METHOD AND APPARATUS FOR MEASURING COHERENCE LENGTH OF LASER BEAM

摘要

PROBLEM TO BE SOLVED: To more accurately measure a coherence time of a laser beam.;SOLUTION: A frequency of a measured laser beam is linearly swept (2). The frequency-swept laser beam is branched into two lines (3-1). An optical circulator 4 emits one of the branched laser beams into an optical fiber 5 to collect Rayleigh scattered light generated in the optical fiber 5, and then the Rayleigh scattered light and the other of the branched laser beams are multiplexed (3-2). A light receiving element 6 detects a photocurrent from the multiplexed light, and then the Fourier transform is performed on a current value of the detected photocurrent so that power spectra of the photocurrent are analyzed (7-11). The analysis is repeated several times to obtain an ensemble average of the power spectra as a function of a delay τ so that a standard deviation in the ensemble average of the power spectra in the delay τ is calculated. Using the standard deviation that is proportional to an absolute value of a coherence function γ(τ) in the delay τ, the absolute value of the coherence function γ(τ) is obtained.;COPYRIGHT: (C)2013,JPO&INPIT