Knowledge Bank

A new method of Tunable Diode Laser (TDL) spectrum digitization is presented. While the TDL frequency is slaved to an internally coupled Fabry Perot Interferometer $(icFPI)1$, this interferometer is tuned in a step by step manner. The extrema of a HeNe laser interference pattern trigger periodic temporary stabilization of the interferometer to the HeNe laser frequency. Thus at each step, the infrared spectroscopic data, characterized by a very stable and stationnary frequency, are collected into a computer. This technique is combined with a confocal Fabry Perot etalon, thus providing a frequency scale accuracy of about $3.510-5cm-1$ over a $1cm-1$ scan. The method is shown to be consistent with high resolution Fourier transform and heterodyne spectroscopy results, based on relative position measurements of $N2O$ absorption lines in the $2220-2240cm-1$ spectral region.