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BACKGOUND-FREE SATURATION SPECTROSCOPY WITH A FREQUENCY-OFFSET PUMP

James Snyder, Rama K. Raj, D. Blöch, M. Ducloy

Published Jan 1, 1980• 0 citations
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Abstract

We report the development of a simple method for eliminating coherent background noise and fluctuations from saturation spectroscopy signals. With this technique, which utilizes a traveling-wave acousto-optic modulator to simultaneously frequency-shift and modulate the saturating beam, we have routinely observed zero background, Doppler-free saturation resonances in the $I_{2}$ at 514.5 nm. With a low-noise laser or high pump modulation frequency, we have achieved detection sensitivity approaching the fundamental quantum limit.

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•Jun 18, 1984•0 citations
We report the development of a simple method for eliminating coherent background noise and fluctuations from saturation spectroscopy signals. With this technique, which utilizes a traveling-wave acousto-optic modulator to simultaneously frequency-shift and modulate the saturating beam, we have routinely observed zero background, Doppler-free saturation resonances in the I2I_{2}I2​ at 514.5 nm. With a low-noise laser or high pump modulation frequency, we have achieved detection sensitivity approaching the fundamental quantum limit.
We report on a technique for obtaining dispersive saturated absorption features by two pump beams derived from an acousto-optic modulator. One of the beams is frequency shifted by the modulator allowing for a variable frequency offset of the resulting signal. They are used to saturate the atomic transition in the low-density vapour of the lamp. The sensitivity of the technique is sufficient to observe clear signals from isotopes of calcium unresolved by the inhomogeneous broadening and with natural abundances of less than 0.2%. The technique is used for offset locking the frequency of a Ti:Sapphire laser used for laser cooling and trapping of calcium.
We have shown earlier that hyperfine spectroscopy in a vapor cell using co-propagating pump-probe beams has many advantages over the usual technique of saturated-absorption spectroscopy using counter-propagating beams. The main advantages are the absence of crossover resonances, the appearance of the signal on a flat (Doppler-free) background, and the higher signal-to-noise ratio of the primary peaks. Interaction with non-zero-velocity atoms causes additional peaks, but only one of them appears within the primary spectrum. We first illustrate the advantages of this technique for high-resolution spectroscopy by studying the D2D_2D2​ line of Rb. We then use an acousto-optic modulator (AOM) for frequency calibration to make precise hyperfine-interval measurements in the first excited P3/2P_{3/2}P3/2​ state of 85,87^{85,87}85,87Rb and 133^{133}133Cs.