Abstract
Several groups1,2 are studying the use of optical phase shifts to initiate soliton formation in transient stimulated Raman scattering. Our experiments use a generator-amplifier Raman laser pumped by a frequency-doubled Nd:YAG laser at 532 nm. The Raman medium is hydrogen at 1-100 atm. We use an electrooptic crystal to place a π phase shift in the Stokes beam between the generator and amplifier. This shift momentarily reverses the direction of gain. The phase shift is produced by modulating the amplitude of the Stokes envelope through zero using polarizers and a Pockels cell. Numerical calculations indicate that solitons can be initiated by switching the Pockels cell voltage over a time of several nanoseconds. Development of the temporal pulse is shown in Fig. 1. Once initiated the soliton pulse can narrow to a width of a few picoseconds if the collisional dephasing time (1/Γ) is 60 ps. The width W (HWHM) of the evolving pulse is shown in Fig. 2 (⨉). The solid curve is the pulse width predicted by steady- state theory, which is initially valid because the field envelopes change slowly compared with 1/Γ.
© 1987 Optical Society of America
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