| "Spectrum" is among the few crucial concepts running through the whole physics, which frequently appear in every branch of science. "Spectral analysis" is not only a technology of numerical or theoretical analysis, but also a series of lab techniques, including spectrum, mass spectrum, and energy spectrum. "Spectroscopy" is a study of the interaction between electromagnetic wave and matter using spectrum. Spectrum technology is widely used in measurement of atomic energy level structure. The gaseous atoms have neglectible interaction with each other, and hence the energy levels are immune to surrounding atoms, so they are ideal medium in which atomic energy levels can be measured distortionless. However, since the thermal motion, the detailed informations of the atomic energy levels are submerged in the Doppler background. In order to eliminate the influence of the Doppler background, many kinds of high-resolution spectrum were developed. For the excited level complying with electric dipole transition from the ground state, there are saturated absorption spectrum (SAS) and polarization spectrum (PS), etc. For the excited level which is dipolar forbidden from the ground, one can use two-photon transiton spectroscopy, optical-optical double-resonance (OODR) spectrum technology, etc. Atomic energy level structure, level lifetime, the interaction between nucleus and the outer electrons, can be measured and studied by employing high-resolution spectrum. On the other hand, with the development of the technology of laser cooling and trapping of neutral atoms, magneto-optical trap (MOT) has become a mature technology to cool atoms. Cold atoms, due to their low speed, can effectively eliminate the Doppler effect, so MOT is widely used in high resolution laser spectroscopy and high-precision quantum frequency standards.In this paper, based on the ladder type of atomic energy level system, we have studied the atomic excited state high resolution spectrum as well as the study of new type of two-color magneto-optical trap (TCMOT). Mainly innovative works are as follows:(1) A new technique of double-resonance optical pumping (DROP) spectrum, which has signal-to-noise ratio (SNR) and narrow linewidth, is obtained in Rb 5S1/2-5P3/2-4D5/2(5D5/2) level systems. Thanks to the atomic coherence effect in ladder-type atomic level system, we further narrow the spectral linewidth. This is benefit to measure the small hyperfine splittings which are from a few MHz to dozens MHz.(2) We have developed a frequency calibration method to eliminate nonlinear scanning of laser frequency, consisting a waveguide phase type electro-optic modulator (EOM) and a stable FP cavity. By fine adjusting the cavity length and tuning frequency of the radio frequency (RF), the spectral peak and FP peak appear synchronously, so the errors arising from nonlinear scanning of laser frequency can be eliminated. This method does not require expensive optical frequency comb (OFC), nor complex laser-cold atomic system. Moreover, it can be used in measurement of other atoms. Eventually, we dertermine the hyperfine structure (HFS) constants of 4D5/2 and 5D5/2 states in two isotopes of rubidium atoms. Among them, the accuracy of HFS constants for 4D5/2 state are the international highest accuracy at present. Using HFS constants, we firstly calculate the value of hyperfine anormaly for rubidium isotope D state, and comparatively analysis them together with hyperfine anormalies for S and P states.(3) Based on ladder-type level Cs 6S1/2-6P3/2-7S1/2, the TCMOT with 852+1470 nm were abtained for the first time in the world. We have studied in two type of TCMOT based on traditional MOT:type-I, one of the three pairs of 852 nm CTBs in a conventional Cs MOT is replaced with a pair of the 1470 nm CTBs; type-II, one of the three pairs of 852 nm CTBs in a conventional Cs MOT is replaced with with one 852 nm CTB plus another counter-propagating 1470 nm CTB. Both the type-I and type-II TCMOTs can cool and trap atoms on both the red-and blue-detuning sides of the two-photon resonance. We measured and analyzed qualitatively the dependence of peak fluorescence (cold atom number) on the two-photon detuning, the intensity of CTBs, etc. These results provide optimized experimental parameters to trap atoms and pave the first step towards application of type-? Cs TC-MOT for 852 and 1470 nm entangled photon pair generation. This may have potential application in quantum telecommunication.The above works are based on the atomic ladder-type atomic system, the HFS measurement and related laser frequency stabilization technology, will be used to precisely control both one-photon and two-phpton laser detunings in the TCMOT experiment. Also, they explore the possibility of photon pairs preperation in TCMOT based on the four-wave mixing (FWM) procces, which is significant for quantum communication and quantum information processing. |
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