Femtosecond Time-Resolved Third-Order Nonlinear Response of 4-(N, N-Diethylamino)-β-Nitrostyrene Solutions in the Nonresonant Region—Experimental Evidence of Group-Velocity Dispersion Effec—

We measure the femtosecond time-dependent, third-order nonlinear optical response for 4-(N, N-diethylamino)-β-nitrostyrene (DEANST) dissolved in N, N-dimethylformamide (DMF) from 0.1 to 1.4 M concentrations in the nonresonant region using time-resolved degenerate four-wave mixing (DFWM) spectroscopy. It is found that the DFWM signal profile with delayed responses depends on the concentration. This concentration dependence is determined to be mainly due to the group-velocity dispersion effect of the DEANST solution at the high concentration and the nonlinear response of the DMF solvent at the low concentration, but not due to the change in third-order nonlinear response of DEANST itself.     

Third-order nonlinear optical response in quantum dot–metal nanoparticle hybrid structures

Third-order nonlinear optical response of a semiconductor quantum dot, modulated by the metal nanoparticle (MNP), has been studied by using the effective mass and the rotating wave approximation. Considering multiple effects in the local and nonlocal optical response of the MNP, the dependence of the dispersion and the absorption on the size of the hybrid system are investigated in detail. By controlling the geometrical parameters of the hybrid structure and the direction of the electric field polarization, a significant enhancement of the nonlinear response is shown. The enhancement factor is nearly two orders of the magnitude, which is consistent with the experiment. Compared to the results obtained with the local effect, the center frequency shows blueshift obviously in the case of the nonlocal effect. In particular, the presence of the MNP leads to a strong absorption band appearance, which promises applications in the field of light transmission and the optical switching.     

Dynamic nonlinear effect on lasing in a random medium

We have studied both experimentally and numerically the dynamic effect of nonlinearity on lasing in disordered medium. The third-order nonlinearity not only changes the frequency and size of lasing modes, but also modifies the laser emission intensity and laser pulse width. When the nonlinear response time is longer than the lifetime of the lasing mode, the nonlinearity changes the laser output through modifying the size of the lasing mode. When the nonlinear response is faster than the buildup of the lasing mode, positive nonlinearity always extracts more laser emission from the random medium due to the enhancement of single particle scattering.     

Theory of enhanced second-harmonic generation in some artificial materials

We review the recent theoretical investigation on enhanced second-harmonic generation (SHG) in soft nonlinear optical materials based on ferrofluids, graded metallic films, and graded metal-dielectric films of anisotropic particles. The SHG of soft ferrofluid-based nonlinear optical materials possess magnetic-field controllabilities, i.e., magnetic-field-controllable anisotropy, red-shift and enhancement, which are caused to appear by the shift of a resonant plasmon frequency due to the formation of the chains of the coated nanoparticles. Both graded metallic films and graded metal-dielectric films of anisotropic particles can serve as a novel optical material for producing a broad structure in both the linear and SHG response and an enhancement in the SHG signal, due to the local field effects.      

非线性调频信号激励下非线性系统的最优共振响应

非线性调频(NLFM)信号在雷达、通信、信号处理中应用广泛,该类信号所激励下的非线性系统响应有着丰富的信息,通过共振来增强NLFM信号具有一定实际意义与价值.本文主要研究了受到不同类型NLFM信号所激励的非线性系统共振现象,提出了实时尺度变换方法来处理高频NLFM信号,克服人为选择造成信号输出响应较差的缺点.同时,提出实时谱放大因子作为共振评价指标,准确评价NLFM信号激励下的系统共振响应,讨论系统参数对系统最优共振响应的影响,参数选择在合理的区间内即可实现最优共振响应,不仅实现信号特征的大幅增强,还保持信号时频特征的连续性.最后,将实时尺度变换方法和固定尺度变换方法进行对比,说明所提方法处理NLFM信号的优越性.     

Effect of nonlinear absorption in estimation of order of nonlinear optical process by fluorescence intensity

We report the effect of nonlinear absorption on the fluorescence signal. Attenuation of the incident beam intensity (I) in the medium due to nonlinear absorption reduces the fluorescence signal. We show that fluorescence signal proportional to I² is not always indicative of two-photon absorption process but such a dependence can be obtained for three or four-photon absorption process due to attenuation of the pump beam by nonlinear absorption. This reduction in the fluorescence signal due to nonlinear absorption is found to be more sensitive in the higher order nonlinear optical processes.     

Goldstone mode of a magnon Bose−Einstein condensate in MnCO<Subscript>3</Subscript>

The dependence of the enhancement of the Raman scattering on the size of a dielectric column is measured in structures with the spatial modulation of the height and lateral sizes of the dielectric coated with a thick metal layer (10–80 nm). It is established that, in the case of a thick metal coating (silver, gold, and copper coatings are used) at dimensions of the dielectric column close to the laser pump wavelength, considerable enhancement of the Raman signal oscillating upon the variation of the geometrical dimensions of the structure is observed. It is shown that the observed resonance enhancement of the Raman signal is associated with the transformation of the electromagnetic radiation into localized plasmon–polariton modes, and the efficiency of such transformation is determined by the commensurability of the wavelength of the plasmon–polariton mode and the planar size of the metal film. For different metal coatings, the dependence of the enhancement of the Raman scattering on the laser wavelength is measured.     

Nonlinear diffraction due to the transient polarization in a thin film of atomic gases*

Nonlinear optical response of a thin layer of rarefied atomic vapor is examined by taking into account the atomic motion as well as collisions with the cell walls. Extraordinary pattern of self-diffraction spectrum due to the transient polarization is predicted. It is shown that the spectra are Doppler free and depend strongly upon the vapor thickness. A new possibility of signal enhancement is revealed and a simple device is suggested to enhance greatly the nonlinear reflection signal from a resonant vapor layer. Received: 3 July 1997/Accepted: 5 December 1997     

光伏碲镉汞探测器在波段内连续激光辐照下的非线性响应机理研究

利用波段内连续激光, 辐照禁带宽度为0.33 eV的中波光伏碲镉汞探测器. 实验结果表明, 随着辐照激光光强的逐渐增大, 探测器从线性响应过渡为非线性响应. 当探测器进入非线性状态, 探测器的开路电压随激光光强的增大而减小, 且在激光开启辐照时开路电压信号迅速下跳, 在激光停止辐照时开路电压信号迅速上跳. 通过考虑激光辐照下探测器的温度场分布以及温度对p-n结内建电场的影响, 结合考虑机械快门在开启和关闭时对激光光强变化的影响, 建立了光伏探测器在波段内连续激光辐照下的解析模型, 模型计算结果与实验结果吻合得较好. 研究表明, 激光辐照过程中的非线性响应, 主要由温度对p-n结内建电场的影响决定, 激光开启和关闭时的开路电压的幅值是由光强和温度共同决定.     

Characterizing cochlear mechano-electric transduction with a nonlinear system identification technique: the influence of the middle ear

Previously a third-order polynomial equation characterizing mechano-electric transduction was obtained from a nonlinear system identification procedure applied to an ear canal acoustic signal and cochlear microphonic (CM/AC). In this paper, we examine the influence of the linearity and frequency response of the intervening middle ear on the nonlinearity, frequency response, and coherence of the third-order polynomial model of mechano-electric transduction (MET). Ear canal sound pressure (AC), cochlear microphonics (CM), and stapes velocity (SV) were simultaneously recorded from Mongolian gerbils. Linear and nonlinear transfer and coherence functions relating stapes velocity to the acoustic signal (SV/AC), CM to the acoustic signal (CM/AC), and CM to the stapes velocity (CM/SV) were computed. The results showed that SV/AC was linear while CM/AC and CM/SV were not, indicating that the nonlinearity of CM/AC was not due to nonlinearity of the middle ear. The frequency response of the linear term of CM/AC was similar to that of ST/AC but differed from that of CM/SV while the cubic term of CM/AC was similar to that of CM/SV. This indicates that the frequency dependence of CM/AC was due to both the middle ear and frequency dependence of the inner ear. Finally the fit of the polynomial model of MET without the middle ear (CM/SV) did not improve from the fit including the middle ear (CM/AC). A cochlear model of the CM indicated that the lack of improvement was due to the limitations of a third-order polynomial equation characterizing the hair cell transducer function.     

All-optical switching in subwavelength metallic grating structure containing nonlinear optical materials

All-optical switching based on a subwavelength metallic grating structure containing nonlinear optical materials has been proposed and numerically investigated. Metal-dielectric composite material is used in the switching for its larger third-order nonlinear susceptibility (approximately 10(-7)esu) and ultrafast response properties. The calculated dependence of the signal light intensity on the pump light intensity shows a bistable behavior, which results in a significant switch effect. It rests on a surface plasmon's enhanced intensity-dependent change of the effective dielectric constant of Kerr nonlinear media, corresponding to a transition of the far-field transmission from a low- to high-transmission state. The study of this switching structure shows great advantages of smaller size, lower requirement of pump light intensity, and shorter switching time at approximately the picosecond level.     

乙醇在电感耦合等离子体质谱中的增强效应研究

本文报道了乙醇在ＩＣＰ－ＭＳ中的溶剂效应。详细研究了入射功率和载气流量等条件与乙醇溶剂效应的相关性。并与甘油和铥的基体效应进行了比较。结果表明：乙醇对被分析元素信号有显著影响。     

Dispersive nonlinearity and bistability of polar media

The nonlinear optical response of polar materials (ionic crystals and polar semiconductors) is studied. Within the generalized Born-Huang theory, the nonlinear response of a system is found to exhibit a characteristic peak near the polariton resonance. As an example, the transparency of a plate (Fabry-Perot cavity) of a weakly nonlinear polar material is studied. It is shown that the dependence of the output signal intensity on the incident radiation intensity exhibits a bistable behavior for the systems under study.     

Photoelectric properties of magnetically sensitive MOS structures

The photoelectric properties of MOS structures having compensation regions near the field electrode have been studied experimentally. It is shown that the presence of such regions can lead to the appearance of a number of features in the integrated photoelectric properties: the presence of a large photovoltage signal in enhancement, dependence of the form of the photovoltage frequency dependence on the intensity of the light flux, and distortion of the shape of the photovoltage signal in inversion. The presence of compensation regions can be established using measurements of the distribution of the photovoltage over the area of the structure and measurements of the voltage dependence of the phase of the integrated photovoltage signal. The increase or decrease of the photovoltage signal in enhancement after exposure to a weak magnetic field is due to the rearrangement of the impurity-defect structure in the near-surface layer of the semiconductor, leading to the appearance of compensated semiconductor regions near the field electrode. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 82–87, May, 1998.     

Optical properties of excitons in semiconductor (InP)-insulator quantum wires

Features in the spectra of absorption, luminescence, and luminescence efficiency obtained under sample excitation with differently polarized laser radiation, and the nonlinear dependence of the luminescence intensity on the excitation level are explained as due to excitonic transitions in semiconductor (InP)-insulator (chrysotile asbestos) quantum wires. The measured excitonic-transition energies in the quantum wires are in quantitative agreement with calculations. The calculations took into account both the size quantization in a quasi-one-dimensional structure and the “dielectric enhancement” of excitons (the noticeable increase of the exciton binding energy and of the excitonic-transition oscillator strength associated with the increased attraction between the electron and the hole due to the large difference between the dielectric permittivities of the semiconductor and the dielectric matrix).     

Visualization of the hot chocolate sound effect by spectrograms

We present an experimental and a theoretical analysis of the hot chocolate effect. The sound effect is evaluated using time–frequency signal processing, resulting in a quantitative visualization by spectrograms. This method allows us to capture the whole phenomenon, namely to quantify the dynamics of the rising pitch. A general form of the time dependence volume fraction of the bubbles is proposed. We show that the effect occurs due to the nonlinear dependence of the speed of sound in the gas/liquid mixture on the volume fraction of the bubbles and the nonlinear time dependence of the volume fraction of the bubbles.     

Nonlinear optical response from composites based on nanostructures consisting of an absorbing core and metallic shell near the plasmon resonance

The object of experimental study and numerical simulation is the nonlinear optical response from composites with nanoparticles consisting of a nonlinearly absorbing dielectric core and a metallic shell. It is shown that a small spread in nanoparticle sizes near the plasmon resonance may significantly change the dependence of the nonlinear optical response on the concentration of nanoparticles of each size.     

Hyperfine structure of the electron spin resonance of phosphorus-doped Si nanocrystals

Electronic states of P donors in Si nanocrystals (nc-Si) embedded in insulating glass matrices have been studied by electron spin resonance. Doping of P donors into nc-Si was demonstrated by the observation of optical absorption in the infrared region due to intraconduction band transitions. P hyperfine structure (hfs) was successfully observed at low temperatures. The observed splitting of the hfs was found to be much larger than that of the bulk Si:P and depended strongly on the size of nc-Si. The observed strong size dependence indicates that the enhancement of the hyperfine splitting is caused by the quantum confinement of P donors in nc-Si.     

Biexcitonic fingerprint in the nondegenerate four-wave-mixing signal of weakly confined cadmium sulfur quantum dots

Nondegenerate four-wave mixing is analyzed with respect to biexcitonic contributions in the third-order nonlinear susceptibility x((3)) . The presence of biexcitons causes a distinct asymmetry in the frequency dependence of self-diffraction. By measurement of the dependence of the intensity of the self-diffracted signal on detuning between the two incident laser beams, the biexciton binding energy is determined to be E(XX)=7.8 meV for cadmium sulfur quantum dots of R=7.5 nm embedded in glass. Thus, even for weakly confined II-VI quantum dots with R~2.7a(B) , a confinement-induced enhancement of E(XX) was found.     

Wavelength dependence of second-harmonic generation at the copper surface

The wavelength dependence of the second-harmonic (SH) generation efficiency has been measured in copper. A strong enhancement of the SH generation has been observed at the onset of interband transitions. Above the absorption edge the second-order polarization is dominated by the nonlinear response of bound electrons.