Strong Pump Laser Research Articles

Improvement of spectral resolution by using the excitation dependence of dipole–dipole interaction in a dense atomic gas

We have studied the selective reflection from the interface between a dense rubidium (Rb) atomic vapor and a transparent dielectric. A remarkable narrowing of the spectrum, which can be used to improve the resolution of spectroscopy of dense media, has been demonstrated. This narrowing results from the reduction of the dipole–dipole interaction between atoms when the Rb vapor is excited by a strong pump laser. By using this technique, we have resolved the hyperfine structure of the Rb D2 line, which is hidden by collisional broadening.

Velocity selective optical pumping and repumping effects with counter and copropagating laser radiations for D2 lines of rubidium

The effects of a strong control or pump laser, counter propagating or copropagating with the probe beam, on the probe absorption spectra of 85Rb and 87Rb-D2 transitions have been investigated inside a room temperature Rb vapour cell. In both cases a set of strong velocity selective resonance dips are observed at different velocities. Their movements across the Doppler broadened probe absorption profile have been studied for different lock frequencies of the control laser. These spectra are modified by optical pumping effects due to the presence of another hyperfine component of the ground state. A repumping laser, from the dark hyperfine component of the ground level transfers almost 75% of the atoms from the dark state to the pump probe cycle hence reducing the optical pumping effect. A numerical simulation is done to explain the observed spectra. The effect of a control laser on the Lamb dip spectrum of the probe laser has also been investigated. The control beam is used to improve the strength of a weak hyperfine dip on the Doppler broadened probe spectrum. The strength of the hyperfine dip increases by a factor of 3.2 in presence of the control laser. The observed dips show that pump-probe spectroscopy can be used as velocity selectors of atoms.

Continuous-wave supercontinuum laser based on an erbium-doped fiber ring cavity incorporating a highly nonlinear optical fiber

We experimentally demonstrate a novel erbium-doped fiber based continuous-wave (cw) supercontinuum laser. The laser has a simple ring-cavity structure incorporating an erbium-doped fiber and a highly nonlinear dispersion-shifted fiber (HNL-DSF). Differently from previously demonstrated cw supercontinuum sources based on single propagation of a strong Raman pump laser beam through a highly nonlinear fiber, erbium gain inside the cavity generates a seed light oscillation, and the oscillated light subsequently evolves into a supercontinuum by nonlinear effects such as modulation instability and stimulated Raman scattering in the HNL-DSF. High quality of the depolarized supercontinuum laser output with a spectral bandwidth larger than 250 nm is readily achieved.

Velocity-selective resonance dips in the probe absorption spectra of Rb D 2 transitions induced by a pump laser

We report experimental observation of velocity-selective resonances in the Doppler-broadened probe absorption spectra of 85Rb and 87Rb D 2 transitions in the presence of a strong co-propagating pump laser locked to a frequency within the Doppler profile of the transition. The set of three dips having the separation of allowed hyperfine transitions move along the Doppler profile while the pump laser frequency is tuned. This indicates a resonance between the pump laser frequency and the velocity shifted probe laser frequency.

Anomalous electromagnetically induced transparency in photonic-band-gap materials

The phenomenon of electromagnetically induced transparency has been studied when a four-level atom is located in a photonic band gap material. Quantum interference is introduced by driving the two upper levels of the atom with a strong pump laser field. The top level and one of the ground levels are coupled by a weak probe laser field and absorption takes place between these two states. The susceptibility due to the absorption for this transition has been calculated by using the master equation method in linear response theory. Numerical simulations are performed for the real and imaginary parts of the susceptibility for a photonic band gap material whose gap-midgap ratio is 21%. It is found that when resonance frequencies lie within the band, the medium becomes transparent under the action of the strong pump laser field. More interesting results are found when one of the resonance frequencies lies at the band edge and within the band gap. When the resonance frequency lies at the band edge, the medium becomes nontransparent even under a strong pump laser field. On the other hand, when the resonance frequency lies within the band gap, the medium becomes transparent even under a weak pump laser field. In summary, we found that the medium can be transformed from the transparent state to the nontransparent state just by changing the location of the resonance frequency. We call these two effects anomalous electromagnetically induced transparency.

Generation of optical vortices using light-induced phase mask in a V-type system

We experimentally demonstrated that optical vortices with opposite charges could be generated on a probe beam transmitted through a medium composed of rubidium atoms with V-type energy levels when the refractive index of the medium was modified by a strong pump laser beam with an L-shape intensity distribution.

Entanglement in a Bose–Einstein condensate by collective atomic recoil

We address the interaction between a Bose–Einstein condensate and a single-mode quantized radiation field in the presence of a strong far off-resonant pump laser. The generation of atom–atom and atom–field entanglement is demonstrated in the linear regime. The effects of cavity losses are taken into account and an analytic solution of the corresponding master equation is given in terms of the Wigner function of the system.

Radiation to atom quantum mapping by collective recoil in a Bose–Einstein condensate

We propose a scheme to realize radiation to atom continuous variable quantum mapping, i.e., to teleport the quantum state of a single mode radiation field onto the collective state of atoms with a given momentum out of a Bose–Einstein condensate. The atoms-radiation entanglement needed for the teleportation protocol is established through the interaction of a single mode with the condensate in the presence of a strong far off-resonant pump laser, whereas the coherent atomic displacement is obtained by the same interaction with the radiation in a classical coherent field.

X-ray Compton FEL based on charged particles channeling in a crystal

The scheme of X-ray coherent radiation generation by means of a mildly relativistic, high-density, channeled particle beam and a strong counter-propagating pump laser field is investigated. The self-consistent set of Maxwell and relativistic quantum kinetic equations in the high-gain regime are solved.

Nonlinear quantum regime of the x-ray Compton laser.

In this work a scheme of x-ray coherent radiation generation in the nonlinear quantum regime by means of mildly relativistic high density electron beams and a strong pump laser field is investigated. The consideration is based on a self-consistent set of Maxwell and relativistic quantum kinetic equations. The coupled equations are solved in the slowly varying envelope approximation.

EXPERIMENT AND THEORY ON DIFFRACTION FROM LASER-INDUCED PHASE-HOLE IN POLYMER FI LM

Concentric diffraction rings with bright center in the far field and dark center in the near field of the probe beam were experimentally observed when a strong pump laser beam (526nm) and a weak probe laser beam (632.8nm) cross under the no nlinear medium film (Polypyrrylarylenemethine/polyvinyl film).Based on Fresnel-K irchhoff diffraction integral equation,this phenomenon can be explained by the d iffraction effect of the probe beam from the laser-induced phase-hole in the non linear medium caused by the pump beam.The numeric calculations give good agreeme nt with the experimental results.

Stochastic Schrödinger equation. II. A study of the coherence seen in pump-probe experiments that use a strong pump laser

We use the stochastic Schrödinger equation approach to examine an experiment performed by Scherer, Jonas, and Fleming [J. Chem. Phys. 99, 153 (1993)]. They have excited I2 molecules dissolved in n-hexane with a strong, ultrashort pump pulse. This creates moving wave packets on both the excited and the ground electronic states. The coherent motion of these packets is studied by measuring the absorption of a weak probe pulse, as a function of the delay time between the pulses. We show how the oscillations in the signal are connected to different excitation mechanisms and to the interference between various packets created by the lasers. Our purpose is to clarify the dynamics of the packets and to show that the stochastic Schrödinger equation approach can be used to study their decoherence. We did not intend to try to develop a realistic model for the I2 dynamics and its interaction with the solvent and do not perform a detailed comparison with the experiment. Nevertheless, the calculations reproduce, semiquantitatively, the observations.

Quantum optics of a Bose-Einstein condensate coupled to a quantized light field

We consider the interaction between a Bose-Einstein condensate and a single-mode quantized light field in the presence of a strong far off-resonant pump laser. The dynamics is characterized by an exponential instability, hence the system acts as an atom-photon parametric amplifier. Triggered by a small injected probe field, or simply by quantum noise, entangled atom-photon pairs are created which exhibit non-classical correlations similar to those seen between photons in the optical parametric amplifier. In addition, the quantum statistics of the matter and light fields depend strongly on the initial state which triggers the amplifier. Thus by preparing different initial states of the light field, one can generate matter waves in a variety of quantum states, demonstrating optical control over the quantum statistics of matter waves.

Saturation of the weak probe amplification in a strongly driven cold and dense atomic cloud

We present an experimental and theoretical investigation of the weak probe amplification in a cold and optically thick atomic cloud that is highly driven by a strong pump laser. We find that for high optical densities the probe amplification is strongly saturated. We compare our saturation measurements with a model based on dressed-atom population equalization due to re-scattering of spontaneous emission. Good agreement between theory and experiment is obtained only when corrections due to multiple scattering are included.

Dressed-atom spectroscopy of cold Cs atoms

Absorption spectra of cold Cs atoms in a magneto-optical trap under the influence of a strong external pump laser field with arbitrary detuning and intensity have been systematically investigated. The spectra featured the Rabi sidebands of each transition, and their behavior was nicely fitted by the dressed-atom theory. A pronounced dispersion-type profile with sub-natural linewidth at the pump frequency may be attributable to the stimulated Raman process by sublevels that are lightshifted and optically pumped by the pump laser.

Pump-probe spectroscopy of solids with excitation dependent dephasing

The paper provides a new example of the failure of optical Bloch equations in the description of coherent excitation of solids. We consider the absorption spectra of the modulation side bands of a strong pump laser beam in low-temperature solids. The influence of the pump on the impurity-ion dipole dephasing is taken into account. It is shown that a rectangular shaped hole is restored in the absorption spectrum when the Rabi frequency exceeds the fluctuation rate of the local random field responsible for the impurity-ion dephasing.

Interference phenomena in two-photon transitions caused by laser-induced ac-Stark effect

A system is described in which a real molecular state is tuned into and out of resonance with the intermediate level of a two-photon transition, by the laser-induced ac-Stark effect. Two narrow-band CO2 wave-guide lasers are utilized to induce rovibrational transitions in the ν3 ladder of SF6. A weak probe laser monitors the absorption for the [Formula: see text] two-photon transition. Simultaneously, a strong pump laser is in resonance with the [Formula: see text] one-photon transition. The ac-Stark splitting is observed and quantum interferences between two-photon amplitudes involving different intermediate states occur. It is demonstrated that destructive interference allows suppression of the two-photon excitation for an appropriate pump laser power. Simulations based on the Dressed State Picture and the optical Bloch equations show a satisfactory agreement with the experiment.

K2optically pumped lasers using temporally delayed pulses in the counterintuitive sequence

We report increased stimulated emission on some optically pumped laser transitions coupled to suppressed stimulated emission on other transitions when a weak Stokes laser beam and a strong pump laser beam interact with K2 molecules in the counterintuitive sequence. The Stokes laser photons begin to interact with the K2 molecules 3 to 4 ns before the pump laser photons can interact with the K2 molecules. Both the Stokes and the pump laser pulses last for approximately 5 ns and the suppressed and enhanced stimulated emissions coincide with the pump laser pulse. The stimulated emissions described in this paper propagate parallel to the Stokes and pump laser beams.

Nonlinear switching in semiconductor (CdSSe) doped glass

Optical nonlinear switching due to increasing absorption has been observed in a nondegenerate pump and probe experiment in Semiconductor (CdSSe) Doped Glass (SDG). With the proper choice of the parameters, like modulation frequency and light intensity, one hundred percent modulation in a probe laser induced by a strong pump laser was obtained at room temperature. Two nonlinear regimes were observed, with saturated pump absorption being dominant at high pump power.

Resonant excitation of electron-hole pairs in semiconductors: A simplified model.

A simple two-band model of a semiconductor in the presence of an arbitrarily strong pump laser is considered. Restricting the excitation strength to a finite part of the sample leads to a qualitative difference between resonant and nonresonant excitation of electron-hole pairs. For noninteracting electrons the dynamics can be solved exactly in the framework of scattering theory. Optically induced band gaps only show up in the local density of states in the excitation region. A sharp momentum selection rule for increasing excitation region only occurs for small excitation strength, while for larger excitation strength the weakening of the momentum selection rule is related to the width of the optically induced band gap in the infinite system.