Research On Blue-violet Laser Based On Frequency Doubling Of Diode-pumped Cesium Vapor Laser

The blue-violet lasers have many important applications in fundamental research, high-tech product development and national defense projects, including laser spectroscopy, atomic physics, laser medicine, environmental monitoring, laser displays, underwater communication and detection. The blue-violet lasers are commonly produced by frequency doubling of diode-pumped quasi-three-level solid-state Nd3+-lasers (0.9μm). In comparison, the diode-pumped alkali vapor lasers (DPALs) have many preferred properties, such as higher quantum efficiency, larger stimulation absorption/emission cross section, smaller refraction index perturbation and narrower emission linewidth, having the potential to develop more efficient blue-violet lasers. So in this dissertation, the theoretical and experimental research on the blue-violet laser based on frequency doubling of Cs-DPAL is carried out.1. Key technologies of Cs-DPAL are introduced, including the linewidth match between the diode lasers and absorption line of Cs atom, fine-structure mixing and the pump technology. Using the rate equations, effects on the Cs-DPAL output power by temperature of Cs vapor cell, linewidth of diode laser, pressure of buffer gases and reflectivity of output coupler are calculated and analyzed. Two types of Cs-DPAL are constructed. When the Cs-DPALs are operating in continuous-wave (CW) mode with pump power of 10 W, the output powers are 0.55W and 1.44W, respectively. When the Cs-DPALs are operating in pulsed mode with pump power of 16W, the output powers are 0.692W and 2.6W, respectively. The beam quality is measured for both Cs-DPALs, and the beam quality factors are Mx2=1.02, My2=1.13 and Mx2=2.13, My2=2.66.2. Using the second-harmonic generation (SHG) theory of Gaussian beam under far field condition, effects of focusing parameter and crystal temperature on the SHG efficiency are calculated for the commonly used crystals, LBO, BBO, BIBO and ppKTP, when they are used for extra-cavity frequency doubling of Cs-DPAL by type Ⅰ phase matching. Effects of the radius and position of Cs laser beam waist in the nonlinear crystal on the SHG efficiency for type Ⅱ phase matching are analyzed. The two constructed Cs-DPALs are used for extra-cavity SHG. For the Cs-DPALs operating in pulsed mode with beam quality factors of Mx2=1.02, My2=1.13 and Mx2=2.13, My2=2.66, the blue-violet laser powers are 9.5μW and 11.2μW, respectively. Influence of beam quality on SHG efficiency is discussed and analyzed.3. Based on rate equations, two algorithms are developed to describe the intracavity frequency doubling of Cs-DPAL. The second harmonic (SH) power, optimal length of nonlinear crystal and frequency doubling of Cs-DPAL in quasi-two level limit are calculated and analyzed by the two algorithms. Using a LBO crystal the experiment of intracavity frequency doubling of Cs-DPAL is carried out. For the Cs-DPAL operating in CW and pulsed mode with pump power of 16W, the SH powers are 0.22mW and 0.36mW, respectively. By Gaussian fitting to the experimental data, the full width at half maximum (FWHM) of the curve for SH power to the crystal temperature is about 4.1℃.4. Using the Split-Step method, the intensity distribution of Cs laser and the second harmonics in the crystal, the SHG efficiency, and beam quality of the second harmonics are simulated and calculated for LBO, BBO and BIBO crystals by type Ⅰ phase matching, respectively. Similar calculation for frequency doubling of Cs-DPAL using a LBO crystal by type Ⅱ phase matching is also carried out. The temperature profile in the crystal for different Cs laser beam waist radii and fundamental powers is calculated. Effects of the temperature profile in the crystal on the SHG process is discussed in detail, including the effects on SHG efficiency, the beam quality and intensity distribution of the second harmonics.