Multiwavelength Ultrafast SRS Oscillation in Pb(MoO4)0.5(WO4)0.5 Mixed Crystal with Combined Frequency Shifts on Stretching and Bending Vibrations of Molybdate and Tungstate Anionic Groups

Abstract

Multiwavelength, near-IR (1000-1400 nm), high-repetition-rate, ultrashort laser pulses converted by cascaded stimulated Raman scattering (SRS) have many potential applications connected with multiphoton interactions of coherent radiation with matter. Utilization of mixed Raman-active crystals can make it possible not only to enrich the generated SRS radiation spectra, but also to improve other the radiation characteristics, in particular, to ensure shortening of the laser pulses. One of the candidates is a Pb(MoO 4 ) x (WO 4 ) 1 – x mixed crystal having two-mode behaviour (corresponding to the molybdate and tungstate anionic groups) for the high-frequency (ν 1 ) stretching vibrations of the anionic groups, but one-mode behaviour for the low-frequency (ν 2 ) bending vibrations of the anionic groups [1] as it shows Fig. 1 (a) for Pb(MoO 4 ) 0.5 (WO 4 ) 0.5 . Single-pass picosecond SRS in Pb(MoO 4 ) 0.5 (WO 4 ) 0.5 has been earlier realized and shown laser frequency conversion only on the two-mode ν 1 (MoO 4 ) and ν 1 (WO 4 ) stretching vibrations [2] . In the present work we demonstrate the synchronously pumped Pb(MoO 4 ) 0.5 (WO 4 ) 0.5 Raman laser operation with combined frequency shifts not only on the two-mode stretching (ν 1 ) Raman frequencies, but also on the one-mode bending ν 2 (MoO 4 + WO 4 ) broadened (Δν 2 = 10 cm –1 ) Raman line, allowing to shorten the (ν 1 + ν 2 )-shifted SRS pulses down to 1/(π c Δν ) ≈ 2 1 ps.