Nonresonant Light Research Articles

Nonresonant inelastic light scattering in the Hubbard model

Inelastic light scattering from electrons is a symmetry-selective probe of the charge dynamics within correlated materials. Many measurements have been made on correlated insulators, and recent exact solutions in large dimensions explain a number of anomalous features found in experiments. Here we focus on the correlated metal, as described by the Hubbard model away from half filling. We can determine the B1g Raman response and the inelastic X-ray scattering along the Brillouin zone diagonal exactly in the large dimensional limit. We find a number of interesting features in the light scattering response which should be able to be seen in correlated metals such as the heavy fermions.

Guided-mode resonant grating filter with an antireflection structured surface.

We describe a new structure of guided-mode resonant grating (GMRG) filters with low sideband reflectance. This GMRG filter consists of a high-index thin film on an antireflective structured surface called "moth-eye structure." Since the high-index film undulates along the surface structure, the film acts as a modulated optical waveguide. An incident light wave satisfying a resonant condition is reflected by the GMRG filter, and nonresonant light waves pass through the filter. This GMRG filter is valid for reducing reflection of nonresonant light waves in a wide spectral range. The resonant reflection of this new filter was investigated by numerical calculation based on an electromagnetic grating analysis. In the case of a triangular antireflective surface structure whose thickness is 2x greater than its period, the sideband reflectance for nonresonant light waves was lower than 0.5% for TM-polarized light in a wide range of wavelengths.

Excited-state four-wave mixing for nonresonant holographic storage in azo-dye-doped polymers

In the past, four-wave mixing for real-time holography storage based on ground-state absorption at the resonant wavelength has been extensively studied in azo-dye-doped polymer films. We report theoreti- cal and experimental studies on the four-wave mixing based on the excited-state absorption at a nonresonant wavelength using ethyl- orange-doped polyvinyl alcohol films. In our experiments, we use two laser beams: a 632.8-nm He-Ne laser as a nonresonant light source for excited-state four-wave mixing and a 488-nm Ar 1 laser as a preexcited light source to enhance the excited-state absorption. To explain the ex- perimental results, we propose a four-level model for the azo-molecule system. The steady state and dynamic behavior of phase conjugation signal in four-wave mixing are simulated by solving rate equations. The theoretical simulations, which are in accord with the experimental re- sults, show that using the preexcited method, four-wave mixing hologra- phy storage can be realized by using a weak laser beam with a nonreso- nant wavelength based on the excited-state process. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00903-X)

Light-induced diffusion and desorption of alkali metals in a siloxane film: Theory and experiment

The light-induced desorption and diffusion of alkali-metal atoms in organic films are interesting fields of investigation. An impressive demonstration is given by the recently observed light-induced atomic desorption (LIAD) effect, where a huge alkali-metal atom desorption from siloxane films, previously exposed to atomic vapors, is induced by weak and nonresonant light. In this paper, experimental data and a one-dimensional theoretical model of the effect are presented. The model gives a good description of the vapor density dynamics by taking into account both the atomic diffusion inside the coating and the surface desorption. General equations are reported and discussed within the limits of experimental interest. The potential barrier at the vapor-surface interface and the activation energy for Rb in (poly)dimethylsiloxane have been determined.

All-fiber bandpass filter with adjustable transmission using cladding-mode coupling

We demonstrate an all-fiber bandpass filter with 2-nm bandwidth and more than 25 dB of nonresonant light suppression (ignoring sidelobes) in a 60-nm-wide spectral range around its central wavelength. This novel device uses a pair of long-period gratings to couple resonant light from the fiber core into the cladding and then back into the core. The amplitude transmission through the filter is dynamically adjustable over a 20-dB range.

Effects of motional states of a trapped atom on its interaction with nonresonant light

We consider modification of an atom-field nonresonant interaction due to the motion of the atom (ion) in a confining potential of the trap. We study the electromagnetic field emitted by the trapped atom for various states of its center of mass. In particular, we study the radiation emitted by the atom when its center of mass is in a superposition of two quantum states and in a statistical mixture of the two states. We show that the differences between these cases are rather elusive, but they can be detected when some particular conditions are satisfied. We point out that they can be used as a way to detect the coherence of the state of the center of mass.

Probing Weakly-Bound Species with Nonresonant Light: Dissociation of He2Induced by Rotational Hybridization

A field-dependent value of angular momentum can be imparted to a 4He2 cluster by the interaction of its anisotropic polarizability with a nonresonant laser field. In this way a centrifugal term is introduced that can be tuned to a critical value sufficient to overcome the potential that binds the dimer. Due to its dependence on the internuclear distance and laser intensity, the critical angular momentum for dissociation is attained at different internuclear separations for different pulsed-laser intensities. As a result, the dependence of the dissociation probability on the laser intensity offers a means to map the potential and/or the polarizability anisotropy. A comparison with experiment thus could provide a test of either. The technique is applicable to other molecules in bound states close to the dissociation limit.

Quantum conversion between laser fields and vibrational wave-packets of particles in a three-dimensional quantized trap

Raman transitions between vibrational states of the center-of-mass motions of single particles confined in a three-dimensional quantized trap are investigated in nonresonant standing-wave light fields, which can be used to observe quantum features transferred from laser fields to vibrational wave-packets of motion.

Differential cross sections for radiation assisted collisions between atoms

We report angle resolved measurements of the excited Na atoms from the process with non-resonant light. The experiment provides a method to probe the NaKr collision pair by a photon. The Na() angular distribution shows an oscillatory structure, which can be used for a test of the NaKr potential curve system. The signal depends strongly upon the polarization of the photon. The effect provides information about the geometric properties of the collision pair.

Dynamics of rubidium light-induced atom desorption (LIAD)

Rubidium desorption induced by weak and non-resonant light has been observed in silane coated cells. The effect is non-thermal and produces a huge variation of the vapor density at room temperature. This effect has been observed, for the first time, by Gozzini et al. with sodium upon similar conditions. The dynamics of this new effect is here discussed and the desorption-adsorption rates are measured.

High field Faraday rotation in a thin film of single crystal EuTe

High magnetic field effects on the magnetic exciton in EuTe were investigated with a Faraday rotation measurement to compare with the usual magnetization measurement. Thin films of EuTe which were epitaxially grown with the hot wall method were used in the experiments. The field dependence of the Faraday rotation for non-resonant light is in good agreement with the normalized magnetization curve. The field dependence for resonant light with the transition (4f) 7–(4f) 6(5d) is not consistent with the magnetization curve. The inconsistency is considered to be due to the non-linear dependence of the rotation angle for resonant light. The temperature charateristics show an increase of the high field Faraday rotation in liquid He temperature corresponding to the short-range order like magnetic polarization around the optically excited Eu 2+ ions.

Thermal-wave-modulated superconducting quantum interference device susceptometry for thin magnetic layers

Thermal waves are excited by a chopped nonresonant light wave in a 3.2 μm EuTe layer on a crystalline BaF2 substrate. The glass fiber optic sample holder is at rest within the pickup coil of a superconducting quantum interference device susceptometer. The thermal wave amplitude (simulated by a two-dimensional heat conduction model) is a function of temperature and chop rate of illumination and modulates only the magnetic properties of the epitaxial layer. Therefore, the novel method has an enhanced dynamic range and sensitivity (resolution of magnetic moment ≤2×10−9 emu) and resolves the antiferromagnetic phase transition of the EuTe layers at TN=9.8 K even for small magnetic fields of 10 G.

Ultrafast optical processes in DC‐field biased quantum‐well structures

AbstractThis paper describes one of the ultrafast optical processes in the dc‐biased quantum‐well structure, ultrafast switching of light emission controlled by electric field effect, and its application for light‐emitting devices. In the fabricated device, injection current for device operation is extremely low (10 A/cm2) and high‐speed switching of light emission (switching time of 300 ps) can be achieved without the influence of a recombination life‐time.Utilizing the amplification of light emission in the microcavity, the external efficiency of the light‐emitting device can be improved, indicating that a switching time of 10 ps with an external efficiency of 10 percent can be achieved.The paper also discusses the ultrafast optical nonlinearity due to virtual charge polarization caused during optical excitation of the quantum‐well structure by nonresonant light, and the physics and applications of utlrafast electric pulse caused by the nonlinerity. In addition, the possibility is discussed of optical detection without optical detection without optical absorption using the virtual excitation.

A novel low-loss inline bimodal-fiber tap: wavelength-selective properties

The tap described is a combination of two elementary devices: a low-loss (resonant) mode converter and a special fused-taper coupler. Efficient coupling of light for a narrow wavelength band (<10 nm) is demonstrated. The center-wavelength of the band can be selected by tuning the resonant condition for intermodal coupling in the mode converter. The uncoupled (nonresonant) light passes through the tap, exhibiting low excess loss (<0.2 dB). The tap has application in linearly tapped fiber optic distribution systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Particulates in aluminum sputtering discharges

Plasma-generated particulates are receiving increasing attention as a possible source of device yield reduction in plasma-assisted etching and deposition processes. We have investigated aluminum sputtering in argon discharges between parallel-plate aluminum electrodes under both direct current and radio frequency excitation. Pulsed laser-induced fluorescence experiments indicate that particulates containing aluminum form in these discharges under conditions in which aluminum sputtering takes place. Under sufficiently powerful laser excitation, the laser acts to dissociate the particles, resulting in an enhanced aluminum-atom laser-induced fluorescence signal. Spatial regions of atomic aluminum fluorescence enhancement coincide exactly with nonresonant light scattering profiles from a low-power helium-neon laser. The pulsed laser was observed to locally deplete particulates on a time scale of seconds. Particle profiles appear to evolve in the discharge on a time scale of tens of minutes to hours. The spatial profile of the particles depends in a sensitive manner on the applied voltage, as well as other discharge variables. At a sufficiently negative dc voltage applied to the cathode, particles were observed to be excluded from the interelectrode region.

Light induced transport and delocalization in transparent amorphous systems

We show that intense nonresonant light fields such as those present in optical fiber may cause localized electronic states to become extended. A threshold criteria is derived for the effect and its implications for change transfer in glasses is discussed. In addition we show that such effects may be important for understanding the yet unexplained efficient second harmonic generation which occurs in germanosilicate optical fibers.

Radiationless transitions and the quantum yield for nonresonant light scattering

The quantum yield for fluorescence can be defined as the ratio of the amount of light scattered as fluorescence or as Rayleigh or Raman scattering to the amount of light removed from an incident beam. Clearly then the quantum yield should go to one for a nonresonant excitation. The conventional theory of radiationless transitons (the Bixon–Jortner model) does not yield this result. We therefore postulate an intermediate state in the radiationless pathway. Then the model does yield the desired frequency dependence of the quantum yield. It may be that the arbitrary variation of the quantum yields of organic molecules may be due to the absence or presence of such an intermediate state.

Observation of continuous-wave self-oscillation due to pressure-induced two-wave mixing in sodium.

Collisional damping can induce a coupling between two nonresonant light beams propagating in an atomic vapor. This coupling is sufficiently important to induce a gain process for a weak probe beam interacting with an intense pump beam. We present here the first observation of a cw oscillation generated by this process using a cell which contains sodium and helium, the pump beam being slightly detuned from the ${\mathrm{D}}_{2}$ resonance line. We also show how the self-oscillation due to four-wave mixing is modified by the presence of a buffer gas.

Highly resolved structure in the formation of Na2+ions from multiphoton ionisation of Na2

The authors observed a highly resolved structure (0.07 AA) in the spectrum of Na2+ ions formed in a Na vapour (1.2*1013 cm-3) irradiated by an intense non-resonant laser light (5*106 W cm-2). It is clearly demonstrated experimentally, by superheating of the vapour, that the ion yield should be attributed to a molecular three-photon ionisation process resonantly enhanced by excited intermediate rovibrational levels of Na2.

Non-resonant light scattering in pyrazine and its quantum yield

The ratio of the fast to the slow component in the decay of the 1B 3u state of pyrazine is shown to vary strongly across the rotational manifold. In P(1) the fast component is absent, between the transitions it is dominant. Therefore, the excitation spectrum depends on the time the fluorescence is registered. The effects are due to non-resonant light scattering (NRLS), which because of its high quantum yield, shows up as unexpectedly strong. NRLS contributes to the fast component.