Development of a double beam, dual wavelength thermal lens using a helium-neon laser

Abstract

A single He-Ne laser was used to develop two types of novel pump and probe configuration thermal lens apparatus. In the first system, the He-Ne laser beam was split into a pump beam and a probe beam by a beam splitter. Two mirrors were used to direct the two counter-propagating beams and to cross at the sample. Alternatively, a pump and probe configuration was achieved from a single laser without the use of a beam splitter. This was accomplished with a special dual output laser, i.e., a laser which provides output from both ends, front and back. The selectivity of these two systems is enhanced by measuring the thermal lens at two different wavelengths, 632.8 and 594 nm. These dual wavelengths were derived from the He-Ne laser by forcing it to oscillate at two transitions: 3s₂-2p₄(632.8 nm) and 3s₂-2p₈(594 nm). Preliminary results have indicated that these instruments are capable of detecting 0.03 µg of palladium(II) via the formation of an ion pair with crystal violet. A comparison is made of the two systems and their applications to general trace analysis.