Research On Dual-Loss-Modulated Low Repetition Rate Subnanosecond Mode-Locking Pulse Lasers And Nonlinear Frequency Conversion Properties

LD pumped ultrafast pulse lasers with large pulse energy, high stability and good beam quality become increasingly more interesting because of their advantages of small size, light weight, robust and long life duration, and have been widely used in the fields of industry, communication, military and medicine etc. With the development of ultrafast solid-state lasers, many exciting advances have been made in the above mention areas. The highest laser intensity generated by the ultrashort laser technology is comparable or even higher than relativistic intensity. The development of ultrafast laser technology makes the study of interaction between laser fields and matters come into nonperturbative and highly nonlinear domain and uncover a lot of new physical effects and phenomenon.Pulse repetition rate, pulse width, per-pulse energy, peak power as well as pulse amplitude stability are important parameters for pulsed lasers. According to these parameters, an active electro-optic Q switcher combined with different passive saturable absorbers were employed as dual-loss modulator to compress the Q-switched envelope, and only one mode-locking pulse underneath the Q-switched envelope was experimental realized; by using the rate equation theory, the pulse compression property of the dual-loss modulator was theoretically studied; the output performances of the dual-loss-modulated Nd:YVO4å’ŒNd:LuxY1-xVO4 laser were comparatively studied; using the nonlinear optics theory, the second harmonic generation of the dual-loss-modulated Q-switched mode-locking laser was researched; by observing high harmonic generated from noble gases, nonlinear frequency conversion in strong electromagnetic field was investigated, and the application of HHG-based EUV source in photoelectron spectrum for volatile liquids was tested. The main contents and creations of this dissertation are listed as follows:1. By employing active electro-optic switcher and passive GaAs saturable absorber simultaneously, a YVO4/NdYVO4 laser was doubly modulated, the fundamental frequency and second harmonic generation output performances of this dual-loss-modulated laser were investigated; with the repetition rate fixed at 1 kHz, average output power, pulse width, per-pulse energy, and peak power as a function of incident pump power was studied; as the pulse width of the Q-switched envelope decreased with the increasing pump power, the Q-switched envelope was compressed until containing only one mode-locking pulse in it and low repetition rate subnanosecond mode-locking pulse operation was realized; the influence of output coupler transmission to the realization of single mode-locking pulse underneath a Q-switched envelope was researched; by considering the influence of inverted population density to the absorption coefficient of laser crystal, the rate equations were used to theoretically simulate the pulse energy, pulse width and pulse shape of this dual-loss-modulated laser, and the theoretical data are basically in accordance with the experimental results.2. Using a transmission-type SESAM combined with the electro-optic switcher, Nd:YVO4 and Nd:Lu0.6Y0.5VO4 laser were doubly modulated; by studying the different performances of these two lasers, the influence of the mixed laser crystal to the realization single mode-locking pulse underneath a Q-switched envelope was analysed; by switching the incident pump power and repetition rate, the operation conditions of the low repetition rate mode-locking pulse laser were discussed.3. In accordance with the operation conditions and nonlinear optical properties of carbon nanotubes, using multi-wall carbon nanotube combined with the electro-optic switcher as the dual-loss modulator, Nd:Lu0.5Y0.5VO4 as the laser material, the output properties of the single mode-locking pulse Nd:Lu0.5Y0.5VO4/KTP green laser were investigated.4. The rise time, fall time as well as pulse width of pulsed laser Q-switched mode-locked by Cr4+:YAG saturable absorber were investigated; by employing different groups of output couplers and saturable absorbers, the symmetry of Q-switched envelope was optimized; based on the optimization, the Cr4+:YAG was introduced to the dual-loss-modulated laser and phenomenon of fast-rising and slow-falling was improved; low repetition rate mode-locking pulse operation was realized and the performances were theoretically analyzed.5. A novel time-preserving single-grating monochromator was used to select one harmonic from high harmonics generated from noble gases Ar and Ne; after the frequency-selection and reimagement of the EUV light spot, photon fluxes of EUV harmonics were measured in an extended energy range; by investigating the photcelectron spectrum of neon atoms, the precision of the monochromator was checked; by measuring photon fluxes under different polarization states, the response of the beamline to the polarization was studied, and the influence of the polarization to the photcelectron spectrum of molecules in liquid environment was investigated.