Effect of the Coupling Beam with Different Intensity Profile upon Rydberg EIT and Rydberg Two‐Color Polarization Spectroscopy with Cesium Ladder‐Type Level

Abstract Electromagnetically induced transparency (EIT) and two‐color polarization spectroscopy (TCPS) with Rydberg atoms are spectroscopic techniques developed based on the interaction between a ladder‐type three‐level atomic system and two light fields. The narrow linewidth and high contrast Rydberg EIT and Rydberg TCPS have important applications in laser frequency stabilization, Rydberg antennas, Rydberg radar and microwave electric fields detection. Here, the EIT and TCPS with cesium Rydberg atoms are investigated using a ladder‐type level system driven by the 509‐nm coupling beam and the 852‐nm probe beam. The 509‐nm coupling beam with three kinds of intensity spatial profile (Laguerre–Gaussian mode, Gaussian mode, Flat‐top mode) is employed one by one in experiments. Due to the different intensity spatial distributions of the three 509‐nm coupling beams, the Autler–Townes (A–T) splitting method is utilized to calibrate the Rabi frequency of the coupling beams. These results show that the linewidth is narrowest when the 509‐nm coupling beam has the Laguerre–Gaussian mode with an equal Rabi frequency among the three cases, the linewidth and contrast of the EIT and TCPS are optimized by varying the beam sizes of the 509‐nm Laguerre–Gaussian beams. The laser frequency stabilization by using of TCPS with three kinds of 509‐nm coupling beams are compared, the Laguerre–Gaussian coupling beam case is more effective for frequency stabilization because of the narrower linewidth.