Showing papers on "Light field published in 1990"

Mechanical Action of Light on Atoms

Abstract: Control of atomic motion with resonant laser light is the most interesting field of research which is rapidly expanding. The book discusses the latest theoretical and experimental achievements in the study of these phenomena. The fundamental questions of the theory of resonant light pressure are given in the book. They are: 1. Optical Stern-Gerlach Effect and Quantization of Atomic Motion in a Light Field; 2. Theory of Light Pressure Force and Atomic Kinetics in a Strong Field; 3. Diffraction and Interference of Atoms; 4. Velocity Bunching Effect, Cooling and Localization of Atoms in Light Field, and 5. Polarization Phenomena and Recoil Effect. The most important experiments are also discussed in this book. While the book may be used to get a primary acquaintance with the subject, specialists will also find the latest theoretical and experimental results and achievements in this field discussed here.

Squeezed light for coherent communications

Abstract: Coherent lightwave communications systems are approaching a limit where the error rates and channel capacities are limited by the quantum properties of light. This is often referred to as the shot-noise limit. If ideal laser light is used in the system, there is no way to avoid this limit. However, new states of the light field called squeezed states have recently been developed that allow an improvement in error rates below the shot-noise limit. Squeezed light concepts and recent experiments are reviewed with emphasis on aspects important to coherent communications. It is shown that channel capacity can be improved using squeezed light by only a factor of two. Larger improvements are in principle possible for error rates, e.g. a factor of three reduction in the number of required photons per bit for a 10/sup -9/ bit error rate. An example of a recent high-performance system is described where optical losses and electronic noise reduce the improvement expected using squeezed light to the 10-20% level. It is concluded that squeezed light only offers significant improvement in bit error rates for very-high-efficiency systems. >

Nonlinear Optics and Spectroscopy

Abstract: ing's vector it follows that the light amplitude at the focal spot would reach 108 volts per centimeter, comparable to the electric field internal to the atoms and molecules responsible for the binding of valence electrons. These are literally pulled out of their orbits in multiphoton tunneling processes, and any material will be converted to a highly ionized dense plasma at these flux densities. It is clear that the familiar notion of a linear optical response with a constant index of refraction, that is, an induced polarization proportional to the amplitude of the light field, should be dropped at much less extreme intensities. There is a nonlinearity in the constitutive relationship which may be expanded in terms of a power series in the electric field components

Nonlinear Mie scattering: electrostrictive coupling of light to droplet acoustic modes.

Abstract: Nonlinear Mie scattering at 532 nm was observed from 23-μm-diameter ethanol droplets excited by picosecond light pulses. Low-order optical modes (l = 2–4), normally hidden at low intensity, became visible as new peaks in elastic scattering spectra at 2 GW/cm2. When higher-Q resonances were selectively excited, the scattered light showed an amplitude-modulated time dependence. The data are explained by electrostrictive generation of acoustic modes of the droplet by the incident radiation and subsequent coupling of the acoustic disturbance back onto the light field.

System characterization of apodized acousto-optic Bragg cells

Abstract: An acousto-optic cell can be characterized in terms of the spatial impulse response or a transfer function that relates the angular plane-wave spectrum of the output light field to that of the input light field. A general methodology for calculating the acousto-optic impulse response and transfer function is developed. This methodology is then specifically applied to the case of acousto-optic cells with and without Hamming apodization of the sound field. Results are obtained and compared with analytical expressions for the conventional Bragg cell for a typical value of the Klein–Cook Q parameter and sound intensity. Finally, implications of the results relating to beam shaping in the scattered light field are discussed.

Vortical force exerted on atoms in resonance light

Abstract: The work is aimed at drawing attention to peculiar properties and the considerable magnitude of the vortical part of the light force which make it important for light-induced effects of atomic drift, cooling and trapping in gas. The author introduces basic notions that specify the vortical force, determine its properties and the functional structure and give estimates in the weak-field limit. The vortical force like the light gradient force and the light frictional force sharply increases in the light field resonantly exciting the atom, but depends quite differently on the resonance detunings, wavevectors, polarisation and light wave phases. The results give insight into how to control the vortex effect of light under what conditions it dominates critically the effect of light friction and gradient forces.

Near threshold two-colour photodetachment of H−

Abstract: The author has calculated the photodetachment probability of the H- ground state near threshold, in the presence of a strong light field of low frequency and a weak light field of higher frequency. The author shows that the evolution of the detachment probability cannot be described in terms of threshold shift.

Large Scale Transverse Interactions in Nonlinear Optical System With 2D-Feedback; Generation, Hysteresis and Interaction Op Wave Structures

Abstract: In this paper we wish, to present the results of theoretical and experimental research of a new class of space-time instabilities of light beams in media with a cubic nonlinearity: instabilities which are driven by coherent transverse interactions of large scale (the typical scale is L ~ d, were d is the beam width). In a light beam in free propagation, and in optical resonators with coherent layouts, transverse interactions are of nature of diffusion and are essentially small in scale. In1,2 we proposed and implemented some arrangement with a so-called two-dimensional feedback, in which the length scaleL can reach values on the order of the beam with. Below we report studies of instabilities which arise under this conditions and which give rise to an entire hierarhy of nonlinear wave dynamics phenomena.

Visualization of light field by fiber probe scanning

Abstract: The light field is visualized by scanning a fiber probe comprising two fibers, one for detecting the light power and the other for displaying the intensity proportional to the detected power.

Effects of light feedback on co_2 laser instabilities

Abstract: The effects of transverse distribution of light field on CO2 laser instabilities are studied by means of light feedback. The phenomena of pulsing frequency shift and chaos in CO2 laser caused by light feedback are observed experimentally. The mechanism of laser instabilities resulting from the transverse distribution is discussed.

Diffracting Atoms from Evanescent Light Fields

Abstract: The demonstration of a mirror for atoms using an evanescent light field to reflect an atomic sodium beam was first reported by Balykin etal.1 following a proposal by Cook and Hill2. In another experiment, Gould etal.3 observed the diffraction of a sodium beam at normal incidence to an optical standing wave transmission grating produced by retroreflecting a laser beam in vacuo. The work reported here aimed to combine these techniques, namely to produce a reflection diffraction grating for atoms consisting of a standing evanescent light wave. Theoretical work by Hajnal and Opat4 predicts that such a grating would have different properties to the transmission grating of Gould etal.3

On the possibility of observing quantum reflection in the scattering of atoms from a nearly resonant light wave

Abstract: We describe design considerations for an experiments on the scattering of optically cooled atoms from a standing wave light field. We discuss importance of atom-field interaction times and standing wave intensities in the context of an experiment which seeks to observe quantum reflection of cold atoms from the pseudo potential which describes the atom-field interaction.

The effect of thermal wavelength on the force experienced by an atom in an optical field

Abstract: In recent years, there has been a great deal of interest in optical cooling and trapping of atoms. In this paper, we discuss the possibility of a change in the force experienced by an atom in a light field when the atom's thermal wavelength becomes larger than the optical wavelength. We argue that there will be no dramatic changes for an atom at equilibrium with the light field, and that the light force will be effective even for an atom whose wavepacket is arbitrarily large.

Mixing of light pressure forces in a three-state atom

Abstract: Supermolasses1 which holds atoms much longer than the ordinary optical molasses and inhomogeneities in the distribution of atoms in optical molasses2 are current cases of unexpected spatial properties of optically cooled and/or trapped atom clouds. As a speculative explanation, I put forward that mixing of the wave vectors of the driving light field which takes place on a multistate atom produces long wavelength optical forces, whose effect on the motion of the atom enormously exceeds the influence of the forces familiar from two-state atomic models.

Spectral shifting of femtosecond pulses in atmospheric density plasmas

Abstract: Using amplified 100 femtosecond (fs.) laser pulses at 620 nanometer (nm.) center wavelength, we employed pump‐probe spectroscopy to investigate interactions of atmospheric density gases and plasmas with a strong light field. With a pump pulse focused to 101 6 W/cm2, ionization dynamics are the principal source of phase modulation and produce a pronounced spectral blue shift on the pump pulse or on an appropriately timed probe pulse, which in favorable cases can be seen as a color change by the naked eye. These shifts are modelled by an ab initio Keldysh‐Drude theory of strong field ionization adapted to the experimental focal geometry. At pressures of several atmospheres, anomalously large blue shifts are observed with selected gases. Impact ionizatioin, induced when electrons possessing large amplitude quivering motion in the strong light field collide with neighboring atoms, is proposed as a mechanism for these large shifts, and is incorporated into a quantitative model. Finally, observation of spectral shifts of a time‐delayed probe and of luminescence provide diagnosics of collisional and recombination dynamics of the laser‐produced plasma.