A THERMAL PHASE-LOCKED LOOP FOR FREQUENCY STABILIZATION OF INTERNAL-MIRROR HE-NE LASERS (LAMBDA=0.633 MU-M)

Abstract

A new servo circuit based on the thermal phase-locked loop (TPLL) has been developed for frequency stabilization of internal-mirror He-Ne laser. A feedback signal proportional to the fluctuation in the frequency of the laser is down-converted through a voltage-controlled oscillator (VCO) and compared in a phase/frequency circuit with that of a frequency reference. The detected phase difference then drives a heater wrapped around the laser tube for tuning the laser cavity length. The frequency stability achieved is +/- 1.0 x 10(-9) over a period of several hours.