We revisit and improve the optical heterodyne technique for the measurement of the laser coherence, by digital acquisition of the beat-note and numerical analysis of the resulting signal. Our main result is that with the same experimental setup we reach the very "short-time linewidth" with the highest accuracy as well as the frequency noise spectrum.
Sensors based on optical fibers have well known advantages over conventional electromechanical sensors. They offer electrically passive operation and immunity from electromagnetic fields because the fiber is entirely made with dielectric materials. We present a novel acousto-optic system structure. The pump laser, circulator and receiver system including one interferometer used as discriminator, must be placed on electronic board with low electric consumption (< 1A). It is demonstrated we can detect very low acoustic signal, the same level as Deep Sea State Zero Noise if the acoustooptical sen sitivity is sufficient high. Hence, the Noise equivalent pressure of this novel acoustooptical system is optimized .
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