Space continuous atom laser in one dimension

Cold atom physics in space station arouses a lot of interest of scientists. We investigate the dynamical output process of the space continuous atom laser by solving nonlinear Gross–Pitaevksii equations numerically. Slow-moving continuous atom beams in two directions are observed simultaneously. The slow-moving coherent atom beams can be used as a source of atom interferometer to realize long-time measurements. We also control the output of space atom laser by adjusting the output coupling strength.

Influence of the virtual photon field on the squeezing properties of an atom laser

This paper investigates the squeezing properties of an atom laser without rotating-wave approximation in the system of a binomial states field interacting with a two-level atomic Bose-Einstein condensate. It discusses the influences of atomic eigenfrequency, the interaction intensity between the optical field and atoms, parameter of the binomial states field and virtual photon field on the squeezing properties. The results show that two quadrature components of an atom laser can be squeezed periodically. The duration and the degree of squeezing an atom laser have something to do with the atomic eigenfrequency and the parameter of the binomial states field, respectively. The collapse and revival frequency of atom laser fluctuation depends on the interaction intensity between the optical field and atoms. The effect of the virtual photon field deepens the depth of squeezing an atom laser.

One-dimensional atom laser in microgravity

Using coupled Gross–Pitaevksii(GP)equations,we simulate the output of one-dimensional pulsed atom laser in space station.We get two atom laser pulses propagating in opposite directions with one pulsed RF coupling.Compared with atom laser under gravity,the laser pulse in microgravity shows much slower moving speed,which is suitable to be used for long-term investigations.We also simulate the output flux at different coupling strengths.

Sensitivity function analysis of gravitational wave detection with single-laser and large-momentum-transfer atomic sensors

Recently, a configuration using atomic interferometers （AIs） had been sug- gested for the detection of gravitational waves. A new AI with some additional laser pulses for implementing large momentum transfer was also put forward, in order to reduce the effect of shot noise and laser frequency noise. We use a sensitivity function to analyze all possible configurations of the new AI and to distinguish how many mo- menta are transferred in a specific configuration. By analyzing the new configuration, we further explore a detection scheme for gravitational waves, in particular, that ame- liorates laser frequency noise. We find that the amelioration occurs in such a scheme, but novelly, in some cases, the frequency noise can be canceled completely by using a proper data processing method.

Broadening of Cr nanostructures in laser-focused atomic deposition

This paper presents the experimental progress of laser-focused Cr atomic deposition and the experimental condition. The result is an accurate array of lines with a periodicity of 212.8±0.2 nm and mean full-width at half maximum as approximately 95 nm. Surface growth in laser-focused Cr atomic deposition is modeled and studied by kinetic Monte Carlo simulation including two events： the one is that atom trajectories in laser standing wave are simulated with the semiclassical equations of motion to obtain the deposition position; the other is that adatom diffuses by considering two major diffusion processes, namely, terrace diffusion and step-edge descending. Comparing with experimental results （Anderson W R, Bradley C C, McClelland J J and Celotta R J 1999 Phys. Rev. A 59 2476）, it finds that the simulated trend of dependence on feature width is in agreement with the power of standing wave, the other two simulated trends are the same in the initial stage. These results demonstrate that some surface diffusion processes play important role in feature width broadening. Numerical result also shows that high incoming beam flux of atoms deposited redounds to decrease the distance between adatoms which can diffuse to minimize the feature width and enhance the contrast.

Control of the Atomic Ionization with Short and Intense Chirped Laser Pulses

We investigate a two-photon ionization process in a real hydrogen atom by short and intense chirped laser pulses. Our simulation of the laser-atom interaction consists on numerically solving the three-dimensional time-dependent Schrodinger equation with a spectral method. The unperturbed wave functions and electronic energies of the atomic system were found by using an accurate L2 discretisation technique based on the expansion of the wave functions on B-spline functions. We show the efficiency of chirped laser pulses to control the ionization yield and the transfer of the population to the 2p bound state involved in the ionization path.

Controlling quantum coherence of atom laser by light with strong strength

A new method for controlling the quantum coherence of atom laser by applying input light with strong strength is presented within the framework of quantum dynamical theory. Unlike the case of rotating wave approximation(RWA), we show that the non-classical properties, such as sub-Poisson distribution and quadrature squeezed effect, can appear in the output atom laser beam with time. By choosing suitable initial RF phase, a steady and brighter output of squeezed coherent atom laser is also available.

Strange Attractors in the Resonance Interaction of Two-State Atoms with Single-Mode Laser Field

The resonance interaction of two-state atoms with single mode field is described theoretically by using the semi-classical theory and Jaynes-Cummings model. The nonlinear characteristics of this system are calculated by using FFT and Runge-Kutta methods. The chaotic strange attractors in this system are obtained from the numerical results.

Multiphoton Ionization of Potassium Atoms in Femtosecond Laser Fields

We study the multiphoton ionization of potassium atoms in 800 nm and 400 nm femtosecond laser fields.In the 800 nm laser field,the potassium atom absorbs three photons and emits one electron via one photon resonance with the 4p intermediate state with the help of the ac-Stark shift.The resonance feature is clearly shown as an Autler-Townes(AT) splitting and is mapped out in the electron kinetic energy spectrum.In a 400 nm laser field,although one photon resonance is possible with the 5p state,no splitting is observed.The different transition amplitudes between 4s-4p and 4s-5p explain the observed results.Due to the AT effect,an unexpected peak in the photoelectron energy spectrum that violates the dipole transition rule is observed.A preliminary explanation involving the spin-orbit interaction in the p state is given to account for this component.The observed ATsplitting in the electron kinetic energy distribution can be used as an effective method to calibrate the intensity of a laser field.

The influence of divergence angle on the deposition of neutral chromium atoms using a laser standing wave

The characteristics of neutral chromium atoms in the standing wave field are discussed. Based on a semi-classical model, the motion equation of neutral atoms in the laser standing wave field is analyzed, and the trajectories of the atoms are obtained by simulations with the different divergence angles of the atomic beam. The simulation results show that the full width at half maximum （FWHM） of the stripe is 2.75 nm and the contrast is 38.5 ： 1 when the divergence angle equals 0 mrad, the FWHM is 24.1 nm and the contrast is 6.8：1 when the divergence angle equals 0.2 mrad and the FWHMs are 58.6 and 137.8 nm, and the contrasts are 3.3 ： 1 and 1.6 ： i when the divergence angles equal 0.5 and 1.0 mrad, respectively.

Implementation of quantum search scheme by adiabatic passage in a cavity-laser-atom system

This paper proposes a scheme for implementing the adiabatic quantum search algorithm of different marked items in an unsorted list of N items with atoms in a cavity driven by lasers. N identical three-level atoms are trapped in a single-mode cavity. Each atom is driven by a set of three pulsed laser fields. In each atom, the same level represents a database entry. Two of the atoms are marked differently. The marked atom has an energy gap between its two ground states. The two different marked states can be sought out respectively starting from an initial entangled state by controlling the ratio of three pulse amplitudes. Moreover, the mechanism, based on adiabatic passage, constitutes a decoherence-free method in the sense that spontaneous emission and cavity damping are avoided since the dynamics follows the dark state. Furthermore, this paper extends the algorithm with m（m〉2） atoms marked in an ideal situation. Any different marked state can be sought out.

REDISTRIBUTION OF IMPURITY ATOMS AI, Si, Mn AND Cu IN Ni DURING LASER MELTING

An explanation of the redistribution of impurity atoms such as Al, Si, Mn and Cu in pure nickel during low speed laser melting is made by one-dimensional analysis model for heat transfer. The solid-liquid interface solute redistribution seems to be the principal cause that makes the impurity atoms redistribute in the depth direction. The diffusion of impurity atoms from low to high temperature zones and their surface selective evaporation are believed to be noticeably contributed to the redistribution.

Ionization Process of Atoms by Intense Femtosecond Chirped Laser Pulses

We numerically investigate the ionization mechanism in a real hydrogen atom under intense fem to second chirped laser pulses. The central carrier frequency of the pulses is chosen to be 6.2 eV (λ = 200 nm), which corresponds to the fourth-harmonic of the Ti:Sapphire laser. Our simulation of the laser-atom interaction consists on numerically solving the three-dimensional time-dependent Schrodinger equation with a spectral method. The unperturbed wave functions and electronic energies of the atomic system were found by using an L2 discretization technique based on the expansion of the wave functions on B-spline functions. The presented results of kinetic energy spectra of the emitted electrons show the sensitivity of the ionization process to the chirp parameter. Particular attention is paid to the important role of the excited bound states involved in the ionization paths.

Optimization of laser focused atomic deposition by channeling

Laser focused atomic deposition is a unique and effective way to fabricate highly accurate pitch standards in nanometrology.However,the stability and repeatability of the atom lithography fabrication process remains a challenging problem for massive production.Based on the atom-light interaction theory,channeling is utilized to improve the stability and repeatability.From the comparison of three kinds of atom-light interaction models,the optimal parameters for channeling are obtained based on simulation.According to the experimental observations,the peak to valley height of Cr nano-gratings keeps stable when the cutting proportion changes from 15%to 50%,which means that the channeling shows up under this condition.The channeling proves to be an effective method to optimize the stability and repeatability of laser focused Cr atomic deposition.

Joint Operation of Atomic Force Microscope and Advanced Laser Confocal Microscope for Observing Surface Processes in a Protein Crystal

We demonstrated the insitu observation of a moving atomic force microscope (AFM) cantilever using a laser confocal microscope combined with a differential interference microscope (LCM-DIM). The AFM cantilever scanned or indented the {110} surface of a hen egg-white lysozyme crystal in a supersaturated solution. Using a soft cantilever, we could observe the step growth with high time resolution by LCM-DIM and perform quantitative measurements of the step height by AFM simultaneously. In addition, a hard cantilever was used with LCM-DIM to observe the dynamics of crystal surface scratching and indentation. In the supersaturated solution, the small steps generated from the scratched line aggregated to macro steps, and subsequently flattened the surface.

Phase-related noise characteristics of 780 nm band single-frequency lasers used in the cold atomic clock

We propose a method to directly measure phase-related noise characteristics of single-frequency lasers in the 728–980 nm band based on a 120°phase difference interferometer.Differential phase information of the laser under test is demodulated via the interferometer.Other parameters related to the phase noise characteristics such as linewidth at different observation time, phase/frequency noise, power spectrum density of phase/frequency fluctuation, and Allan deviation are further obtained.Frequency noise as low as 1 Hz^2/Hz can be measured using our system.Then the phase-related noise characteristics of two commercial lasers frequently used in cold atomic clocks are studied systematically by the method.Furthermore, several influencing factors and their relative evolution laws are also revealed, such as the pump current and frequency-locking control parameters.This would help to optimize the laser performance, select laser sources, and evaluate the system performance for cold atomic physics applications.

Interaction of intense laser pulses with hydrogen atomic clusters

The interaction between intense femtosecond laser pulses and hydrogen atomic clusters is studied by a simplified Coulomb explosion model. The dependences of average proton kinetic energy on cluster size, pulse duration, laser intensity and wavelength are studied respectively. The calculated results indicate that the irradiation of a femtosecond laser of longer wavelength on hydrogen atomic clusters may be a simple, economical way to produce highly kinetic hydrogen ions. The phenomenon suggests that the irradiation of femtosecond laser of longer wavelength on deuterium atomic clusters may be easier than that of shorter wavelength to drive nuclear fusion reactions. The product of the laser intensity and the squared laser wavelength needed to make proton energy saturated as a function of the squared cluster radius is also investigated. The proton energy distribution calculated is also shown and compared with the experimental data. Our results are in agreement with the experimental results fairly well.

Role of XUV Photons in Atomic High-Order Above-Threshold Ionization Processes in IR+XUV Two-Color Laser Fields

We investigate the above-threshold ionization of an atom in a combined infrared （IR） and extreme ultraviolet （XUV） two-color laser field and focus on the role of XUV field in the high-order above-threshold ionization （HATI） process. It is demonstrated that, in stark contrast to previous studies, the XUV laser may play a significant role in atomic HATI process, and in particular, the XUV laser can accelerate the ionized electron in a quantized way during the collision between the electron and its parent ion. This process cannot be explained by the elassical three-step model Our results indicate that the previously well-established concept that HATI is an elastic recollision process is broken down.

High-order harmonic generation spectrum of an excited one-dimensional Coulomb atom in an intense laser field

Response of the wave packet of a one-dimensional Coulomb atom to an intense laser field is calculated using the symmetrized split operator fast Fourier method. The high-order harmonic generation （HHG） of the initial state separately being the ground and excited states is presented. When the hardness parameter a in the soft Coulomb potential V（x） =-1√x^2＋α is chosen to be small enough, the so-called hard Coulomb potential V（x）=1/｜x｜ can be obtained. It is well known that the hard one-dimensional Coulomb atom has an unstable ground state with an energy eigenvalue of - 0.5 and it has no states corresponding to physical states in the true atoms, and has the first and second excited states being degenerate. The parity effects on the HHG can be seen from the first and second excited states of the hard one-dimensional Coulomb atom. The HHG spectra of the excited states from both the soft and hard Coulomb atom models are shown to have more complex structures and to be much stronger than the corresponding HHG spectrum of the ground state of the soft Coulomb model with a = 2 in the same laser field. Laser-induced non-resonant one-photon emission is also observed.

基于飞秒激光与纳秒激光协同多光子诱导荧光的火焰中氢原子瞬态检测

为了准确测量碳氢燃料燃烧过程中原位氢原子,提出了飞秒-纳秒激光协同激发的氢原子瞬态在线探测策略。以243 nm的飞秒激光经过双光子过程将基态氢原子激发到2S能级,随后这些氢原子再被656 nm的纳秒激光激发到3P能级,通过探测3P-2S的荧光发射,实现了宽当量比范围的氢原子无干扰瞬态在线测量。实验结果表明:通过飞秒-纳秒协同的方式,可以有效降低激光光解产生的氢原子对原位氢原子探测的干扰。