A Practical Study Of The Nanosecond Beta Barium Borate Optical Parametric Oscillators

Abstract: Based on the elaborate study on the advance of the optical parametric oscillators in resent fifteen years, it is clearly pointed that the material foundation of the BBO-OPO was provided due to the discovery of the new type nonlinear crystal BBO, LBO and CLBO etc and the emerge of the high quality pump source especially the diode lasers. However, as optical parametric oscillators are mainly used in the research area of spectroscopy etc, and the applications of spectroscopy have a high demand for the resolution of the lasers, namely beam linewidth, ours practical study of BBO-OPO mainly take the efforts for seeking the theoretical support of the decreasing linewidth and improving the beam quality of output, and practical experimental methods as well as increasing the conversation of the parametric beams, and providing convenient tuning systems for the OPO applications.Our mainly work in theoretical study are described as followings. As pulsed OPOs work in a transient regime, a dynamic model is applied to analyzes its operation characteristics, and a result of the numeral simulations for the transient regime parametric process is presented and it is fitted the experimental result very well. Thus it provides theoretical foundation for the OPOs practical parametric designs. Based on these foundations, we give a perfect scheme of the BBO OPOs: single pass amplification coefficient of the OPG under different pump intensity is calculated; collinear type-I and type-II phase matching tuning curve pumped by the Q switch Nd:YAG various harmonics as well as noncollinear type-I tuning curve are calculated in details; the effect of the walkoff for the nonlinear effect coefficient and the group velocity matching are analyzed; the acceptance angle in parametric process is calculated; the numerical threshold of the BBO OPO is calculated; the process of the saturation and depletion of the pump beam are analyzed; the relationship of the conversion efficiency and reflectance of output mirror are discussed; various linewidth controlling methods are discussed; the improvement of the beam quality applying the unstable cavity is discussed; and the crystal BBO design is considered.In the part of the experimental designs, a experimental configuration of an unstable cavity by use of two BBO crystals compensating the walkoff effect and pumped by reflection is presented, and two set of controlling systems designs of open and closed loop are also presented; We realized closed loop controlling system of BBO optical parametric oscillator tuning system, by using American General Scanning Inc.'s controller to control BBO crystal's rotation, and scaled the output wavelength with Charge Coupled Device. The system's relative wavelength tuning error is less than 0.04%. We also demonstrated 354.7 nm pumped type-I phase matching BBO-OPO's theoretical and experimental curve of output wavelength versus crystal tuning angles. The tuning curve of type-I phase matching of BBO OPO are measured with accuracy; the maximum conversation in total of the system is about 31% at 615.6 nm, and it is fitted well with the GTP formula; in the end we compared the output linewidth and unstable cavity far field beam quality of the BBO OPO under the condition of type-I phase matching and type-II phase matching, it is proved that we can obtain the parametric output of linewidth less than 0.3 nm and the beam divergence angle approaching diffraction limits by take the advantages of type-II phase matching and unstable cavity designs.The optimum configurations of OPOs are determined by the pump beam quality in nonlinear crystals. In order to obtain the maximum conversion efficiency we always hope the pump source is operated at the maximum level, thus to raise the input pump energy, we have to apply the Galilean telescope to input the pump beam, but it will lead to the bad pump beam quality and the large output beam linewidth. If we like to obtain the narrow linewidth parametric beam output, applying soft apertures to input pump beam is helpful, but it wi...