Beam Quality Improvement Of Semiconductor Laser Diodes With External Cavity Feedback

The model characteristics and oscillation characteristics of a semiconductor laser are analyzed in detail. Beam quality improvement of different kinds of semiconductor lasers include laser diode array and broad area laser diode with external cavity feedback are studied and single-lobed far-field patterns with single longitudinal mode laser output is achieved.In the dissertation, a simple- external cavity geometry that has good mode discrimination and insensitivity misalignment of the cavity elements is analyzed in detail with ray transfer matrices and investigated on a laser diode array. With this kind of setup, a laser beam with 0.46?far field divergence angle, which corresponding to 1.12 times the diffraction limit is obtained.Another novel external cavity geometry through which the feedback laser beam can oscillate in the external cavity is studied on the broad area laser diode. With this kind of setup, a laser beam with 320mW output power, 0.53?far field divergence angle, which corresponding to 1.3 times the diffraction limit is obtained.Improvement the external cavity geometry with FP etlon, with the longitudinal mode selection of grating and FP etalon, a laser beam with 140mW output power, 0.44?far field divergence angle, which corresponding to 1.08 times the diffraction limit, spectral line width of 0.02nm (10 GHz) is obtained.The optical characteristic of the index-guide, gain-guide laser diode array and the broad area laser diode is calculated using supermode theory and broad-area mode theory. Also, based on the broad-area mode theory, the mode characteristic of external cavity semiconductors is studied. The dependence of output power, threshold and oscillation frequency on external cavity are presented and compared with experiment result.Laser diode pumped Gr4+, Nd3+:YAG self Q-switched laser is also studied in the dissertation. Under the condition of the CW pumping and pulsed pumping, high repetition rate, narrow pulse width laser beam are all obtained. In order to stabilize the single pulse output, pre-pumping technology with the rectangular pulsed pump electric current on the certain pre-current is used on laser diode. The stabilizing efficiency was very significant.