Abstract
The characteristics of a tunable Stokes laser based on the cascaded stimulated polariton scattering and stimulated Raman scattering in KTiOPO4 crystal were studied experimentally and theoretically. When the pumping wavelength was 1064 nm, the Stokes laser output wavelength was able to be tuned discontinuously from 1112.08 nm to 1113.64 nm, from 1114.94 nm to 1115.77 nm, and from 1117.37 nm to 1119.92 nm, and the maximum output power appeared at 1118.86 nm. With a pulse repetition frequency of 7 kHz and a pump power of 6.0 W, the maximum output power of the Stokes laser reached 734 mW, and the corresponding diode to laser conversion efficiency was 12.2%. The rate equations describing the temporal evolutions of the fundamental and Stokes waves by noncollinear stimulated polariton scattering and the Stokes wave by collinear stimulated Raman scattering were derived. They were used to simulate the tunable Stokes laser. The calculated results were in agreement with the experimental results on the whole.
Highlights
KTiOPO4 (KTP) is an excellent nonlinear crystal
Stimulated polariton scattering (SPS) is an efficient frequency down-conversion effect, which contains both the second-order and third-order nonlinear optical effects [15]. It will occur when a crystal with both infrared and Raman activities is pumped by a strong pumping laser beam, parametrically generating a terahertz (THz) wave and a red-shifted wave called Stokes wave [16]
The optical scheme of the Q-switched intracavity SPS-stimulated Raman scattering (SRS) laser based on KTP is illustrated in Stokes waves resonated in the Stokes cavity (M3 and M4)
Summary
KTiOPO4 (KTP) is an excellent nonlinear crystal. It has many outstanding properties, such as broad high transparency in visible and near-infrared regions, reliable chemical and mechanical stability, high laser-induced damage threshold [1,2], and large nonlinear coefficient [3]. Stimulated polariton scattering (SPS) is an efficient frequency down-conversion effect, which contains both the second-order and third-order nonlinear optical effects [15] It will occur when a crystal with both infrared and Raman activities is pumped by a strong pumping laser beam, parametrically generating a terahertz (THz) wave and a red-shifted wave called Stokes wave [16]. By using the cascaded SPS and SRS effects in RbTiOPO4 crystal, the obtained Stokes wavelengths could be tuned from 1107.7 to 1108.1 nm, from 1109.0 to 1112.7 nm, from 1114.3 to 1115.1 laser wavelengths could be tuned from 1107.7 to 1108.1 nm, from 1109.0 to 1112.7 nm, from 1114.3 to nm, and from 1117.8 to 1121.1 nm [17]. Stokes laser (named as SPS-Stokes wave) could be obtained through noncollinear phase-matching.
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