Abstract
A narrow absorption feature in an atomic or molecular gas (such as iodineor methane) is used as the frequency reference in many stabilized lasers.As part of the stabilization scheme an optical frequency dither is appliedto the laser. In optical heterodyne experiments, this dither is transferredto the RF beat signal, reducing the spectral power density and hence thesignal to noise ratio over that in the absence of dither.We removed the dither by mixing the raw beat signal with a dithered localoscillator signal. When the dither waveform is matched to that of thereference laser the output signal from the mixer is rendered dither free.Application of this method to a Winters iodine-stabilized helium-neonlaser reduced the bandwidth of the beat signal from 6 MHz to 390 kHz,thereby lowering the detection threshold from 5 pW of laser power to 3 pW.In addition, a simple signal detection model is developed which predictssimilar threshold reductions.
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