High-power UV light generation in picosecond pulse trains

• Published in: 2013 Conference on Lasers & Electro-Optics Europe & International Quantum Electronics Conference CLEO EUROPE/IQEC p. 1
• Main Authors: Martyanov, Mikhail, Divall, Marta, Gacheva, Ekaterina, Hessler, Christoph, Fedosseev, Valentin
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01.05.2013
• Subjects: Crystals; Frequency conversion; Laser beams; Optical distortion; Power lasers; Radio frequency
• DOI: 10.1109/CLEOE-IQEC.2013.6800883

This paper focuses on the investigation of detrimental UV induced effects during fourth harmonic generation (FHG) in BBO crystals. An accumulation of partly recoverable UV two-photon induced optical defects has been observed in the 140 s train generated by frequency quadrupled 1.5 GHz Nd:YLF laser with about 300 W UV power per train, even for a relatively low peak pulse intensity of about 100 MW/cm 2 . BBO crystals with length of 4.2, 8.5 and 12 mm have been tested. In a shorter crystal less distortion have been observed for the same UV output power. Although the growth of optical defects is attributed to the UV two-photon absorption, the already accumulated defects lead to a linear absorption of green and UV co-propagating pulses which in turn results in train envelope degradation due to deterioration of a phase-matching and thermal beam distortion. The UV beam exhibited focusing behavior on a short distance (crystal length) which cannot be explained by temperature dependence of BBO refractive indexes. The UV beam focusing is addressed as a strong photo-elastic effect, caused by the stress induced by essentially non-uniform temperature distribution inside the beam propagation volume.