Polarization effects during the interaction of counterpropagating waves in isotropic resonant media

Using the method of nonlinear polarization spectroscopy in the oppositely propagating laser beams of different power at a wavelength of 3.39 μm, we study, both theoretically and experimentally, the mechanisms of the formation of dichroism and birefringence during the interaction of arbitrarily polarized fields of resonant radiation with gaseous methane under conditions of low pressure of the gas in the cell and saturation of the operating transition F ₂ ⁽²⁾ by the field of a strong wave. Spectral forms of the polarization resonances of the test-wave intensity at the output of the polarization spectrometer are studied experimentally. Based on the vector theory of light interaction with matter, we present an exhaustive theoretical interpretation of the experimental data on the dependence of the polarization state of a weak wave on the intensity of a linearly or circularly polarized high-power counterpropagating wave. A new technique of measuring the induced nonlinear anisotropy for test-field waves and the macroscopic parameters of the resonant gas is developed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 72–93, January 2007.     

Magneto-optical resonances in the field of counterpropagating waves

The resonance of the intersection of sublevels in a probe laser field resonant to the cyclic transition corresponding to the D ₂ ⁸⁷Rb line has been investigated in a zero magnetic field. The strong effect of an additional laser field acting on the adjacent transition has been revealed. In a cell without the buffer gas and antirelaxation coating, the amplitude of the probe-field absorption resonance can increase by more than an order of magnitude in the presence of a counterpropagating wave. The effect is observed at the laser frequency tuned to the cross resonance, when the counterpropagating waves simultaneously act on moving atoms at the cyclic and open transitions with the common lower level. The theoretical analysis of the effect of the additional field on the electromagnetically induced absorption resonance is in agreement with the experimental data.     

近地面三阵子天线估计电磁波到达角和极化参数

从自由空间中的三阵子天线求入射电磁波极角和方位角的基本原理出发, 结合电场各个分量与极化方式之间的关系给出了左手极化波计算波达角的公式, 及地球表面上方三阵子天线判断入射波极化方向的方法; 本文提出了一种新颖的滤除地面反射波的方法, 保证了波达角的求解精度; 利用获得的高精度的波达角和测得的电场强度, 计算出了电磁波的各种极化参数, 这些极化参数可以作为电离层研究和电磁波在电离层中传播研究的参考. 关键词： 地球表面 三阵子天线 波达角 极化参数     

微纳光纤环形腔海水温度的谐振光谱分析

微纳光纤环形腔作为传感器件,具有灵敏度高、响应快的优点,因而越来越广泛地应用在传感领域。环形腔的谐振光谱直接反映外界环境的变化,因此谐振光谱分析对探测环境参数至关重要。从理论和实验研究了微纳光纤环形腔谐振光谱与海水温度的关系。首先,数值计算了基模(HE₁₁)两个垂直偏振态的传播常数随光纤直径和探测波长的变化关系,计算结果表明传播常数随光纤直径增大而增大,随波长增大而减小,同时计算了传播常数随海水温度的变化,海水温度越高,传播常数越大,表明海水温度的变化会影响到模式的传播常数,因而可以通过测量谐振光谱的变化得知海水温度的变化。其次,搭建了海水温度传感实验系统,获得了微纳光纤环形腔海水温度的谐振光谱,实验发现同时存在两套谐振峰,分别对应基模的TE模和TM模,两个偏振模式的传感灵敏度分别为5.54和5.24 pm·℃-1。最后,探讨了基模两个偏振态谐振光谱的产生原因,由于结型耦合区的扭曲耦合使得两个偏振态分离,并对两个偏振模式的谐振强度进行了分析。两个模式的谐振强度不同,而且随着波长的增加,一个模的谐振强度不断增强,另一个模的谐振强度逐渐减弱。这是由于不同耦合态的耦合系数和衰减决定的,而且他们随着波长而改变。实验结果与理论计算相吻合。     

Scattering properties of an individual metallic nano-spheroid by the incident polarized light wave

The scattering properties of a metallic nano-spheroid under the illumination of different polarized light waves are investigated using 3D boundary element method. The influences of different geometrical sizes of the nano-spheroid and incident directions of the illuminating light wave on the scattering spectrum are studied for different incident polarized light waves. The results show that the metallic nano-spheroid has two intrinsic resonant modes, corresponding to different polarization states and resonant wavelengths. The scattering enhancement, the resonant wavelength, and the location of the enhanced optical field are strongly dependent on the polarization properties of the illuminating light waves, and they can be modulated by appropriately choosing the polarization directions of the incident light wave.     

Coherent hole burnings induced without saturation field in a Doppler broaden four-level N-type atomic system

We display the phenomenon of the hole burning which appearing without saturation field under the effect of different parameters. Theoretically the effect of spontaneously generating coherence (SGC) on the probe polarization spectrum in a Doppler broadened four-level N-type atomic system are investigated when the two driven and probe fields are arranged in copropagating and counterpropagating configurations which play an important role in appearing the coherent hole-burning (CHB) phenomenon. The condition of appearing the hole burning in the polarization spectrum at the presence of spontaneously generating coherence (SGC) and the nonradiative decay rates is that the wave number fields are different.     

Mode interactions of a single field laser

Interactions of single mode, counterpropagating laser fields in a gaseous, high gain, inhomogeneously broadened medium were investigated as a function of frequency. Large deviations (50%) from empty resonator frequencies indicate very strong coupling between the single operating TEM_00q mode and the dispersive medium. Magnitude of the frequency shift was determined with heterodyne detection by comparing the laser field to a reference laser stabilized at the transition line center. Comparison of experimental results and theoretical models provide a set of resonant dispersion parameters which define the medium in the presence of the optical field.     

显微物镜聚焦光场任意三维偏振方向的控制

线性偏振光在显微物镜焦斑处入射,与径向偏振光相干叠加产生三维偏振光场,通过调节两束光光强比率和入射线偏振光偏振方向实现聚焦光场任意三维偏振方向的控制.基于矢量光场衍射理论建立了仿真计算模型,对所提三维偏振方向控制方法的可行性进行理论验证和实验评估.构建实际控制光路并进行初步测试,实验结果表明了该方法的可行性,且相比于其他三维偏振控制方法,本文所提方法和其控制光路更为简单易实现.     

一种提高相对论返波管功率容量的方法

 对相对论返波管实验中射频击穿现象进行了分析和数值模拟研究,发现谐振反射器和慢波结构的局部场增强诱导了场致电子发射,引起了金属表面的射频击穿,通过研究分析,提出采用分布反馈式谐振反射器,并采用梯形倒角非均匀慢波结构替换正弦慢波结构的方法来抑制射频击穿。数值模拟研究表明,在微波功率2 GW时,改进后的反射器最大场强由1.4 MV/cm降低为570 kV/cm,慢波结构表面最大电场由1.1 MV/cm降低到780 kV/cm。改进后的结构在二极管电压765 kV时获得了微波功率2.2 GW、脉宽45 ns的实验结果,微波功率和脉宽得到显著提升。     

Miniature plasmonic wave plates

Linear birefringence, as implemented in wave plates, is a natural way to control the state of polarization of light. We report on a general method for designing miniature planar wave plates using surface plasmons. The resonant optical device considered here is a single circular aperture surrounded by an elliptical antenna grating. The difference between the short and long axis of each ellipsis introduces a phase shift on the surface plasmons which enables the realization of a quarter wave plate. Furthermore, the experimental results and the theoretical analysis show that the general procedure used does not influence the optical coherence of the polarization state and allows us to explore completely the surface of the unit Poincaré sphere by changing only the shape of the elliptical grating.     

Counterpropagating waves on the sea surface (Results of Natural Microwave Experiment)

This paper is devoted to the analysis of the results of the natural experiment on the study of nonlinear dynamics of surface waves by microwave methods. During the experiment, waves traveling in opposition to the wind and the dominant wave system were detected by high-resolution microwave radar methods. An analysis of the results of microwave sounding made it possible to obtain a space-frequency spectrum of counterpropagating waves, to estimate their intensity, and to relate the fact of counterpropagating wave generation to experimental conditions. It was shown that the generation of counterpropagating waves under conditions of this experiment can be interpreted on the basis of the mechanism of the cubic interaction of surface gravity waves.     

Forces exerted on atoms by stochastic laser fields

We present analytical results and numerical simulations for the force exerted on moving atoms in the fields of two counterpropagating waves whose amplitudes or phases are described as stochastic processes. We assume that one field repeats the other with some delay, as would occur when the two fields derive from a common source through a beam splitter and mirrors. We show that, just as with the force exerted by the field of two counterpropagating sequences of π-pulses, or two counterpropagating bichromatic or frequency-modulated waves, the force on an atom in counterpropagating stochastic waves may considerably exceed the force exerted by the field of a single running wave. For comparison we also discuss the interaction of an atom with two counterpropagating waves when one of them is monochromatic and the other one has a stochastic phase. In this case the force substantially exceeds the force exerted by the field of a single running wave but appreciably smaller then the radiative force in the counterpropagating waves in which one field repeats the other with some delay.     

Engineering noon states in cavity QED

Based on presently available experimental advancements, we present a theoretical technique to generate single-mode electromagnetic-field entangled NOON states between two resonators. A two-level atom interacts dispersively with a standing wave field, which results in Bragg diffraction and thus a superposition of atomic external degrees of freedom. Later, a resonant interaction of the atom with two different resonators in the presence of a Ramsey field and a Stark field entangles the two resonators in their NOON state. We further discuss the experimental parameters necessary to realize the scheme in the laboratory and calculate the corresponding success probability.     

Nonstationary parametric amplification of polychromatic radiation propagating in an extended absorbing resonant medium

An experimental and theoretical study of the two-wave interaction (of a probe wave and a pumping wave) of wide-band multimode laser pulses with an optically dense extended resonant medium (metastable neon atoms in a positive glow-discharge column) is presented. Depending on the pumping power and characteristics of the medium, various regimes of interaction between the field and the matter, leading to qualitatively different types of amplification spectra, are realized: a cooperative interaction regime at low pumping powers corresponds to amplification spectra consisting of two peaks, which lie on both sides of the absorption line; in the regime of nonstationary Rabi oscillations (Rabi flopping), the amplification appears in the form of an isolated peak at a frequency close to the resonance in the substance; under certain interaction conditions, a dispersive shape of amplification spectra is observed. A significant gain in the probe field (by several times at a length of 10 cm) is obtained as a result of a nonstationary population inversion upon rotation of the Bloch vector of the resonant medium under the action of a strong pumping field in the course of propagation of the two waves.     

Pulse shaping via modulation of resonant absorption

Propagation of monochromatic linearly polarized plane electromagnetic wave through resonantly absorbing anisotropic medium with frequency-modulated response is studied analytically and numerically. Frequency modulation is assumed to be provided by means of either mechanical vibration of a solid sample or modulation of quantum transition frequency by a driving low-frequency electromagnetic field. Possibility of generation of train of pulses with polarization of the incident field as well as with orthogonal polarization is shown. For each polarization, optimal combinations of values of four parameters that provide maximal ratio of peak pulse intensity to the average output intensity is found numerically. Possible realization of this resonant method of pulse shaping in laser crystal Dy²⁺:CaF₂ is discussed.     

Threshold characteristic of intracavity optical parametric oscillator pumped by all-solid-state Q-switched laser

We derive the threshold pump intensity for a singly resonant intracavity optical parametric oscillator (IOPO)based on a temporal coupled field model.Particular attention is Paid to the dependence of the intracavity singly resonant OPO(SRO)threshold intensity on the signal wave output coupling.Meanwhile,a Nd:YAG laser pumped KTiOPO4(KTP)IOPO for eye-safe laser output is studied experimentally.The experiment is performed with four signal wave output reflectivities of 60%,70%,80%,and 90%,respectively.The measured values are in good agreement with the theoretical results.With an output coupler reflectivity of 80%,a peak power of 70 kW at 1572 nm has been obtained at a repetition rate of 3.5 kHz.The pulse width is 4.9 ns.Such investigation is helpful to identifying suitable operational regime of low pump intensity.     

Doppler-free transitions induced by strong double-frequency optical excitation

The possibilities to achieve Doppler-free transitions influenced by two strong radiations with different frequencies are discussed. Derived expressions show that two-photon absorption ceases to be Doppler-free with the intensity increase of equal-frequency counterpropagation light beams. On the contrary, absorption of distinct-frequency counterpropagating waves and moreover copropagating Stokes light scattering appears to be Doppler-free under a proper pump field intensity. Applications of these induced Doppler-free transitions to resonant nonlinear optics of gas-phase media are considered. The importance of the new features resulting from the growth of both the interacting fields is stressed.     

Simultaneous achievement of polarization attraction and Raman amplification in isotropic optical fibers

We present a theoretical analysis and experimental demonstration of the combined effects of polarization attraction and Raman amplification in isotropic optical fibers. The polarization attraction process is based on four-wave mixing interaction of counterpropagating pump and signal waves. We show that this technique can be used for the design of a highly efficient nonlinear system that permits the simultaneous processing of repolarization and amplification of light waves in dielectric media.     

Light intensification towards the Schwinger limit

A method to generate ultrahigh intense electromagnetic fields is suggested, based on the laser pulse compression, carrier frequency upshift, and focusing by a counterpropagating breaking plasma wave, relativistic flying parabolic mirror. This method allows us to achieve the quantum electrodynamics critical field (Schwinger limit) with present-day laser systems.     

Electron–Nuclear Spin Dynamics in Semiconductor QDs

This work presents an overview of investigations of the nuclear spin dynamics in nanostructures with negatively charged InGaAs/GaAs quantum dots characterized by strong quadrupole splitting of nuclear spin sublevels. The main method of the investigations is the experimental measurements and the theoretical analysis of the photoluminescence polarization as a function of the transverse magnetic field (effect Hanle). The dependence of the Hanle curve profile on the temporal protocol of optical excitation is examined. Experimental data are analyzed using an original approach based on separate consideration of behavior of the longitudinal and transverse components of the nuclear polarization. The rise and decay times of each component of the nuclear polarization and their dependence on transverse magnetic field strength are determined. To study the role of the Knight field in the dynamic of nuclear polarization, a weak additional magnetic field parallel to the optical axis is used. We have found that, only taking into account the nuclear spin fluctuations, we can accurately describe the measured Hanle curves and evaluate the parameters of the electron–nuclear spin system in the studied quantum dots. A new effect of the resonant optical pumping of nuclear spin polarization in an ensemble of the singly charged (In,Ga)As/GaAs quantum dots subjected to a transverse magnetic field is discussed. Nuclear spin resonances for all isotopes in the quantum dots are detected in that way. In particular, transitions between the states split off from the ±1/2 doublets by the nuclear quadrupole interaction are identified.