Research On Spectral Beam Combining Of Diode Laser Array

Spectral beam combining(wavelength beam combing) is the most simple and effective method to improve the beam quality, to stable the wavelength and to narrow the linewidth of the output for a semiconductor laser array. Each emitter of the semiconductor laser array is locked at different wavelength by the feedback from the external cavity. All the beams are arranged in the same propagation direction by the dispersion of the grating, because of their different incident angles and different wavelengths. The coincidence of all the beams from the emitters is realized in the space, achieving the spectral beam combining. The overall beam quality and brightness of the semiconductor laser array are improved. As result, the application of the semiconductor laser source in of industrial, medical and military are extended.Spectral beam combination of the semiconductor laser arrays was studied by simulation, theoretical analysis and experimental research based on the spectral beam combination structure and principle. Some of the key issues, including the smile effect, a wide spectrum of a single beam combined array, crosstalk between each emitter and the beam quality degradation, in spectral beam combination are solved.The high power, high brightness, narrow linewidth semiconductor laser source are obtained eventually by the combination of multiple bars. The frequency conversion experiment after spectral beam combining are conducted. The second harmonic generation and sum frequency beams are obtained at the end. The main completed work is as follows:The beam shaping element(BTS) has been added in the spectral beam combination structure. The cross section of the laser beams is rotated by 90 degrees. So the slow axis distribution of each beam is in the vertical direction and the fast axis is in the horizontal direction. Then spectral beam combining is conducted in the horizontal direction. The deviation of vertical space due to smile effects becomes the horizontal displacement. The horizontal displacement leads to only an insignificant deviation from the wavelength that each emitter should be locked at, having no effect on the beam quality of the combining output beam in the non-combining dimension. The smile effect which can’t be avoided in the traditional spectral beam combining is solved. The overall beam quality and the overall efficiency are improved. It makes the foundation for high power, high brightness, narrow linewidth semiconductor laser combination source.This paper puts forward methods of replacing the transform lens by a grating and a collimating lens based on wavelength beam combining. It can effectively overcome the beam quality degradation and the crosstalk between adjacent emitter. The decline of the overall beam quality is avoided after beam combining. It can also improve the overall efficiency, while reducing the whole optical path. The narrow linewidth output of spectral beam combination is achieved, providing methods and approaches to achieve a narrow linewidth of spectral beam combining semiconductor laser source.The transform lens in the traditional spectral beam combining systems is replaced by two optical lenses. The functions of the transform lens, collimating the output of each emitter, and drawing all of the emitter outputs to a common location at the grating, are achieved by the two optical lenses. The first lens used for focusing doesn’t need to collimate the beams from each emitter, so the distance between the focusing lens and the front face of the diode laser bar is no longer to be the focal length of the transformer lens and can be very short. So the optical path of the system is reduced by approximately half. It makes using a transform lens with long focal length possible, and provides the possibility to achieve a narrow linewidth for semiconductor laser beam combination.With the help of relay optics and a transform lens with long focal length, the whole wavelength of a spectral beam combined laser bar could be narrowed. Three separate transform lenses are used instead of a transform lens to avoid off-axis aberrations of a spherical transform lens. The high power, high brightness and the narrow linewidth laser source by spectral beam combining multiple semiconductor laser bars are realized.We has invested the nonlinear frequency conversion of the semiconductor laser array after spectral beam combination. The sum frequency between each emitter after spectral beam combination is proposed for the first time. The experiment of the second harmonic generation and sum frequency has been conducted, obtaining the blue light. The frequency conversion efficiency is measured.