Investigation of a passively Q-switched Raman laser at 1176 nm with Nd3+:YAG/Cr4+:YAG/YAG composite crystal and a coupled cavity

To reduce the thermal lens effect and increase the efficiency, a composite crystal of Nd3+:YAG/Cr4+:YAG/YAG and a coupled cavity structure were employed in our passively Q-switched YVO4-based Raman laser system. Both the simulation and the experiment results showed that the undoped YAG crystal bonded in the end-face of Cr4+:YAG crystal can speed up the heat transfer of Cr4+:YAG crystal and reduce the temperature difference between its side surfaces and the center significantly, and the coupled cavity structure can improve the laser performance, especially at high pump power. The maximum output power of Raman laser of 0.92 W at 1176 nm was obtained with an optical-to-optical efficiency of 11.51%. The corresponding repetition rate and the pulse width is 53.5 kHz and 3.22 ns, respectively.