Diode-pumped 2148-nm Nd:YAG/Cr^4+:YAG microchip laser system for the detection of NO

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-microm transition in Nd:YAG to detect NO by laser-induced fluorescence. A significant challenge was the development of an environmentally stable coating to provide the necessary discrimination between the 1.074-microm laser line and the stronger transition at 1.064 microm. The exact position of the fifth-harmonic frequency was determined by use of NO fluorescence excitation spectra to be 46556 +/- 1.5 cm(-1). With a pulse energy of approximately 50 nJ of fifth-harmonic light, we observed a detection sensitivity for NO of approximately 15 parts per billion by volume in a simple, compact optical system.