Study of the effect of repump laser on atomic line filter

Abstract

The improvement in the performance of an atomic line filter (ALF) under the action of a repump laser is reported in the current experimental work. We address the issue of repumping by including an additional laser coupling the 5S1/2(F=1)→5P3/2(F′′=2,1,0) hyperfine levels whereas the optical filter action is exhibited through a pump–probe laser-induced excited state absorption {5S1/2(F=2)→5P3/2(F′=3)→5D3/2(F′′=3)} of the Rb87 atom. It is found that the application of the repump mechanism considerably influences the characterizing parameters (i.e., transmittance and width) of the ALF. To optimize the performance of the ALF, it is required to carefully choose the detuning and intensity of the repump laser for a fixed set of pump–probe combination. For this purpose, the effect of systematic change in detuning and intensity of the repump laser on the ALF signal is studied in detail. For example, it is experimentally found that ALF considerably benefits (∼30%) in transmittance from selective repumping of atoms. It is to be noted that, unlike earlier reports, where the frequency scale of the filter is calibrated with Faby–Perot etalons of comparatively larger free spectral range, the marking is done here with the help of double resonance optical pumping (DROP) signals. The DROP signals, which originate from two-photon coupling within the 5S→5P→5D hyperfine domain, also act as an indicator of the existing “Radiation Trapping” process in the cascade medium. The current study may help in improving the performance of narrow-bandwidth ALF, which is useful for free space optical communication systems and laser spectroscopy.