The absorption characteristics and the response time of the Cs atomic resonance filter (AEF) filled with 5 torr Ar bufier gas have been investigated theoretically and experimentally when AEF was irradiated with the free-run XeCl/Pb blue lase r(pulse width:40ns). The near infrared fluorescence pulse with 40 ns and 150 ns (FWHM) pulse duration have been detected at the side of and behind the AEF respectively.