External cavity feedback laser diode bar with narrow bandwidth and good beam quality

An off-axis external cavity with double feedback is designed to simultaneously reduce spectral bandwidth and improve the beam quality of the laser diode bar. The external cavity is made up of a high-reflection mirror and a blazed grating, where the selected spatial mode can be amplified. The grating can also provide a spectral-sensitive feedback to the laser diode bar. In addition, a half-wave plate is inserted into the grating-feedback branch to control the feedback light amount, and the output laser is taken from the grating-feedback branch. The bandwidth and the beam parameter product are respectively reduced to 0.15 nm and 283 mm·mrad for laser diode bar with the external cavity at a drive current of 16 A. The center wavelength is almost unchanged as the temperature varies, the laser