LAUSR

A microwave electric field sensing has been set up based on a three-color electromagnetically induced absorption in rubidium vapor cell via cascading transitions. All transitions are irradiated by infrared lasers: a 780 nm laser servers as probe to monitor the optical transmittancy via transition 5S1/2→P3/2;, a 776 nm laser and a 1260 nm laser are used to couple the states 5P3/2 and 5D5/2 and states 5D5/2 and 44F7/2, respectively. We find that a frequency detuning ∼2π × ( - 40) MHz of the 776 nm dressing beam prefers to a better signal-to-noise ratio for the probe beam. The off-resonance greatly depresses the double resonance pumping effect. A demonstration measurement for the electric field of microwave 1.18988 GHz, corresponding to the coupling resonance between two adjacent Rydberg states 44F7/2 and 44F9/2, gives a sensitivity of 55.79(23)nVcm-1/Hz and a smallest discernible electric field of 78.9(33) nVcm-1 in time scale of 500 ms.