Active local oscillator power stabilization for a hot electron bolometer heterodyne receiver

We report on the application of a new technique for actively stabilizing the power of a far infrared gas laser as the local oscillator (LO) in a superconducting hot electron bolometer (HEB) heterodyne receiver system at 2.5 THz. The technique utilizes PID feedback control of the local oscillator intensity by means of a voice-coil based swing arm actuator placed in the beam path. The HEB itself is used as a direct detector to measure incident LO power whilst simultaneously continuing to function as heterodyne mixer. Results presented here demonstrate a factor of 50 improvement in the measured total power and spectroscopic Allan variance time. Allan times of 30 seconds and 25 seconds respectively are shown for large and small area HEB's with a measured effective noise fluctuation bandwidth of 12 MHz. The technique is versatile and can be applied to any LO source and at any LO frequency.