Abstract
In using lasers for spectroscopy and other precision measurements, the amount of absorption or dispersion that can be delected in a sample is often limited by the technical noise on a laser rather than the fundamental limits of the sample. With hopes of using diode lasers for quantum limited detection of atoms and molecules, we studied the amplitude noise characteristics of these lasers. We are also interested in achieving very high spectral resolution, so we have incorporated optical feedback techniques to stabilize the frequency and narrow the linewidth of diode lasers. Some of the spectral characteristics of the amplitude noise on lasers with optical feedback (for narrowing) differ from the noise on unaltered lasers. The fractional amplitude noise level on diode lasers is relatively tow when compared with traditional tunable laser sources, but it is still well above the fundamental shot noise level. For room temperature AlGaAs lasers operating at spectroscopically useful power levels, the amplitude noise is typically 20 dB above the shot noise level. The spectral distribution of this noise has been measured from a few hertz out to beyond the relaxation oscillation frequency at a few gigahertz. When these Users are antireflection coated on one facet and coupled with optical feedback to extended cavities (for tuning and reduced linewidths), the amplitude noise spectrum is altered significantly. In the case of strong optical feedback from gratings, the amplitude noise on these lasers can be within 5 dB of the shot noise level over broad spectral regions.
© 1990 Optical Society of America
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