GaN-based blue Littman-type grating-coupled external-cavity semiconductor laser

A Littman-type grating-coupled external-cavity (EC) semiconductor laser is demonstrated, utilizing a high-power GaN-based blue laser diode. The distribution of diffracted light beams on the grating is calculated using the grating diffraction equation for various incident angles. An optimal range of incident angles, specifically from 10.4° to 39.8°, where only positive first-order diffracted light occurs, has been determined. When set at an incident angle of 35°, the EC laser exhibits a maximal output power of 266 mW with a wavelength tuning range of 3.1 nm (453.7-456.8 nm), and a spectral linewidth narrower than 0.09 nm under an injection current of 1500 mA. Furthermore, the laser output beam has excellent directional stability during wavelength tuning, showing potential for applications in high-resolution spectroscopy and laser cooling and trapping.