Phase-shift Cavity Ring-down Technique for Detection of NO2 in PPM Concentration

A phase-shift cavity ring-down spectroscopy (PS-CRDS) experimental set-up has been established using a broadband diode laser for the measurement of phase shift due to absorption of NO 2 in a sealed off cavity ringdown cell. The PS-CRDS technique is verified by optimising various parameters of CRDS cavity and excitation laser. The PS-CRDS signals were measured on the first harmonics using a lock-in-amplifier. The square modulated laser pulses were used in the experiment to obtain the decay time. Measurements of the signal strengths at different CRDS cavity lengths wre also carried out to verify the detection sensitivity for ppm level concentration measurement of trace gases.