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5Competition between stimulated Raman scattering and nonlinear phase modulation in crystals under pumping by powerful
subpicosecond laser
S.N. Smetanin*, D.P. Tereshchenko, Yu.A. Kochukov, A.G. Papashvili, K.A. Gubina, V.V. Bulgakova, A.A. Ushakov, V.E. Shukshin, E.E. Dunaeva, I.S. Voronina, L.I. Ivleva
Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilova 38, 119991, Moscow, Russia
Multiwavelength ultrafast laser sources with wavelengths in a range of 1000-1300 nm of the therapeutic transparency window of biological tissue are of high importance for optical multiresonance biomedical diagnostics [1]. Non-invasive exposure to biological tissue requires the use of ultrashort laser pulses with a duration of about 1 ps and shorter. Increasing the number of spectral components of ultrafast laser radiation in this range can be realized by transient stimulated Raman scattering (SRS) in scheelite-type crystals (BaWO4, SrWO4, SrMoO4, and others) having dual Raman modes with comparable integral cross-sections of Raman scattering [2]. However, decreasing the laser pulse duration shorter than the Raman mode dephasing time of the order of 1 ps leads to competition between SRS and nonlinear phase modulation (self-phase modulation of the pump pulse and cross-phase modulation of the Stokes pulse) suppressing such highly transient SRS [3]. Recently, highly transient, multiwavelength, single-pass SRS generation on dual Raman modes (888 cm-1 and 327 cm-1) has been obtained in a SrMoO4 crystal under ultrafast single-pulse pumping by a powerful, subpicosecond, 1030-nm Yb fiber laser [4]. A controllable negative chirp of the input pump laser pulse compensating a positive chirp of the pump pulse self-phase modulation in the crystal allowed increasing SRS conversion efficiency into one of four (1066, 1134, 1177, and 1261 nm) radiation components with the combined Raman shifts in the desired range.
In this contribution, for the first time to our knowledge, competition between highly transient SRS on dual Raman modes and nonlinear phase modulation in crystals is investigated under conditions of not only chirping of input subpicosecond pump pulses, but also using a double-pulse pumping scheme [5]. In the double-pulse scheme, the second pump pulse, delayed relative to the first pump pulse for a delay of the order of a dephasing time of the Raman mode, is efficiently scattered on the vibration coherently driven by the first pump pulse. As a result, more efficient and simultaneous Raman generation on dual Raman modes in the desired range of 1000-1300 nm has been achieved in a wide range of the chirped pump pulse durations for the double-pulse than for the single-pulse pumping scheme.
This research was supported by Russian Science Foundation - Project No 24-12-00448 (https://rscf.ru/project/24-12-00448/).
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