Diode-Pumped Nd:YAG/Cr(4+):YAG MicroChip-Laser System at 214.8 nm for the Detection of NO

摘要

A passively Q-switched 214.8-nm Nd:YAG/Cr(4+):YAG microchip-laser system for the detection of NO was designed, constructed, and tested. The system uses the fifth harmonic of the 1.074-micrometers transition in Nd:YAG to detect NO at the few-parts-per-billion level. A significant challenge was the development of an environmentally stable coating to provide the necessary discrimination between the 1.074-micrometers laser line and the stronger transition at 1.064 micrometers. The exact position of the fifth-harmonic frequency was determined using NO fluorescence excitation spectra to be 46556/ cm. We observed a detection sensitivity for NO of about 15 ppb(v) in a simple, compact optical system. Earlier observations of SO2 imply a similar or better sensitivity for the current system, while green-light excitation of NO2 fluorescence yielded a detection limit of order 1 ppm(v). Applications of the laser system described here include explosives sensors based on detection of NO from thermal decomposition, and NO(x)/SO(x) monitors for trucks, aircraft and stationary sources.