Saturated-interference spectroscopy.
The background in saturation spectroscopy is decreased by balancing the probe beam, in amplitude and phase, against a second probe, using a configuration like a Jamin interferometer. This improves the signal-to-noise ratio. If the phase is adjustable to provide best balance while the laser is tuned, the signal is proportional to the square of the absorption, and the line width is accordingly reduced.
Kowalski
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Department of Physics, Stanford University, Stanford, California 94305, USA.
Hill
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Schawlow
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