Nd: The Yvo <sub> 4 </ Sub> And Nd: The Gdvo <sub> 4 </ Sub> Crystal Self-activate The Self-raman Conversion Laser

The stimulated Raman scattering (SRS) can shift the laser frequency over a fixed frequency gap to produce new laser lines. The Raman laser wavelength is determined by the wavelength of the fundamental pump laser and the Raman shift of the Raman-active crystal. SRS possesses many attractive features such as beam clean-up, pulse compression, no need for phase matching, and high conversion efficiency. Compared with the traditional gas and liquid Raman media, the Raman crystals offer high gain, high molecule density, good thermal and mechanical properties. A good number of crystals have been found to be Raman-active, such as Ba(NO₃)₂, BaWO₄, KGd(WO₄)₂, YVO₄ and GdVO₄ crystals. The Raman lasers by using crystal media have the advantages of compactness, high efficiency and high stability and have wide applications in such ares as Information, Communication, Medicine, National defence, and so on.Nd:YVO₄ and Nd:GdVO₄ crystals are isomorphs. They have the advantages of high absorption coefficient, large emission cross-section, high absorption over a wide pumping wavelength bandwidth and polarization emitting feature, and have been recognized as excellent laser media for diode pumping. In 2001 Kaminskii et al. found YVO₄ and GdVO₄ were Raman-active, predicted that Nd:YVO₄ and Nd:GdVO₄ would be promising self-Raman laser crystals in the visible and near infrared spectral regions.By using Nd:YVO₄ and Nd:GdVO₄ crystals as both gain media and Raman media, we make a sysmetic research on the characteristics of the self-Raman lasers with Nd:YVO₄ and Nd:GdVO₄ crystals. The rate equations are used to describe the Raman pulse characteristics, the theoretical results are in agreement with the experimental results on the whole. The main content of this dissertation is as follows:1. A 1176 nm Raman laser is obtained by use of self-Raman conversion in a diode-pumped actively Q-switched a-cut Nd:YVO₄ 1064 nm laser. The characteristics including the average output power, pulse width, pulse energy and peak power versus the incident pump power and pulse repetition rate are measured. The widths of the typical fundamental pulses at 1064 nm and the Raman pulses at 1176 nm are 26.3 ns and 9.0 ns, respectively. At a repetition rate of 20 kHz and an incident pump power of 8.46 W, an average output power of 0.38 W at 1176 nm and an optical-to-optical conversion efficiency of 4.5% are obtained. The rate equations are used to describe the performance of the self-Raman actively Q-switched a-cut Nd:YVO₄ laser. Experimentally measured and theoretically calculated pulse energies and pulse widths at 1176 ran for the pulse repetition rates of 10, 20, and 30 kHz are compared, the theoretical results are in agreement with the experimental results on the whole.2. A 1179 nm Raman laser is obtained by use of self-Raman conversion in a diode-pumped actively Q-switched c-cut Nd:YVO₄ laser. The characteristics including the average output power, pulse width, pulse energy and peak power versus the incident pump power and pulse repetition rate are measured. The rate equations are used to describe the performance of the self-Raman actively Q-switched c-cut Nd:YVO₄ laser.3. A 1173 nm Raman laser is obtained for the first time by use of the self-Raman conversion in a diode-pumped actively Q-switched a-cut Nd:GdVO₄ 1063 nm laser. The characteristics including the average output power, pulse width, pulse energy and peak power versus the incident pump power and pulse repetition rate are measured. The widths of the typical fundamental pulses at 1063 nm and the Raman pulses at 1173 nm are 33.0 ns and 13.8 ns, respectively. At a repetition rate of 30 kHz and an incident pump power of 9.6 W, an average output power of 0.8 W at 1173 nm is obtained and the corresponding optical-to-optical conversion efficiency is 8.3%. The maximum pulse energy is 70.7μJ with an incident pump power of 9.6 W and a pulse repetition rate of 10 kHz, the corresponding peak power is 5.2 kW. The rate equations are used to describe the performance of the self-Raman actively Q-switched a-cut Nd:GdVO₄ laser.4. By using c-cut Nd:GdVO₄ as the gain medium and the Raman medium simultaneously, and using two Cr⁴⁺:YAG crystals with different initial transmissions as the saturable absorbers, the passively Q-switched operation of the self-Raman c-cut Nd:GdVO₄ laser at 1176 nm is realized. The characteristics including the average output power, pulse width, pulse repetition rates, pulse energy and peak power versus the incident pump power are measured. The obtained maximum output average power is 0.24 W with respect to the incident power of 5.7 W and the corresponding conversion efficiency is 4.2% with saturable absorber initial transmission of 91%. The rate equations are used to describe the performance of the self-Raman passively Q-switched c-cut Nd:GdVO₄ laser. The theoretical results are in agreement with the experimental results on the whole.