Manybody-effects in nonlinear optics of semiconductors

The given paper studies and analyzes optical properties of semiconductor structures intended for realization of modulators. The paper considers such optical properties as absorption, transmission and refraction. The dependence of these properties on wavelength, temperature and other factors is investigated. The selection of corresponding semiconductor material for realization two versions of optical modulator, namely, for transmission and refraction is carried out.

Cathodoluminescence (CL) is a very powerful technique for studying the optical properties of semiconductor structures, especially low-dimensional structures (structures with sub-micron features). We will give a number of examples of studies, where CL has been used to study a variety of low-dimensional semiconductor structures. We will also compare the CL technique with other techniques for studies of luminescence with high spatial resolution.

We consider a model of Raman scattering for a two-dimensional S=1/2 Heisenberg antiferromagnet which includes a dynamical spin-phonon interaction. We observe a broadening of the line shape due to increased coupling with excited high-energy spin states. Our results are close to a model of random, static exchange interactions, introduced in this context by Haas et al. [J. Appl. Phys. 75, 6340 (1994)], which, when extended to large numbers of spins, explains experiments in the parent insulating compounds of high-${\mathit{T}}_{\mathit{c}}$ superconduc- tors. \textcopyright{} 1996 The American Physical Society.

Deep-UV nonlinear optical (NLO) materials have attracted much academic and technical attention due to their capability of producing coherent light of wavelengths below 200 nm. As a well-known branch of NLO materials, researchers have obtained many deep-UV NLO crystals with superior properties in π-conjugated system materials (such as borate systems and carbonate systems). However, due to structural and property limitations, the research developments have encountered difficulties in balancing NLO properties. Recently, scientists started to pay attention to the non-π-conjugated system of deep-UV NLO materials. As far as we know, the non-π-conjugated deep-UV NLO materials could be divided into six categories: phosphates, sulfates, borophosphates, borosilicates, fluorides, and silicates. This review focuses on the research advances of deep-UV NLO materials with non-π-conjugated functional groups and summarizes and discusses the deep-UV NLO crystals on the basis of the performance criteria of “deep-UV transmission–large NLO effect–large birefringence”. By analyzing the structure–property relationships of these materials, we summarize the microscopic mechanism restricting the balance of properties and new functional groups, which may provide new ideas and help the explorations of deep-UV NLO materials.

Crystal growth is an important branch of solid state physics and material science. The Growth of Nonlinear Optical (NLO) materials crystals receives much importance nowadays because NLO materials have various applications in modern technologies like Laser technology, optoelectronics, and fiber optics, etc. Potassium dihydrogen phosphate (KDP) is a well known nonlinear optical (NLO) material with different applications. Since most of the amino acids exhibit NLO property, it is of interest to dope them in KDP. In the present study, amino acid L-Phenylalanine doped KDP crystals have been grown by slow evaporation solution growth technique. In present study powder XRD analysis was carried out which show that pure and L-Phenylalanine doped KDP crystals have tetragonal symmetry. The doping of L-Phenylalanine was confirmed by FT-IR and paper chromatography. Thermal analysis has been performed on the grown crystals.The SHG efficiency of L-Phenylalanine doped KDP crystals was found to be increasing with a doping concentration of L-Phenylalanine. Introduction. The demand for high quality large size KDP single crystal increases due to its application as frequency conversion crystal in inertial confinement fusion [1, 2]. KDP belongs to scalenohedral (twelve faced) class of tetragonal crystal system [3]. With the aim of improving the second harmonic generation (SHG) efficiency of KDP, researchers have attempted to modify KDP crystals by doping different types of impurities. The non-linear optical (NLO) and other properties of the crystal have been improved by doping of organic impurities [4-9]. KDP doped with amino acids like L-glutamine acid, L-gistidine, and L-valine was reported [10]. Kumaresan et al. [11] has reported the thermal dielectric properties of amino acids such as L-glutamic acid, L-histidine and L-valine doped KDP crystals. They found improved NLO properties of the KDP crystal and modifications in the structural, optical, mechanical, and electrical properties, too. Parikh [12] has reported the SHG efficiency of L-arginine doped KDP crystal. Kumaresan et al. [13] has also reported the effect of metal ion and amino acid doping on the optical properties of KDP crystal. Muley et al. [5] has studied thermal, NLO properties of KDP crystal doped with L-arginine and L-alanine. Suresh Kumar and Rajendrababu [6] studied the effects of L-arginine, L-histidine and glycine on the growth of KDP single crystals and observed that addition of amino acid enhances transparency, thermal stability and NLO efficiency of KDP crystals. Amino acid family crystals are playing an important role in the field of non-linear optical organic molecular crystal. Among them L-Phenylalanine (LPA) with chemical formula (C6H5CH2CH(NH2)COOH) is the α-amino acid with a non-reactive hydrophobic benzyl side chain. The physical, chemical and non-linear optical properties of KDP are enhanced by adding optically active amino acids as dopants.The growth and characterization of Single crystals of KDP doped with amino acids namely glycine, arginine, alanine, tryptophan, histidine have been reported earlier [5-8]. In the present work, single crystals of Potassium dihydrogen phosphate (KDP) added

Effects of magnetic dipolar interaction between like nuclei on two-quantum (TQ) free decay were examined in a multi-level NMR system, Al in Al 2 O 3 . TQ free decay was observed using a TQ π/2-pulse followed by a probe pulse. The effect of probe pulse was carefully examined to deduce the intrinsic decay time of the TQ coherence. The second moments for two- and three-quantum transitions were calculated. The observed decay time is in good agreement with that obtained from the calculated second moment by assuming Gaussian decay. Basic equations for TQ resonance are also presented.

Charge separated molecules with strong zwitterionic character make especially interesting species for quadratic Non Linear Optical (NLO) doped materials because of their large dipole moments and rather large quadratic hyperpolarizabilities. Furthermore, their sensitivity to the dielectric environment brands them as good candidates for checking the validity of formalisms relating geometrical structure and NLO properties. We have carried out an experimental and theoretical study on two phenoxide pyridinium derivatives with different inter ring twist angle, combining UV-visible, IR and NLO spectroscopies supplemented by semi-empirical and density functional calculations. Experimentally, changing the polarity of the solvent allows us to explore only a small range of twist angles. However, changing the pyridinium nitrogen atom from para to meta position gives essentially the same compound but with a larger twist angle. Changes in solvent polarity and position substitution give rise to a combined enhancement of the quadratic response by an order of magnitude, showing experimentally the possibility of tuning NLO properties of chromophores to be used as doping agents in NLO applications.

Photonic integrated circuits hold great potential for realizing quantum technology. Efficient single-photon detectors are an essential constituent of any such quantum photonic implementation. In this regard waveguide-integrated superconducting nanowire single-photon detectors are an ideal match for achieving advanced photon counting capabilities in photonic integrated circuits. However, currently considered material systems do not readily satisfy the demands of next generation nanophotonic quantum technology platforms with integrated single-photon detectors, in terms of refractive-index contrast, band gap, optical nonlinearity, thermo-optic stability and fast single-photon counting with high signal-to-noise ratio. Here we show that such comprehensive functionality can be realized by integrating niobium titanium nitride superconducting nanowire single-photon detectors with tantalum pentoxide waveguides. We demonstrate state-of-the-art detector performance in this novel material system, including devices showing 75% on-chip detection efficiency at tens of dark counts per second, detector decay times below 1 ns and sub-30 ps timing accuracy for telecommunication wavelengths photons at 1550 nm. Notably, we realize saturation of the internal detection efficiency over a previously unattained bias current range for waveguide-integrated niobium titanium nitride superconducting nanowire single-photon detectors. Our work enables the full set of high-performance single-photon detection capabilities on the emerging tantalum pentoxide-on-insulator platform for future applications in integrated quantum photonics.

Summary form only given. For the application of ultrafast optical devices in future OTDM or WDM network, the intersubband transition (ISBT) provides attractive features such as large optical nonlinearity with ultrafast response. The material system available for achieving ISBT at optical communication wavelength is, however, limited. Although the ISBT at 1.5 /spl mu/m have been reported in In/sub 0.53/Ga/sub 0.47/As/AlAs, the large lattice mismatch makes it difficult to grow, and the electron leakage into the X valley of the barriers reduces the absorption. Alternatively, GaN/AlN and InGaAs/AlAsSb have attracted attention because of their large /spl Delta/E/sub 0/, reduced electron leakage, and the design flexibility of the lattice-matched system. ISBT by use of InGaAs/AlAsSb has been recently observed by our group at 1.5 /spl mu/m. However, its optical nonlinearity has not yet been reported. We show that the InGaAs/AlAsSb exhibits a larger nonlinearity than GaN due to the large dephasing time (T/sub 2/) stemming from the small effective mass (m/sub e/*) and LO phonon energy (/spl planck//spl omega//sub LO/), and that the conduction band nonparabolicity plays only a minor role.

The growth and overlap of research in the fields of photonic crystals (PhCs) and nonlinear optics should lead to new exciting, active functions and high-efficiency nonlinear optical applications because nonlinear optical effects in PhCs may allow for significant advances in various optical processes by using resonantly stored light and anomalous band dispersions, in combination with nonlinear optical host materials. To show the experimental and theoretical evidences of great potentials of the nonlinear PhCs for the realization of the high-efficient and very compact nonlinear optical devices and applications, we have examined the typical second- and third-order nonlinear optical responses and the photonic band structure of the nonlinear two-dimensional (2D) PhC waveguides. We have demonstrated for the first time the second harmonic generation (SHG), the sum-frequency mixing (SFM) in the ultraviolet (UV) region, and the strong enhancement of the SHG intensity originating from the photonic band resonance in this waveguide. Moreover, by probing the nonlinear optical changes of the band resonances in angle-resolved reflectivity,we have shown direct evidence that the nonlinear optical changes arising from modifications of the photonic bands by purely optical means are dominated by the dispersion nature and the group velocity of the photonic bands, which are essential for the realization of desirable nonlinear applications, such as practical all-optical switching devices with very low operational power and ultra-small dimensions. These results agree well with the bhavior predicted from band structures, indicating that the design of nonlinear optical properties of material systems is realistically possible by band dispersion and group velocity engineering.

The hydrodynamic interaction between a submerged non-lifting body and lifting bodies, i.e., hydrofoils, is studied. So far it has been confirmed that the hydrofoil producing the downward lifting force reduces the wave resistance drasticly due to the hydrodynamic interaction with the non-lifting body. This paper investigates the hydrodynamic interaction effect on the unsteady hydrodynamic forces, the added wave resistance and the wave field through model test and numerical computation by Rankine panel method. Numerical results and experimental results are compared and the hydrodynamic interaction effect is discussed. We have found good agreement between numerical and experimental results and it has been confirmed that the interaction effect is not so significant in the present case.

We report the observation of room-temperature optical nonlinearities near 970 nm in InAs/GaAs short-period strained-layersuperlattices (SPSLSs) grown by migration-enhanced epitaxy on GaAs substrates. A typical sample structure consists of six repetitions of two monolayers of InAs and five monolayers of GaAs; this sequence is followed by 25 nm of GaAs, and the entire structure is repeated 50 times. Room-temperature absorbance measurements show clearly resolved excitonic features, and time-resolved photoluminescence indicates a carrier lifetime approaching a nanosecond in these samples. Nonlinear transmission and degenerate four-wave mixing (DFWM) measurements were made with a synchronously mode-locked Styryl 13 dye laser, which produced pulses of 4 ps duration tunable over 950-990 nm. Strong bleaching of the n = 1 heavy-hole excitonic absorption and a large DFWM signal associated with this absorption change were observed. Specifically, a differential transmission (ΔT/T) of 0.43 was measured for a peak pump irradiance of approximately 35 MW/cm2. For the same excitation conditions, the DFWM diffraction efficiency was approximately 4 × 10-4. Measurements were made as a function of wavelength, time delay between the pumps and probe, and pump fluence for several distinct structures. The strengths of the nonlinearities and the carrier dynamics in the various structures will be discussed.

Tunable nonlinear optical enhancement of α-FeOOH nanorods/RGO composites

An accurate numerical analysis of the flows associated with rotor/stator configurations in turbomachinery can be very helpful in optimizing performance. In this study, the unsteady, thin-layer, Navier-Stokes equations are solved using a system of patched and overlaid grids for a rotor/stator configuration of an axial turbine. The equations necessary for an accurate transfer of information between the several grids are briefly described within the framework of an iterative, implicit algorithm. Results in the form of Mach number contours, time-averaged pressures, unsteady pressures, amplitudes, and phase are presented. The numerical results are also compared with experimental data and the agreement is found to be good. HE aerodynamic processes associated with the flow of fluid through turbomachines pose one of the toughest challenges to the computational fluid dynamicist. The un- steady nature of the flow, the complex geometries involved, the motion of some parts of the system relative to others, and the periodic transition of the flow from laminar to tur- bulent are some of the factors that contribute to the com- plexity of the problem. A clear understanding of these types of flows is essential for the optimization of the performance of turbomachiner y. In this study, an attempt is made to analyze two-dimensional flow past the rotor/stator con- figuration of an axial turbine using state-of-the-art computa- tional tools and computing facilities. The two-dimensional analysis of stator airfoils in isolation or rotor airfoils in isolation is a relatively straightforward task. Such an analysis is valid when the two rows of blades are set far enough apart so that the interaction effects are minimal. However, the desire to minimize engine length re- quires the stator and rotor airfoils to be closely spaced. Clearly, the interaction effects will become more important as the axial gap between the rows is reduced. In fact, the flow becomes periodically unsteady for small values of the axial gap. The experimental results of Ref. 1 show that the temporal pressure fluctuation (the difference between the minimum and maximum pressure values) near the leading edge of the rotor can be as much as 12% of the exit dynamic pressure when the axial gap is reduced to 15% of the chord length (for the operating conditions and geometry chosen). Hence, it is important that the rotor and stator airfoils be treated as a single system when the interaction effects become predominant. A computational tool that provides the design engineer with the necessary aerodynamic data can be used to great advantage in redesigning rotor and stator airfoils to enhance performance. Such a tool has to accurately simulate the unsteady flow associated with rotor/stator con- figurations exhibiting a strong interaction. A finite-differe nce solution to the Navier-Stokes equations requires the generation of a computational grid for the

Structural and femtosecond third-order nonlinear optical properties of electron donor – acceptor substituted chalcones: An experimental and computational approach