Effect of the Coupling Beam with Different Intensity Profile upon Rydberg EIT and Rydberg Two‐Color Polarization Spectroscopy with Cesium Ladder‐Type Level
Rui Chang, Tao Wang, Yuhui Yang, Lili Hao, Jun He, Junmin Wang
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.
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.
Two-color polarization spectroscopy (TCPS) of cesium 6S1/2-6P3/2-8S1/2 (852.3 nm + 794.6 nm) ladder-type system in a room-temperature vapor cell are investigated. The frequency of 852.3 nm laser used as a pump beam is locked on one of the hyperfine transitions between the ground state 6S1/2 and excited state 6P3/2 by the saturated absorption spectroscopy technique, which can populate some atoms on the 6P3/2 excited state and induce anisotropy in the atomic medium. The frequency of 794.6 nm laser serving as a probe beam is scanned across the whole 6P3/2→8S1/2 transition to ascertain this anisotropy, and thus the TCPS is obtained. In experiment, we measure and analyse the influence of frequency detuning of 852.3 nm pump laser on TCPS, and especially reveal that some of hyperfine energy levels of intermediate excited state 6P3/2, which has no direct interaction with the 852.3 nm pump laser, are also populated by a small fraction of atoms with a specific speed in the direction of pump laser beam due to Doppler effect, so they also have contribution to the TCPS when the 794.6 nm probe laser is scanned to the resonance transition line between the 6P3/2 and 8S1/2 states after the Doppler frequency shift has been considered. In addition, we prove that the atomic coherence like electromagnetically induced transparency effect obviously results in a narrower line width of TCPS in the case of counter-propagating experimental configuration than that in the case of pump beam co-propagating with the probe beam in the Cs vapor cell. Finally, we apply the TCPS with dispersive shaped feature to frequency stabilization with no modulation, and the frequency fluctuations of 794.6 nm laser are ～0.5 MHz and ～9.2 MHz for the frequency-locking and free running in ～225 s, respectively. The above research work is expected to play a role in precisely measuring the atomic energy level structure and its related hyperfine structure constant (magnetic dipole and electric quadrupole coupling constants), and also in stabilizing the laser frequency to the excited state transition especially for the optical fiber communication, two-color laser cooling/trapping neutral atoms, optical filter, etc.
An experimental investigation of two-color polarization spectroscopy (TCPS) is presented based on the cesium 6S1/2 – 6P3/2 – 8S1/2 (852.3 nm + 794.6 nm) ladder-type system in a room-temperature vapor cell. The dependency of line shapes of TCPS on the power of a 852.3 nm pump and a 794.6 nm probe laser is measured in detail, and we confirm that the linewidth of TCPS in a counter-propagating configuration between the pump and probe laser beams is obviously narrower than that of a co-propagating configuration, due to the atomic coherence effect. It is helpful for laser stabilization of the excited state transition using TCPS without frequency modulation.
Rydberg atoms are highly excited atoms with large principal quantum number n, big sizes (~n2) and long lifetimes (~n3). Rydberg atoms are very sensitive to an external field due to the large polarizabilities of Rydberg atoms (~n7). Electromagnetically induced transparency (EIT) of Rydberg atom provides an ideal method to detect Rydberg atoms without destroying atoms, and can be used to measure the external direct current and radio frequency (RF) field. In this paper, we study the EIT effect of a cesium ladder-type three-level atom involving Rydberg state exposed to a weak RF field. The ground state (6S1/2), the excited state (6P3/2) and Rydberg state (48D5/2) constitute the Rydberg three-level system, in which the probe laser couples 6S1/2(F=4)6P3/2(F'=5) transition, whereas the coupling laser scans across the 6P3/248D5/2 Rydberg transition. The coupling laser (510 nm laser, propagating in the z-axis direction and linear polarization in the y-axis direction) and the probe laser (852 nm laser, linear polarization in the y-axis direction) counter-propagate through a 50-mm-long cesium vapor cell at room temperature, yielding Rydberg EIT spectra. Rydberg EIT signal is detected as a function of the detuning of the coupling laser. When a weak RF (80 MHz) electric field polarized in the x-axis direction is applied to a pair of electrode plates located on both sides of the cesium cell, the EIT spectrum of Rydberg 48D5/2 shows the Stark splitting and the even order harmonic sidebands. The experimental results are analyzed by using the Floquet theory. The simulation results accord well with the experimentally measured results. Furthermore, we also investigate the influence of the self-ionization effect of Rydberg atom on the Stark spectrum by changing the RF frequency. We put forward a proposal to avoid the effect of ionization by placing electrode plates in the cesium cell. In the weak RF-field domain, mj=5/2 Stark line crosses mj=1/2, 3/2 sidebands, these cross points provide an antenna-free method of accurately calibrating the RF electric field based on Rydberg atoms.
Rydberg atoms, with large principal quantum number, exhibit certain properties, such as long lifetimes and strong interactions with fields and other atoms, which have been extensively investigated recently. One of the properties is the electromagnetically induced transparency (EIT) of Rydberg ladder system, which can be used to measure the radio frequency (RF) field with high sensitivity. In this paper, we investigate the quantum coherent effect of cesium Rydberg atom in a three-level ladder system involving the ground state (6S1/2), the excited state (6P3/2) and 49S1/2 Rydberg state in room temperature vapor cell. The probe laser (852 nm) drives the transition of 6S1/2(F=4)→6P3/2(F'=5), while the coupling laser (510 nm) couples the Rydberg transition of 6P3/2 (F'=5)→nS1/2. A typical electromagnetically induced transparency spectrum is obtained when the weak probe laser is scanned through the transition of 6S1/2(F=4)→6P3/2(F'=5) and the coupling laser tuning to Rydberg transition. The two-photon RF spectra are observed when the RF field with a frequency of ～16.9 GHz couples the Rydberg transition of 49S1/2→47D3/2, where the EIT signal is split into two EIT peaks due to the interaction between the RF field and Rydberg atoms. The dependences of EIT splitting on the power of RF field are investigated. The results show that the EIT splitting increases with the power of RF field, which can inversely be used to measure the RF field with a higher spatial resolution in the future.
Through the cascade excitation of 852-nm continuous-wave (CW) laser and 509-nm nanosecond pulsed laser, the electromagnetically-induced transparency (EIT) spectroscopic signals of ladder-type three-level cesium atoms with Rydberg state are obtained by using a room-temperature cesium vapor cell. The power of 509-nm pulsed laser beam is ~176 W, while the pulse repetition frequency ranges from 300 kHz to 100 MHz and can be continuously adjusted. The laser pulse duration runs from 1 to 100 ns and can be continuously adjusted. The relationship between Rydberg EIT spectroscopic signals and 509-nm nanosecond pulsed laser parameters is investigated experimentally. By changing the pulse repetition frequency and the pulse duration of the 509-nm nanosecond pulsed laser, the comb-like Rydberg atomic spectrum is obtained by using a room-temperature cesium vapor cell. Within a certain range of repetition frequency and pulse duration, the envelope of spectral lines shows a regular pattern, and the spacing between the transmission peaks is consistent with the pulse repetition frequency. By changing the 509-nm laser pulse repetition frequency and pulse duration, atoms with the specific velocity group can be excited to Rydberg state. Reducing the repetition frequency of the 509-nm pulsed coupling laser can further increase the number of atoms in the Rydberg state in comparison with the case of finite velocity group pumping of cesium atoms by a continuous-wave laser. When the repetition frequency of the 509-nm pulsed laser approaches the EIT linewidth, the number of cesium Rydberg atoms can be increased by up to 10 times. In the parameter optimization process, the dynamic characteristics of pulsed excitation in multi-level atoms, as well as the interaction characteristics between arbitrarily shaped laser pulses and multi-level atomic systems, should be considered. Pulsed laser pumping can achieve the interaction between the laser field and atomic group with a specific velocity, and its developed atomic frequency comb spectra can be used for electric and magnetic field measurements. The multi-peak structure of the spectrum can be used to more accurately determine the intensity, frequency, and phase of the microwave electric field by measuring spectral variations. This high-sensitivity and high-resolution measurement capability is crucial for precisely measuring microwave electric fields. The pulsed coupling laser can excite atoms in a specific velocity group to the Rydberg state. High-density Rydberg atoms can improve the signal-to-noise ratio of the measured spectrum, which has potential applications in quantum sensing and quantum measurement based on Rydberg atoms.
Abstract We present the electromagnetically induced transparency (EIT) spectra of cold Rydberg four-level cascade atoms consisting of the 6S1/2 → 6P3/2 → 7S1/2 → 60P3/2 scheme. A coupling laser drives the Rydberg transition, a dressing laser couples two intermediate levels and a weak probe laser probes the EIT signal. We numerically solve the Bloch equations and investigate the dependence of the probe transmission rate signal on the coupling and dressing lasers. We find that the probe transmission rate can display an EIT or electromagnetically induced absorption (EIA) profile, depending on the Rabi frequencies of the coupling and dressing lasers. When we increase the Rabi frequency of the coupling laser and keep the Rabi frequency of the probe and dressing laser fixed, flipping of the EIA to EIT spectrum occurs at the critical coupling Rabi frequency. When we apply a microwave field coupling the transition 60P3/2 → 61S1/2, the EIT spectrum shows Autler–Townes splitting, which is employed to measure the microwave field. The theoretical measurement sensitivity can be 1.52 × 10−2 nV⋅cm−1⋅Hz−1/2 at the EIA–EIT flipping point.