Standing-wave Laser Field Research Articles

Driving Alkali Rydberg Transitions with a Phase-Modulated Optical Lattice.

We develop and demonstrate a spectroscopic method for Rydberg-Rydberg transitions using a phase-controlled and -modulated, standing-wave laser field focused on a cloud of cold ^{85}Rb Rydberg atoms. The method is based on the ponderomotive (A^{2}) interaction of the Rydberg electron, which has less-restrictive selection rules than electric-dipole couplings, allowing us to probe both nS_{1/2}→nP_{1/2} and nS_{1/2}→(n+1)S_{1/2} transitions in first order. Without increase in laser power, third- and fourth-order subharmonic drives are employed to access Rydberg transitions in the 40 to 70GHz frequency range using widely available optical phase modulators in the Ku band (12 to 18GHz). Measurements agree well with simulations based on the model we develop. The spectra have prominent Doppler-free components with linewidths ≲200 kHz. The method paves the way for optical Doppler-free high-precision spectroscopy of Rydberg-Rydberg transitions and for spatially selective qubit manipulation with μm-scale resolution in Rydberg-based simulators and quantum computers, provided that magic states are chosen and that the atoms are sufficiently cold.

Unidirectional reflectionless anti-parity-time-symmetric photonic lattices of thermal atoms

We experimentally demonstrate an anti-parity-time (anti-$PT$)-symmetric photonic lattice in thermal cesium atoms driven by two standing-wave laser fields. Such a lattice possesses anti-$PT$-symmetric susceptibility, of which the real (imaginary) part is an odd (even) function of position. By manipulating the intensities and phases of the two standing-wave fields, we experimentally observe unidirectional reflectionless propagation at the exceptional points. Our work provides a platform to study the scattering property of anti-$PT$-symmetric systems.

Population density gratings creation and control in resonant medium by half-cycle terahertz pulses

Electromagnetically induced gratings (EIG) are created by standing-wave laser field in resonant media. Such gratings can be also created by few-cycle electromagnetic pulses counter-propagating in the medium via coherent Rabi oscillations of atomic inversion. In this case, instantaneous cross-section of the pulses in the medium is not necessary for grating formation. In this paper, we revise our recent results in study of such grating formation and their control by few-cycle pulses coherently propagating in a resonant medium. We demonstrate the grating formation and their control in three-level medium excited by three subcycle THz pulses.

Optical localization of a nitrogen-vacancy center in three-dimensional space via probe absorption

We demonstrate the three-dimensional localization of a single nitrogen-vacancy (NV) center in nanodiamond by the use of position-dependent standing-wave laser fields in an external magnetic field. We show that various localization phenomena including cask-like, disc-like, cylinder-like, and sphere-like patterns can be achieved by monitoring the probe absorption spectrum in two different coupling formalisms. By selecting an appropriate combination of system parameters, we can localize an individual NV center within a subspace at a deterministic position, which is a consequence of quantum interference. Furthermore, this deterministic positional control of coherent NV centers may have potential applications in NV-based nanostructures, such as sensing and quantum information-processing devices.

A high-energy electron density modulator driven by an intense laser standing wave

AbstractA high energy electron density modulator from a high-intensity laser standing wave field is studied herein by investigating the ultrafast motion of electrons in the field. Electrons converge at the electric field antinodes, and the discrete electron density peaks modulated by the field located at the corresponding laser phases of kx = nπ, (n = 0, 1, 2, …), that is, the modulation period is 1/2 the wavelength of the individual laser. We also discussed the influence of the laser parameters such as laser intensity and waist size on the beam modulator. It is shown that a long interaction length (waist) or sufficiently high field intensity is essential for relativistic electron density modulation.

Light-force-induced shift in laser spectroscopy of atomic helium

A laser-power-dependent shift has been observed in various atomic beam spectroscopy measurements, which was often treated by extrapolating the results to the zero-field limit. Here we present an experimental and theoretical study of this effect in the measurements of the $2{\phantom{\rule{0.16em}{0ex}}}^{3}S\ensuremath{-}2{\phantom{\rule{0.16em}{0ex}}}^{3}P$ transition frequency of $^{4}\mathrm{He}$. The light-force-induced shift was attributed as a result of modulated atomic trajectories induced by the standing-wave laser field and consequent distortions in the lineshape. Modulation of the beam spatial distributions was detected by imaging atoms at high laser power and was also simulated by the Monte Carlo wave-function approach. The nonlinear behavior of the light-force-shift was observed experimentally and reproduced by the simulations. The systematic shift in the extrapolated result at the zero-field limit was analyzed. As a consequence of this effect, a correction of +0.50(80) kHz was added to our previous result on the $2{\phantom{\rule{0.16em}{0ex}}}^{3}{S}_{1}\ensuremath{-}2{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{1}$ transition frequency [Phys. Rev. Lett. 119, 263002 (2017)], and the reevaluated value is 276 734 477 704.3(1.6) kHz.

Efficient three-dimensional atom localization using probe absorption in a diamond-configuration atomic system

A new scheme for three-dimensional (3D) atom localization is proposed based on measuring the probe absorption spectra in a four-level diamond-configuration atomic system, in which the atom interacts with three orthogonal standing-wave laser fields. Due to spatial-dependent interaction between atom and fields, position information of the atom can be obtained by measuring the absorption spectra of the weak probe field. The results show that atom localization properties can be significantly improved and some interesting spatial localization structures such as double-layer lantern-like, single-layer lantern-like, gourd-like, cylinder-like, and ellipsoid-like patterns can be achieved when we adjust system parameters properly. Most importantly, we can find the atom at a particular position in 3D space with 100% probability under appropriate conditions.

Deflection of a molecular beam using the bichromatic stimulated force

We demonstrate that a bichromatic standing-wave laser field can exert a significantly larger force on a molecule than ordinary radiation pressure. Our experiment measures the deflection of a pulsed supersonic beam of CaF molecules by a two-frequency laser field detuned symmetrically about resonance with the nearly closed $X (v=0) \rightarrow B (v'=0)$ transition. The inferred force as a function of relative phase between the two counterpropagating beams is in reasonable agreement with numerical simulations of the bichromatic force in this multilevel system. The large magnitude of the force, coupled with the reduced rate of spontaneous emission, indicates its potential utility in the production and manipulation of ultracold molecules.

3D atom microscopy in the presence of Doppler shift

The interaction of hot atoms with laser fields produces a Doppler shift, which can severely affect the precise spatial measurement of an atom. We suggest an experimentally realizable scheme to address this issue in the three-dimensional position measurement of a single atom in vapors of rubidium atoms. A three-level Λ-type atom–field configuration is considered where a moving atom interacts with three orthogonal standing-wave laser fields and spatial information of the atom in 3D space is obtained via an upper-level population using a weak probe laser field. The atom moves with velocity v along the probe laser field, and due to the Doppler broadening the precision of the spatial information deteriorates significantly. It is found that via a microwave field, precision in the position measurement of a single hot rubidium atom can be attained, overcoming the limitation posed by the Doppler shift.

Quantum–classical correspondence in chaotic dynamics of laser-driven atoms

This paper is a review article on some aspects of quantum–classical correspondence in chaotic dynamics of cold atoms interacting with a standing-wave laser field forming an optical lattice. The problem is treated from both (semi)classical and quantum points of view. In both approaches, the interaction of an atomic electic dipole with the laser field is treated quantum mechanically. Translational motion is described, at first, classically (atoms are considered to be point-like objects) and then quantum mechanically as a propagation of matter waves. Semiclassical equations of motion are shown to be chaotic in the sense of classical dynamical chaos. Point-like atoms in an absolutely deterministic and rigid optical lattice can move in a random-like manner demonstrating a chaotic walking with typical features of classical chaos. This behavior is explained by random-like ‘jumps’ of one of the atomic internal variable when atoms cross nodes of the standing wave and occurs in a specific range of the atom-field detuning. When treating atoms as matter waves, we show that they can make nonadiabatic transitions when crossing the standing-wave nodes. The point is that atomic wave packets split at each node in the same range of the atom-field detuning where the classical chaos occurs. The key point is that the squared amplitude of those semiclassical ‘jumps’ equal to the quantum Landau–Zener parameter which defines the probability of nonadiabatic transitions at the nodes. Nonadiabatic atomic wave packets are much more complicated compared to adiabatic ones and may be called chaotic in this sense. A few possible experiments to observe some manifestations of classical and quantum chaos with cold atoms in horizontal and vertical optical lattices are proposed and discussed.

Coherent conditions of electron–photon backscattering light in a wiggle magnetic field

In order to get a γ-laser by the backscattering of electron–photons in a wiggle magnetic field, the length of an effective backscattering region is postulated to be small enough. The paper demonstrates that the condition is only a sufficient one; it is not a necessary condition. The necessary condition is given. The backscattering of electron–photons in a wiggle magnetic field can produce a γ-laser. It is possible that the amplitude of the γ-laser is small. The amplitude can be significantly increased by increasing the magnetic induction of the wiggle magnetic field, by reducing the wavelength of the wiggle magnetic field, and by making the monochromaticity of an incident electron beam better. In a laser standing wave field or a superposition field of a wiggle magnetic field and a laser standing wave field, the backscattering of electron–photons can produce a quasi-laser with a shorter wavelength.

Realization of position-dependent absorption based on biexciton coherence in a Quantum Dot Nanostructure

In this letter, the two-dimensional (2D) spatial-dependent of probe absorption based on biexciton coherence is investigated by monitoring the probe absorption spectra in a Quantum Dot (QD) Nanostructure. We find that due to the quantum interference which is set up by two control pulses that couples to a resonance of the biexciton, the 2D spatial distribution of probe absorption spectrum can be controlled via adjusting the system parameters. We study the effect of controlling parameters of the QD system on spatial distribution of the probe field absorption for two different cases in which the QD interacts with the standing-wave laser fields; first, when two laser fields which couple to a biexciton state, correspond to the two orthogonal standing-wave fields and couple the different transitions. Second, when only one of laser fields correspond to the combination of two orthogonal standing-wave fields, while the other one corresponds to a traveling-wave field. Results exhibit different interesting 2D absorption patterns.

Atom position measurement in a four-level Lambda-shaped scheme with twofold lower-levels

The two-dimensional position dependent probe absorption spectrum of a driven four-level Λ-type atomic system with twofold lower-levels interacting with two orthogonal standing wave laser fields and one microwave field is investigated. It is found that due to the position dependent nature of atom–field interaction, the spatial distribution of the atom can be controlled by scanning the resulting absorption spectra of the weak probe field. The effect of different controlling parameters of the system such as detunings, the intensity of standing wave fields as well as the relative phase of applied fields on the position measurement uncertainty of the atom is then discussed. We show that by properly adjusting the system parameters, different spatial structures of localization as ‘∞’-like, spot-like, deltoid-like and elliptic like patterns can be designed, so that high-precision and high-resolution atom localization can be engineered.

Impact of Spontaneous Emission on the form and Dynamics of Atomic Wave Packets in an Optical Lattice

Using the Monte Carlo wave-function method, we study the influence of spontaneous emission on dynamics of a Gaussian atomic wave packet with two internal states placed initially at a node or antinode of a standing-wave laser field. Without spontaneous emission, the wave packet at a node is known to split both in the position and momentum spaces because of the optical Stern–Gerlach effect. We show that the spontaneous-emission events suppress splitting, causing a strong broadening of the wave packet in both spaces. As for a wave packet placed initially at an antinode, spontaneous emission causes a localization of the atomic wave packet in the first potential well both in the position and momentum spaces as compared to the coherent evolution.

Motion-induced X-ray and terahertz radiation of electrons captured in laser standing wave

The motions of charged particles in electromagnetic fields composed of two or more laser beams show a variety of forms due to the adjustable properties of electromagnetic fields. In this paper, we consider the periodic laser standing wave field composed of two laser beams with opposite propagating directions. The movement of electrons in the standing wave field shows a periodic behavior, accompanied with the obvious radiation, especially when electrons are captured by the laser standing wave field. This phenomenon has aroused much interest of us. Under the existing experimental conditions, the free electron beam with low energy from an electron gun or the relativistic electron beam generated from laser acceleration can be easily obtained and injected into the periodic standing wave field. In this paper, using the single-electron model and the classical radiation theory of charged particles, we study the motion and radiation processes of low and high energy electrons in the polarized laser standing wave field. The results show that when the direction of incident electrons with low-speed is perpendicular to the direction of the laser standing wave electric field, the one-dimensional nearly periodic motion of electrons evolves into a two-dimensional folded movement by gradually increasing the light intensity of the laser standing wave field, and the strong terahertz radiation at micrometer wavelength is produced. High energy electrons generate the high-frequency radiation with the wavelength at several nanometers when the incident direction of high energy electrons is perpendicular or parallel to the direction of the laser standing wave electric field. In the case of low-energy electron, the motion of electron, frequency and intensity of radiation are affected by the laser intensity. In the case of incident high-energy electrons, the laser intensity affects the intensity of electronic radiation, and the initial electron energy influences radiation frequency. The bigger the incident electrons energy, the higher the frequency of radiation is. #br#We can obtain electron beams with different energies by laser acceleration, and they can be promising small radiation sources for terahertz and X-ray by using the electron beam radiation in a laser standing wave field. These studies also provide a basis for experimental researches and the applications of electron radiation in a laser standing wave field.

Dynamic generation and manipulaition of electromagnetically induced 2D phtonic band-gaps

We study the steady optical responses of a four-level Tripod cold 87Rb atomic system, which is driven by two mutually perpendicular strong standing-wave laser fields. It is found that satisfying the condition of a proper detuning between two strong fields, one nearly perfect structure of double photonic band-gap, where reflectivity can reach 95%, can be generated along each direction, respectively. Shifting a strong field (two strong fields) to a travelling-wave field (two travelling-wave fields), we can achieve a reflectivity platform and a transmissivity window (two transmissivity windows). Our new findings are beneficial to a novel all-optical switching and routing, which may have applications in complex all-optical information networks.

Ionization of Rydberg atoms by standing-wave light fields

When electromagnetic radiation induces atomic transitions, the size of the atom is usually much smaller than the wavelength of the radiation, allowing the spatial variation of the radiation field's phase to be neglected in the description of transition rates. Somewhat unexpectedly, this approximation, known as the electric dipole approximation, is still valid for the ionization of micrometre-sized atoms in highly excited Rydberg states by laser light with a wavelength of about the same size. Here we employ a standing-wave laser field as a spatially resolving probe within the volume of a Rydberg atom to show that the photoionization process only occurs near the nucleus, within a volume that is small with respect to both the atom and the laser wavelength. This evidence resolves the apparent inconsistency of the electric dipole approximation's validity for photoionization of Rydberg atoms, and it verifies the theory of light-matter interaction in a limiting case.

Study on the channel effect of deposition characteristics of neutral atoms in the laser standing wave field

Based on semiclassical theory, a model of the interaction between neutral atoms and the laser standing wave field has been established in this article. The trajectories and the deposition characteristics are analyzed with channel effect, and the full width at half maximum of nano-grating is 96.70, 0.532 and 12.16 nm when the divergence angle, spherical and chromatic aberration are discussed, respectively. The simulation results show that the contrast of the stripes decreases with the increasing divergence angle of the atomic beam. Also, the contrasts of the stripe are 85.2:1 and 5.33:1 when the divergence angles equal 0.1 and 0.3 mrad. Owing to the scission of the stripe, the quality of the deposition deteriorates with a divergence angle over 0.5 mrad.

Three-Dimensional Analysis of Divergence Aangle on Deposition of Chromium Atoms in Laser Standing Wave Field

Three-dimensional analysis of the effects of atom beam divergence angle on the process of fabricating nanograting is discussed based on the three-dimensional motion model of Cr atoms in Gaussian standing wave laser field. From the simulative results it can be seen that Atomic beam spreading plays an important role in determining the deposition nanometer quality, so the preparation of a high-collimated and transversely cooled atomic beam, typically under 0.6mrad, is essential to minimize the severely disadvantageous effects for deposition of atoms in laser standing wave

Cavity-mediated cooling of a trappedΛ-type three-level atom using a standing-wave laser field

Cavity-mediated cooling of a trapped<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Λ</mml:mi></mml:math>-type three-level atom using a standing-wave laser field