Measuring Transmittance In Rubidium Vapour Cells Using An Extremely Weak Coherent Field Of Light

The absorptive properties of the atomic transition in the Rb-85 D2 (A) line (5S(1/2)-5P(3/2)) at 780.0 nm are measured by using a continuous tunable diode laser and a CCD detector in Rb vapour cell under the condition of extremely weak incident intensity. When the intensity of incident light decreases from 420 pW/cm(2) to 0.03 pW/cm(2), the transmittance is found to be independent of the incident intensity within our experimental accuracy.