Research On All Solid-State Quasi-CW Passively Q-Switched Laser

Laser-diode (LD) pumped passively Q-switched lasers are simple, compact, easy to operate and inexpensive, have wide application in the fields of range measuring, remote sensing, information storage, medicine, etc. The Cr⁴⁺: YAG crystal is a well-known solid-state saturable absorber widely used for Q-switching the Nd3+-doped solid-state lasers,has a large saturable absorption cross-section in the 0.9¹.2μm spectral region, high damage threshold and excellent thermal and optical properties. Quasi-cw (QCW) diode-pumped passively Q-switched Nd: YAG laser with the Cr⁴⁺: YAG as a saturable absorber, can obtain pulses with high peak power and narrow pulse width. The main content and innovative points in the dissertation can be summarized as follows:1. Made a detailed analysis for various properties of Cr⁴⁺: YAG crystal and a summary of its main characters as staturable absorber and laser crystal. Presented recent development of Cr⁴⁺: YAG passively Q-switched laser. The review and prospect of passively Q-switching technology was also presented.2. A theoretic analysis was made for diode-pumped passively Q-switched laser and the expression of threshold was given. Numerical simulations have showed the temporal evolutions of the population inversion in laser crystal and the intracavity photon by solving the rate equations. The properties of output pulses were studied by numerical methods, and the variation of single pulse energy and pulse width with the pump rate or reflectivity of the output coupler was obtained.3. General experimental research on QCW diode-pumped passively Q-switched Nd: YAG laser have been done. The output power and pulse width of the pulse at 1064nm was studied by experiments under different cavity-length and reflectivity of output coupler, when using Cr⁴⁺: YAG saturable absorber with the small-signal transmission of 35.9%, 29%, respectively. The maximal pulse energy of 6 mJ with 10 ns pulse width and the shortest pulse width of 6 ns with pulse energy of 4.1 mJ were achieved by using Cr⁴⁺: YAG crystal with the small-signal transmission of 29%.4. Done some experimental research on QCW diode-pumped intracavity frequency doubling passively Q-switched Nd: YAG/KTP green laser, using Cr⁴⁺: YAG as a saturable absorber. When the small-signal transmission of Cr⁴⁺: YAG is 35.9%, Q-switched green laser with pulse energy of 0.27mJ, pulse width of 12ns and peak power of more than 20 kW was obtained.