DUAL-LASER CROSSED-BEAM THERMAL LENS SPECTROPHOTOMETER PUMPED WITH A SEMICONDUCTOR DIODE-ARRAY LASER

A simple and compact dual-laser crossed-beam thermal lens spectrophotometer pumped with a semiconductor diode-array laser, emitting up to 100 mW of power at 818 nm, is described. The pump laser aperture was located at a very small distance from the cell wall and was not focused. The He-Ne probe beam was made to pass near the cell wall, almost grazing the wall inner surface, crossing the pump beam at right-angles with respect to the beam propagation direction, but parallel to the major axes of the narrow elliptical lobes emitted by the array. Owing the particular spatial characteristics of the pump beam, a thermal lens signal with a complex spatial distribution was obtained. Univariant and simplex optimization of the set-up were performed using CuSO4 and phosphomolybdenum blue solutions. Limits of detection of absorbance were 3.9 x 10(-4) in CCl4, 3.4 X 10(-4) in 2-butanol, 1.1 x 10(-3) in ethyl acetate and 3.0 x 10(-3) in water.