A Near-Infrared Diode Laser Spectrometer of High Resolution and Wide Scanning Range

We have constructed a simple and inexpensive diode laser spectrometer in which the source is locked to and tracked by a scanning Fabry–Perot interferometer and in which absolute frequency measurements are made by markers generated by a further Fabry–Perot interferometer, itself locked either to a selected spectral line of the sample or to the saturated absorption of a D2 line in atomic Rb at 780 nm. With this technique we have been able to obtain near-continuous spectra stretching over the range from 12 640 to 12 780 cm-1 at Doppler-limited resolution. In this paper we describe the principles of the spectrometer along with absolute frequency measurements of a number of overtone rovibrational transitions in two isotopomers of acetylene. The combination relations formed by these transitions demonstrate the accuracy of our measurements to be typically ±0.0002 cm-1.