Laser enhanced positron capture

The production of antihydrogen via positron-antiproton radiative capture can be enhanced considerably by the process of stimulated photon emission. The gained yield of antihydrogen due to this process is evaluated for experimental conditions, where a positron beam is merged with antiprotons circulating in a storage ring, and the overlap area of both beams is illuminated with intense laser light. The scaling characteristics of the laser-induced gain are pointed out, considering the influence of particle and laser beam properties, as well as competing processes like reionization and free-free transitions. A gain factor of at least an order of magnitude seems achievable by stimulating positron capture, either into high-lying bound states using CO₂ laser light or into then=2 state by means of a pulsed dye laser.     

SBS相位共轭补偿现象的实验研究与图示化分析

通过实验观察了受激布里渊散射相位共轭波前补偿现象,分析了单横模激光、波前弱畸变及强畸变激光受激布里渊散射现象的差异.由于工作介质中强烈的热畸变所引起的波前破碎效应,高功率固体激光器的输出光束一般都不是理想的高斯型单横模,而是具有弱畸变或强畸变波前结构的光束,其包含多个子光束.只有总能量足够大的激光束被聚焦到布里渊介质中时,其包含的所有子光束才能各自按单横模受激布里渊散射规律产生后向散射光,再合并而实现完全的相位共轭波前反转,否则就只能实现部分相位共轭波前反转,即部分相位共轭补偿.     

光的受激放大

求解在激发作用下通过活性介质的光的输运方程与活性介质中的粒子反转数方程,我们得到在具有任意形式输入下的光子数与粒子反转数的时空分布函数的解析表达式;并以一个方形脉冲或一系列方形脉冲为例进行讨论。此外,我们还研究了强光注入laser对laser的稳定工作点的影响,以及在一定条件下通过微扰方法给出这时laser内的光子数与粒子反转数的形式解,对以红宝石laser为例所作的计算表明通过注入强光有可能成为加强巨脉冲的手段之     

Nonlinear Characteristics of an Intense Laser Pulse Propagating in Partially Stripped Plasmas

The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three general expressions governing the nonlinear optic behavior, based on the photon number conservation, are obtained by considering the partially stripped plasma as a nonlinear optic medium. The numerical result shows that the presence of the bound electrons in partially stripped plasma can significantly change the propagating property of the intense laser pulse.     

Nonlinear Characteristics of an Intense Laser Pulse Propagating in Partially Stripped Plasmas

The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three general expressions governing the nonlinear optic behavior, based on the photon number conservation, are obtained by considering the partially stripped plasma as a nonlinear optic medium. The numerical result shows that the presence of the bound electrons in partially stripped plasma can significantly change the propagating property of the intense laser pulse.     

Quantum fluctuations in second-harmonic light generation

Second-harmonic light generation (SHLG) is analyzed from the viewpoint of the photon statistics of the fundamental and generated beams versus the path traversed by the two waves in the medium. The calculations lead to an anti-bunching effect for coherent incident light.     

On the possible production and detection of coherent low-energy neutrino beams

Seminal experiments are discussed to prove or disprove the possibility of producing and detecting collimated coherent beams of low-energy neutrinos with the assistance of lasers. Expressions are given for the relative probability that a laser-beam-aligned co- or counter-propagating neutrino-antineutrino pair is emitted instead of a laser photon, during stimulated de-excitations of lasable excited states inside a lasing medium. For a neodymium laser this probability is approximately 10^?7. To detect coherent beams of epithermal neutrinos and antineutrinos emitted from a pulsed high-power laser, it is anticipated that resonant non-absorptive stimulated de-excitations of lasing levels by neutrinos can be exploited to register their fly-through in a second near-threshold laser.     

Unidirectional saturation spectroscopy,I theory and short dipole lifetime limit

High-intensity multimode laser theory is used to derive the absorption coefficients for 1) a coherent light beam (probe) interacting with a possibly inhomogeneously broadened medium in the presence of an intense second corunning beam, and for 2) the sedibands of a weakly modulated light beam interacting with the medium. The general expressions are specialized to non-saturating probes and the short dipole-lifetime limit, yielding coherent pulsation-dip formulas. These are given for both homogeneous and inhomogeneous broadening and typically consist of simple power-broadened Lorentzians with widths equal to the smaller level-decay constant. The amplitude modulation case features pulsation dips twice as deep as the single-probe case, while the frequency modulation case exhibits no pulsation dip at all. Spectroscopic methods are discussed including the heterodyne advantage obtained with collinear light beams.     

Theoretical Investigation of Tunable Goos-Hänchen Shifts in a Four-Level Quantum System

Goos-Hänchen (GH) shifts in the reflected and transmitted light have been discussed in a cavity with four-level quantum system. It is realized that the refraction index of intracavity medium can be negative by manipulating the external coherent laser fields. For the negative refraction index of intracavity medium, the GH shifts of reflected and transmitted light beams have been analyzed in a parametric condition. It is found that due to modulation of laser signals and relative phase between applied fields, large and tunable GH shifts in reflected and transmitted light beams can be obtained.     

EPR light beams and non-Gaussian quantum distributions in the time domain

We investigate time-dependent properties of Einstein-Podolsky-Rosen (EPR) light beams generated in nondegenerate optical parametric oscillator (NOPO) driven by a sequence of laser pulses with Gaussian time-dependent envelops. The peculiarities of EPR beams are discussed on the base of quadrature squeezing and also in the framework of phase-space Wigner functions for EPR beams which are combined on a half beam splitter. We also investigate the Wigner functions of intensity-correlated twin beams following the conditional photon state-preparation scheme. It is demonstrated that the Wigner functions involve negative values in parts of the phase space for the schemes with one-, two-, and three-photons.     

Unidirectional saturation spectroscopy, I theory and short dipole lifetime limit

High-intensity multimode laser theory is used to derive the absorption coefficients for 1) a coherent light beam (probe) interacting with a possibly inhomogeneously broadened medium in the presence of an intense second corunning beam, and for 2) the sedibands of a weakly modulated light beam interacting with the medium. The general expressions are specialized to non-saturating probes and the short dipole-lifetime limit, yielding coherent pulsation-dip formulas. These are given for both homogeneous and inhomogeneous broadening and typically consist of simple power-broadened Lorentzians with widths equal to the smaller level-decay constant. The amplitude modulation case features pulsation dips twice as deep as the single-probe case, while the frequency modulation case exhibits no pulsation dip at all. Spectroscopic methods are discussed including the heterodyne advantage obtained with collinear light beams. Work performed as a Humboldt awardee in Germany. Work supported in part by the Space and Missiles Systems Organization, Los Angeles, California. Work supported by the “Deutsche Forschungsgemeinschaft”.     

On the observation of vacuum birefringence

We suggest an experiment to observe vacuum birefringence induced by intense laser fields. A high-intensity laser pulse is focused to ultra-relativistic intensity and polarizes the vacuum which then acts like a birefringent medium. The latter is probed by a linearly polarized X-ray pulse. We calculate the resulting ellipticity signal within strong-field QED assuming Gaussian beams. The laser technology required for detecting the signal will be available within the next three years.     

Approximated Vector Potential of Intense Laser Pulses in a Pair Plasma

A （3＋1 ）-dimensional Kadomtse-Petviashvili （KP） equation for nonlinearly interacting intense laser pulses with an electron-positron （e-p） plasma is derived. Taking into account the combined action of the relativistic particle mass increase and the relativistic light ponderomotive force, using the perturbation method, and allowing different types solution, we discuss the analytical solution of （3＋1）-dimensional KP-I equation, and give the approximate solutions of vector potential of the intense laser pulse in e-p plasma. Our results may be significantly useful in understanding the nonlinear wave propagation and interaction of intense laser beams in an e-p plasma.     

New physical techniques for IC functional analysis of on-chip devices and interconnects

Localization of functional fails in ICs makes use of physical interactions that the devices produce under electrical operation. The focus is on electroluminescence (keyword: photon emission) and signal responses to stimulation by scanned beams of laser light or particles. In modern chip technologies access of this information is only available through chip backside. This paradigm shift requires a full revision of chip analysis techniques and processes. This has also been a kick-off of a rush in development of new methodologies. Here, an overview is given which parameters are crucial for successful analysis techniques of the future and how photon emission, laser based techniques and new preparation techniques based on focused ion beam (FIB) open the path into this direction.     

Investigating the QED vacuum with ultra-intense laser fields

In view of the increasingly stronger available laser fields it is becoming feasible to employ them to probe the nonlinear dielectric properties of the vacuum as predicted by quantum electrodynamics (QED) and to test QED in the presence of intense laser beams. First, we discuss vacuum-polarization effects that arise in the collision of a high-energy proton beam with a strong laser field. In addition, we investigate the process of light-by-light diffraction mediated by the virtual electron-positrons of the vacuum. A strong laser beam “diffracts” a probe laser field due to vacuum polarization effects, and changes its polarization. This change of the polarization is shown to be in principle measurable. Also, the possibility of generating harmonics by exploiting vacuum-polarization effects in the collision in vacuum of two ultra-strong laser beams is discussed. Moreover, when two strong parallel laser beams collide with a probe electromagnetic field, each photon of the probe may interact through the “polarized” quantum vacuum with the photons of the other two fields. Analogously to “ordinary” double-slit set-ups involving matter, the vacuum-scattered probe photons produce a diffraction pattern, which is the envisaged observable to measure the quantum interaction between the probe and strong field photons. We have shown that the diffraction pattern becomes visible in a few operating hours, if the strong fields have an intensity exceeding 10²⁴W/cm².     

Self-modulation of Bessel-Gaussian wave beams in a medium with cubic nonlinearity

A semi-discrete dynamic model has been developed for the formation of the spatial structure of wave fields in a medium with cubic nonlinearity. The characteristic features of self-focusing and conical modulation of intense Bessel-Gaussian light beams of different orders have been studied in different stages of their evolution during propagation. It has been shown that as a result of nonlinear refraction, in the far zone wave structures are formed consisting of three spatially separated conical beams. Increasing the cone angle of the wave vectors leads to a decrease in the effect of conical modulation of the radiation, and improves the structural stability of the beam. The considered self-modulation effects can be used for passive limiting of the laser radiation power. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 626–630, September–October, 2006.     

三能级固体激光介质对抽运光吸收的理论研究

从激光介质中光能量的传输方程和描述脉冲激光的能级跃迁速率方程出发，研究了激光介质对抽运光的吸收特性.理论分析表明，固体激光介质对抽运光的吸收不仅是指数函数吸收方式，当抽运光的能量密度增大到一定程度时激光介质对抽运光的吸收变为非指数函数吸收，吸收深度增加.以红宝石晶体为例进行了具体的理论计算，结果显示出了随抽运光能量密度增大介质吸收的变化规律. 关键词： 抽运 激光介质 光传输方程 光吸收     

Stimulated emission depletion microscopy with a supercontinuum source and fluorescence lifetime imaging

We demonstrate stimulated emission depletion (STED) microscopy implemented in a laser scanning confocal microscope using excitation light derived from supercontinuum generation in a microstructured optical fiber. Images with resolution improvement beyond the far-field diffraction limit in both the lateral and axial directions were acquired by scanning overlapped excitation and depletion beams in two dimensions using the flying spot scanner of a commercially available laser scanning confocal microscope. The spatial properties of the depletion beam were controlled holographically using a programmable spatial light modulator, which can rapidly change between different STED imaging modes and also compensate for aberrations in the optical path. STED fluorescence lifetime imaging microscopy is demonstrated through the use of time-correlated single photon counting.     

Waveguides formed by incoherent dark solitons

We demonstrate experimentally optical guidance of coherent light beams, using incoherent light. Such guidance is made possible by generation of partially spatially incoherent self-trapped dark beams (dark incoherent solitons) in a noninstantaneous nonlinear medium. In the one-dimensional case, the incoherent solitons induce single and Y-junction planar waveguides, whereas in the two-dimensional case, they form circular waveguides. These experiments introduce the possibility of controlling high-power laser beams with low-power incoherent light sources such as LED's or lightbulbs.     

Femtosecond time-resolved optical polarigraphy: imaging of the propagation dynamics of intense light in a medium

A time-resolved imaging technique for visualizing ultrafast propagation dynamics of intense light pulses in a medium has been demonstrated. The method probes the instantaneous birefringence induced by a pulse in the medium. Through consecutive femtosecond snapshot images of intense femtosecond laser pulses propagating in air, ultrafast temporal changes in the two-dimensional spatial distribution of the optical pulse intensity were clearly seen.