Quantum interference spectra at the difference-frequency generation in four-level atomic systems

Analytical expressions of the spectral functions have been derived for a number of induced excitations that occur near the difference-frequency generation in a four-level atomic system interacting with three laser fields. The spectral heights and subnatural line widths of the induced peaks depend on the intensities of the laser fields involved. The maximum heights of the induced peaks take positive, zero and negative values, indicating that the processes of absorption (attenuation), dark resonance and stimulated emission (amplification) are likely to occur near the difference-frequency generation, respectively. Received: 15 March 2002 / Revised version: 17 June 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +1-613-954-5242     

Propagation of light-pulses at a negative group-velocity

This paper deals with the apparent superluminal propagation of electromagnetic pulses in a linear dispersive medium. One specifically examines the possibility that the pulse leaving the medium may be nearly identical to the incident one (low distortion) and in significant advance of it (strongly negative group-delays). Favourable conditions are obtained in a dilute medium where the required anomalous dispersion originates in an ensemble of narrow absorption or gain lines. Analytical expressions of the advancement of the pulse centre-of-gravity and of the lowest order distortion are established from the transfer-function of the medium. The experiments already achieved with arrangements involving a single absorption-line or a gain-doublet are analysed in detail and compared. The considerable difficulties to overcome in order to attain advancements comparable to the pulse width without important distortion are pointed out. New and promising schemes involving a narrow dip in a gain profile or absorption-doublets are proposed. Received 4 July 2002 / Received in final form 8 November 2002 Published online 4 February 2003 RID="a" ID="a"e-mail: bruno.macke@univ-lille1.fr RID="b" ID="b"Unité Mixte de Recherche de l'Université et du CNRS (UMR 8523)     

Absorption spectrum of a resonantly driven degenerate V-type atom with a dc-field coupling between excited states

We study the absorption spectra of a degenerate V-type atom, where a resonant driving field and a probe field drive different branches of transitions and a dc field is applied to drive the transition between two excited states. The effects of vacuum induced coherence (VIC) on the absorption spectra are investigated. It is demonstrated that in some special cases the VIC can lead to the depression of absorption and narrow resonance. The origin of these features are discussed. When the pump field and the dc field have the same intensity, it is interesting to find that the whole absorption spectrum comes mainly from the absorptions induced by the interferences among different transitions between dressed states.     

Boundary reflection from curved liquid surfaces and its application

A boundary light reflection from curved liquid surfaces was discovered. Due to the wetting effect, the liquid surface near the plate which was inserted into the liquid was deformed. When a collimated light beam vertically illumined the curved liquid surface, special reflective patterns of a strip-shape dark region in the center and the visibility interference fringes on both sides was observed for the up-curved liquid surface. The width of the dark region increases with the decreasing width of the incident beam. The relation of the dark region width and the incident beam width was derived theoretically. The slope and the height of curved liquid surface were obtained directly from measuring the dark central region width of the reflection pattern and the incident beam width. Furthermore, the analytic expression of the profile of the curved liquid surface was derived. As a result, it shows that an effective and practical technique for measuring the characterization of curved liquid surface was found.     

Development of the Technique for Fabricating Submicron Moire Gratings on Metal Materials Using Focused Ion Beam Milling

A focused gallium ion （Ga＋） beam is used to fabricate micro/submicron spacing gratings on the surface of porous NiTi shape memory alloy （SMA ）. The crossing type of gratings with double-frequency （25001/mm and 50001/mm） using the focused ion beam （FIB） milling are successfully produced in a combination mode or superposition mode. Based on the double-frequency gratings, high-quality scanning electron microscopy （SEM） Moird patterns are obtained to study the micro-scale deformation of porous NiTi SMA. The grating fabrication technique is discussed in detail. The experimental results verify the feasibility of fabricating high frequency grating on metal surface using FIB milling.     

Local Modulation of Double Electromagnetically Induced Transparency Spectrum

The double electromagnetically induced transparency induced by two coupling fields can be realized in a fourlevel tripod-type atom. Such double transparency spectra can be locally modulated by using the weak coherent fields to perturb the coupling transitions. These investigations within this scheme can be independent of Doppler broadening by properly orienting these fieds.     

Detection of surface acoustic waves by scanning tunneling microscopy

A new method for the investigation of ultrasonic waves on surfaces of solids based on scanning tunneling microscopy is presented. A sinusoidal high frequency signal is added to the tip voltage. Hence the tunneling current contains a component whose frequency is the difference of the frequencies of the acoustic wave field and the ac tip voltage. Amplitude and phase of this component carry the full information about the wave field.     

Enhancement and Suppression of Four-Wave Mixing in a Four-Level Atomic System

We report observations of the enhancement and suppression of four-wave mixing （FWM） in an electromagnetically induced transparency window in a Y-type ^85 Rb atomic system. The results show the evolution of the dressed effects （from pure enhancement to partial enhancement/suppression, and finally into pure suppression） in the degenerate-FWM processes. Moreover, we use the perturbation chain method to describe the FWM process. Finally, we observe the polarization dependence of the enhancement and suppression of the FWM signal.     

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 （C4oH82） 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 400μs is obtained.     

Spin Hall effect of light in one-dimensional photonic crystal

We established a general propagating model to investigate the spin Hall effect of light in one-dimensional photonic crystal. A polarized (spin dependent) Gaussian beam which was incident obliquely through one-dimensional photonic crystal was demonstrated. Having decomposed a polarized Gaussian beam into different plane wave components charactering individual wave vectors, we revealed the transmission coefficient and reflection coefficient of each plane wave which propagates through the one-dimensional photonic crystal. It enabled us to obtain exact solution to the electric field of transmitted and reflected beams, and the analytical formula of light intensity, accordingly. A method based upon the partial differentials with the intensity distribution of the transmitted and reflected Gaussian beams was presented to determine the transverse and longitude shifts explicitly. Spin dependent shifts in one-dimensional photonic crystal provide alternative evidence for the spin Hall effect of light.