Callaghan Innovation Research Papers

Back to Research Papers

TitleA method to lower the detection limit for optical beat signals from a frequency-dithered stabilized laser
Publication TypeJournal Article
Year of Publication2001
AuthorsCooper, S.J., Howick E., McLeod D., Wright D., King B.T., and Stedman G.E.
JournalMeasurement Science and Technology
Pagination1726 - 1733
Date Published2001
ISSN09570233 (ISSN)
KeywordsAbsorption, laser, Laser applications, Lasers, Optical beat signals, Optical variables measurement, Signal to noise ratio
AbstractA narrow absorption feature in an atomic or molecular gas (such as iodine or methane) is used as the frequency reference in many stabilized lasers. As part of the stabilization scheme an optical frequency dither is applied to the laser. In optical heterodyne experiments, this dither is transferred to the RF beat signal, reducing the spectral power density and hence the signal to noise ratio over that in the absence of dither. We removed the dither by mixing the raw beat signal with a dithered local oscillator signal. When the dither waveform is matched to that of the reference laser the output signal from the mixer is rendered dither free. Application of this method to a Winters iodine-stabilized helium-neon laser 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 predicts similar threshold reductions.

Back to top