LASER PHASE NOISE REJECTION BY TWO-WAVE MIXING PHOTOREFRACTIVE INTERFEROMETRY

摘要

The capability of a two-wave-mixing photorefractive interferometer to reject laser phase noise using almost identical path lengths for the reference and signal beams was demonstrated experimentally. It was shown that a linear cavity laser can achieve performances similar to a significantly more expensive non-planar-ring oscillator laser of the same power with the appropriate matching of the reference and signal path lengths. Also, it was demonstrated that the two-wave-mixing photorefractive interferometer can perform shot-noise limited measurements at light levels higher than what is possible with a conventional dual-cavity Fabry-Perot interferometer. Combined with its ability to reject amplitude noise, the photorefractive interferometer can be used to achieve very sensitive measurements with the appropriate levels of collected light. In this paper, it was also demonstrated that the speckle effect caused by composite surface roughness should not limit the use of a photorefractive interferometer for composite inspection. However, the proposed scheme to compensate for the Doppler shift created by scanning the detection laser beam on a surface still remains to be demonstrated in actual composite inspections to consider the two-wave photorefractive interferometer as a replacement of the confocal Fabry-Perot interferometer currently used in LaserUT systems.