Anticorrelations in Nondegenerate Parametric Three-Wave Interaction

It is shown that the anticorrelations in the photon numbers of the signal and the idler wave, respectively, generated in parametric three-wave interaction under suitable conditions, violate an inequality well-known in classical communication theory. Hence, it must be concluded that these anticorrelations reflect a typical quantum mechanical feature of light. In fact, this nonclassical behaviour is responsible for the occurrence of photon antibunching in the superposition field made up of both the signal and the idler wave, as will be pointed out in some detail.     

Generation of THz Radiation by Laser Plasma Interaction

This paper presents the three wave parametric decay process to generate the Terahertz (THz) radiations in magnetized plasma. The pump wave (Laser beam) is considered in the extraordinary mode (x‐mode), propagating perpendicular to the background magnetic field. This pump wave decays into an upper hybrid wave and a THz wave which is in magnetosonic mode. The appropriate expressions for the coupling coefficients of the threewave interaction and THz wave amplitude have been derived. Subsequently, the growth rate of this decay instability is also calculated. Various laser and plasma parameters were optimized and we report efficiency of the order of ～1.4 × 10^–2 for current scheme. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Material for Difference-Frequency Generation of Terahertz Radiation

Optics and Spectroscopy - The possibility of efficient difference-frequency generation of terahertz radiation in a metamaterial representing a structure consisting of alternating layers of a...     

THz Radiation Generation via the Interaction of Ultra‐short Laser Pulses with the Molecular Hydrogen Plasma

In this paper, a two dimensional Particle In Cell‐Monte Carlo Collision simulation scheme is used to examine the THz generation via the interaction of high intensity ultra‐short laser pulses with an underdense molecular hydrogen plasma slab. The influences of plasma density, laser pulse duration and its intensity on the induced plasma current density and the subsequent effects on the generated THz signal characteristics are studied. It is observed that the induced current density in the plasma medium and THz spectral intensity are increased at the higher laser pulse intensities, laser pulse durations and plasma densities. Moreover, the generated THz electric field amplitude is reduced at the higher laser pulse durations. A wider frequency range for the generated THz signal is shown at the lower laser pulse durations and higher plasma densities. Additionally, it is found that the induced current density in hydrogen plasma medium is the dominant factor influencing the generation of THz pulse radiation. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Doubling of THz Radiation Frequency in Nonlinear Borate Crystals

Russian Physics Journal - The use of nonlinear oxide crystals for radiation generation and conversion into terahertz (THz) range using the nonlinear crystal optics methods is a new promising...     

Parametric X Radiation from Electrons in Mosaic Crystals

A simple model for calculating the contribution of diffraction of actual photons to the measured spectrum of parametric x radiation (PXR) from relativistic electrons in mosaic crystals is suggested. It is shown that the diffraction of real photons of bremsstrahlung and transition radiation in mosaic crystals whose thickness t is about 0.01 of the radiation length makes a significant contribution to the measurable emission spectrum. The spectra and angular distributions of PXR from electrons with energies 500 and 900 MeV have been measured in mosaic pyrolytic graphite crystals. It is demonstrated that with consideration of diffraction of actual photons in the mosaic crystal, including diffraction of PXR photons, all experimental data presently available agree well with the results of calculations for the suggested model.     

Spectral Modeling of Difference-Frequency Generation in the Case of Two-Frequency Interaction of Ultrasound Waves

Acoustical Physics - A spectral algorithm is considered for describing nonlinear generation of an acoustic wave of difference frequency formed as the interaction of two high-intensity pump waves...     

Far-infrared quasi-local modes of ZnTe in CdTe

We report the very far-infrared absorption spectra of the mixed-crystals Cd_1-xZn_xTe for small x in the temperature range of 4.2K–150K and the wavenumber region of 20cm⁻¹–100cm⁻¹. The quasi-local mode induced by ZnTe in CdTe and CdTe-like 2TA two-phonon creations are observed, to be best of our knowledge, for the first time. The frequencies of the modes are estimated by using the mass-defect model combined with Green's functions calculations. Besides, the temperature dependence of the absorption peak is well explained in the light of the characteristics of the modes.     

d-core transitions in ZnTe,CdTe and HgTe

Summary We have measured the reflectivity spectra of monocrystalline ZnTe, CdTe and HgTe between 5 and 35 eV. We have interpreted the sharp structures above approximately 10 eV as transitions originating in the metal uppermostd levels. The structures give a picture of the projected densities of states of the conduction bands and supply a better understanding of their states.

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Riassunto Abbiamo misurato gli spettri di riflettività di monocristalli di ZnTe, CdTe ed HgTe tra 5 e 35 eV. Oltre i 10 eV gli spettri presentano delle strutture fini, interpretate come transizioni che hanno origine nei livellid piú alti del catione. Questa interpretazione permette di ricavare una rappresentazione schematica della densità proiettata degli stati di conduzione e di ottenere una migliore comprensione sulla natura degli stati finali stessi.

     

Diffraction of Light Beams at Parametric Interaction in Nonlinear Photonic Crystals

We consider the parametric amplification of a light beam in nonlinear photonic crystals (NLPCs) under a high-frequency pump and periodic spatial modulation of the coefficient of nonlinear coupling of the waves. We study the behavior of the intensity of the amplified diffracting beam using the matrix approach. We compare our results with the parametric interaction of beams in homogeneous nonlinear optical crystals. We show that the analysis of diffraction effects at nonlinear optical interaction in NLPCs, taking into account only noncompensated quasi-phase mismatching, is incorrect.     

Generation of Entanglement Between Two Noninteracting Qubits via Interaction with Nonclassical Radiation Field

We study the interaction between a single-mode quantized field and a quantum system composed of two qubits. We suppose that two qubits initially be prepared in the mixed and separable state, and study how entanglement between two qubits arises in the course of evolution according to the Jaynes-Cummings type interaction with nonclassical radiation field. We also investigate the relation between entanglement and purity of qubit subsystem. We show that different photon statistics have different effects on the dynamical behavior of the qubit subsystem. When the qubits are initially prepared in the maximally mixed and separable state, for coherent state field we cannot find entanglement between two qubits; for squeezed state field entanglement between two qubits exists in several short period of time; for even and odd coherent state fields of large photon number, the dynamical behavior of the entanglement between two qubits shows collapse and revival phenomenon. For odd coherent state field of small photon number, the entanglement with both qubits initially prepared in maximally mixed state can be stronger than that with both qubits initially prepared in pure states. For fields of small photon number, the entanglement strongly depends on the states they are initially prepared in. For coherent state field, and odd and even coherent state fields of large photon number, the entanglement only depends on the purity of the initial state of qubit subsystem. We also show that during the evolution the unentangled state may be purer than the entangled state, and the maximum degree of entanglement may not occur at the time when the qubit subsystem is in the purist state.     

Generation of Entanglement Between Two Noninteracting Qubits via Interaction with Nonclassical Radiation Field

We study the interaction between a single-mode quantized field and a quantum system composed of two qubits. We suppose that two qubits initially be prepared in the mixed and separable state, and study how entanglement between two qubits arises in the course of evolution according to the Jaynes-Cummings type interaction with nonclassical radiation field. We also investigate the relation between entanglement and purity of qubit subsystem. We show that different photon statistics have different effects on the dynamical behavior of the qubit subsystem. When the qubits are initially prepared in the maximally mixed and separable state, for coherent state field we cannot find entanglement between two qubits; for squeezed state field entanglement between two qubits exists in several short period of time; for even and odd coherent state fields of large photon number, the dynamical behavior of the entanglement between two qubits shows collapse and revival phenomenon. For odd coherent state field of small photon number, the entanglement with both qubits initially prepared in maximally mixed state can be stronger than that with both qubits initially prepared in pure states. For fields of small photon number, the entanglement strongly depends on the states they are initially prepared in. For coherent state field, and odd and even coherent state fields of large photon number, the entanglement only depends on the purity of the initial state of qubit subsystem. We also show that during the evolution the unentangled state may be purer than the entangled state, and the maximum degree of entanglement may not occur at the time when the qubit subsystem is in the purist state.     

中红外差频光源应用于实际大气水汽浓度测量

基于非线性光学效应,采用差频发生技术(Difference frequency generation)和准相位匹配技术(Quasi-phase matching),在周期性极化的铌酸锂晶体(PPLN)中产生了中红外的可调谐激光源。泵浦光是一个功率为1 W、调谐范围在770到870 nm之间的连续可调谐钛宝石激光器。信号光是一个功率为1 W、单频连续的Nd∶YAG激光器。当晶体的光栅周期为20 μm、温度调谐范围内在室温到200 ℃之间时,能够产生2.8 μm附近的、功率约为1～2 μW的差频光源。基于这个光源,采用直接吸收光谱方法测量了实验室大气中的水汽(001←000)吸收带的吸收光谱。依据大气中水汽分子在8.5 cm的吸收光程条件下的吸收光谱,成功地测量得到了大气中的水汽浓度。     

ZnTe晶体中光学整流产生的THz辐射及其电光探测研究

借助抽运-探测技术研究了ZnTe晶体中光学整流产生的太赫兹(THz)辐射，利用ZnTe晶体的线性电光效应探测THz辐射场分布，观察到了较窄(约为0.2 ps)的THz场分布及相应较宽(响应超过4 THz，半峰宽约为2.4 THz)的THz频谱，并运用琼斯矩阵对实验结果进行了理论拟合. 研究了飞秒激光脉冲波长(750—850 nm)、脉冲宽度(56—225 fs)和晶体旋转与THz辐射产生的关系. 同时改变探测光偏振方向进行偏振调制，并从理论上分析了偏振调制对THz辐射探测的影响. 关键词： THz辐射 光学整流 电光探测 ZnTe     

Generation of THz Radiation from Laser Beam Filamentation in a Magnetized Plasma

The terahertz (THz) frequency radiation production as a result of nonlinear interaction of high intense laser beam with low density ripple in a magnetized plasma has been studied. If the appropriate phase matching conditions are satisfied and the frequency of the ripple is appropriate then this difference frequency can be brought in the THz range. Self focusing (filamentation) of a circularly polarized beam propagating along the direction of static magnetic field in plasma is first investigated within extended‐paraxial ray approximation. The beam gets focused when the initial power of the laser beam is greater than its critical power. Resulting localized beam couples with the pre‐existing density ripple to produce a nonlinear current driving the THz radiation. By changing the strength of the magnetic field, one can enhance or suppress the THz emission. The expressions for the laser beam width parameter, the electric field vector of the THz wave have been obtained. For typical laser beam and plasma parameters with the incident laser intensity ≈ 10¹⁴ W/cm², laser beam radius (r₀) = 50 μm, laser frequency (ω₀) = 1.8848 × 10¹⁴rad/s, electron plasma (low density rippled) wave frequency (ω₀) = 1.2848 × 10¹⁴ rad/s, plasma density (n₀) = 5.025 × 10¹⁷cm^–3, normalized ripple density amplitude (μ)=0.1, the produced THz emission can be at the level of Giga watt (GW) in power (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrogen-acceptor interaction in CdTe and ZnTe studied by photoluminescence

Photoluminescence studies on CdTe and Znte implanted with hydrogen and deuterium at 150keV in the fluence range 10¹⁴–10¹⁵ cm^-2 are reported. In CdTe the introduction of hydrogen (deutrium) makes the recombination lines of excitons bounds to residual acceptors to disappear. The donor bound excitons are not affected. In ZnTe the intensity of the principal acceptor-bound exciton (Cu) is much reduced. In both crystals a new sharp line (H) appears with an adjacent structure on the low energy side. Short time annealings in the temperature range 150–250°C lead to the disappearance of the sharp lines (H) and to the recovery of the initial spectrum. These results shows that hydrogen is able to interact with acceptors in CdTe and ZnTe leading to the formation of a new exciton trapping centre. Possible microscopic models for this isoelectronic-like complex are proposedl     

Influence of the thickness of CdTe and ZnTe layers on cathodoluminescence spectra of strained CdTe/ZnTe superlattices with quantum-dot layers

The influence of the thickness of ZnTe barrier layers on the cathodoluminescence spectra of strained CdTe/ZnTe superlattices containing layers of quantum dots with an average lateral size of approximately 3 nm has been investigated. In samples with thick barrier layers (30, 15 nm), the cathodoluminescence spectra of quantum dots exhibit one band with a maximum at E = 2.03 eV. It has been revealed that, at a barrier layer thickness of ∼3 nm, the luminescence band is split. However, at a ZnTe layer thickness of 1.5 nm, the luminescence spectrum also contains one band. The experimental results have been interpreted with allowance made for the influence of elastic biaxial strains on the energy states of light and heavy holes in the CdTe and ZnTe layers. For the CdTe/ZnTe heterostructure with quantum dots in which the thickness of the deposited CdTe layer is 1.5 monolayers and the thickness of the barrier layer is 100 monolayers, the cathodoluminescence spectrum contains 2LO-phonon replicas. This effect has been explained by the resonance between two-phonon LO states and the difference between the energy states in the electronic spectrum of wetting layer fragments.     

Proposal of a Microwave-Driven Semiconductor Superlattice Oscillator for Generation of THz Radiation

We present the proposal of a microwave-driven semiconductor superlattice oscillator. We show that the interplay of a microwave pump field with a synchronous harmonic field can make a semiconductor superlattice to a gain medium for the harmonic field. Placing the superlattice in a resonator for the harmonic field allows the operation of an oscillator. The gain mechanism is based on Bloch oscillations of miniband electrons. The gain is mediated either by the interaction of the high-frequency field with the single electrons or with space charge domains or with both. The microwave-driven superlattice oscillator should be suitable for generation of coherent radiation up to several THz.