New observations on DUV radiation at 257 nm and 206 nm produced by a picosecond diode pumped thin-disk laser

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The deep ultraviolet (DUV) radiation at 257 nm and 206 nm was generated as the 4th and 5th harmonic frequencies from the fundamental wavelength of 1030 nm of the diode pumped high-power Yb:YAG thin disk laser PERLA at a repetition rate of 77 kHz. The pulse duration was 1.5 ps. The application potential of such high-energy DUV pulses covers science (spectroscopy, photoelectron generation), medicine and mainly industry (efficient material processing, lithography). We used two CLBO crystals as convertors into DUV radiation. The 4th harmonic was generated by frequency quadrupling of the fundamental beam and the 5th harmonic as sum frequency 1w+4w. The 1 W output power of the 5th harmonic ranks among the highest ever attained for picosecond pulses. We measured external effects of the two-photon absorption (TPA) of the DUV photons, i.e. the mismatching angle due to the heat released in the TPA process and the TPA coefficient. We also studied experimentally and in simulations the time delay between the 4w- and 1w-pulses and found the right timing for the highest 5th harmonic output. Further, we studied the 5w-output power under different ratios between the 4w- and 1w-inputs. It was stated for the first time that for picosecond pulses a great abundance of 1w-photons is beneficial for the 5th harmonic generation, but only in correspondingly short crystals.

(a) Dependence of the output power of the 5th harmonic emerging from the CLBO crystal on the input power of the 1st harmonic, i.e. fundamental beam. The input power of the 4th harmonic was kept constant 4.2 W. The right axis shows the percentage of the 4w-photons converted into 5w-photons. (b) Spectrum of the 5th harmonic with the note on the width of the curve at the half of maximum.
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(a) Dependence of the output power of the 5th harmonic emerging from the CLBO crystal on the input power of the 1st harmonic, i.e. fundamental beam. The input power of the 4th harmonic was kept constant 4.2 W. The right axis shows the percentage of the 4w-photons converted into 5w-photons. (b) Spectrum of the 5th harmonic with the note on the width of the curve at the half of maximum.

Contact: Hana Turčičová