[Development and Output Characteristics of 785 nm Portable Grating-Coupled External Cavity Tunable Semiconductor...

Aiming at the miniaturization requirement of shifted excitation Raman spectroscopy test system, a portable grating-coupled external cavity (EC) tunable semiconductor laser in Littrow configuration is designed and fabricated with a commercial 785 nm high-power laser diode as the gain device. By using a new wavelength tuning method, aiming to change the position of gain device relative to the collimating lens in the horizontal direction, a miniaturized device with the size of 140 mm×65 mm×50 mm is designed. Compared to the traditional wavelength tuning method which is to change the light incident angle by rotating the diffraction grating, this new tuning method reduces the translational distance of semiconductor gain device effectively, thus it is conductive to the fast and broad wavelength tuning of portable EC laser. The experimental results show that the EC laser has a wide wavelength tuning range. Under any injection current from 340 to 900 mA, a wavelength tuning range of more than 10 nm can be realized. Especially at 900 mA, good performance including a 11.67 nm-wavelength tuning range from 779.40 to 791.07 nm, a less than 0.2 nm-spectral linewidth, an up to 280 mW-output power, and a more than 25 dB-amplified spontaneous emission suppression ratio is presented, which fully meets the basic testing requirements of shifted excitation Raman spectroscopy. Moreover, 1.35 nm-electric wavelength tuning range is achieved by applying a mini-piezoelectric actuator. This indicates that the home-made 785 nm portable grating-coupled EC tunable semiconductor laser is suitable as the light source of portable shifted excitation Raman spectroscopy testing system to eliminate the fluorescence background of Raman spectrum.