Zur Theorie der nichtstationären Resonanzfluoreszenz an bewegten Molekülen. II. Untersuchungen zur hochauflösenden Resonanzfluoreszenzspektroskopie

Non-stationary Theory of Resonance Fluorescence for Moving Molecules. II. Highly Resolved Fluorescence Spectroscopy With respect to tke Doppler-effect a formula for the spectral energy density of fluorescence radiation of gases (vapours) generated by resonance scattering of short laser pulses is derived. The spectral energy density consists of a coherent and an incoherent part which differs in a characteristic way. The coherent fluorescence radiation reproduces the spectrum of the laser light. Informations about the homogeneous line widths are obtained only from the incoherent spectra. The results of numerical calculations of highly resolved spectra in forward and backward directions under different conditions are discussed.     

Effect of quantum interference processes on the angular distribution of the spontaneous radiation in the D line of alkali-metal vapors in a laser wave field

The resonance fluorescence of a degenerate V-type three-level atom in the field of an intense monochromatic wave with arbitrary polarization composition is investigated. The equations of motion, the general form of the radiation relaxation operator, and the analytical expressions for the angular distribution of the intensity of the spontaneous radiation from atoms, and the total intensity of the resonance fluorescence for such systems are obtained. The angular distribution of the spontaneous radiation from atoms for the D line of alkali-metal vapors is investigated. It is predicted theoretically that the intensity of the resonance fluorescence will decrease as the intensity of the pump wave increases in observations in a direction of the electric field vector of the laser wave.     

The influence of quantum interference effects on the resonance fluorescence spectra of a degenerate three-level atom

The resonance fluorescence spectra of a degenerate three-level atom of the V-type in the field of an intense monochromatic wave with an arbitrary polarization composition are investigated. Analytical expressions are derived for the resonance fluorescence spectra, and the angular distribution of spontaneous fluorescence of atoms is analyzed for the D-line emitted by vapors of alkali atoms. It is shown that the number of lines in the spectrum may decrease in the case of the linear polarization of spontaneous radiation. The radiation relaxation operator is obtained for the D-line of alkali metals in the case when an atom is near the metal surface. Interference effects for such systems are analyzed.     

Zur Theorie der nichtstationären Resonanzfluoreszenz an bewegten Molekülen. I Räumliche Energiedichte der Fluoreszenzstrahlung

Non-stationary Theory of Resonance Fluorescence for Moving Molecules. I. Spatial Energy Density of the Fluorescence Radiation The time dependence of the spatial energy density of the fluorescence radiation of an ensemble of moving molecules generated by resonance scattering of intense laser pulses is calculated. Particulary the influence of the duration and the intensity of short laser pulses upon the coherent and incoherent part of the fluorescence radiation of a Doppler-broadened gas is studied. The validity of the conception ?inhomogeneous relaxation time”? is discussed. Within the framework of resonance fluorescence scattering the phenomenon of photon echo is treated.     

Die kinetischen Eigenschaften der Elektronen des anisothermen homogenen stationären Neon-Plasmas im Ionisierungsgradbereich von 10−9 bis 10−2

The time dependence of the spectral and spatial energy density of the fluorescence radiation of an atomic system generated by the resonance scattering of an intense laser pulse was calculated. Particularly the influence of the duration and the intensity of the incident laser pulse and of the atomic relaxation constants upon the fluorescence radiation has been studied.     

Investigation of amplified spontaneous X-ray laser radiation using the equation for the transverse correlation function of the field

A physical model, based on the solution of the quasi-optics equation for the transverse correlation function (TCF) of the field amplitude, is developed for investigating the brightness, angular divergence, and spatial coherence of the amplified spontaneous emission in a laboratory X-ray laser. The model takes account of the spontaneous source of radiation, diffraction, regular refraction, regular amplification taking account of saturation, nonresonance absorption, scattering by small-scale fluctuations of the electron density and the gain, and scattering by random hose-like deviations of the extended plasma medium of the X-ray laser. It is established that the TCF method makes it possible to obtain the final result much more quickly than the basic Monte Carlo method for the parabolic equation for the field amplitude. As a result of the statistical linearization of the equation for the transverse correlation function in the presence of gain saturation, this method overestimates the absolute values of the average intensity of the amplified spontaneous radiation, but the maximum overestimation does not exceed 10%. It is found that fluctuations of the optical parameters of the medium of the X-ray laser degrade the quality of the amplified spontaneous radiation beam, and they are the analog of the nonresonance absorption from the standpoint of the effect on the brightness of the laser and therefore decrease the observed gain. For the characteristic conditions of an X-ray laser with a quasistationary generation scheme, the contribution of small-scale gain fluctuations and random hose-like deviations of the plasma filament of the laser to the scattering of the amplified spontaneous radiation is much smaller than the contribution of small-scale density fluctuations. Calculations of the amplified spontaneous radiation in an X-ray laser, which is produced by unilateral irradiation of a curved target and possesses an asymmetric plasma electron density profile in the gain zone, are performed. It is shown that in the gain saturation regime the coherence length and the coherent power of the amplified spontaneous radiation can be substantially increased, realizing in the gain zone a convex electron density profile instead of a typical concave profile. It is found that this improvement of the coherence occurs only under conditions such that the characteristic depth of the small-scale density fluctuations does not exceed several percent of the typical regular values of the density in the gain zone.     

准波导结构下染料薄膜的荧光光谱和放大自发辐射光谱特性

通过对RhB/PMMA和Rh6G/PMMA染料薄膜的荧光光谱和放大自发辐射(ASE)光谱的实验测量和理论分析,研究了准波导结构染料薄膜的荧光光谱和ASE光谱特性。实验上采用连续激光和脉冲激光照射,分别测量准波导结构RhB/PMMA和Rh6G/PMMA染料薄膜的荧光光谱和ASE光谱,发现荧光峰和ASE峰随着染料掺杂浓度和薄膜厚度的增加产生红移;理论上考虑准波导结构下薄膜中染料的自吸收效应,类比激光器谐振腔模型,分析低阶导模传输的增益特性,获得了荧光光谱与ASE光谱中荧光峰和ASE峰对应波长与染料掺杂浓度的关系,数值计算与实验测量相吻合。结果表明,准波导结构下薄膜中染料自吸收效应导致荧光峰及ASE峰发生红移,改变染料掺杂浓度,可以在较大调谐范围实现ASE。     

On Green's function for cylindrically symmetric fields of polarized radiation

Analytic expressions for Green's function describing the process of transfer of polarized radiation in homogeneous isotropic infinite medium in case of cylindrical symmetry and nonconservative scattering are obtained. The solution is based on the set of systems of Abel integral equations of the first kind obtained using the principle of superposition, and the known expression of Green's function for radiation fields with plane-parallel symmetry. Eigenvalue decompositions for the corresponding matrices of generalized spherical functions are found. Using this result the systems of Abel integral equations are diagonalized, and the final solution is obtained.     

Influence of interference effects of spontaneous emission on the behavior and spectra of resonance fluorescence of a three-level atom in a strong wave field

An investigation is made of the influence of quantum interference processes accompanying radiative relaxation of excited states on the population dynamics, total intensity, and spectra of the resonance fluorescence of three-level V-type atoms. Analytic expressions are obtained for the total intensity and spectra of the resonance fluorescence taking into account the off-diagonal nature of the radiative relaxation operator. It is shown that quantum interference process can substantially alter the total spontaneous emission intensity of the atoms and the population dynamics of the atomic levels, as well as the resonance fluorescence spectra.     

Formation of metastable molecular states at the resonance scattering of two atoms in a laser radiation field

Using the Dirac’s method, the formation of metastable molecular states at the resonance scattering of two atoms in the laser radiation field is considered. Expressions for the metastable level populations and the resonance scattering cross sections are obtained. In the case of an exact resonance with the laser radiation, the graphs for populations and resonance scattering cross sections, which have two peaks due to the Autler–Townes effect, are obtained. These results play an important role in the study of the controlled chemical reaction and for the understanding of the processes in the quantum systems of the Bose–Einstein condensate at low temperatures, as well as in the various optical processes in atomic gases.     

用于托卡马克装置的中性氢密度绝对测量的激光共振荧光散射仪

本文描述了一种新的高温等离子体的诊断方法。即用激光共振荧光法测量托卡马克高温等离子体中的中性氢密度。整个测量系统用瑞利散射进行绝对定标。文章具体描述了HT-6B托卡马克装置上的共振荧光散射仪及其中性氢密度的测量结果。     

One- and two-photon resonance fluorescence of a three-level atom at high photon densities

We consider the possible physical processes that may arise in a three-level atom when only two of its levels interact with a strong electromagnetic field and when the atomic transition frequency is nearly equal to once and twice the frequency of the laser field, respectively. There have been found pronounced cooperative effects in the spectrum of the two-level system, which is in resonance with the laser field, arising from the presence of the third level. The excitation spectra describing the transitions from the first excited state into the second excited state and from that to the ground state consist, apart from the two central peaks, of two pairs of sidebands which are induced by the laser field of the neighbouring system. Detailed expressions of the spectral functions for the physical processes of one- and two-photon resonance fluorescence have been derived and discussed in the limit of high photon densities. The excitation spectrum of the low frequency modes has been considered and discussed in detail. It is found that quantum beats in spontaneous emission may appear in the spectra of the one- and two-photon resonance fluorescence arising from the interference between the two atomic transition frequencies and the frequency of the laser field. The importance of the low frequency modes that occur in the processes in question has been pointed out.     

Instantaneous shifted‐excitation Raman difference spectroscopy (iSERDS)

Shifted‐excitation Raman difference spectroscopy (SERDS) is an experimental method to recover spontaneous Raman spectra despite the presence of strong fluorescence interference. The common scheme requires a tunable laser source and recording two spectra after each other. In this paper, an approach for instantaneous SERDS (iSERDS) is presented utilizing a broadband light source. The broadband radiation is spatially dispersed in the focal plane inside the object of investigation. The generated scattering signal is imaged onto the slit of an imaging spectrograph. The individual pixel lines on the detector represent Raman spectra with slightly shifted excitation wavelength and hence allow SERDS spectra to be derived. The proposed iSERDS technique is a suitable approach for obtaining Raman spectra from fluorescing samples provided they are homogenous on the length scale of the measurement volume. Copyright © 2014 John Wiley & Sons, Ltd.     

Mathematical modeling of the dynamics of photoreactions of a five-level molecule

A mathematical modeling of the time evolution of the populations of the states of a five-level molecule during transformation of resonant monochromatic irradiation and spontaneous emission from the highest-energy state excited by a short pulse of light is performed. The formalism of the optical Bloch equations and quantum theory of radiation are applied a composite system consisting of a molecule and a quantized radiation field. The results of simulation of the evolution of the population of the states of the molecule in the case of spontaneous emission are similar for both of these two approaches, but differ significantly in the case of conversion by the molecule of monochromatic radiation. These differences are the greater, the higher the intensity of resonance Rayleigh scattering or (and) relaxed fluorescence, as a result of which the molecule returns to the initial ground state. An explanation of the nature of these differences is given.     

Emission spectra and intrinsic optical bistability in a two-level medium

Scattering of resonant radiation in a dense two-level medium is studied theoretically accounting for local field effects and renormalisation of the resonance frequency. Intrinsic optical bistability is viewed as switching between different spectral patterns of fluorescent light controlled by the incident field strength. Response spectra are calculated analytically for the entire hysteresis loop of atomic excitation. The equations to describe the non-linear interaction of an atomic ensemble with light are derived from the Bogolubov-Born-Green-Kirkwood-Yvon hierarchy for reduced single particle density matrices of atoms and quantised field modes and their correlation operators. The spectral power of scattered light with separated coherent and incoherent constituents is obtained straightforwardly within the hierarchy. The formula obtained for emission spectra can be used to distinguish between possible mechanisms suggested to produce intrinsic bistability in experiments.     

Collective Scattering of Electromagnetic Waves from a Relativistic Magnetized Plasma

Recently, laser and microwave scatterings have become one of the important diagnostic means for plasma. Laser and microwave correlative scattering spectrum is determined by particle-density fluctuations in a weak turbulent plasma. In a relativistic plasma, on the basis of complete electromagnetic interaction between particles, a general expression for particle density fluctuations and spectra of laser and microwave scattering from a magnetized plasma are derived. The laser and microwave scattering spectra provide information on electron density and temperature, ion temperature, resonance and nonresonance effects.     

Resonance Raman detection of carotenoid antioxidants in living human tissues

We have used resonance Raman scattering as a novel noninvasive optical technology to measure carotenoid antioxidants in living human tissues of healthy volunteers. By use of blue-green laser excitation, clearly distinguishable carotenoid Raman spectra superimposed on a fluorescence background are obtained. The Raman spectra are obtained within less than a minute, and the required laser light exposure levels are well within safety standards. Our technique can be used for rapid screening of carotenoid levels in large populations and may have applications for assessing antioxidant status and the risk for diseases related to oxidative stress.     

Interference phenomena at the elastic collision of atoms with formation of the Feshbach resonance in the presence of laser radiation field

Resonant scattering of atoms with formation of the Feshbach resonance in the presence of a laser radiation coupling the levels of two bound atoms (a molecule) is considered. The laser field leads to a second resonance in scattering and broadening of resonances, which facilitates the possibility of experimental observation of asymmetry of the total scattering cross-section arising because of interference between resonant and potential scatterings. The effects associated with interference of the two channels of decay of a bound system of two atoms (a molecule) in the laser field are studied. An expression is obtained for the scattering length in collision of two cold atoms in the field of laser radiation.     

Investigation of inverse Raman scattering using the method of intra-cavity spectroscopy

The detectability of Raman absorption lines is enhanced by inserting the Raman sample into the cavity of a broad-band dye laser where the sample is simultaneously pumped by monochromatic radiation. With this technique we were able to detect Raman samples with good scattering efficiencies in a concention of 10^?3 mole/? or to obtain nearly complete Raman spectra within a time interval of 30 nsec.Exposures in which the dye laser radiation and the strong monochromatic radiation are polarized parallel or perpendicularly to each other are compared with spontaneous Raman spectra which are polarized parallel or perpendicularly.