Non-Markovian dynamics in a dense atomic vapor

Two- and three-pulse photon echo spectroscopy in a dense potassium vapor reveals a non-Markovian correlation function of frequency fluctuations. Through comparison with calculations using an exciton picture a slowly-decaying component of the correlation function is attributed to long-range resonant interactions. A time-resolved photon echo experiment shows the photon-echo-like behavior at short timescales.     

Infrared spectroscopy of a dense potassium vapor jet

In this paper we report the development of new apparatus for the containment and study of dense alkali metal vapors, and the use of the apparatus to study the infrared spectra of potassium vapor. The apparatus is the first to employ aerodynamic confinement of a dense alkali vapor. We have recorded absorption spectra, thermal emission spectra, and laser-induced emission spectra of dense potassium vapor. These techniques all reveal a spectral feature near 1.1 μm which we believe originates in ³Σ⁺_g→³Σ⁺_u transitions of the K₂ molecule.     

Ultrafast optical spectroscopy of large-momentum excitons in GaAs

Highly energetic excitons with wave vectors much larger than that of an absorbed photon are excited in thin GaAs films. We observe propagation beats between three polariton modes up to 300 meV above the absorption edge employing femtosecond transmission spectroscopy. The dispersion relations of the coherent excitations are measured. Ultrafast exciton damping via scattering with nonequilibrium carriers and with phonons is investigated. The dynamics is found to deviate strongly from the relaxation of free carriers. Theoretical simulations are in quantitative agreement with the data.     

Diode laser noise-spectroscopy of low-frequency atomic fluctuations in rubidium vapor

We have observed resonant features in the spectrum of the fluctuations of a linearly polarized diode laser beam transmitted through a rubidium vapor cell, corresponding to the evolution of the atomic spin in the presence of a constant magnetic field. The observed resonances occur at a noise frequency corresponding to twice the Larmor frequency of ground state rubidium atoms and are due to two-photon Raman processes involving the carrier frequency and the noise sideband. We observed noise resonances for frequencies of the order of one MHz via heterodyne detection. Due to nonlinear Faraday rotation, we detected emitted light with polarization orthogonal to the incident field. The influence of the laser light fluctuations on the transmitted light noise spectrum was investigated by using two diode laser sources with different spectral bandwidths. The observed features are in qualitative agreement with a semiclassical theoretical model that treats laser fluctuations up to first order.     

Adiabatic frequency conversion of optical information in atomic vapor

We experimentally demonstrate a communication protocol that enables frequency conversion and routing of quantum information in an adiabatic and thus robust way. The protocol is based on electromagnetically induced transparency (EIT) in systems with multiple excited levels: transfer and/or distribution of optical states between different signal modes is implemented by adiabatically changing the control fields. The proof-of-principle experiment is performed using the hyperfine levels of the rubidium D1 line.     

薄原子蒸汽膜的双光子光谱及Dicke窄化

薄原子蒸汽膜的单光子Dcike窄化吸收光谱可以拓展到双光子情形，以级联三能级系统为例,从理论上得到了亚多普勒结构的双光子吸收光谱，其线型表现出和单光子过程相似的与膜厚和探测光波长的比值(L/λ)相关的周期性.当L/λ=(2n+1)/2(膜厚为半波长的奇数倍)时，吸收谱线窄化现象明显.当L/λ=2n/2(膜厚为半波长的偶数倍)时，单光子情形的谱线窄化现象消失，而双光子情形的谱线仍表现为亚多普勒结构，尤其在异侧入射的情形下，可以获得极窄的双光子谱线结构. 这种结构来自原子与腔壁碰撞的消激发效应和双光子过程的抽运-探测机制的贡献. 关键词： 薄原子蒸汽膜 双光子光谱 Dicke窄化     

Random scattering by atomic density fluctuations in optical lattices

We investigate hitherto unexplored regimes of probe scattering by atoms trapped in optical lattices: weak scattering by effectively random atomic density distributions and multiple scattering by arbitrary atomic distributions. Both regimes are predicted to exhibit a universal semicircular scattering line shape for large density fluctuations, which depend on temperature and quantum statistics.     

Hybrid optical pumping of optically dense alkali-metal vapor without quenching gas

Optical pumping of an optically thick atomic vapor typically requires a quenching buffer gas, such as N2, to prevent radiation trapping of unpolarized photons which would depolarize the atoms. We show that optical pumping of a trace contamination of Rb present in K metal results in a 4.5 times higher polarization of K than direct optical pumping of K in the absence of N2. Such spin-exchange polarization transfer from optically thin species is useful in a variety of areas, including spin-polarized nuclear scattering targets and electron beams, quantum-nondemolition spin measurements, and ultrasensitive magnetometry.     

Non-Markovian dynamics in a dense potassium vapor

Transient four-wave mixing experiments on a dense potassium vapor, which has a dephasing time long compared to the collision duration, reveal distinct signatures of non-Markovian dynamics. Theoretical fits assuming stochastic fluctuation of the excited-state frequencies confirm that the two-time correlation function has a finite temporal width.     

On the hyperfine spectral lines of an atomic copper vapor laser

The hyperfine structure of energy levels of copper atom and its transition probabilities were considered. The resonance and metastable levels of the copper atom are split into hyperfine structures, due to the magnetic dipole moment and the electric quadrupole moment. In this paper, a succinct introduction to the relevant theory of the hyperfine spectral structure and experimental observations of elemental copper vapor laser is presented.     

Stroboscopic backaction evasion in a dense alkali-metal vapor

We explore experimentally quantum nondemolition measurements of atomic spin in a hot potassium vapor in the presence of spin-exchange relaxation. We demonstrate a new technique for backaction evasion by stroboscopic modulation of the probe light. With this technique we study spin noise as a function of polarization for atoms with spin greater than 1/2 and obtain good agreement with a simple theoretical model. We point that, in a system with fast spin exchange, where the spin-relaxation rate is changing with time, it is possible to improve the long-term sensitivity of atomic magnetometry by using quantum nondemolition measurements.     

Theoretical and experimental treatment of the spectral interferences in atomic absorption spectroscopy

Spectral line interference may occur in atomic absorption spectroscopy, when there is a significant overlap of the emission line profile with the absorption line profiles of any interfering species in the flame. The presence of the spectral interference can cause errors in the measurements of the net absorbance, and in the background correction.Both theoretical calculations and experimental observations reported in this paper provide a remark of this interference effect. It can be concluded from the experimental results, that the spectral interference is located close to the resonance wavelength of the analyte.Two different examples representing various types and degrees of spectral interference are discussed.     

Resonance luminescence of a nonuniformly heated dense vapor

The thermal luminescence spectra of a dense, nonuniformly heated resonance medium (sodium vapor) are investigated experimentally under conditions when the resonance corrections to the relative permittivity are not small compared to unity and the photon mean free path is comparable to the wavelength of the radiation. The shape of the recorded spectra agrees well with a previously developed general theory of resonance radiation transfer which predicts a strong asymmetry of the spectra. The prospects for performing more-sensitive measurements in order to make a quantitative check of the theoretically predicted anomalous intensity (an order of magnitude higher than in the standard theory of resonance radiation transfer) of the radiation from a dense nonuniform medium are discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 1, 15–19 (10 January 1997)     

Ultrafast spectroscopy of metals

Application of time-resolved femtosecond spectroscopy to the investigation of the ultrafast electron kinetics in metallic materials is reviewed. The main experimental techniques are presented and the results obtained on electron scattering processes discussed in bulk metals and nanoparticles, focusing on the energy redistribution processes (electron–electron and electron–phonon coupling) and electronic transport. Application of the femtosecond techniques to the investigation of the acoustic vibrations of metal films and nanoparticles is also presented.     

Ultrathin atomic vapor film transmission spectroscopy: analysis of Dicke narrowing structure

Transmission sub-Doppler spectroscopy with confined atomic vapor film between two dielectric walls is theoretically studied. Because of atoms flying from wall to wall, where they get de-excited, the atomfield interaction time is anisotropic so that the contribution of slow atoms is enhanced, a sub-Doppler transmission spectroscopy (Dicke narrowing effect) can be obtained when the thickness of the film is much small or comparable with the wavelength even at small angle oblique incidence. It is feasible to get a sub-Doppler structure in a new region (L ＜λ/4) in experiments.     

Ultrafast laser system based on noncollinear optical parametric amplification for laser spectroscopy

We report the experimental demonstration of transform-limited sub-6 fs pulses at an optimal central wavelength by a tunable noncollinear optical parametric amplification(NOPA) source. Meanwhile, a white light continuum in the near-infrared(NIR) range from 900 to 1100 nm is also successfully generated by focusing the unconverted800 nm beam during NOPA generation on a sapphire rod. Both visible-pump/visible-probe and visible-pump/NIR-probe experiments are realized using the same laser system. As examples, ultrafast photo-induced exciton dynamics inside two kinds of materials are investigated by the visible-pump/visible-probe and visible-pump/NIR-probe spectroscopy, respectively.     

Ultrafast relaxation of excited Dirac fermions in epitaxial graphene using optical differential transmission spectroscopy

We investigate the ultrafast relaxation dynamics of hot Dirac fermionic quasiparticles in multilayer epitaxial graphene using ultrafast optical differential transmission spectroscopy. We observe differential transmission spectra which are well described by interband transitions with no electron-hole interaction. Following the initial thermalization and emission of high-energy phonons, the electron cooling is determined by electron-acoustic phonon scattering, found to occur on the time scale of 1 ps for highly doped layers, and 4-11 ps in undoped layers. The spectra also provide strong evidence for the multilayer structure and doping profile of thermally grown epitaxial graphene on SiC.