Open Parth Cavity Ring Down Spectrometer (OPCRDS)

Open-path cavity ring down (OPCRD) technique with variable cavity length was developed to measure optical extinction including scattering and absorption of air in laboratory environment at 635 nm wavelength. By moving the rear cavity mirror of the ring-down cavity to change cavity length, ring-down time with different cavity lengths is experimentally obtained and the dependence of total cavity loss on cavity length determined. The extinction coefficient of air is determined by the slope of linear dependence of total cavity loss on cavity length. This variable-cavity-length OPCRD technique can be used for absolute extinction measurement and real-time environmental monitoring without closed-path sample cells and background measurements.