Knowledge Bank

Absolute calibration of diode laser spectral scans normally requires a spectral line of know frequency within the continuous tuning region of each laser mode. Since these discrete are only $\sim$ $cm-1$ wide, it is often the case that no such frequency marker exits or is convenient for a particular mode. However, with the combined fringe pattern from two etalons arranged in series in the laser beam, a small grating monochromator can be used to determine the exact number of fringes between any two spectral positions, so that calibration can be extended among widely separated modes. This method has been used for mode separations up to $17cm-1$. A double beam dual-channel signal averaging spectrometer will be described, and techniques for stablizing diode laser output and etalon fringe patterns will be discussed.