Xiao Lian-Tuan

Photoassociative Production and Detection of Ultracold Polar RbCs Molecules

We have produced ultracold polar RbCs molecules via photoassociation starting from laser-cooled 85Rb and 133Cs atoms in a dual-species, forced dark magneto-optical trap. The formed electronically excited RbCs* molecules correlated to the Rb(5S1/2) + Cs(6P1/2) dissociation limit are observed by trap loss spectroscopy. Following the decay of these excited RbCs* molecules, the formed ground state molecules are directly ionized by a two-photon single-color pulse dye laser, which is a new ionization mechanism for ground state RbCs molecules and thence detected by time-of-flight mass spectroscopy.

Transmission properties and imaging of monolayer graphene oxide in external electric field

The recent boom in graphene oxide (GO) based sensor and optical materials requires to improve and control the GOs optoelectronic properties. It is reported here that the optical transmission and fluorescence spectra of monolayer GO can be controlled by means of external electric field. The imaging of GO under electric fields shows the absorption and emission anisotropy, the transmission and fluorescence spectra demonstrate the electrically reversible features. The polarity effects of the functional groups in GO under electric field induced changes of electronic density of localized states as well as the optical properties, meanwhile, demonstrated the electric field direction dependent polarity results.

Saturation of Photoassociation in Cs Magneto-optical Trap

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 0g− state have been found.

Effect of Background Noise on the Photon Statistics of Triggered Single Molecules

We theoretically derive exact expressions for Mandels Q parameter of the triggered single molecular source, which is inferred from the probabilities PRS(n) using the record of each photon detection event based on Hanbury Brown and Twiss detection. The real triggered source is recognized as an ideal single photon source with a Poissonian statistics background. How to decrease the background and to increase the efficiency are discussed. It is established that the sub-Poissonian statistics formation can be determined by comparing the measured QRS of the real single triggered molecular with QC of the Poissonian source containing the same mean photons. By this method, we also give an efficient way to measure signal-to-background ratios of triggered single photons.

Experimental Measurement of the Absolute Frequencies and Hyperfine Coupling Constants of 133Cs Using a Femtosecond Optical Frequency Comb

High resolution two-photon spectrum of the transitions 6S1/2 → 6P3/2 → 8S1/2, 9S1/2 and 6S1/2 → 6P1/2 → 7D3/2 in neutral 133Cs are presented in a room-temperature vapor cell using a femtosecond optical frequency comb. Spectra are obtained by scanning the repetition frequency of the femtosecond optical frequency comb over the two-photon hyperfine structure. The centroid frequency of the 6S1/2 → 8S1/2, 9S1/2, 7D3/2 transitions are 729009798.80(17) MHz, 806761363.96(11) MHz, and 780894762.595(23) MHz, respectively. The hyperfine coupling constants of the corresponding states are also obtained. The results are consistent with the previous measurements.

High sensitive detection of high-order partial wave scattering in photoassociation of ultracold atoms

We report on the observation of enhanced high-order partial wave scattering from atom-atom interaction via changing the temperature of a magneto-optical trap in the process of photoassociation. The high-order scattering partial wave is directly manifested through the large signal amplitude of the rovibrational resonance levels of trap-loss spectroscopy from photoassociation.

Photon Counting Optical Time Domain Reflectometry Applying a Single Photon Modulation Technique

Photon-counting optical time domain reflectometry (v-OTDR) is typically used in a mode with spatial resolution in the centimeter range. Here we demonstrate a 1550nm v-OTDR system to optimize the discriminate voltage of a single photon avalanche detector using a single photon modulation and demodulation technique, which shows obvious improvement in the signal intensity. The intensity of signal is doubled when the discriminator voltage is optimized from 184 mV to 162 mV.

Direct measurement of the surface dynamics of supercooled liquid-glycerol by optical scanning a film

The surface dynamics of supercooled liquid-glycerol is studied by scanning the thickness of the glycerol film with single photon detection. Measurements are performed at room temperature well above the glycerols glass transition temperature. It is shown that the surface dynamics of the glycerol film is very sensitive to the temperature. The linear relationship between the thickness of the film and the viscosity predicted by the Vogel–Fulcher–Tammann–Hesse (VFTH) law is also presented experimentally.

Research on ultracold cesium molecule long-range states by high-resolution photoassociative spectroscopy

In this paper, an ultra-high resolution photoassociation spectroscopy study on photoassociation of cesium atoms is reported. The cold cesium gas in the magneto-optical trap is illuminated by a photoassociation laser with red-tuning as large as 40 cm−1 below the 6S1/2 + 6P3/2 dissociation limit, and the photoassociation to the excited state ultracold molecule is detected. High signal-to-noise ratio is obtained by using the lock-in detection of the fluorescence from the modulated cold Cs atoms. The 0g−, 1g and 0u+ long-range states which correspond to 6S1/2 + 6P3/2 dissociation limit are present in the photoassociation spectrum. The effective coefficients of leading long-range interactions and the corresponding vibrational quantum number are obtained using LeRoy-Bernstein Law. It is found that photoassociation process creates rotating molecules and the high J value is a hint that higher partial waves participate in the PA process in the presence of trapping laser.

Experimental Observation of Autler?Townes Splitting in Sub-Doppler Selective Reflection Spectroscopy

We present an experimental study of Autler–Townes splitting of non-linear selective reflection spectroscopy in a Λ-type driven three-level system. The sub-Doppler reflection spectroscopy is observed and the Autler–Townes splitting is measured as functions of the different coupling laser intensity and detuning. The coherent drive splits the excited state into two dressed states and an Autler–Townes splitting emerges in the probe reflection. The experimental results are in good agreement with theoretical fit.