Internal temperature determination for laser noise cancellers

Abstract

Noise cancellers of the type described by Hobbs [Appl. Opt. 36, 903 (1997)], used in dual-beam laser spectroscopy, provide an analog logarithmic output that is monotonic in, but not linearly related to, the sample absorbance. If the goal of a spectroscopic experiment is to determine an absolute absorbance or a spectral lineshape, rather than simply a line location, the conversion function between detector output and absorbance needs to be known. That function depends on the internal temperature of the transistors used in the device’s current splitter, and an incorrect assumption about the temperature leads to errors in absorbance or distortions in the extracted lineshape. Neither the original design nor a commercial implementation (Newport Nirvana) gives a direct indication of the temperature. A simple laboratory procedure for determining the transistor temperature is described.