A narrow-linewidth continuous-wave single-frequency tunable 318.6-nm ultraviolet laser system with watt-level output power is developed in our experiment based on well-developed fiber lasers, fiber amplifiers, and efficient laser frequency conversion technique. Cesium 6S1/2—nP3/2 (n = 70—94) single-photon Rydberg excitation in a room-temperature cesium atomic vapor cell is realized by using our ultraviolet laser system. The single-photon Rydberg excitation signal is obtained via the V-type three-level atomic system which contains 6S1/2 (F = 4) ground state, 6P3/2 (F = 5) excited state and one of nP3/2 (n = 70—94) Rydberg states. When cesium atoms populated on the ground state are partially excited to Rydberg state by the ultraviolet laser, absorption of 852.3-nm probe beam which is locked to 6S1/2 (F = 4)—6P3/2 (F ′ = 5) hyperfine transition will decrease. In this way, the cesium Rydberg states are detected. The quantum defects for cesium nP3/2 (n = 70—94) Rydberg states are experimentally measured with a high-precision wavemeter. The variation trend of experimentally measured data deviates from that of calculated values. Due to the fact that the cesium vapor cell is positioned in a magnetic shielding tank, the Zeeman effect can be ignored. Considering that the polarizability of Rydberg atoms is proportional to (n*)7, in which n* is the effective principal quantum number, the Rydberg screen effect of cesium atomic vapor cell cannot completely protect cesium atoms from being perturbed by an external DC electric field. Therefore the residual DC electric field existing inside the cesium vapor cell will have a significant influence on quantum defect measurement of Rydberg atoms. Using the theoretical model of Stark effect and the relationship between polarizability of Rydberg atoms and the effective principal quantum number n*, the corrected experimental value of quantum defect for cesium nP3/2 (n = 70—94) Rydberg states is found to be ~(3.5591 ± 0.0007). The corrected experimental value of quantum defect is consistent with the calculation.
A narrow-linewidth continuous-wave single-frequency tunable 318.6-nm ultraviolet laser system with watt-level output power is developed in our experiment based on well-developed fiber lasers, fiber amplifiers, and efficient laser frequency conversion technique. Cesium 6S1/2—nP3/2 (n = 70—94) single-photon Rydberg excitation in a room-temperature cesium atomic vapor cell is realized by using our ultraviolet laser system. The single-photon Rydberg excitation signal is obtained via the V-type three-level atomic system which contains 6S1/2 (F = 4) ground state, 6P3/2 (F = 5) excited state and one of nP3/2 (n = 70—94) Rydberg states. When cesium atoms populated on the ground state are partially excited to Rydberg state by the ultraviolet laser, absorption of 852.3-nm probe beam which is locked to 6S1/2 (F = 4)—6P3/2 (F ′ = 5) hyperfine transition will decrease. In this way, the cesium Rydberg states are detected. The quantum defects for cesium nP3/2 (n = 70—94) Rydberg states are experimentally measured with a high-precision wavemeter. The variation trend of experimentally measured data deviates from that of calculated values. Due to the fact that the cesium vapor cell is positioned in a magnetic shielding tank, the Zeeman effect can be ignored. Considering that the polarizability of Rydberg atoms is proportional to (n*)7, in which n* is the effective principal quantum number, the Rydberg screen effect of cesium atomic vapor cell cannot completely protect cesium atoms from being perturbed by an external DC electric field. Therefore the residual DC electric field existing inside the cesium vapor cell will have a significant influence on quantum defect measurement of Rydberg atoms. Using the theoretical model of Stark effect and the relationship between polarizability of Rydberg atoms and the effective principal quantum number n*, the corrected experimental value of quantum defect for cesium nP3/2 (n = 70—94) Rydberg states is found to be ~(3.5591 ± 0.0007). The corrected experimental value of quantum defect is consistent with the calculation.
We demonstrate a single-photon Rydberg excitation spectroscopy of cesium (Cs) atoms in a room-temperature vapor cell. Cs atoms are excited directly from 6S1/2 ground state to nP3/2 (n = 70 - 100) Rydberg states with a 318.6 nm ultraviolet (UV) laser,and Rydberg excitation spectra are obtained by transmission enhancement of a probe beam resonant to Cs 6S1/2, F = 4 - 6P3/2, F' = 5 transition as partial population on F = 4 ground state are transferred to Rydberg state .Analysis reveals that the observed spectra are velocity-selective spectroscopy of Rydberg state, from which the amplitude and linewidth influenced by lasers'Rabi frequency have been investigated. Fitting to energies of Cs nP3/2 (n = 70 -100) states, the determined quantum defect is 3.56671(42). The demodulated spectra can also be employed as frequency references to stabilize the UV laser frequency to specific Cs Rydberg transition.
Nowadays the long-range dipole-dipole interaction between highly-excited Rydberg atoms at micrometer distance become promising way to establish the atom-atom quantum entanglement and to implement the two-qubit logic gate. For alkali metal atoms, single-photon excitation from the ground state to the desired Rydberg state demands powerful narrow-linewidth ultra-violet (UV) laser, which is very challenging. Maybe just because of this, the studies of single-photon Rydberg excitation of alkali metal atoms are rare. Alternatively people have employed the two-photon or three-photon Rydberg excitation scheme. However, comparing with the single-photon Rydberg excitation, the two-photon or three-photon scheme has following drawbacks: atomic decoherence due to the photon scattering from the lower and upper transitions, and light shift of the involved ground state and Rydberg state due to the lower and upper transition laser beams. Thanks to the efficient laser frequency conversion technology with PPXX material and the well-developed commercial fiber laser as well as fiber amplifier, we have implemented a tunable 318.6-nm UV laser system based on the cavity-enhanced second-harmonic generation following the single-pass sum-frequency generation of 1560.5-nm and 1076.9-nm fiber-amplified lasers. More than 2-Watt output of the 318.6-nm UV laser has been achieved with a typical linewidth of smaller than 10 kHz. Employing the UV laser system we have demonstrated a single-photon Rydberg excitation spectroscopy of cesium (Cs) atoms. Partial Cs atoms can be directly excited from 6S_1/2 ground state to nP_3/2 (n = 70 - 100) Rydberg states, and Rydberg excitation spectra are obtained with transmission enhancement of a probe beam locked to Cs 6S_1/2 (F = 4) - 6P_3/2 (F’ = 5) cycling transition because partial population on the ground state (F = 4) are transferred to Rydberg state. The quantum defect for Cs nP_3/2 (n = 70 -100) Rydberg states is determined experimentally. Further more, the demodulated single-photon Rydberg excitation spectrum is employed to stabilize the UV laser to specific Cs Rydberg transition to improve the laser frequency stability. References: [1] Opt. Express 25 (2017) p.22510; [2] J. Opt. 19 (2017) 045501; [3] J. Opt. Soc. Am. B 33 (2016) p.2020; [4] Opt. Commun. 370 (2016) p.150. Funding: the National Natural Science Foundation of China (61475091).
The spectra of Rydberg atoms are of great significance for studying the energy levels of Rydberg atoms and the interaction between neutral atoms, especially, the high-precision spectra of Rydberg atoms can be used to measure the energy level shifts of Rydberg atoms resulting from the dipole-dipole interactions in room-temperature vapor cells. In this paper we report the preparation of cesium Rydberg states based on the cascaded two-photon excitation of 509 nm laser and 852 nm laser in opposite, and the measurements of the fine structure of cesium Rydberg states. In this experiment, the 509 nm laser is generated by the cavity-enhanced second-harmonic generation from 1018 nm laser with a periodically-poled KTP crystal and has a maximum power of about 1 W, and the 852 nm probe laser is provided by an external-cavity diode laser with a maximum output power of 5 mW and a typical linewidth of 1 MHz. By scanning the frequency of 509 nm coupling laser, it is presented that the Doppler-free spectra based on electromagnetically-induced transparency (EIT) of 509 nm coupling laser and 852 nm probe laser. The velocity-selective EIT spectra are used to study the spectral splitting of 6S1/26P3/257S(D) ladder-type system of cesium Rydberg atoms in a room-temperature vapor cell. The powers of 852 nm probe laser and 509 nm coupling laser are 0.3 upW and 200 mW, respectively. Their waist radii are both approximately 50 m. The intervals of hyperfine splitting of the intermediate state 6P3/2(F'=3, 4, 5) and fine splitting of 57D3/2 and 57D5/2 Rydberg states are measured by a frequency calibrating. Concretely, the velocity-selective spectrum with a radio frequency (RF) modulation of 30 MHz is used as a reference to calibrate the Rydberg fine-structure states in the hot vapor cell, where the RF frequency precision is smaller than a hertz on long time scales and the EIT linewidth is smaller than 13 MHz. The experimental value of the fine structure splitting of 57D3/2 and 57D5/2 Rydberg states is (354.72.5) MHz, that is in consistence with the value of 346.8 MHz calculated by Rydberg-Ritz equation and quantum defects of 57D3/2 and 57D5/2 Rydberg states. The experimental values of hyperfine splitting of intermediate state 6P3/2(F'=3, 4, 5) are also coincident with the theoretical calculated values. The dominant discrepancy existing between the experimental and calculated results may arise from the nonlinear correspondence of the PZT while the 509 nm wavelength cavity is scanned, and the measurement accuracy influenced by the spectral linewidth. The velocity-selective spectroscopy technique can also be used to measure the energy level shifts caused by the interactions of Rydberg atoms.
We demonstrate the single-photon excitation spectra of cesium Rydberg atoms by means of a Doppler-free purely all-optical detection with a room-temperature vapor cell and a 319 nm ultra-violet (UV) laser. We excite atoms directly from 6S1/2 ground state to 71P3/2 Rydberg state with a narrow-linewidth 319 nm UV laser. The detection of Rydberg states is performed by monitoring the absorption of an 852 nm probe beam in a V-type three-level system. With a strong coupling light, we observe the Autler-Townes (AT) doublet, and the dependences of the separation and linewidths on the coupling intensity are experimentally investigated, which is consistent with the prediction based on the dressed state theory. Moreover, the AT splitting can be used to measure the Rabi frequency. In an external magnetic field, the Rydberg spectra of nondegenerate Zeeman sublevels are demonstrated. The splitting of the spectrum is of great significance for studying the characteristics of Rydberg atoms.
We demonstrate the single-photon Rydberg excitation of cesium atoms in a magneto-optical trap (MOT). We excite atoms directly from 6S1/2ground state to nP3/2(n = 70-100) Rydberg state with a narrow-linewidth 319-nm ultra-violet laser. The detection of Rydberg states is performed by monitoring the reduction of fluorescence signal of the MOT as partial population on 6S1/2(F = 4) ground state are transferred to Rydberg state. We clearly observe Autler-Townes doublet in the trap-loss spectra due to the cooling lights. Utilizing the large electric polarizibility of Rydberg atoms, we observe Stark splitting in the Autler-Townes doublet induced by background DC electric fields. We investigate the dependence of Stark shift on electric fields by theoretical analysis, and then infer the DC electric field from the measured Stark splitting. We find that there is a 44.8(4) mV/cm DC electric field in the vicinity of the cold ensemble. It indicates that high-lying Rydberg atoms can be used as sensors for DC electric fields.
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.