Zhang Shougang

A long-term frequency-stabilized erbium-fiber-laser-based optical frequency comb with an intra-cavity electro-optic modulator*

We demonstrate an optical frequency comb based on an erbium-doped-fiber femtosecond laser with the nonlinear polarization evolution scheme. The repetition rate of the laser is about 209 MHz. By controlling an intra-cavity electro-optic modulator and a piezo-transducer, the repetition rate can be stabilized with high servo bandwidth in a range of 3 kHz, enabling long-term repetition rate phase-locking. The in-loop frequency stability of repetition rate is about 1.6E-13 at 1 second integration time, limited by the measurement system; and it is inversely proportional to integration time in short term. Furthermore, using a common path f-2f interferometer, the carrier envelope offset frequency of the frequency comb is obtained with a signal-to-noise ratio of 40 dB in 3 MHz resolution bandwidth. Stabilized carrier envelope offset frequency exhibits a deviation of 0.6 mHz at 1 second integration time.We demonstrate an optical frequency comb based on an erbium-doped-fiber femtosecond laser with the nonlinear polarization evolution scheme. The repetition rate of the laser is about 209 MHz. By controlling an intra-cavity electro-optic modulator and a piezo-transducer, the repetition rate can be stabilized with a high-bandwidth servo in a frequency range of 3 kHz, enabling long-term repetition rate phase-locking. The in-loop frequency stability of repetition rate is about 1.6×10−13 in an integration time of 1 s, limited by the measurement system; and it is inversely proportional to integration time in the short term. Furthermore, using a common path f– 2f interferometer, the carrier envelope offset frequency of the comb is obtained with a signal-to-noise ratio of 40 dB in a 3-MHz resolution bandwidth. Stabilized carrier envelope offset frequency exhibits a deviation of 0.6 mHz in an integration time of 1 s.

Observation of Autler-Townes Effect in Electromagnetically Induced Transparency

We report an experimental observation of Autler-Townes doublet splitting in electromagnetically induced transparency (EIT) resonance. The splitting is introduced by a coherent microwave field, which perturbs a three-level A-type EIT system through an auxiliary level. The doublet splitting of EIT resonance is demonstrated in two cases, where the microwave field shares a common lower level with coupled or probe transition, respectively. The dependence of doublet splitting on microwave field intensity and detuning is measured. This may provide a feasible way of manipulating the atomic states with both laser and microwave field.

Ground state of rotating ultracold quantum gases with anisotropic spin-orbit coupling and concentrically coupled annular potential

Motivated by recent experimental realization of synthetic spin—orbit coupling in neutral quantum gases, we consider the quasi-two-dimensional rotating two-component Bose—Einstein condensates with anisotropic Rashba spin—orbit coupling subject to concentrically coupled annular potential. For experimentally feasible parameters, the rotating condensate exhibits a variety of rich ground state structures by varying the strengths of the spin—orbit coupling and rotational frequency. Moreover, the phase transitions between different ground state phases induced by the anisotropic spin—orbit coupling are obviously different from the isotropic one.

Calculation of Ion Equilibrium Temperature in Ultracold Neutral Plasmas

We provide a fast iteration method to calculate the ion equilibrium temperature in an ultracold neutral plasma (UNP). The temperature as functions of electron initial temperature and ion density is obtained and compared with the recent UNP experimental data. The theoretical predictions agree with the experimental results very well. The calculated ion equilibrium temperature by this method can be applied to study the UNP expansion process more effectively.

Enhanced Spin Depolarization and Storage Time in a Rb Vapor

The experiment of measuring the spin depolarized time and light storage time in a Rb vapor under different conditions is performed. Typically, these measurements are accomplished in three different containers: atoms in a bare glass cell, atoms in a buffer gas cell, and atoms in a tetracontane (C40H82) coating cell. The increasing depolarization and storage times are observed in both the buffer gas cell and the tetracontane coating cell. In the latter case, a storage time greater than 400 μs is obtained.

Attosecond-Resolution Er:Fiber-Based Optical Frequency Comb*

Highly stable frequency-controlled optical frequency combs are key elements of many applications in time-frequency and optical-metrology domains. In this work, we demonstrate a highly stable frequency-controlled erbium-fiber-based optical frequency comb system. Its repetition rate is phase-stabilized to a continuous-wave laser with both an intra-cavity electro-optic modulator and a piezo-transducer; while the carrier-envelope-offset frequency is phase-locked to a radio-frequency signal generator by controlling the pump power. In-loop relative frequency stabilities of the comb are below 1 × 10−16 at 1 s, and integrate down to low 10−20 level at 104 s. The corresponding timing uncertainties are 100–200 as over the full measurement range.

The pulsed optically pumped Rb frequency standards in National Time Service Center

In this paper we report a laboratory prototype of pulsed optically pumped (POP) rubidium frequency standard. In POP operation the pumping, interrogation, and detection phases are separated in time, avoiding the coupling between microwave and optical coherence. The POP 87Rb vapor-cell frequency standard was studied experimentally based on the detection of free induction microwave signal or optical absorption signal. Ramsey fringes were obtained based on 87Rb in buffer gas, with FWHM of 65Hz and 150Hz for microwave and optical central Ramsey fringes respectively. The atomic quality factor was on the order of 108. With microwave detection, the achieved frequency stability was 1.2×10-12τ-1/2(τ=1~100s).

Calculation of the Spin-Dependent Optical Lattice in Rubidium Bose-Einstein Condensation

We provide a theoretical study to calculate the spin-dependent optical lattice with rubidium Bose—Einstein condensation (BEC) in a steady magnetic field. The optical dipole potential variation at different Zeeman levels are obtained. We also show that atoms can be transported in three dimensions by changing the polarization of the trapping field. An explanation of this transportation process in an atomic coordinate is presented.

An investigation for combining optical and magnetic state selector in the cesium beam installation [Cs frequency standard]

Describes an investigation into combining optical and magnetic state selector in the Cs beam installation. It was found that some characteristics in such a set-up are advantageous and attractive. The Ramsey resonance line-width observed is only about 1/3 of that obtained in general optical pumping case, and the mean velocity of signal atoms is slowed down to about 110 m/s.