| With the development of laser technology, lasers have been widely used in every aspect of our lives, such as laser marking, laser welding, material cutting and surface treatment; laser ranging, laser weapon, laser guidance and laser radar; and laser hairdressing, laser radiation therapy, laser cutting tumors, etc. These applications are using the feature of high density of lasers. But in the scientific research, there have higher requirements for the performance parameters of the laser:continuous-wave (cw) single-frequency laser. High power cw single-frequency lasers have been widely used in experiments of quantum optics, quantum information, high resolution spectroscopy and cold atom, and with the progress of research, scientists put forward more and more demands of the laser, such as long-term power stability, good frequency stability, high beam quality and high output power.In this thesis, we start the investigation of high power cw single-frequency laser with wavelength of 1.06μm,532 nm and 1.5μm, respectively. The investigation of the all-solid-state cw single-frequency 1.06μm laser is the basic study; then through the second harmonic process, developing the all-solid-state cw single-frequency intracavity frequency doubled green laser; finally, by the optical parametric process, we obtain the cw single-frequency 1.5μm laser. We carried out a series of research results as follows.(1) We have demonstrated a cw single-frequency Nd:YVO4 laser at 1.06μm by LD dual-end pumped at 808nm. A dual-end pumping scheme was employed to realizes homogeneous absorption along the length of laser crystal, so that the defects such as serious thermal aberration, bulging of the entrance faces, and stress fracture risks that are encountered in the one-end pumping configuration were decreased. The measured maximum output was 18.5 W with a conversion efficiency of 41.2%. The stability of the output power was better than±0.4% in three hours. The beam quality was measured of M2<1.05. The noise characteristics of the laser were also investigated. The intensity noise and the phase noise reached the shot noise limit (SNL) at analysis frequency of 4 MHz.(2) Based on a polarized and dual-end pumping scheme, a stable, high power and high beam quality cw single-frequency Nd:YVO4/LBO green laser by directly pumped at 880nm has been fabricated. A single-polarization direction for the pump beams was selected to solve the problem of different absorption coefficients of orthogonal polarizations in the Nd:YV04 crystal. A measured maximum output power of 11.6W at 532 nm was obtained with a conversion efficiency of 22.3%. The stability of the green output was better than±0.5% and no mode hopping was observed over a period of five hours. The beam quality parameters were measured to be Mx2=1.03 and My2=1.02. The intensity noise of the green laser was reduced to the SNL at an analysis frequency of 3.5 MHz and phase noise was 1.3 dB above the SNL in the range of 2 to 20MHz.(3) We present a 1.5μm cw single-frequency intracavity singly resonant optical parametric oscillator (SRO) based on periodically poled lithium niobate (PPLN). The SRO is placed inside the ring cavity of a single-frequency 1.06μm Nd:YVO4 laser pumped by a LD. The device delivers a maximum single-frequency output power of 300 mW at the LD pump power of 18W, and the measured signal wavelength is 1.57μm.(4) We report a cw single-frequency 1.5μm laser source obtained by extracavity SRO based on PPLN. The SRO was pumped by a cw single-frequency Nd:YVO4 laser at 1.06μm.1.02 W of single-frequency signal light at 1.5μm was obtained at pump power of 6W. At the output power of around 0.75W, the power stability was better than±1.5% in 30 minutes and no mode hopping was observed, and the frequency stability was better than 8.56 MHz in one minute. The signal wavelength could be tuned from 1.569 to 1.592μm by varying the PPLN temperature. And the 1.5μm laser exhibits low noise characteristics, the intensity noise of the laser reaches SNL at analysis frequency of 4 MHz, and phase noise is about 1 dB above the SNL for frequency from 10 to 20 MHz. The creative works are as follows:(1) Analyzed the advantages of dual-end pumping and direct pumping scheme, which was employed to reduce the thermal effects in the laser crystal, and experimentally verified these advantages:compared to the one-end pumping configuration, thermal lens effect reduced about 40% in the dual-end pumping scheme; in direct pumping scheme, the thermal effects are accounted for 50% of traditional pumping method.(2) A stable, high power and high beam quality cw single-frequency Nd:YVO4/LBO green laser has been fabricated by directly pumped at 880nm. A single-polarization direction for the pump beams was selected to solve the problem of different absorption coefficients of orthogonal polarizations in the Nd:YVO4 crystal. A measured maximum output power of 11.6W at 532 nm was obtained with a conversion efficiency of 22.3%. The stability of the green output was better than±0.5% over a period of five hours.(3) A cw single-frequency 1.5μm laser source was obtained by intracavity SRO. The device delivers a maximum single-frequency output of 300 mW at the LD pump power of 18W.(4) Theoretically analyzed the noise characteristics of the signal generated by extracavity SRO. In our experiment, a 1.02 W of cw single-frequency signal at 1.5μm was obtained by an extracavity SRO. We measured the intensity noise and phase noise of the signal; the experimental results are good agreement with the theoretical analysis.
|
PDF Full Text Request