The Study Of Spectral Beam Combining By Volume Bragg Grating

Thermal effect is the main limitation to achieve high power laser during the development of high power laser technology. Thermal loss will reduce the energy transfer efficiency along the increscent power. Spectral Beam Combing (SBC) combines multiple beams with different wavelengths and low thermal losses into one single beam and provides an effective way to get high power laser. The theory and experiment of SBC by transmitting Volume Bragg Grating (VBG) are studied in this thesis.The physical model of two channels and three channels SBC by transmitting VBG are built based on the wavelength selection of VBG. The diffraction efficiency of VBG , the VBG's absorption and the ratio of the incident power with different wavelengths are the main factors affecting the combining efficiency of SBC. Two physical models of multi-channels SBC using single transmitting VBG and multi-transmitting VBG are presented. The optimum way of SBC and the optimum combining channels can be chosen for different values of diffraction efficiency of the incident beams and the VBG's absorption .Two beams'SBC is carried out by VBG basing on cationic ring-opening polymerization and the doublet spectra output of copper vapor laser. The combining efficiency beyond 65% is achieved and the angle of divergence is 0.46mrad when the incident beams'angle of divergence is 0.11mrad. The factors affecting combining efficiency are studied in the experiment. The combining efficiency will fall when the ratio of the incident beam's power matching Bragg condition and detuning Bragg condition increases; The combining efficiency will increase when the angle of divergence becomes small. The experiment of SBC by acousto-optic crystal is complete, which proves that SBC by acousto-optic crystal is feasible.