We investigate coherent accumulation processes in three-level atoms excited by a train of ultrashort pulses the case where atomic relaxation times are greater than laser repetition period. In this situation resonances field with system determined frequency comb rather spectrum single pulse. Using density matrix formalism, we develop perturbative theory that is valid for arbitrary pulse shapes. The excitation Doppler-broadened vapor hyperbolic-secant and $0\ensuremath{\pi}$ analyzed. It shown...

An experimental investigation of the coherent interaction femtosecond pulses with two resonant sequential transitions Rb atoms is presented. Fluorescence from atomic system exhibits beating at a frequency given by difference in transitions. The results are interpreted terms quantum interference induced coherence and its field that cooperative emission process.

We study the field intensity fluctuations of two independent four-wave mixing signals generated in a cold rubidium sample as well transmission signals. employ an experimental setup using single CW laser to induce nonlinear process forward geometry either parallel and circular or orthogonal linear polarizations input fields. Even though spectra each configuration are significantly different due distinct level structures scenario, both cases present intensit-intensity cross-correlation also...

This study aimed to test the hypothesis that organic volume is main variable for explaining optical properties and predictive degree of diffusion enamel histological points at zones natural caries (NEC; surface layer, SL, n = 30, body lesion, BL, 58) normal (NE, 131). Molars with either NEC or NE were quantitatively analyzed regarding mineral, water volumes (considered as effective pore volume), opacity (predicted in 94% cases by NEC), more easily available diffusion,...

This paper analyzes the result of a temporal coherent control experiment using trains ultrashort laser pulses in situation where repetition period is smaller than relaxation times system. We focus on accumulative effects present sequential two-photon absorption. It shown that stimulated emission due to accumulation population excited state give an important contribution coherently controlled process. Excellent agreement obtained comparison between experiments rubidium vapor and theory,...

Summary The main problem in interpreting birefringence of dental enamel under polarizing microscopy is the lack physical constants able to allow Wiener equation be applied directly composition such tissue. present study introduces a new approach circumvent this constraint. Because nonmineral phase heterogeneous, its refractive index can computed terms components (namely, water, which partially replaced by immersion medium, and organic matter), thereby providing more acceptable used equation....

We use a 1 GHz femtosecond laser as tool to perform coherent spectroscopy in an atomic vapor. The action of the ultrashort pulse train over various velocity groups or selective group rubidium atoms is probed by diode using velocity-selective repetition rate spectroscopies. In particular, we show that frequency separation modes comb allows distinguishing different hyperfine levels within Doppler broadened profile. data are good agreement with numerical and analytical results.

We report on observations of four-wave mixing in rubidium vapor via two-photon resonant excitation with nd and (n+2)s states, for n=14–20. The intensity the generated beam is studied a collinear configuration, results are consistent predictions theoretical model based semiclassical Maxwell–Bloch equations, considering interference effects associated multiple pathways internally fields. have also observed spectral broadening lines, which well described by linear dependence atomic density,...

We present new results on the coherent control of a four-wave mixing signal in rubidium vapor involving Rydberg levels. By varying relative polarizations laser beams responsible for nonlinear process, we atomic excitation routes and thus quantum interference medium. observed fringes as function further developed theoretical model based density-matrix formalism that is very good agreement with our experimental results.

Summary The aim of this study is to extend, for a larger range mineral volume ( V 1 ) and different aqueous immersion media, the model calculating refractive index non‐mineral phase human dental enamel proposed by Sousa et al . Published experimental birefringence data carious developing in air media with indexes were interpreted. For 48%≤ ≤ 95%, quantitative estimates on contents consistent values described literature derived. New polynomial relationships as function content (48%≤ 95%) are...

We present an analysis of coherent population trapping in a three-level Λ system when excited by ultrashort pulse train near the one- and two-photon resonances. Numerical results using Bloch equations give transient response clearly reveal comb electromagnetically induced transparency (EIT) lines. An analytical solution to describe EIT lines is derived steady-state regime weak field limit. Moreover, numerical indicate that selective velocity spectroscopy makes possible observation Doppler...

Application and development of new methods in caries prevention is paramount importance to reduce the incidence chronic cases disease preserve dental structure. In this work, we tested nanosecond pulsed Nd:YAG laser on enamel surface examining changes laser-induced by means SEM, EDS, FTIR. SEM revealed, existence melted zone bubble inclusions when 40 J/cm 2 (τ=6 ns, 5 Hz) was applied human sound surface. The morphological alteration 10 20 (τ=200 7 no presented melting aspect, but a greater...

We present a theoretical analysis of the spatial shape two symmetric signals degenerate four-wave mixing induced by Gaussian beams in thin sample two-level atoms. Our calculations take into account full and spectral dependencies relevant nonlinear susceptibilities that govern processes. This reveals interesting effects. The first one is total power incident affects transverse profile at medium exit their free propagation. second influence characteristics on longitudinal both generated upon...

We have employed a sample of cold cesium atoms in magneto-optical trap to study nonlinear spectroscopy and four-wave-mixing optical phase conjugation using noncycling transition. Reflectivities the order 1% been measured for moderate levels pump power large angular aperture. In particular, we performed three-level V-type system observed directly ac Stark splitting ${6\mathrm{S}}_{1\mathrm{/}2}$, F=4 ground state.

Optical-pumping-induced population-grating transfer between hyperfine levels of the cesium ${D}_{2}$ line is observed through four-wave mixing in a sample cold atoms. Diffraction efficiencies order 1% have been measured for large range angular apertures. We studied dependence diffracted signal limit small atomic velocities and discussed its application nondestructive diagnostic trap dynamic. Image processing with nearly degenerate frequency conversion was also demonstrated using this...

We report on the combined action of a cw diode laser and train ultrashort pulses when each them drives one step 5S-5P-5D two-photon transition in rubidium vapor. The fluorescence from 6P_{3/2} state is detected for fixed repetition rate femtosecond while cw-laser frequency scanned over D_{2} lines. This scheme allows velocity selective spectroscopy large spectral range including 5D_{3/2} 5D_{5/2} states. results are well described simplified domain picture, considering interaction group with...

The storage of broadband single photons from a parametric-down-conversion source is capability with the potential to foster significant development in field quantum information. A particular challenge this problem, however, mismatch between short-lived photon and long-lived memories, which translates into quite different frequency bands for two systems. Ultimately, difficulty can be mapped problem how narrowband medium efficiently absorb pulse light. Here we present detailed approach...

An unexpected interference effect between four-wave mixing excitation routes in rubidium vapor is observed using a combination of cw diode laser and 1-GHz femtosecond pulse train. The generated coherent blue light analyzed by scanning the frequency repetition rate comb. In both cases, induces an Autler-Townes splitting, large separation doublet structure due to configuration copropagating fields. Remarkably, rate, narrow peak appears as signature interfering pathways. A nonperturbative...

We report the investigation of a collimated blue light generated in rubidium vapor due to combined action an ultrashort pulse train and cw diode laser. Each step two-photon transition 5S - 5P$_{3/2}$ 5D is excited by one lasers, induced coherence between 6P$_{3/2}$ states responsible for generating beam. Measurements excitation spectrum reveal frequency comb structure, indicating that each individual mode inducing nonlinear process. The strong signal dependency on atomic density...

We have observed an interference in four-wave mixing involving two Rydberg states that play the key role of near two-photon resonant intermediate levels. This interference, due to coherence nonlinear process, can be explained either classically or quantum mechanically and it depends on lasers' polarizations detunings. performed calculations are very good agreement with experimental data. Our results provide new information about system, such as ionization rates levels ratio reduced matrix...

Abstract We present experimental measurements showing the combination of orbital angular momentum (OAM) content incident light beams in two distinct processes degenerate four-wave mixing induced hot rubidium vapor. These processes, driven by same fields, must satisfy topological charge (TC) selection rules, which impose OAM conservation. rules are readily obtained from so-called overlap integral and allow us to control relations between nonlinear signals, particular, characterize conditions...

We investigate how tailoring the phase of optical field allows us to select different routes induced by time-delayed femtosecond pulse pairs exciting a two-photon transition in rubidium atoms. It is shown that introducing an external one pulses, pathways leading interferences can be eliminated, leaving only quantum interferences.