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[Experimental study of ultralow frequency modulation photoassociation spectrum].

Lirong Wang, Jie Ma, Yanting Zhao, Liantuan Xiao, Suotang Jia

Published Dec 1, 2014• 0 citations

Abstract

In the present paper, ultracold cesium atoms were obtained in magnetic optical trap using the laser cooling technology. The number of ultracold atoms is 10(7). The temperature of ultracold atoms is about 200 μK and the diameter of the ultracold atoms cloud is about 400 μm. The ultracold cesium molecules of excited states were formed using the photoassociation of ultracold atoms. The resolution of vib-rotational spectrum was studied under different scan rates of photossociation laser in the experiment. The resolution of vib-rotational spectrum becomes high when the scan rate of photossociation laser becomes slow. The cold atoms fluorescence was obtained using the high sensitive avalanche photo detector and the high resolution vib-rotational spectrum of ultracold cesium molecule in its first excited state of with dissociation limit long range state was obtained. The ultracold ground molecule was formed by controlled Raman photoassociation and the photoassociation laser must be locked to atom-molecular hyperfine transitions. The ultracold atoms photoassociation spectrum was modulated using ultra-low frequency. The first-order differential signal was optimized by changing modulation amplitude and modulation frequency. It provides a feedback signal to correct error of the laser. The laser frequency satisfies experimental requirement to form ultracold ground molecules using the controlled Raman photoassociation. This work is important for studies of ultracold atoms and molecules in confined space.

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In the present paper, ultracold cesium atoms were obtained in magnetic optical trap using the laser cooling technology. The number of ultracold atoms is 10(7). The temperature of ultracold atoms is about 200 μK and the diameter of the ultracold atoms cloud is about 400 μm. The ultracold cesium molecules of excited states were formed using the photoassociation of ultracold atoms. The resolution of vib-rotational spectrum was studied under different scan rates of photossociation laser in the experiment. The resolution of vib-rotational spectrum becomes high when the scan rate of photossociation laser becomes slow. The cold atoms fluorescence was obtained using the high sensitive avalanche photo detector and the high resolution vib-rotational spectrum of ultracold cesium molecule in its first excited state of with dissociation limit long range state was obtained. The ultracold ground molecule was formed by controlled Raman photoassociation and the photoassociation laser must be locked to atom-molecular hyperfine transitions. The ultracold atoms photoassociation spectrum was modulated using ultra-low frequency. The first-order differential signal was optimized by changing modulation amplitude and modulation frequency. It provides a feedback signal to correct error of the laser. The laser frequency satisfies experimental requirement to form ultracold ground molecules using the controlled Raman photoassociation. This work is important for studies of ultracold atoms and molecules in confined space.

A high resolution photoassociation spectrum of ultracold cesium atoms is reported in this paper. A photoassociation laser with its frequency red detuned below 6S1/2+6P3/2 dissociation limit acts on the cold cesium atoms in magnetic optical trap and the excited ultracold molecules generated in the photoassociation process are observed. In order to obtain a high signal-to-noise ratio, the trapping laser is amplitude modulated using acousto-optic modulator and the fluorescence signal is demodulated by lock-in technique. The results are discussed using the density matrix equations.

The high resolution spectrum of ultracold Cs2 pure long range 0g- state is experimentally measured using modulated trap loss spectroscopic technology. Based on Double photoassociation spectroscopic technique, precise frequency difference reference signals are constructed to accurately calibrate the resonant frequency intervals of the ro-vibrational levels, thus obtaining the relationship between the frequency interval of rotational level and the rotational quantum number. The experimental data are fitted by the non-rigid rotational model, and the molecular rotational constants corresponding to different vibrational levels in the ultracold Cs2 pure long range 0g- state are acquired. The experimental results demonstrate a linear decrease of the rotational constant with the increase of vibrational quantum number, and the linear decreasing rate is -0.41m MHz0.01 MHz.

An ultrahigh resolution photoassociation spectrum of caesium atoms in a magneto-optical trap is presented. Hyperfine structure of the excited state molecule is obtained by using the lock-in method based on modulated cold atoms in this spectrum. Amplitude of resonant lines related to the rotational levels increases with photoassociation laser intensity, and saturation effect of photoassociation of cold atoms is observed in our experiment. The saturation intensity of photoassociation is deduced by fitting the experimental data to a saturation model based on scattering theory. Differences among saturation intensities of different rotational progressions in the ν = 55 vibrational state of the caesium molecular long-range 0 g − state have been found.

The cold-molecule field concerns the physics and the applications of molecular systems with translational temperature well below the 1 К range. The possibility of controlling all the motion as well as the internal quantum state of a sample of molecules is a long-term goal that opens the possibility for many new experiments and measurements ranging from fundamental constants to quantum chemistry and quantum computation. Although, direct laser cooling of the translational degree of freedom of molecules is still waiting for further technological or theoretical breakthroughs and ideas, many different techniques have proven to be successful in producing different types of cold as well as ultracold (i.e. T < 1 mK) molecules. In this chapter, we will concentrate on the description of one of these techniques: the photoassociation of laser cooled atoms. We will report on the status of the art of this technique for the case of cesium atoms, describing all the main experimental findings. In particular, we will illustrate the different photoassociation schemes for molecule formation, the detection schemes through photoionization, the molecule trapping in a magnetic or dipolar trap, the vibrational cooling into a single vibrational state and finally the present prospects for rotational cooling.

Ultracold polar RbCs molecules are produced via photoassociation in a dual dark-SPOT magneto-optical trap, in which ultracold rubidium and cesium atoms with high densities are formed by laser cooling and trapping. The a3∑+ triplet metastable state ultracold RbCs molecules with 104/s production rate are detected using resonance-enhanced two-photon ionization. The ultra-high resolution rovibrational spectra of (2)0+, (3)0- and (2)0- rovibrational states are observed by scanning the photoassociation laser frequency. The rotational constants of (2)0+, (3)0- and (2)0- vibrational states are 0.00349 cm-1, 0.00649 cm-1 and 0.00372 cm-1 by fitting respectively.