate of 1 kHz and pulse energy up to 10 mJ [ 14 , 23 ]. The generated beam ( Figure 1 c) was guided through the galvanometer scanner without F-theta lens into the optical module developed by Meopta-optika, s.r.o., consisting of a DOE beamsplitter, 100 mm focusing lens and a polarizing beamsplitter for pattern observation on the sample surface.…”

Using harmonic beam combining to generate pulse-burst in nonlinear optical laser

“…In Ref. [11] the back-conversion occurred in a 10-mm thick LBO with a peak power density larger than 4 GW/cm 2 . To achieve a high SHG efficiency, we incident FW with several hundreds of MW/cm 2 into LBO.…”

“…through crystals unchanged because they usually need a much higher peak power density for frequency back-conversion to the FW. [11] The output average power of pulse-burst can be increased by adding HW pulses with HBC, but the peak power density of output is maintained. In a nutshell, the HBC can add arbitrary laser beams into pulse-burst all passively without precise phase controlling or polarization modulation.…”

“…[9,10] Besides, combining several pulses into a burst can achieve higher output average power without increasing the peak power density. [7] Especially in nonlinear optical (NLO) lasers, a high peak power density can cause back-conversion and reduce efficiency, [11] the time gap between pulses also can avoid the back-conversion. So NLO with BC is suitable for burst mode lasers.…”