Zhang Yichi

Precise measurement of the line width of the photoassociation spectra of ultracold molecules by using a frequency shifter

We propose a technique to precisely measure the line width of the photoassociation spectra of the excited cesium molecule by using a frequency shifter to generate two laser beams with a precise frequency difference. A series of photoassociation (PA) spectra are recorded with two laser beam induced molecular lines, whose peak separation serves as an accurate frequency ruler to measure the line width of the PA spectra. The full width half maximum line width was studied as a function of PA laser intensity. The extrapolated value at zero laser intensity is (34.84 ? 0.22) MHz. By analyzing other broadening mechanisms, a value of (32.02 ? 0.70) MHz was deduced. It is shown that this scheme is inexpensive, simple, robust, and is promising for applications in a variety of other atomic species.

Two-photon spectrum of 87Rb using optical frequency comb*

The high precision two-photon excitation measurements for 5S1/2 (Fg = 2) to 5D5/2 (Fe = 4 to 1) of 87Rb are performed by using an optical frequency comb. The two counter-propagating femtosecond pulses (5S1/2 → 5P3/2 at 780 nm, and 5P3/2 → 5D5/2 at 776 nm) act on 87Rb vapor, and the Doppler broadened background signal is effectively eliminated. The temperature and power dependences of the two-photon spectrum are studied in this paper.

High resolution photoassociation spectra of an ultracold Cs2 long-range 0u+ (6S1/2 + 6P1/2) state

In this paper, ultracold cesium molecules are formed through photoassociation technology, which is carried out in a magneto-optical trap. High resolution photoassociaion spectra with the rotational progressions up to J = 7 are obtained. Three rovibrational levels of the long-range 0u+ state of Cs2 below the (6S1/2 + 6P1/2) dissociation limit are specifically investigated. By fitting their binding energy intervals to the non-rigid rotational model, the rotational constant of the long-range 0u+ state is determined. A proportional dependence of the value of the rotational constant on the vibrational quantum number is demonstrated.

Effect of stimulated Brillouin scattering on the gain saturation of distributed fiber Raman amplifier and its suppression by phase modulation

For distributed fiber Raman amplifiers (DFRAs), stimulated Brillouin scattering (SBS) can deplete the pump once occurring and consequently generate gain saturation. On the basis of such a theory, theoretical gain saturation powers in DFRAs with various pump schemes are obtained by calculating SBS thresholds in them, and the experimental results show that they are in excellent agreement with the calculation results. The saturation power of the DFRA with a 300 mW forward pump is as low as 0 dBm, which needs to be enhanced by phase modulation, and the effect is quantitatively studied. A simple model taking both modulation frequency and index into consideration is presented by introducing a correction factor to evaluate the effect of phase modulation on the enhancement of saturation power. Experimentally, it is shown that such a correction factor decreases as the modulation frequency increases and approaches zero when the modulation frequency becomes high enough. In particular, a phase modulation with a modulation frequency of 100 MHz and a modulation index of 1.380 can enhance the saturation power by 4.44 dB, and the correction factor is 0.25 dB, in which the modulation frequency is high enough. Additionally, the factor is 1.767 dB for the modulation frequency of 25 MHz. On this basis, phase modulations with various indexes and a fixed frequency of 25 MHz are adopted to verify the modified model, and the results are positive. To obtain the highest gain saturation power, the model is referable. The research results provide a guide for the design of practical DFRAs.

A direct frequency comb for two-photon transition spectroscopy in a cesium vapor

A phase-stabilized femtosecond frequency comb is used to measure high-resolution spectra of two-photon transition 62S1/2-62P1/2,3/2-82S1/2 in a cesium vapor. The broadband laser output from a femtosecond frequency comb is split into counter-propagating parts, shaped in an original way, and focused into a room-temperature cesium vapor. We obtain high-resolution two-photon spectroscopy by scanning the repetition rate of femtosecond frequency comb, and through absolute frequency measurements.

Research on Supplier Multistage Evaluation Considering Discount Rate

With the increasing importance of building partnership in supply chain, it is more important for core enterprise to evaluate suppliers in the long run multistagely. Considering discount rate, the paper researches the group decision-making method of AHP multistagely, brings forward the concept of weight-vector with discount rate (WVDR) and the concept of synthetical weight-vector with discount rate (SWVDR). More, the paper brings out a concept of consensus degree and a frame of interactive decision-making with consensus degree for supplier multistage evaluation considering discount rate. In the end, an example of supplier evaluation is offered and the result is satisfactory.