On Nonlinear Resonant Absorption of Surface Waves

We consider the resonant absorption of surface waves in a cold electron plasma by taking into account the nonlinear change in the electron density profile which is caused by the wave pressure in the transition layer. Equations, which describe the time evolution of the amplitudes of the electric fields of the surface waves, are obtained and solved. It is shown that the time-behaviour of the surface waves can be significantly different from that obtained from linear theory, and nonlinear effects can thus change the rate of absorption of the surface wave energy and can also stabilize linear surface wave instabilities.     

Absorption of Long Waves by Nonresonant Parametric Microstructures

Using simple acoustical and mechanical models, we consider the conceptual possibility of designing an active absorbing (nonreflecting) coating in the form of a thin layer with small-scale stratification and fast time modulation of parameters. Algorithms for space-time modulation of the controlled-layer structure are studied in detail for a one-dimensional boundary-value problem. These algorithms do not require wave-field measurements, which eliminates the self-excitation problem that is characteristic of active systems. The majority of the considered algorithms of parametric control transform the low-frequency incident wave to high-frequency waves of the technological band for which the waveguiding medium inside the layer is assumed to be opaque (absorbing). The efficient use conditions are found for all the algorithms. It is shown that the absorbing layer can be as thin as desired with respect to minimum spatial scale of the incident wave and ensures efficient absorption in a wide frequency interval (starting from zero frequency) that is bounded from above only by a finite space-time resolution of the parameter-control operations. The structure of a three-dimensional parametric black coating whose efficiency is independent of the angle of incidence of an incoming wave is developed on the basis of the studied one-dimensional problems. The general solution of the problem of diffraction of incident waves from such a coating is obtained. This solution is analyzed in detail for the case of a disk-shaped element.     

Phonon-Assisted Exciton Absorption in CdSe/CdS Colloidal Nanoplatelets

JETP Letters - The features of the nonresonant absorption of CdSe nanoplatelets with a CdS shell are studied in the case of excitation to the exciton absorption edge by high-power nanosecond laser...     

Electromagnetic Forces on Plasma Particles in the Presence of Resonant and Nonresonant Plasma Turbulence

Nonlinear forces on plasma particles in the presence of a test nonresonant wave and resonant plasma wave turbulence are calculated. The important feature of the considered nonlinear effect is that the forces due to the nonresonant test wave act on the plasma particles in the absence of linear and nonlinear resonances between the wave and the particles. Although in a closed plasma-wave system the process is balanced by the quasilinear interaction between the plasma resonant turbulence and plasma particles (leading to nonstationarity and inhomogeneity of the system), in open systems the effect can be significant.     

Sound Absorption of Locally Resonant Sonic Materials

The acoustic properties of locally resonant sonic materials with viscosity are theoretically investigated by using the multiple-scattering approach. We find that the absorption of a two-layer slab dominates the wave attenuation in the resonant frequency region under the condition of moderate or high viscous level. The fundamental mechanism operating in local resonance for absorption is investigated for the viability by the mode translation in the scattering process of a single scatterer. Finally the absorption performance in a multi-layer system is discussed.     

Saturation of Exciton Absorption in CdSe/CdS Nanoplatelets under Transient Excitation Conditions

JETP Letters - Nonlinear absorption of light by colloidal CdSe nanoplatelets with a CdS shell is investigated under the conditions of transient single-photon generation of excitons. By changing the...     

Localization of a Three-Level Cascade Atom via Resonant Absorption

We show that it is possible to localize a three-level cascade atom under the resonance condition when it passes through a standing-wave field. The localization peaks appear at the nodes of the standing-wave field, the detecting probability is 50% in the subwavelength domain, and the peaks are narrower on the resonance than the off- resonance. The absorption is the same as that in the usual two-level medium at the nodes and is greatly suppressed outside the nodes due to the Autler-Townes splitting. This is in sharp contrast to the lambda scheme, in which the localization is impossible under the same resonance condition due to the depletion of population of the initial state by the probe field at the nodes and the electromagnetically induced transparency outside the nodes.     

Nonlinear Dynamics of Wave Fields in Nonresonant Media: From Envelope Solitons toward Video Solitons

We analyze a new class of soliton solutions for a wave field, which describes propagation of soliton-like structures of a circularly polarized electromagnetic field comprising a finite number of field-oscillation periods in a transparent nonresonant medium. The considered solutions feature a smooth transition from the soliton solutions of Schröodinger type, which correspond to long pulses with a large number of field oscillations, to extremely short, virtually single-cycle video pulses. We show that such solutions can also be important for linearly polarized laser fields. The structural stability of few-optical-cycle solitons is demonstrated numerically, including the case of their collision. Based on stability analysis and with allowance for the genealogic relation between the obtained wave solitons and the solitons of the nonlinear Schröodinger equation, we argue that the former solitons can play the same fundamental role in the nonlinear dynamics of the considered wave fields. In particular, it is shown by numerical simulations that the few-optical-cycle solutions turn out to be the basic elementary components of such a dynamical process as the temporal compression of an initially long pulse to a pulse of very short duration. In this case, the minimum duration of a compressed pulse is determined by soliton structures of about minimal duration.     

Nonresonant Nonlinearity of Silver Nanoparticles

Results of experimental investigations of the process of nonlinear refraction in composite materials based on silver nanoparticles in the region far from the plasma surface resonance of the nanoparticles (λ = 1064 nm) are presented. The reflection Z-scanning technique was used for measurements, which made it possible to determine both the sign and the values of nonlinear refractive indices and real parts of the 3rd-order nonlinear susceptibility of composite materials. The mechanism responsible for the process of nonlinear refraction in specimens is discussed. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 650–653, September–October, 2005.     

Observation of Two-Photon Absorption and Nonlinear Refraction in AlN

Two-photon absorption(TPA) and nonlinear refraction in AlN single crystals are revealed with the single beam Z-scan technique.A large TPA coefficient of 13±3 cm/GW at 355 nm and third-order nonlinear refractive indices of-1.91±0.38 x 10~(-13) cm~2/W at 355 nm,1.79±0.36×10~(-13) cm~2/Wat 532 nm and 1.61±0.32× 10~(-12) cm~2/W at 1064 nm are derived.It is inferred that the TPA-generated free carriers are responsible for the large negative nonlinear refractive index at 355 nm,while the oxygen impurity induced bandgap narrowing may account for the large third-order nonlinear refractive indices at 532 nm and 1064 nm.The large nonlinear optical responses of AlN promise wide applications in the deep ultraviolet nonlinear optical devices.     

Intensity-Dependent Optical Nonlinear Absorption and Refraction of Gold Nanorods

Au nanorods dispersed in aqueous solution were prepared with the electrochemical method. The absorption spectrum shows two absorption peaks corresponding to the perpendicular and transverse surface plasma resonance absorption of the nanorods. The third-order optical nonlinear properties are investigated by Z-scans. The signs of the nonlinear absorption coemcient and refractive index are reversed as the intensity of incident laser increases, which is due to the shape change of the gold nanoparticles melted by the intense laser pulses.     

Effect of Resonant Electrons on Propagation of Nonlinear Electrostatic Drift Waves

A modified Korteweg-de Vries equation in a two-dimensional space comprising the externla magnetic field and the direction normal to a density gradient is derived for a plasma consisting of warm ion fluid (?i = 3) and nonisothermal electrons (?e > 1). The effect of ionic temperature and resonant electrons (both trapped and free electrons) on the amplitude and the width of the drift solitary wave is examined.     

稀土材料的超快共振非线性光学特性研究

用抽运-探测技术测量光学响应材料非线性极化率的方法，研究了稀土材料非线性折射率的共振增强和超快响应的非线性动力学过程。测得钕玻璃的三阶非线性折射 率强度系数为10^-14cm^2/W，比其基质的非线性折射率强度系数提高了2个量级。用该方法研究了Nd:YVO4、Er:YAG等晶体的超快非线性响应过程。实验结果与理论分析表明，抽支-探测技术是测量非线性极化率的简单而又灵敏的方法。这一测量技术对研究与开发超高速光响应器件具有重要的实用价值。     

强非线性吸收下Z扫描衍射模型及实验研究

根据光的衍射理论,建立了非线性光学介质对高斯光束的开孔Z 扫描理论模型.数值计算表明,当相移比值Γ≤0.15,出射光功率随入射光功率的增加出现振荡衰减现象;当Γ>0.15,在输入光强低于某一个值时,输出随输入的增加而线性增加;当输入光强超过该值后,输出功率不再增加甚至趋于零.实验采用Nd∶YAG脉冲激光,在波长为532 nm,脉宽8 ns条件下,对含3.5%和7.0%碳纳米管的聚苯胺/碳纳米管复合体薄膜（PANI/MWCNT）的非线性吸收特性进行了研究.计算表明,该类化合物的激发态吸收截面积远大于其基态吸收截面积,具有很强的反饱和吸收.     

Collisions of Single-Cycle and Subcycle Attosecond Light Pulses in a Nonlinear Resonant Medium

By numerically solving the system of Maxwell–Bloch equations, we have examined theoretically collisions of extremely short single-cycle and unipolar subcycle pulses in a nonlinear resonant medium under conditions that the light interacts coherently with the medium. The dynamics of the electric field of structures of light-induced polarization and inversion difference has been considered in the situation in which pulses are overlapped in the medium. We show that the states of the medium (to the right and to the left of the overlap region of the pulses) may differ. In particular, we show that polarization waves with different characteristics can exist in the regions of the medium that are located on opposite sides of the overlap region of the pulses. These waves travel in different directions and have different spatial frequencies.     

细菌视紫红质膜非线性吸收特性及其光子学应用

对细菌视紫红质膜在两束非同频光照射下的非线性吸收特性进行了详细的理论分析,并讨论了细菌视紫红质膜非线性吸收特性有光子学方面的一些新应用。     

Nonresonant tripling and sum-frequency mixing in Hg

Nonresonant frequency tripling and sum-frequency mixing of pulsed dye-laser radiation generates in Hg vapor continuously tunable coherent vuv radiation in the wavelength range _vuv=132-185nm. Laser pulse powers of 1–2 MW produce vuv light pulses of 0.6–1.5 W (2–4.8×10⁹ photons/pulse).