Studies On Single Longitudinal Mode Palsed 1178nm Lasers And Novel Dual-wanelength Lasers

This dissertation includes two parts:one is the research of single longitudinal mode 1178 nm lasers, the other is the study of solid-state dual-wavelength lasers.589-nm lasers have wide applications in many fields such as medicine, information storage, laser radar, atmospheric sounding, and so on. Especially, narrow-linewidth 589-nm radiation with high power can efficiently stimulate resonant fluorescence of sodium-layer in the atmpsphere to generate "sodium laser guide star". It is an important technology in adaptive optics and has significient applications in astronomy and military. One of the effective methods to obtain 589-nm lasers is the second harmonic generation (SHG) of 1178-nm lasers. Therefore, it is necessary and important to do some research on 1178-nm lasers.With the rapid development of laser technology, people begin to put forward more requirements to the laser wavelength. Lasers with dual-wavelength radiations have attracted much attention in recent years. Solid-state dual-wavelength lasers have some good characteristics such as small size, light weight, high stability and high efficiency. Therefore, they have been applied widely in the areas of medical, laser ranging, spectral analysis, holographic interferometry, differential absorption laser lidar and nonlinear frequency conversion.In this dissertation, by using Nd:GGG crystal as the laser gain medium, BaW04 crystal as the Raman medium and etalons as the element of compressing the linewidth, we studied the output characteristics of a single longitudinal mode 1178 nm Raman laser. By using CaW04 crystal as the Raman medium, we studied a single longitudinal mode 1178 nm crystalline Raman amplifier. Then, the tuning characteristics of a LiF:F2- color center laser was studied and the single longitudinal mode laser of 1178 nm was realized. The output characteristics of an electro-optically Q-switched dual-wavelength tunable Nd:Glass laser were researched. The output characteristics of an electro-optically Q-switched Nd：YLF dual-wavelength laser at the wavelengths of 1047 nm and 1053 nm were investigated. The main contents of this dissertation are as follows:1. The output characteristics of the single longitudinal mode 1178 nm Nd:GGG/BaWO4 Raman laser were demonstrated. A fiber coupling quasi-continuous wave (QCW) LD with a repetition rate of 50 Hz and a pulse duration of 2 ms was used as the pump source. Two etalons with the thicknesses of 1.8 mm and 15 mm were used to compress the linewidth. With an average pump power of 2.14 W and a repetition rate of 20 kHz, the maximal average output power was obtained to be 30 mW. The pulse width was 6.2 ns and the line width was less than 130 MHz.2. The Single longitudinal mode 1178-nm CaWO4 crystalline Raman amplifier was acheived. The pump source was a 1064-nm single-frequency pulsed laser with about 7 ns pulse width. A single longitudinal mode continuous wave (CW) 1178 nm signal laser with an average power of 2 W was amplified in the CaWO4 Raman crystals. After three stages of amplification, the energy of the amplified Raman radiation was 26.7 mJ and the pulse width was 2.9 ns, corresponding to a peak power of 9.2 MW. The overall Raman amplification ratio was up to 4.6×106. The linewidth was less than 500 MHz.3. The high-repetition-rate Littrow-grating tuned LiF:F2-color center laser was studied. The pump source was a QCW diode-side-pumped acousto-optically Q-switched 1064 nm Nd:YAG laser. When the macro pulse duration was 300 μs, the duty cycle was 0.09 and the Q-switched repetition rate was 50 kHz, the average output power of the Nd:YAG laser was 2.5 W. The tuning range was 1085 nm to 1275 nm with a spectral line width of 0.2 nm. The maximum average output power of 277 mW was obtained at 1155.5 nm.4. We researched the output characteristics of the Littman-grating tuned LiF:F2- color center laser. The tuning ranged was 1105 nm-1215 nm with a spectral line width of 0.04 nm. The maximum average output power of 135 mW was obtained at 1155.5 nm.5. The Single longitudinal mode 1178 nm LiF:F2- color center laser was realized. The pump source was a QCW diode-end-pumped AO Q-switched 1064 nm TEMoo mode Nd:YVO4 laser. When the duty cycle was 0.1 and the Q-switched repetition rate was 30 kHz, the maximum average output power of the Nd:YVO4 laser was 0.82 W. With Littman-grating, an F-P etalon (thickness 15mm, R1178= 50%) and a beam expander (1:2.2), the stable single longitudinal mode 1178 nm laser was realized. The line-width was less than 1.5 GHz.6. The flash-lamp pumped electro-optically Q-switched dual tunable wavelength Nd:Glass laser was demonstrated. An Nd:Glass rod was selected as the laser medium and a KD*P crystal was employed as the Q-switch. A cubic polarizer was placed in the cavity to divide the randomly polarized radiation into two orthogonally polarized beams. Each beam was tuned by a Littman-grating and output independently. For Q-switched operation, the tuning ranges were 1050.1 nm-1061.6 nm and 1050.5 nm-1060.2 nm for the horizontal and vertical polarizations, respectively. When the horizontally polarized output was fixed at 1059.1 nm, the synchronized vertically polarized one can be tuned from 1051.5 nm to 1057.5 nm.7. The flash-lamp pumped electro-optically Q-switched dual-wavelength Nd:YLF laser was demonstrated. Two Nd:YLF crystals placed in two cavities were employed to generate orthogonally polarized 1047-nm and 1053-nm radiations, respectively. The two cavities were jointed together by a polarizer and shared the same electro-optical Q-switch. Two narrow-band pass filters were used to block unexpected oscillations at the hold-off state of the electro-optical Q-switch. In this case, electro-optical Q-switching was able to operate successfully. With pulse synchronization realized, the maximum output energies of 66.2 mJ and 83.9 mJ were obtained for 1047-nm and 1053-nm lasers, respectively.The main innovations of this dissertation are as follows:1. For the first time, the single longitudinal mode crystalline Raman laser was demonstrated. By employing Nd:GGG/BaW04 scheme, and the using of two etalons with the thicknesses of 1.8 mm and 15 mm, single longitudinal mode 1178-nm Raman radiation was obtained, the linewidth was less than 130 MHz. At the duty cycle of 0.1, the maximum average output power was 30 mW, with a pulse repetition rate of 20 kHz and a pulse duration of 6.2 ns.2. For the first time, the single longitudinal mode 1178 nm CaWO4 crystalline Raman amplifier was studied. A three-stage amplifier system was designed and the highest output pulse energy of the amplified Raman radiation was 26.7 mJ, with a pulse duration of 2.9 ns. The overall Raman amplification ratio was up to 4.6×106 and the linewidth was less than 500 MHz.3. The high-repetition-rate tunable LiF:F2-color center laser was demonstrated. The tuning range with the Littrow-grating was 1085 nm-1275 nm and the tuning range with the Littman-grating was 1105 nm-1215 nm.4. We studied the Nd:YVO4 laser pumped single longitudinal mode 1178 nm LiF:F2-color center laser for the first time. By using Littman-grating, F-P etalon and beam expender, the stable single longitudinal mode 1178 nm laser was realized and the linewidth was less than 1.5 GHz.5. For the first time, the flash-lamp-pumped electro-optically Q-switched Nd:Glass tunable dual-wavelength laser was demonstrated. By using an Nd:Glass as the laser medium, a polarizer as the beam splitter and gratings as the tuning elements, the tuning ranges of the two radiations were 1050.1 nm-1061.6 nm and 1050.5 nm-1060.2 nm, respectively. When the wavelength of the horizontal polarization was 1059.1 nm, the tuning range of the vertical polarization was 1051.5 nm-1057.5 nm.6. The flash-lamp-pumped electro-optically Q-switched Nd:YLF dual wavelength laser was demonstrated for the first time. Two Nd:YLF crystals were used to generate orthogonally polarized 1047-nm and 1053-nm radiations. The two cavities were jointed together by a polarizer. Two narrow-band pass filters were used to block unexpected oscillations at the hold-off state of the electro-optical Q-switch. With pulse synchronization realized, the maximum output energies of 66.2 mJ and 83.9 mJ were obtained for 1047-nm and 1053-nm lasers, respectively.