Nonlinear Optics

We consider some nonlinear phenomena in metamaterials with negative refractive index properties. Our consideration includes a survey of previously known results as well as identification of the phenomena that are important for applications of this new field. We focus on optical behavior of thin films as well as multi-wave interactions.

Single crystals of L-Tartaric acid (C 4 H 6 O 6), an organic nonlinear optical (NLO) material, have been grown by hanging seed solution and submerged seed solution techniques at room temperature. The crystal system has been confirmed from the single crystal X-ray diffraction analysis. The crystalline perfection was evaluated using high-resolution X-ray diffractometry (HRXRD). From this analysis, it was found that the quality of the crystal is quite good. The functional groups were identified using FTIR spectroscopy. UV-vis-NIR spectrum showed the absence of absorption in the wavelength region of 220-900 nm. The second harmonic generation efficiency is 89% compared to that of standard potassium dihydrogen phosphate (KDP). The laser damage threshold value is much higher than that of KDP and closer to that of b-barium borate.

A nonlinear image technique for characterization of the optical nonlinearities is used to investigate the solid semiconductor ZnSe at 600 nm. The method based on a 4f nonlinear image technique with a phase object is used to obtain the diffraction pattern of the nonlinear filter in solid ZnSe located at the Fourier plane by a CCD camera. The nonlinear absorption coefficient and nonlinear refraction index were both obtained by fitting the nonlinear image. Good agreement between the experiment data and the simulated result are obtained indicating a sensitive and powerful method for nonlinear optical measurements.

The simulation of nonlinear wave propagation in the ray regime, i.e., in the limit of geometrical optics, is discussed. The medium involved is nonlinear, which means that the field amplitudes affect the constitutive parameters (e.g., dielectric constant) involved in the propagation formalism. Conventionally, linear ray propagation is computed by the use of Hamilton's ray equations whose terms are derived from the appropriate dispersion equation. The formalism used to solve such a set of equations is the Runge-Kutta algorithm in one of its variants. In the present case of nonlinear propagation, a proper dispersion equation must first be established from which the rays can be computed. Linear ray tracing with Hamilton's ray theory allows for the computation of ray trajectories and wave fronts. The convergence or divergence of rays suggests heuristic methods for computing the variation of amplitudes. Here, terms appearing in the Hamiltonian ray equations involve field amplitudes, which themselves are determined by the convergence (or divergence) of the rays. This dictates the simultaneous computation of a beam comprising many rays, so it is necessary to modify the original Runge-Kutta scheme by building into it some iteration mechanism such that the process converges to the values that take into account the amplitude effect. This research attempts to modify the existing propagation formalism and apply the new algorithm to simple problems of nonlinear ray propagation. The results display self-focusing effects characteristic of nonlinear optics problems. The influence of weak losses on the beam propagation and its self focusing is also discussed. Some displayed results obtained by simulating the modified formalism seem to be physically plausible and are in excellent agreement with experimental results reported in the literature. © 1998 Optical Society of America [S0740-3224 04002-8] OCIS codes: 000.4430, 060.4370, 080.2710, 160.4330, 260.5950. ͑r, t ͒ ϭ ͵ ͑ r 0 , t 0 ͒ ͑ r, t ͒ ͓k͑ rЈ, tЈ͒ • drЈ Ϫ ͑rЈ, tЈ͒dtЈ͔, (2) M. Sonnenschein and D. Censor Vol. 15, No. 4 / April 1998 / J. Opt. Soc. Am. B 1335 0740-3224/98/041335-11$15.00

Bisthiourea Zinc Acetate (BTZA) a semi organic material has been synthesized by slow evaporation method using water as a solvent. The solubility studies have been carried out in aqueous solution in the temperature range 25 ˚C – 45 ˚C. Crystals have been grown from low temperature solution method by slow evaporation of saturated aqueous solution at room temperature. Single Crystal X-ray diffraction study has been carried out to determine the lattice parameter of the grown crystal. The spectral bands have been compared with similar thiourea complexes using FTIR spectrum in the range 400 – 4000 cm-1. Optical transmittance and absorption percentage of the grown crystal have been measured from UV-Vis studies. The thermal behavior has been investigated by thermogravimetric (TGA) and Differential Thermogram analyses (DTA). The mechanical strength and work hardening coefficient of the grown crystal have been analyzed by Vicker’s microhardness method. Keywords: Growth from solutions; X-ray d...

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Two-color laser systems based on a semiconductor laser device and spectrally filtered feedback are studied. By use of a broadband numerical simulator and realistic active-structure optical responses, various two-color lasing configurations are investigated. Five characteristic dynamic regimes are observed and classified as semicoherent, coherent, multimode, chaotic, and multimode chaotic. Practical implications for gigahertz or terahertz signal-generation applications are discussed.

We consider the energy conservation problem for nonlinear-optical three-wave mixing processes at the surface and in the bulk of semi-infinite centrosymmetric lossless media. Because of the intrinsic nonlocality of these processes, the corresponding Manley-Rowe relations differ from those of noncentrosymmetric media. The ensuing restrictions link the surface and bulk nonlinear susceptibility components and may be used to test theories of nonlinear response. Our analysis permits a clear separation of the intrinsic surface contribution that contains the information about the surface structure. [S0031-9007(98)06647-2]

The synthesis and characterization of a series of new olefin-substituted closo-1,12-[C 2 B 10 H 12 ] compounds is described. The reaction of deprotonated closo-1,12-dicarbadodecaborane with 7-methoxycycloheptatriene yields the cycloheptatriene-substituted carborane compound, closo-[1-(1-C 7 H 7)-12-(H)-C 2 B 10 H 10 ] (3). Deprotonation of 3 with butyllithium and subsequent reaction with 3,4-dimethyl-2-cyclopenten-1-one was found to yield the bisolefin-substituted carbinol compound [1-(1-C 7 H 7)-12-(C 5 H 4-1-(OH)-3,4-(CH 3) 2)-C 2 B 10 H 10 ] (5) in good yield. Acidic dehydration of 5 quantitatively converted it into the simple bis-olefin cage compound [1-(1-C 7 H 7)-12-(C 5 H 3-3,4-(CH 3) 2)-C 2 B 10 H 10 ] (6). Finally, thermal treatment of 6 in refluxing toluene was employed to prepare the isomerized cycloheptatriene compound [1-(4-C 7 H 7)-12-(C 5 H 3-3,4-(CH 3) 2)-C 2 B 10 H 10 ] (7) in high yield. These compounds represent the first metal-free cyclopentadiene and bis-olefin large cluster species reported in which the C 5 ring is attached directly to the cage. The complete characterization of products by multinuclear NMR (1 H, 11 B, and 13 C), infrared, UV-visible, and mass spectroscopic analyses is presented. The X-ray crystal structures of 3 and 7 are also reported. X-ray data for 3: triclinic system, space group P1 h with cell constants a) 6.6807(3) Å, b) 10.2939(3) Å, c) 10.3962(4) Å, R) 89.342(2)°,) 74.610(2)°, γ) 83.373(2)°, Z) 2, R1) 0.0487 (wR2 (all data)) 0.1272). X-ray data for 7: monoclinic system, space group P2 1 /c with cell constants a) 7.7207(7) Å, b) 15.8730(14) Å, c) 15.5493(13) Å,) 99.146(2)°, Z) 4, R1) 0.0761 (wR2 (all data)) 0.2050).

An adaptive two step paradigm for the super-resolution of optical images is developed in this paper. The procedure locally projects image samples onto a family of kernels that are learned from image data. First, an unsupervised feature extraction is performed on local neighborhood information from a training image. These features are then used to cluster the neighborhoods into disjoint sets for which an optimal mapping relating homologous neighborhoods across scales can be learned in a supervised manner. A superresolved image is obtained through the convolution of a low resolution test image with the established family of kernels. Results demonstrate the effectiveness of the approach.

We report a sensitive single-beam technique for measuring both the nonlinear refractive index and nonlinear absorption coefficient for a wide variety of materials. We describe the experimental details and present a comprehensive theoretical analysis including cases where nonlinear refraction is accompanied by nonlinear absorption. In these experiments, the transmittance of a sample is measured the propagation path (z) of a focused Gaussian beam. The sign and magnitude of the nonlinear refraction are easily deduced from such a transmittance curve (Z-scan). Employing this technique, a sensitivity of better than 1/300 wavefront distortion is achieved in n2 measurements of BaF2 using picosecond frequency-doubled Nd:YAG laser pulses. In cases where nonlinear refraction is accompanied by nonlinear absorption, it is possible to separately evaluate the nonlinear refraction as well as the nonlinear absorption by performing a second Z scan with the aperture removed. We demonstrate this method for ZnSe at 532 nm where two-photon absorption is present and n2 is negative.

Techniques for active modulation and control of plasmonic signals in future highly-integrated nanophotonic devices have advanced rapidly in recent years, with recent innovations extending performance into the terahertz frequency and femtojoule-per-bit switching energy domains. As thoughts turn towards the development of practical device structures, key technologies are compared in this review and prospects are assessed for the future development of the field. Artist's impression of a hybrid opto-/electro-plasmonic chip combining microelectronic and photonic functionalities.

The nanometer-sized semiconductor crystallites of CdS, CdSe, CdTe, and PbS were formed by chemical procedure in glass films prepared by the sol-gel method. The films are either pure silica, silica ormosils, zirconia or combined zirconia with ormosils. As the sizes of the nanocrystallites decrease, controlled by the preparation method, the band gap shifts to higher energies due to the quantum size effect. Spectroscopic methods of absorption and luminescence allow to determine the shift and atomic force microscopy (AFM) and transmission electron microscopy (TEM) the size of the nanoparticles. X-Ray diffraction for larger nanoparticles provides information on the crystallographic structure of the particles. The potential of the nanocrystallites embedded in glass films in nonlinear optics and electrooptic devices is discussed. 

A new organic nonlinear optical crystal, 4-dimethylaminobenzaldehyde-4-nitrophenylhydrazone (DANPH), has been prepared and investigated with regard to polymorphism, growth, and characterization of the structural and physical properties. Recrystallization of DANPH in various solvents under different conditions showed the existence of three crystalline phases, a co-crystal (form I) of DANPH with benzene in a ratio 4 to 1 in space group P2 ~ 212, red greenish prisms (form II) in space group Cc, and red orange plates (form III) in space group P2Jc. The growth of crystals with interesting linear and nonlinear optical properties (form II) was investigated by using different growth techniques: solution growth, gel growth and physical vapor transport growth. With these methods bulk crystals, very thin plates, and films were grown, respectively. By the analysis of crystal structures and phase stabilities of the forms II and IIl, the mechanism of polymorphism was investigated.

Three kinds of carbazole derived dyes, Caz-MN, Caz-Fu, and Caz-Vm-MN of pushepull molecules were synthesized and their nonlinear optical properties measured. The second harmonic generation (SHG) coefficients, d 33 , of Caz-Fu/PVK[poly(9-vinylcarbazole)] (0.1:0.9) and Caz-Vm-MN/PVK (0.1:0.9) were 2.06 Â 10 À9 esu and 7.3 Â 10 À9 esu, respectively. The electro-optic coefficients (r 33 ) of these PVK blends with dyes were also observed to be 1.23 pm/V, 4.03 pm/V at a wavelength of 632.8 nm. The synthesized novel carbazole based dyes Caz-MN, Caz-Fu, and Caz-Vm-MN were characterized by means of 1 H NMR spectroscopy, IR spectroscopy, thermogravimetric analysis, electro-optic coefficients (r 33 ), and their NLO properties were evaluated by Maker fringe method.

Optics has played a key role in the rapidly developing field of molecular imaging. The spectroscopic nature and high-resolution imaging capabilities of light provide a means for probing biological morphology and function at the cellular and molecular levels. While

We have investigated the nonlinear optical interaction of uniform and kink states of a nematic and a ferrofluid-doped nematic (ferronematic) liquid crystal with an incident laser field. We find that the transition between the permitted uniform oreintational states of these systems is of first order in the case of nematics, and of second order in the case of ferronematics. In the latter case we also find the phenomenon of reentrance. We find new kink states in a magnetic field with topological winding different from π in the case of nematics, and 2π in the case of ferronematics. In ferronematics, due to grain segregation the phase diagrams for uniform and kink states are entirely different. In these systems we find a first or second order structural transformation from a single kink into a pair of kinks. Further, we obtain a rich variety of kink states as the intensity of the laser field is varied.

The molecular linear and nonlinear optical (NLO) properties of a series of seven merocyanine dyes have been studied in solvents covering a broad range of polarity (dioxane to dimethylsulfoxide). The benchmark for the series was the ''Right hand side" zwitterionic chromophore 1, with a short conjugation path and 4-pyridinylidene as the donor group. Optimization strategies to improve the nonlinear response involved an extension of the conjugation path (with one or two ethenyl groups), annelation (pyridine to quinoline), variation of the solvent polarity and partial ring locking of the p-conjugated system. All chromophores have as the acceptor moiety the cyanodicyanomethylidenedihydrofuran heterocycle. Optimising the NLO response of these zwitterionic dyes by decreasing the polarity of the solvent is only possible for the parent chromophore 1. This is because the three other successful strategies employed to further improve the second-order NLO response in polar media, result in detrimental aggregation in nonpolar media.

The authors review the history, current status, physical mechanisms, experimental methods, and applications of nonlinear magneto-optical effects in atomic vapors. They begin by describing the pioneering work of Macaluso and Corbino over a century ago on linear magneto-optical effects (in which the properties of the medium do not depend on the light power) in the vicinity of atomic resonances. These effects are then contrasted with various nonlinear magneto-optical phenomena that have been studied both theoretically and experimentally since the late 1960s. In recent years, the field of nonlinear magneto-optics has experienced a revival of interest that has led to a number of developments, including the observation of ultranarrow (1-Hz) magneto-optical resonances, applications in sensitive magnetometry, nonlinear magneto-optical tomography, and the possibility of a search for parity-and time-reversal-invariance violation in atoms. CONTENTS I. Introduction 1154 II. Linear Magneto-Optics 1155 A. Mechanisms of the linear magneto-optical effects 1155 B. Forward scattering and line crossing 1156 C. Applications in spectroscopy 1158 1. Analytical spectroscopy and trace analysis, investigation of weak transitions 1158 2. Measurement of oscillator strengths 1159 3. Investigation of interatomic collisions 1160 4. Gas lasers 1160 5. Line identification in complex spectra and the search for ''new'' energy levels 1161 6. Applications in parity violation experiments 1161 7. Investigations with synchrotron radiation sources 1161 D. Related phenomena 1162 1. Magnetic depolarization of fluorescence: Hanle effect and level crossing 1162 2. Magnetic deflection of light 1163 3. The mechanical Faraday effect III. Linear vs Nonlinear Light-Atom Interactions A. Perturbative approach B. Saturation parameters IV. Early Studies of Nonlinear Magneto-Optical Effects A. Optical pumping B. Nonlinear magneto-optical effects in gas lasers C. Nonlinear effects in forward scattering D. ''Rediscoveries'' of the nonlinear magnetooptical effects V. Physical Mechanisms of Nonlinear Magneto-Optical Effects A. Bennett-structure effects B. Coherence effects C. Alignment-to-orientation conversion VI. Symmetry Considerations in Linear and Nonlinear Magneto-Optical Effects VII. Theoretical Models A. Kanorsky-Weis approach to low-power nonlinear magneto-optical rotation B. Density-matrix calculations VIII. Nonlinear Magneto-Optical Effects in Specific Situations A. Buffer-gas-free uncoated vapor cells 1. Basic features 2. Peculiarities in the magnetic-field dependence 3. Nonlinear magneto-optical effects in optically thick vapors B. Time-domain experiments C. Atomic beams and separated light fields, Faraday-Ramsey spectroscopy *This paper is dedicated to Professor Eugene D. Commins on the occasion of his 70th birthday.

A recent trend for UV-visible lasers is based on rare-earth doped crystals with self-frequency doubling (SFD). According to its absorption, luminescence, and nonlinear optical properties, the Huntite structured YAB (YAl 3 (BO 3 ) 4 ) is a prospective representative of such materials. Efficient laser emission and SFD have already been demonstrated for Nd:YAB and Yb:YAB crystals. Er, Yb, and Dy doped YAB crystals were grown by the top-seeded flux technique. Narrow absorption lines at 9 K in the Er:YAB spectra proved the good crystal quality and the uniform Er incorporation. Weak satellite lines indicated Er interactions either with other Er ions or crystal defects at high Er concentrations. The good crystal quality was confirmed by the long (1.11 ms) luminescence lifetime at RT in the Yb:YAB crystals. The Yb-transitions were broadened by strong coupling with lattice vibrations. The first growth and spectroscopic investigation of Dy:YAB were reported. Concentration dependent lifetime of the Dy luminescence was observed. r

We present an optoelectronic oscillator (OEO) that is capable of generating complex and rich dynamics including stable periodic oscillations and broadband chaos. The OEO under analysis here is based on a resonant tunneling diode (RTD) oscillator driving a laser diode and a time-delayed feedback loop. The RTD based OEO is well described as a a Liénard oscillator with delayed-feedback. When subjected to external perturbation, the RTD-OEO generates periodic and chaotic states that are controlled by the delayed-feedback loop characteristics. The implemented numerical Liénard optoelectronic oscillator provides a simple way to study time-delayed dynamical systems containing negative resistance oscillators.

The propagation of high intensity laser beams is excessively affected by optical nonlinear effects, thereby the knowledge of the nonlinear refractive indices of the beam guiding media is indispensable in the design of laser systems and experiments. Apart from undesired self-focusing, several areas of modern laser spectroscopy can utilize optical nonlinearity, from LiDAR measurements to filamentation. In this paper we report on a direct measurement of pressure dependent nonlinear refractive index of Ar, N 2 , Ne, Xe, and air between 0.05 mbar and 1 bar, based on the powerful technique called spectrally and spatially resolved interferometry. In this way the total value of nonlinear refractive index is measured, that is the sum of all elementary phenomena contributing to the intensity dependent refractivity of the gases.

In this paper, we deal with the subject of cross-gain modulation (XGM) and cross-phase modulation (XPM) semiconductor optical amplifier-based wavelength conversion of optical channels carrying subcarrier multiplexing signals in a comprehensive way. The equations and models that describe the conversion process and the resulting harmonic and intermodulation distortions are obtained showing the superior performance of XPM over XGM in terms of second-and third-order distortion and contrast ratio. Experimental results for XGM-based wavelength conversion that confirm the results predicted by our theoretical models are presented, and finally, we consider the specific application of wavelength conversion of optical channels carrying full frequency plans such as that of cable television applications.

Thermal and optical properties of glasses of the TeO 2-ZnO, TeO 2-Nb205 and TeO 2-M20-Nb205 (M = Li, K) systems have been investigated. Linear and nonlinear indices of the materials increase with the TeO 2 rate. The highest values are obtained for the niobium tellurite glasses emphasizing the particularly significant role of NbO 6 octahedra in the optical response.

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), ζ-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experi-ments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

A new nonlinear optical material tetrakis thiourea nickel chloride (TTNC) was synthesized and single crystals were grown from mixed solvent of water and isopropanol by both slow evaporation and slow cooling methods. The grown crystals were characterized by powder X-ray diffraction analyses to confirm the crystal structure. The presence of functional groups and the coordination of metal ions to thiourea were confirmed by FTIR and Raman spectroscopy analyses. UV-VIS spectrum was recorded to study the optical transparency of the grown crystals. Thermal properties of the crystals have been by investigated using thermo gravimetric (TG) and differential thermal analyses (DTA), which indicate that the material does not decompose before melting. The second order nonlinear optical property of the grown crystal was examined by Kurtz powder technique and mechanical behavior was studied by Vicker's microhardness test.

We report the development of a methodology for the comprehensive characterization of the linear-and nonlinearoptical properties of a model copolymer, Disperse Red 1, covalently functionalized to a methyl methacrylate backbone. From refractive-index and electro-optic measurements, we have evaluated both fundamental macroscopic and microscopic nonlinear-optical properties. We have measured the refractive indices of the copolymer as a function of chromophore concentration, wavelength, and poling field. For the linear-optical properties we find that the wavelength dependence is well described by a single-oscillator Sellmeier equation and that the poling-field dependence is well described by a simple theory related to the order parameter. From the observed refractive-index anisotropy as a function of poling field, we have obtained an effective dipole moment for the Disperse Red chromophore. We have measured the linear electro-optic effect in these systems as a function of poling temperature, film thickness, poling-field strength, wavelength, and concentration. We have found that the electro-optic coefficients may be modeled by an independent-response two-level dispersion model, from which an independent determination of the effective dipole moment, nonresonant second-order susceptibility x(2), and nonresonant molecular hyperpolarizability 3 have been obtained. N-ethyl)-amino-4'-nitroazobenzene 9 13, 23 -27 (Disperse Red 1) and NN-dimethylaminonitrostilbene 4 1 2 ' 2 9 in guest-host or copolymer form. Most inquiries into the two last-named chromophores have focused on specific aspects of the nonlinearity.

Few-electron atoms interacting with electromagnetic fields provide for privileged scenarios for disentangling elemental correlation mechanisms. We demonstrate that high-order harmonic generation (HHG) from neutral helium presents a distinctive trace of correlation back reaction in the electron dynamics prior to ionization. We identify a mechanism in which the field interacts with one of the electrons, while the second is excited to a Rydberg level through the Coulomb interaction. As back response to this correlated excitation, the first electron is knocked down to a lower level, from which it ionizes to generate high-order harmonics. Unlike other multielectron phenomena, where the electron-field interaction is modified by cross correlations with the rest of the interacting electrons, back reaction is a mechanism of autocorrelation. Our numerical simulations reveal back reaction as a relevant aspect in HHG from correlated two-electron systems, and paves the way to disentangle valence electron-electron correlation dynamics using high-harmonic spectroscopy.

Phase noise is a topic of theoretical and practical interest in electronic circuits, as well as in other fields such as optics. Although progress has been made in understanding the phenomenon, there still remain significant gaps, both in its fundamental theory and in numerical techniques for its characterisation. In this paper, we develop a solid foundation for phase noise that is valid for any oscillator, regardless of operating mechanism. We establish novel results about the dynamics of stable nonlinear oscillators in the presence of perturbations, both deterministic and random. We obtain an exact, nonlinear equation for phase error, which we solve without approximations for random perturbations. This leads us to a precise characterisation of timing jitter and spectral dispersion, for computing which we develop efficient numerical methods. We demonstrate our techniques on practical electrical oscillators, and obtain good matches with measurements even at frequencies close to the carrier, where previous techniques break down. we present can be extended [1] for the MNA (Modified Nodal Analysis) formulation (i.e., DAE formulation) given by d=dt qx + f x = 0. 2 After any small disturbance that does not persist, the system asymptotically settles back to the original limit cycle. See [2] for a precise definition of this stability notion.

The nonstationary parametric interaction of waves in negative-index metamaterials is studied in the second-order dispersion theory. A nonlinear interaction between a long pulse of a strong pump wave and an ultrashort pulse with quadratic phase modulation is considered. The results of calculating the shape of the spectrum of an excited signal wave are presented. A comparison is made with the case of interaction in an ordinary medium. It is shown that the effects of group-velocity dispersion and dispersive spreading in such materials lead to a narrowing of the spectrum of the excited wave. The presence of phase modulation of the exciting idler pulse promotes broadening of the central maximum of the spectrum of the excited signal wave. As the modulation factor increases, the fragmentation of the excited pulse is observed.

We demonstrate the measurement of optical frequency differences between Q-switched laser pulses by using photo-electromotive-force (photo-EMF) optical frequency sensors. The presence of high-peak-power laser pulses affords the photo-EMF frequency sensor with ultrafast response times limited only by the free-carrier lifetime of the sensor material. Such fast response times lead to a broad dynamic range for optical difference frequency measurements with an experimentally demonstrated frequency detection bandwidth in excess of 50 MHz, limited only by the capability of our test equipment. Such a large dynamic range for optical frequency detection makes photo-EMF sensors ideal candidates for adaptive remote sensing of high-speed objects.

A numerical study of second harmonic generation (SHG) in one-dimensional nonlinear photonic crystals based on full nonlinear system of equations, implemented by a combination of the method of finite elements and fixed-point iterations, is reported. This model is derived from a nonlinear system of Maxwell's equations, which partly overcomes the known shortcoming of some existing models relied on the undepleted-pump approximation. We derive a general solution of SHG in one-dimensional nonlinear photonic crystals structures. The convergence of our method is fast. Numerical simulations also show the conversion efficiency of SHG can be significantly enhanced when the frequencies of the fundamental wave are located at the photonic band edges or are assigned to the designed defect states.

Photoinduced non-linear optical effects in large-sized (up to 25 nm) nanocrystallites (NC) of Ge-doped Bi 12 TiO 20 (BTO:Ge) incorporated within olygoether photopolymer matrix have been studied. Photoinduced second harmonic generation (PISHG) was measured. Nd:YAG pulsed laser (l=1.06 mm) was used as a source of photoinducing light. As a fundamental light source for the SHG and two-photon absorption, Er:LiYF 4 laser (l=2.065 mm) was used. We have found that with increasing IR pump power density, the output doubled frequency SHG signal (l=1.03 mm) increases and achieves its maximum value at the pump power density about 0.45 GW/cm 2 and NC size about 12 nm.The values of second-order optical susceptibilities were almost 20% larger than for the pure BTO NC single crystals. With decreasing temperature below 60 K, the SHG signal increases achieving maximal value at LHeT. r

We show how the combination of electromagnetically induced transparency based nonlinear optics and cold atom technology, under conditions of ultraslow light propagation, allows nonlinear processes at energies of a few photons per atomic cross section. [S0031-9007(99)09290-X]

Lithium tetraborate, Li 2 B 4 O 7 films on glass substrate were prepared by chemical solution decomposition (CSD) method. The spin coated film (2000 rpm, 20 sec) was preheated (200°C, 20min) and then annealed at different temperatures (450° -600°C) to form polycrystalline Li 2 B 4 O 7 film. By X-ray diffraction (XRD), the prominent planes are found to be (100), and . The result shows that the main component of the film is Li 2 B 4 O 7 crystalline phase. A slow XRD scan was used to calculate the crystallite size (D) and the average crystallite size was found to be 178nm. The lower cut off wavelength at 325 nm with 75% transparency was measured by the UV-Vis spectra and the spectral dependence of the optical constants (extinction coefficient (K), reflectance(R)) was estimated. The optical energy band gap was found to be 3.62 eV. The nonlinear optical properties were studied by Z-scan experiment using a Q-switched, Nd: YAG laser (532nm, 7ns). The nonlinear absorption coefficient (NLA) β was found to be -5.74 x 10 -5 cm/W. Reverse saturable absorption (RSA) is due to the multi photon absorption process. The high value of β makes the film suitable for optical limiting applications