According to the principle of reflectivity measurement using cavity ring-down spectroscopy, the origin of reflectivity measurement uncertainty was analyzed, we particularly discussed the origin of ring-down time measurement uncertainty, and concluded that the maximum amplitude selection of ring-down curve, the fitting of curve, the time delay of detector, and the dispersity of measurement results were the reasons why. Based on the cavity ring-down spectroscopy method, we built a reflectivity measurement system with the wavelength of 1.319 micron, and obtained the ring-down times of straight and folded cavity respectively. According to the origin of uncertainty, the extensional uncertainty of system was obtained. The result showed the high precision of reflectivity measurement using cavity ring-down spectroscopy.
The spot profile and intensity distribution of output beam from unstable resonator of a DF Laser were measured. The results showed the spot was a ring with 45mm external diameter and the measurement data sufficed for the design requests. But the spot was asymmetric seriously on horizontal direction, which was arose by two possible reason, one was non-uniform distribution of the gain medium , the other was the optic-axis migration to upstream of gain medium.