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ALT'23 The 30th International Conference on Advanced Laser Technologies
LS-I-16
Highly transient stimulated Raman scattering with combined frequency shifts in crystals
S.N. Smetanin, D.P. Tereshchenko, Yu.A. Kochukov, A.G. Papashvili, V.V. Bukin, V.E. Shukshin, E.E. Du-
naeva, I.S. Voronina, L.I. Ivleva
Prokhorov General Physics Institute of the Russian Academy of Sciences, Moscow, Russia
Stimulated Raman scattering with combined frequency shifts on high- and low-frequency Raman modes in scheelite-type crystals at weakly chirped laser pulse duration shorter than a dephasing time of the Raman modes is experimentally investigated.
Development of Raman converters for ultrashort laser pulses shorter than a dephasing time of Raman medium is an important issue of laser physics because of a low Raman gain increment in such highly transient regime of conversion and its suppression due to competing nonlinear phenomena such as self-phase modulation. In this work, highly transient stimulated Raman scattering (SRS) in crystals under pumping by a sub-picosecond 1030-nm laser radiation with the pulse duration shorter than a dephasing time of the crystal Raman modes is experimentally investigated. For the scheelite-type Raman-active crystals (SrMoO4, CaMoO4, and others) owning two (primary, the stretching, and secondary, the bending) Raman modes with similar integral cross-sections, Stokes SRS radiation with not only a high-frequency shift on the primary Raman mode (at 888 cm-1 with the dephasing time of 4 ps for SrMoO4), but also a low-frequency shift on the secondary Raman mode (at 327 cm-1 with the dephasing time of 1 ps for SrMoO4) was obtained. A positive and negative weak chirp increasing the pump pulse duration from 0.24 ps up to 6.5 ps was used to optimize the Raman conversion preventing the issues of the pump pulse self-phase modulation and the Stokes pulse spectral narrowing. SRS generation threshold has been lowered relative to those for the competing nonlinear phenomena with a help of increasing the crystal length (a) up to a temporal walk-off length due to group-velocity mismatch between the pump and Stokes pulses, (b) up to a Rayleigh length of the focused pump beam, and (c) longer than coherence length of Stokes-anti-Stokes parametric coupling. Using the pump pulses with duration shorter than the secondary Raman mode dephasing time (1 ps in SrMoO4) allowed obtaining higher intensity of the low-frequency-shift Stokes SRS component relative to the high-frequency-shift Stokes SRS component.
This research was funded by Russian Science Foundation—Project No 22-22-00708.
