Ultrasensitive thermal lens spectroscopy of water

A recently developed dual-beam configuration that optimizes the thermal lens technique has been used to obtain the absorption spectrum of pure water from 350 to 528 nm. Our results indicate the minimum linear absorption coefficient smaller than 2 X 10(-5) cm(-1) between 360 and 400 nm. This value is lower than previous literature data, and it is blueshifted. Absorption coefficients as small as 2 X 10(-7) cm(-1) can be measured for water using 1 W of excitation power. A detection limit of similar to 6 X 10(-9) cm(-1) (P=1 W) for CCl(4) was estimated, which represents, to the best of our knowledge, the highest sensitivity obtained in small absorption measurements in liquids. (C) 2009 Optical Society of America