Theoretical And Experimental Investigation Of The Classical And Quantum Characteristics In The Nonlinear Optical Process

Since the invention of laser, optics research has entered a new era. Because of the monochrome, directional, high intensity of the laser, it provides a powerful tool for the modern optical research, and greatly promoted the development of nonlinear optics, quantum optics. Nonlinear optics is an important means of laser frequency conversion and generation of non-classical light field, the basis of cutting-edge optical research, so we need theoretical and experimental research on nonlinear optical processes in both classical and quantum properties.In this thesis, we developed laser source at1.06μ.m and1.5μm low-noise laser source firstly, and then obtained532nm and775nm laser through the SHG (Second Harmonic Generation) process, respectively. Meantime, we investigated theoretically and experimentally on the nonlinear phenomena in the SHG process. A3.0±0.2dB CV (Continuous Variables) squeezed vacuum at1.5μm was experimentally generated by means of optical parametric process pumped by the low-noise775nm laser. The non-classical states of light at wavelength of1.5μm can be transmitted with the lowest de-coherence characteristic in a traditional silica-based telecommunication glass fibers due to its ultra-low optical loss. It has many applications in practical quantum information system. In conclusion, we did a series of theoretical and experimental research on the laser source preparation, SHG and optical parametric process, including the following aspects of the research results:(1) We have designed and developed a high power all solid-state CW (Continuous Wave) single-frequency Nd:YVO4laser at1.06μm by LD dual-end pumped at880nm. We designed the laser resonator with thermal lens in calculation, adopted the means of dual-end pumped in the experiment for the smaller thermal effect. By using the Nd:YVO4composite crystal with the doping concentration of0.2%, we obtained the CW single-frequency1.06μm laser with the output of22W when pump power is50W. The corresponding optical conversion efficiency is46.3%. The long-term stability of the output power was better than±0.7%. The laser beam quality was measured of M2<1.05. The intensity noise and the phase noise of the laser reached the SNL (shot noise limit) at analysis frequency of5MHz.(2) The1.06μm laser was frequency doubled by using quasi-phase-matched PPKTP crystal in an external cavity, and532nm laser was generated. We have designed the frequency doubling system, and get the conversion efficiency of75%when phase matched. When phase mismatched, we observed the second-order cascaded process and obtained the nonlinear phase shift. Meantime, we observed the square-wave and staircase curve of self-oscillations. It was caused by the competition between the phase shifts induced by cascading nonlinearity and thermal effect through our analysis. We established the model for the theoretical calculation, the simulation results were in good agreement with experimental phenomena.(3)1.5μm and775nm high power CW single frequency low-noise laser source was prepared from mode cleaners and SHG process. We firstly filtered the1.5μm laser from fiber laser by1.5μm mode cleaner, and then obtained the775nm laser by external cavity frequency doubling using quasi-phase-matched PPLN (Periodically Poled Lithium Niobite) crystal, the maximum output power of775nm laser is552mW when the pump power is770mW, with the conversion efficiency of72%. After that, the775nm laser was filtered by775nm mode cleaner. Finally, the intensity noise of775nm laser reached SNL at analysis frequency of4MHz for S polarization, the intensity noise of1.5μm laser reached SNL at analysis frequency of5MHz for P polarization. Besides, we have investigated the double-ended output resonator of SHG, and the relative phase of fundamental-wave and second-harmonic was analyzed. A good second-harmonic output power can be obtained with controlling the relative phase. The experimental results were basically in agreement with theoretical analysis.(4) A CV squeezed vacuum at1.5μm was experimentally generated by means of optical parametric process pumped by the low-noise775nm laser. We used the prepared1.5μm and775nm high power CW single frequency low-noise laser source and the OPO (Optical Parametric Oscillator) to obtain3.0±0.2dB squeezed vacuum at1.5μm. The nonlinear crystal is PPLN.