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Tunable Vacuum-ultraviolet Laser Generation by Nonlinear Optical Techniques
P. Kumbhakar, G.C. Bhar and T. Kobayashi

There is growing interest on the development of frequency tunable laser sources in ultraviolet (UV) spectral regions having several applications. Different applications need specific ranges of wavelengths and for most applications, wavelength tunability of the laser sources is required, in addition to other desirable characteristics. Exploiting the nonlinear optical (NLO) effects in various potential crystals including in some newly discovered crystals, by employing different novel NLO frequency conversion techniques, generation of widely tunable UV laser radiation have been presented. The NLO frequency conversion techniques that have been employed in the present experiments are SHG and SFM and the used materials are BBO, CLBO, and LB4, which are negatively birefringent uniaxial crystals. Several novel phase-matching techniques, such as noncollinear phase-matching, tangential phase-matching and walk-off compensated scheme have been employed for generation of widely tunable efficient laser radiation. The shortest VUV wavelength generated in the processes is 187.9 nm at room temperature in BBO crystal using Nd:YAG laser radiation as one of the fundamental radiation in a type-I SFM interaction. The shortest achievable wavelength tunability in CLBO crystal is reported to be ~ 195.3 nm, by type-I SFM with Nd:YAG laser radiation at room temperature, although CLBO crystal is transparent down to 180 nm. Another LB4 crystal although transparent below 200 nm, generation below 205 nm is not possible through the presented technique. However, LB4 crystal has been employed for generation of UV laser radiation covering in 205–400 nm spectral region by employing NLO SHG and SFM techniques.

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