A signal processor, which computes the second spatial moment or spot size of a laser beam In two dimensions by optical rather than electronic means, reduces the Impact of spatial noise on thermal lens measurements. The spot size determination Is sufficiently fast to allow time averaging by either transient recording or lock-in amplification; the ultimate speed of computation Is limited only by the transit time of light through the device. The thermal lens detection limits using the optical processor are A m,n = 1.1 X 10~7 for a 1 cm path length In CCI4 and a laser power of 80 mW. This method of spot size detection Is contrasted with photodiode array profiling of the laser beam, which is also used to illustrate the problems of spatial noise In thermal lens measurements.

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While the chemical information provided by electric dichroism spectroscopy can be useful for studying the conformation and electronic structures of molecules in solution, the dichroism signals produced at fields approaching the dielectric strength of organic solvents are extremely small and difficult to detect. A double-beam, laser-based instrument for electric dichroism measurements is described which allows detection of dichroism signals corresponding to changes in absorbance of less than 10−6 with only a 1.2-kV high-voltage source.