Abstract
In order to improve the sensitivity of thermal lens spectrophotometry, a new type of optical configuration was studied. An Ar/sup +/ laser for excitation was focused into a sample cell as usual, but a probe laser was introduced directly without focusing the beam. The laser beams were collimated and isolated with two prisms to eliminate optical interference of the laser beams. A part of the probe laser passing through the sample cell was split out by a quartz wedge and the intensity at the beam center was detected by a photodiode. The signal was measured by a digital lock-in amplifier system. The detection limit of NO/sub 2/ was 5 ppb, using the 488-nm line of the Ar/sup +/ laser (700 mW). The dynamic range of the linear analytical curve was obtained over 4 orders of magnitude. The present method has a distinct advantage over a photoacoustic method with respect to the capability of continuous monitoring of atmospheric NO/sub 2/. 5 figures, 2 tables.
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