Role of noise in the diode-laser spectroscopy of the spectral line profile

摘要

Questions concerning precise measurements of thespectral-line-profile parameters by diode-laser spectroscopic methodswere examined. The instrumental function of a distributed-feedbackdiode laser (λ=1.53μm), consisting of the additive contributions ofthe noise due to sontaneous emission, frequency flucturations, andintensity flucturations was investigated. An analytical formula wasobtained for the spectrum of the diode-laser field formed byfrequency flucturations. The spectral density go of the frequencyfluctuations, determining the width of the central part of theemission line profile of a diode laser, was found by two independentmethods (by fitting to a Doppler-broadened absorption line profileand by finding the intensity of the residual radiation and thesaturated-absorption line with). The parameters Ω and Γ of thespectral density of the frequency fluctuations, coupled to therelaxation oscillations and determining the wing of the diode-laseremission line profile, were determined experimentally. By taking intoaccount the instrumental function of the diode laser, involvingsuccessive convolution with the recorded emission spectra, it waspossible to reproduce correctly the spectral line profile and tosolve accurately the problem of the `optical zero'. The role of thecorrelation between the intensity noise and the diode-laser frequencywas considered.