System Analysis And Experimental Study Of Rb 420nm Ultra-narrow Linewidth Optical Filter

For semiconductor lasers,there are two very important indicators to evaluate its performance:line width and frequency stability.Because the frequency fluctuations and drift of laser in free running,the laser center frequency is usually locked on a highly stable spectral line,such as the laser frequency is locked on the atomic or molecular transition line through optical or electrical feedback to narrow linewidth and achieve stable output frequency.Therefore,it is necessary to provide a frequency reference with a narrow linewidth spectrum for frequency stabilization.420nm wavelength precision spectroscopy and atomic optical filter are typical applications of optical feedback.Compared with conventional interference filters,Faraday anomalous dispersion atomic filter(FADOF)has high background suppression,mechanical strength,imaging capability and high transmittance.Ultra-narrow linewidth optical filter is an important component of laser radar,astronomical observation,free space communication and quantum optics.In this paper,the Doppler absorption spectrum,saturated absorption spectrum,polarized spectrum,ultra-narrow linewidth atomic optical filter spectrum of the isotope 85Rb 420nm wavelength is introduced in theory and experiment.The Faraday effect,circular dichroism and saturation absorption technique are used to obtain ultra-narrow linewidth optical filter.Furthermore,the varying effects of temperature,magnetic field and pump power on the transmission of the atomic filter are discussed.The isotope 85Rb ultra-narrow linewidth atomic optical filter achieves a peak transmission of 2.1%with a bandwidth of 6.7MHz when the pump power is 4.5mW,the probe power is 0.45mW,the temperature of Rb cell is 120 ? and the magnetic field is 5Gs,corresponding to 5 S1,2,F = 3?6P3/2,F' = 3,4(cross-over)transition at 420nm.The bandwidth of ultra-narrow linewidth atomic optical filter spectrum is at least two orders of magnitude smaller than the conventional Faraday anomalous dispersion optical filter and is closer to the natural linewidth.At the same time,the factors that affect the bandwidth of the filter,including the source of system noise,are analyzed and studied.