Frequency stabilization and fine-tuning characteristics of a CW InSb Spin-Flip laser

A study, using heterodyne techniques, of the magnetic field (1-10 kG), electron concentration (10¹⁴- 10¹⁵cm^-3), and alignment dependencies of the tuning characteristics of an InSb spin-flip laser pumped with a 5-μm CO laser is reported. These characteristics vary from a nearly continuously tunable broad-band (100-MHz) output to quasi-continuous single-mode hopping and pulling with mode tuning rates varying from greater than 75 MHz/G to less than 30 MHz/G. Large variations in the tuning rate are observed within a single-mode tuning range of less than 1 GHz. The frequency and magnetic-field dependencies of the InSb index of refraction have been measured in the near-resonance regime and a simple theoretical fit to the dispersion data is carried out. A hybrid frequency and phase-lock closed-loop system to maintain the output frequency of the spin-flip laser at a variable frequency offset from the frequency of a CO local-oscillator laser has been constructed. This system results in three major improvements in the operating characteristics of the spin-flip laser: 1) the output frequency is accurately calibrated relative to the CO-laser frequency, 2) the tuning of the spin-flip laser can be controlled in a well-calibrated fashion by varying the frequency offset, and 3) the frequency jitter and stability of the spin-flip is reduced to kHz.