Unmodulated-Type Frequency Stabilization of a PbSnTe Diode Laser

The frequency of a PbSnTe diode laser around 10.6 μm was stabilized to one of the absorption lines of C₂H₄ without frequency modulation by controlling the injection current. Two different methods were tried: one used light after absorption and the other used light after absorption and reference light for comparison. From the analysis of the linear approximate models of the experimental systems, the frequency fluctuations, which here are taken to represent the peak-to-peak widths over a period of 5 minutes, were estimated to be 9.3× 10^-8 in the former case and 2.2× 10^-8 in the latter. The analysis also clarified that frequency fluctuations are underestimated when obtained by the usual method, which is a simple conversion of the control error signals. These values were over one order smaller than the values obtained from the linear approximate models.