Abstract
Thermal lens spectrophotometry was examined using the CO2 laser as an exciting source for trace analysis of benzene in air. Thermal lens signal was recorded by a digital lock-in amplifier system. The sample gas of benzene was generated continuously by the Permeater (Kitazawa, diffusion tube). The detection limit was 500 ppb for benzene with the 9.639 μm line of the CO2 laser (output power : 20 W). This method is useful for the determination of the substances which have no absorption band at the visible region.
