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The Study On Optical Parametric Oscillators From Continuous-Wave To Nanosecond-Pulse

Posted on:2006-12-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:C X DengFull Text:PDF
GTID:1118360182470638Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
The optical parametric oscillators are the devices that can generate tunable optical radiation with high degree coherence. Following the scientific and technical development of lasers and second-order nonlinear optical crystals, the theory and technology of the optical parametric oscillators also develop gradually. The characteristics of the optical parametric oscillators from continuous-wave to nanosecond-pulse have been studied mainly in theory and with experiment in this dissertation. The major works in the dissertation are presented as the following. The generalized theories of the threshold and conversion efficiency of optical parametric oscillators with single pass interaction have been developed by the Green's function approach and perturbation approach. The electric fields of the pump and the non-resonant idler waves are expressed as series, in the effective second-order nonlinear coefficient. The focused fundamental Gaussian beam with elliptical cross section, the effects of diffraction, arbitrary focusing, arbitrary waist locations of the beams, phase mismatching, beams walk-off, and small linear absorption are included in the derivation. The results provide an appropriate description of a steady-state operating, generalized optical parametric oscillator with collinear phase matching, The plane wave theory has been derived to describe the intensity characteristics of an intracavity continuous-wave singly resonant optical parametric oscillator. The Gaussian beam theory has been developed to describe the power characteristics of an intracavity continuous-wave singly resonant optical parametric oscillator, the theory describe this kind of optical parametric oscillator more properly. The second-order nonlinear interaction is treated as the output loss of the laser. The nonlinear reflectivity of the laser, and the intensity or power characteristics of the signal and idler waves are obtained, based on the solutions for the characteristic equations describing the laser. The properties of the quasi-three-level,four-level, end-pumped laser gain mediums are taken into account in the plane wave theory. Under the mean-field approximation and beyond the mean-field approximation, the characteristics of the intracavity continuous-wave singly resonant optical parametric oscillator with ring cavity are analyzed in the plane wave theory. Under the mean-field approximation, the characteristics of the intracavity continuous-wave singly resonant optical parametric oscillator with stand wave cavity are analyzed in the plane wave theory. While in the Gaussian beam theory, the properties of the four-level, end-pumped laser gain medium are taken into account. Under the mean-field approximation, the characteristics of the intracavity continuous-wave singly resonant optical parametric oscillator with stand wave cavity are analyzed. The Gaussian beam theory has been developed to describe the power characteristics of a steady-state operating, ring cavity, singly resonant optical parametric oscillator with intracaivity optical amplification. The pump threshold of the singly resonant optical parametric oscillator can be greatly reduced with suitable parameters of the optical amplifier. Under the mean-field approximation and without the second-order nonlinear crossing coupling, there are four operating domains for a singly resonant optical parametric oscillator with intracaivity optical amplification, meanwhile there exits a minimum pump threshold for the singly resonant optical parametric oscillator. The characteristic of the end-pumped laser gain medium taken as optical amplifier is considered. The generalized characteristics of singly resonant optical parametric oscillator are also considered in the derivation. The dynamic equations have been derived to describe the characteristics of Cr4+:YAG laser and intracavity singly resonant optical parametric oscillator pumped intracavity by a passively Q-switched Nd:YAG laser. The Cr4+:YAG is used as the saturable absorber and laser gain medium. Under suitable conditions, the Cr4+:YAG laser gain medium can amplify the SRO signal wave generated in the second-order nonlinear interacting process if the wavelength of this wave is in the range of the gain spectrum of Cr4+:YAG.. The influence of relaxing time of the intermediate level on Cr4+:YAG saturable absorber and laser, as well as the intracavity singly resonant optical parametric oscillator are considered in the analyses. This intermediate level is between the higher excited state and the upper laser level of Cr4+:YAG. For the approximation of undepleted incident waves, the plane wave and focused Gaussian beam theories of optical difference frequency generation and singly resonant optical parametric oscillation in multiple crystals are derived. The focused fundamental Gaussian beam with elliptical cross section, the effects of diffraction, arbitrary focusing, arbitrary waist locations of the beams, phase mismatching, beams walk-off, and small linear absorption are included in the analyses. The results are applied to the analysis of singly resonant optical parametric oscillation with two pump wave walk-off compensating crystals, and difference frequency generation with two walk-off compensating crystals. The results indicate that the pump threshold can be greatly reduced by use this kind of singly resonant optical parametric oscillator. While the conversion efficiency and the beam quality can be improved in the difference frequency generation with two walk-off compensating crystals. The theory has been derived to describe the characteristics of the simultaneous doubly resonant optical parametric oscillation and frequency doubling in the four-level laser cavity. The basic characteristics of this kind of optical parametric oscillator have been analyzed. By using Nd:YAG laser and KTiOPO4 crystal, the possibility and the characteristics realizing simultaneous doubly resonant optical parametric oscillation and generation of green optical radiation have been analyzed theoretically and experimentally.
Keywords/Search Tags:Nonlinear, optics Optical parametric oscillator, Phase-matching, Walk-off compensating, Optical amplification, End-pump, Nd:YAG laser, Passive Q-switching
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