Development Of 319nm UV Laser System And Its Application In Single-photon Rydberg Excitation Of Cesium Atoms

Rydberg atoms are atoms with at least one electron excited to a state with high principal quantum number n.Their big size,huge polarizabilities and long lifetime give rise to strong dipole-dipole interactions,long interaction time,and extreme sensitivity to external electric fields,which is of great significance for quantum optics and quantum information.Experiments that use Rydberg atoms require excitation of Rydberg states.When compared with the more common two-photon excitation method,single-photon Rydberg excitation is advantageous because it eliminates channels for decoherence through photon scattering and ac Stark shifts from the intermediate state.Therefore,it becomes a new and extremely challenging technology for preparing the Rydberg atoms.Based on commercial fiber lasers,fiber amplifers,quasi-phase-matched(QPM)nonlinear frequency conversion materials and efficient nonlinear frequency conversion technology,we demonstrate a high-power narrow-linewidth ultraviolet(UV)laser system at 318.6nm,and research the single-photon Rydberg excitation of cesium atoms in room-temperature vapor cell and cold atomic ensemble.Main contents are as follows:1.We give a brief introduction about the basic properties of Rydbeg atoms and its research status in quantum information field.We also introduce some basic knowledge of nonlinear optics and laser cooling and trapping.2.We realize a narrow-linewidth high-power 637.2nm laser device by single-pass sum-frequency generation(SFG)of two infrared lasers at 1560.5nm and 1076.9nm in PPMg O:LN crystal.We also study the behavior of crystals with different poling periods.The detailed experiments show that the output red lasers have very good power stability and beam quality.Over 8.75 W of single-frequency continuously tunable 637.2nm laser is finally realized.3.Based on the 637.2 nm red light,we demonstrate a 318.6nm UV laser system from cavity-enhanced second harmonic generation(SHG)with a BBO crystal in a home-made ring cavity.Results show that it is a high-power,narrow-linewidth,and continuously tunable UV laser source with maxium power of 2.26 W.4.We demonstrate single-photon Rydberg excitation of Cs atoms in a room-temperature vapor cell with the 318.6 nm UV laser.Analysis reveals that the observed spectra are velocity-selective spectroscopy of n P3/2(n=70-100)Rydberg state,fitting to energies of n P3/2 states,the quantum defect was obtained.5.We prepare a magneto-optical trap(MOT)of Cs atoms for single-photon Rydberg excitation,and realize the Rydberg excitation and detection of n P3/2 states by fluorescence trap-loss spectra.We also observe the Rydberg blockade in cold atomic ensemble.The innovations of this work:1.Because the gain medium at 637.2 nm is very scarce.At present,the commercial high-power red laser source is mainly provided by the liquid dye laser,which cannot work stably for a long time.We demonstrate a solid-state high power 637.2nm laser system which has the advantage of stable operation and convenient maintenance.2.Realization of high-power UV laser by SFG or SHG from infrared laser is a universal technique,but it is limited by the severe UV absorption of the nonlinear crystal and the resulting thermal effect.We overcome these difficulties by the optimal selection of crystal,design of the doubling cavity and control of the experimental details,and finally realize a high-quality 318.6nm UV laser system.3.We observe the velocity-selective spectra of Cs n P3/2(n=70-100)states by optical detection of a single-photon Rydberg excitation in a room-temperature vapor cell.Besides,we also demonstrate the detection of Rydberg atoms in cold atomic ensemble with the fluorescence trap-loss spectra.