This PDF file contains the front matter associated with SPIE Proceedings Volume 7354, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

We review some of our recent results on experimental light-induced periodic structures and their role in controlling light in discrete optics considering advanced features based on phase engineering and multiplexing of optically-induced lattices. While in the past only rather simple geometries like diamond, square, or hexagonal lattices were studied, we focus onto more complex photonic structures. Among them, we will present anisotropic triangular lattices, superlattices and three-dimensional lattices. We also study the propagation and localization of light in these structures - from simple waveforms to complex topological structures carrying phase dislocations.

The features of linear and nonlinear propagation of light beams in one-dimensional photorefractive photonic superlattices in bulk lithium niobate and in planar waveguides on this material are experimentally studied. The superlattices are optically induced in bulk samples and in planar waveguides using two-beam holographic recording method and optical projection scheme with coherent and incoherent light sources.

Photostability measurements have been made on host-guest films containing amorphous polycarbonate and an organic chromophore with a high 2^nd order nonlinear optical figure of merit. We find that the rate of photodegradation strongly depends on the oxygen partial pressure. At very low oxygen partial pressures (1.4×10^-5 bar) the average number of photons required to photodegrade a chromophore is as high as 1×10⁹ at 655 nm. Encapsulation leads to an initial rapid decrease in the photodegradation rate due to the trapped oxygen and a gradual photodegradation where 2×10⁹ photons are required to photodegrade a chromophore. There is an anomalous increase and then decrease in the photoluminescence intensity during ultraviolet irradiation.

We present experimental results on noncollinear second harmonic generation from III-V nitrides structures, discussing the collinear and noncollinear configuration as a function of polarization state of both fundamental and generated beams .

In this paper we present a novel ultra-high-speed polymer electro-optic modulator that incorporates high permittivity material cladding on the side walls of the device. We show that by packing the side walls of the modulator with this material and varying the width of the dielectric stack and electrodes that broadband operation can be achieved whilst maintaining a very low drive voltage in a compact device. The full-wave finite element analysis is employed in order to determine any frequency dispersion effects with respect to the modulators half-wave voltage-length product, characteristic impedance, microwave effective index and microwave dielectric losses.

We have developed a model based on a Green function approach to numerically investigate the second harmonic generation process in two dimensional metallic nano-objects. The linear optical response of metals in the visible regime is modeled by taking into account both free and bound electrons contributions. On the other hand, at this stage, only the contribution of free electrons is considered for the nonlinear response. Both bulk and surface nonlinear polarization source terms have been evaluated for objects of arbitrary shape. We show that our model has the potential for further improvements and could be a useful tool to investigate second harmonic emission by single or periodically arranged metallic sub-wavelength objects in a dielectric host material.

We present a gallium antimonide-based semiconductor saturable absorber mirror (SESAM) operating at 2 μm wavelength region. GaSb-based material system is the preferred choice for fabricating surface-normal devices operating beyond 2 μm because it enables the use of highly reflective semiconductor reflectors and quantum wells for wide wavelength range. For the purpose of generating short laser pules, the SESAM was carefully designed to attain a large modulation depth. The device was utilised successfully to passively Q-switch a 2 μm Tm³⁺-/Ho³⁺ -doped fiber laser, demonstrating record-short Q-switch pulses of about 20 ns.

Because of their strong nonlinear optical properties, Platinum(II) acetylides are investigated as potential chromophores for optical power limiting (OPL) applications. The strong excited state absorption and efficient intersystem crossing to the triplet states in these materials are desired properties for good OPL performance. We recently reported on OPL and photo-physical properties of Pt(II)-acetylide chromophores in solution, modified with thiophenyl or triazole groups. [R. Westlund et al. J. Mater. Chem. 18, 166 (2008); E. Glimsdal et al. Proc. SPIE 6740, 67400M (2007)] The chromophores were later incorporated into poly(methyl-methacrylate) (PMMA) glasses. A variety of doped organic solids were prepared, reaching concentrations of up to 13 wt% of the guest molecule. Raman spectra of the doped solid devices proved that the chemical structure of the nonlinear dyes remains intact upon the polymerization of the solid matrix. Luminescence spectra confirm that the basic photo-physical properties (absorption, emission and inter-system crossing) observed for the solute molecules in THF are maintained also in the solid state. In particular, the phosphorescence lifetime stays in the order of μs to ms, just as in the oxygen evacuated liquid samples. Also, the wavelength dependence and time-dynamics of the triplet absorption spectra of the dyes, dissolved in THF solution and dispersed in solid PMMA matrices, were investigated and compared. Ground state UV absorption spectra between 300 and 420 nm have corresponding broad band visible triplet-triplet absorption between 400 and 800 nm. The triplet state extinction coefficients were determined to be in the order of 10⁴ M^-1cm^-1.

We analyze in this work the second harmonic amplification of χ⁽²⁾ nonlinear process in membrane type GaAs circular photonic crystal. This unconventional kind of photonic crystal is well suited for the generation of whispering gallery modes due to the circular symmetric periodic pattern. The Gaussian beam of a fundamental pump signal at 1.55 μm defines a whispering gallery mode resonance and generates a second harmonic mode at 0.775 μm in the central missing hole micro-cavity. The periodic pattern and the micro-cavity are tailored and optimized in order to generate a second harmonic conversion efficiency of 50 %. We predict the resonances by an accurate 2D time domain model including χ⁽²⁾ nonlinearity and also by a 3D Finite Element Method FEM. Moreover, by using a 3D membrane configuration, we predict a quality factor of the second harmonic mode of the order of 35000.

Temporal characteristics of band-edge photonic crystal are precisely analyzed using a high-resolution up-conversion system. The InGaAs/InP photonic crystal laser operates at room temperature at 1.55 μm and turn on times ranging from 17ps to 30ps are measured.

The photonic crystal (PhCr) sample of a proper shape can exhibit good resonator properties with extremely high Q-factor. The resonator standing modes may be excited by an external source through the special inputs and be controlled due to nonlinear coating. We study typical 1D and 2D photonic resonators of rectangular form with nonlinear inclusions as an important element of logical devices. Depending on the beam intensity and chosen working point near the photonic band edge, the reflectivity may drastically change thus performing the logic operations. The seeming nonlinear band shift effect arises in linear PhCr's total internal reflection area due to nonlinear covering layer. Two main signal processing schemes exist in logic devices made on the base of photonic resonators. We analyze theoretically the resonator parameters for CdS/CdSe and CdS/SiO₂ photonic crystals covered with nonlinear doped glasses and preferring processing scheme for IR wavelengths. General design of logic gates and adder design are discussed. Novel calculation method based on 1D resonator's eigenstates analytical basis is used to obtain 2D spectrum.

We describe properties of entangled photon pairs generated by spontaneous parametric down-conversion in periodically poled nonlinear crystals. These materials can serve as a useful bright source of photon pairs which properties can be tailored on demand. Especially photon pairs with broad spectra and sharp temporal features can be observed. Both uniform and chirped poling are considered. Spectral properties of the generated photons, photon fluxes, coincidence-count patterns in a Hong-Ou-Mandel interferometer, entropy of entanglement, as well as transverse profiles of intensities of the generated photon fields are discussed. Also the correlation area of two photons comprising a photon pair has been studied as it depends on parameters of periodical poling. Attention is also paid to structures with randomly distributed boundaries.

Photon Logic gates based on quantum coherence have been presented for Boolean logic operations of NAND. The present photon logic gates use quantum coherence in a three-level system interacting with resonant Raman optical fields. In a specific condition of ultraslow light, the quantum coherence can be greatly enhanced so that ultralow power light can be used for photon switching applications. Unlike conventional optical switching methods, the photon switching is free from the population relaxation constraint but relies on quantum coherence (phase relaxation). By combing two photon switches in parallel, we performed Boolean logic gate operations.

Current optical fiber-communication networks increasingly rely on wavelength-division multiplexing (WDM) technologies in conjunction with optical time-division multiplexing (OTDM) of individual WDM channels. The combination of high-repetition-rate data streams with a large number of WDM channels has pushed transmission rates to nearly 1 TB/s, creating a demand for all-optical transmission sources that can generate pico-second modelocked pulses at various wavelengths. Through nonlinear mode-coupling in a wave-guide array and a periodically applied multi-notch frequency filter, robust multi-frequency mode-locking can be achieved in a laser cavity in both the normal and anomalous dispersion regimes. We develop a theoretical description of this multiplewavelength mode-locking, and characterize the mode-locked solutions and their stability for an arbitrary number of frequency channels. The theoretical investigations demonstrate that the stability of the mode-locked pulse solutions of multiple frequency channels depends on the degree of inhomogenity in gain saturation. Specifically, only a small amount of inhomogeneous gain-broadening is needed for multi-frequency operation in the laser. In this presentation, the conditions on the system parameters necessary for generating stable mode-locking is explored for arbitrary number of frequency channels. The model suggests a promising source for multi-frequency photonic applications.

Investigation of pulse shortening by passive negative feedback in mode locked train from 2.4 at. % crystalline Czochralski grown Nd:YAG in a bounce geometry under QCW diode pumping is reported. For passive mode locking a semiconductor saturable absorber with 33 quantum wells grown on GaAa substrate acting also as nonlinear element for passive negative feedback by beam defocusing was used. Temporal diagnostics was performed with high speed digital oscilloscope with bandwidth of 9 GHz combined with fast photodiode which enabled direct observation of pulse shortening along extended pulse trains from single laser shot. Efficient pulse shortening from 120 ps in the beginning of the train to 35 ps for pulses at the end of the extended train containing more than 100 pulses was achieved.

A completely analytical theory of chirped-pulse oscillators is presented. The theory is based on an approximate integration of the generalized nonlinear complex Ginzburg-Landau equation. The obtained parametric space of a chirped-pulse oscillator allows easy tracing the characteristics of both solid-state and fiber oscillators operating in the positive dispersion regime.

In the presence of a high-intensity optical field, electrons are released from atoms on an attosecond time scale. Moreover, in the tunnelling regime, this process displays a strong sensitivity to the carrier-envelope phase (CEP) of a few-cycle light pulse. Tunnelling ionization - a fascinating quantum mechanical phenomenon - leads to a quasi-stepwise increase of free electron density and, as a consequence, of the refractive index of the medium. These steps of the refractive index, corresponding to half-cycles of the driving optical field, impose a transient attosecond phase mask. By scattering probe light off this mask we detect quasi-periodic higher-order harmonics, the spectrum of which, unlike that of the harmonics originating from intrinsic nonlinearity or driven by electron re-collisions, do not depend on the probe intensity and recollision dynamics. The implemented noncollinear pump-probe experimental technique allows optical harmonics generated due to a tunnelling-ionization-induced modulation of the electric current to be spatially separated from the harmonics originating from atomic and ionic nonlinear susceptibilities, enabling background-free time-resolved detection of electron-tunnelling-controlled harmonic spectra and offering an attractive solution for attosecond optical metrology of gases and bulk solids.

Theoretical analysis on second harmonic (SH) generation with phase matched grating in waveguide is presented from the viewpoint of device design. Usually high intensity sources are necessary in order to observe a SH in a χ⁽²⁾ nonlinear structure. For this purpose, the novel proposed design takes into account a double grating effect which enhances the guided SH signal along the waveguide. In the presented structure two grating are considered: the first grating, considered at the interface between air and core, is designed in order to obtain an efficient SH conversion process by considering the quasi phase matching (QPM) condition; the second grating, placed at the interface between the core and the substrate region, increases the SH power along the propagation direction through the coupling with the substrate modes generated by the diffraction effect. The novelty of this work is in the combined effect of the two gratings. The grating lengths and periods are designed by considering the nonlinear coupled mode theory with the effective dielectric constant (EDC) assumption. The analysis includes three dimensional (3D) cases where phase matching is involved, in particular the model is applied to a GaAs/AlGAs waveguides with fundamental wavelength at λ_FU=1.55 μm and SH signal at λ_SH =0.775 μm.

We present an ultrafast depolarizer based on four-wave mixing (FWM) in highly nonlinear optical fiber (HNLF), in which a completely polarized laser beam with any fixed state of polarization (SOP) mixed with an unpolarized pump can be instantaneously converted into an unpolarized idler wave. The degree-of-polarization (DOP) of the idler wave is experimentally measured to be 0.33 when the DOPs of the polarized signal and unpolarized pump are 0.986 and 0.036, respectively. We analyze the beam couplings between a polarized beam and a completely unpolarized pump in the ultrafast depolarizer by using vector FWM theory. The nonzero DOP of the idler wave ascribes to the polarization dependence of the FWM conversion efficiency. The speed of the depolarizer is determined by the intrinsic nonlinear response of silica, which could be just a few femtoseconds.

The feasibility of the cascaded second and third harmonic generation in two-sectioned periodically poled lithium tantalate crystal is analyzed. Simulation using computational non-linear optical model rigorously coupled with the thermal model suggests that 20-30 % efficiency can be achieved for 3 W power 2.2 ns pulsed 1.064 μm laser operating at frequency 6.8x10³ Hz if the crystal is composed with optimized section lengths for: (i) 8.0 μm periodic first-order SHG structure and (ii) 6.6 μm periodic third-order THG structure. Significant inhibition of THG efficiency can be due to the heat release of SH and TH along the crystal, associated thermal dephasing and lenzing which can be effectively inhibited by decreasing the crystal cross-section dimensions to the practical minimum of 200x200 μm.

We present in this work the scalar potential formulation of second harmonic generation process in χ⁽²⁾ nonlinear analysis. This approach is intrinsically well suited to the application of the concept of circuit analysis and synthesis to nonlinear optical problems, and represents a novel alternative method in the analysis of nonlinear optical waveguide, by providing a good convergent numerical solution. The time domain modeling is applied to nonlinear waveguide with dielectric discontinuities in the hypothesis of quasi phase matching condition in order to evaluate the conversion efficiency of the second harmonic signal. With the introduction of the presented rigorous time domain method it is possible to represent the physical phenomena such as light propagation and second harmonic generation process inside a nonlinear optical device with a good convergent solution and low computational cost. Moreover, this powerful approach minimizes the numerical error of the second derivatives of the Helmholtz wave equation through the generator modeling. The novel simulation algorithm is based on nonlinear wave equations associated to the circuital approach which considers the time-domain wave propagating in nonlinear transmission lines. The transmission lines represent the propagating modes of the nonlinear optical waveguide. The application of quasi phase matching in high efficiency second harmonic generation process is analyzed in this work. In particular we model the χ⁽²⁾ non linear process in an asymmetrical GaAs slab waveguide with nonlinear core and dielectric discontinuities: in the nonlinear planar waveguides a fundamental mode at λ=1.55 μm is coupled to a second-harmonic mode (λ=0.775 μm) through an appropriate nonlinear susceptibility coefficient. The novel method is also applied to three dimensional structures such as ridge waveguides.

Magnetic semiconductors such as Ga_1-xMn_xAs have attracted a great interest in the last years due to their high potential as advanced-performance materials in optical detection and in novel spintronic devices. The carrier dynamics and the nonlinear optical response in low-temperature-grown GaAs/Ga_1-xMn_xAs heterostructures represent an interesting topic much less explored than their electronic transport and/or structural studies. We report our optical investigations of Ga_1-xMn_xAs films, grown with different Mn concentrations and subject to annealing conditions, by time-resolved, femtosecond pump-probe, differential reflectivity measurements. The analysis of the carrier relaxation times at low temperatures is presented and discussed according to nonequilibrium theories for electron scattering in magnetic materials.

We present the results of theoretical studies of the generation process of terahertz radiation arising via interaction of fewcycle laser pulses propagating in an isotropic nonlinear medium. Numerical time-integration by the finite-difference method of the system of nonlinear Maxwell equations has been performed. We consider the interaction of mutuallyorthogonal linearly polarized pulses, both having the central wavelength of 1.98 μm, duration of 30 fs and the energies of 30 nJ, propagating along the normal to the <110> plane in the 1 mm-thickness GaAs crystal. The process of formation of a terahertz pulse arising via spectral filtration of supercontinuum formed in the spectra of pump pulses at the output of nonlinear crystal is studied. The dependences of both current frequency of the pump pulses on time for different lengths of nonlinear crystal and of pump pulse durations on the crystal length are obtained.

We describe results of experiments on laser-driven proton acceleration and corresponding laser-plasma diagnostics performed with the multi-10-TW J-KAREN laser. The laser consists of a high-pulse-energy oscillator, saturable absorber, stretcher, Optical Parametric Chirped Pulse Amplifier (OPCPA), two 4-pass Ti:Sapphire amplifiers, and compressor. The final amplifier is cryogenically cooled down to 100 K to avoid thermal lensing. The laser provides ~30 fs, ~ 1 J, high-contrast pulses with the nanosecond contrast better than 10¹⁰. The peak intensity is 10²⁰ W/cm² with the 3- 4 μm focal spot. Using few-μm tape and sub-μm ribbon targets we produced protons with the energies up to 4 MeV. The tape target and repetitive laser operation allowed achieving proton acceleration at 1 Hz. We found significant differences in stability and angular distribution of proton beam in high-contrast and normal-contrast modes. The plasma diagnostics included interferometry and measurement of the target reflectivity. The latter provides convenient diagnostics of the laser contrast in the ion acceleration, harmonics generation, and other laser - solid target interaction experiments.

Successful second harmonic generation from the radiation of Pr:YAP laser has been demonstrated. The flash-lamp pumped Pr:YAP laser was operated in Q-switched pulsed regime with 0.5 Hz repetition rate at room temperature. For Qswitching, electro-optical modulator based on LiNbO3 Pockels cell in quarter-wave configuration was employed. The pulses with an energy and length of 5 mJ and 50 ns were reached, respectively, at 747 nm wavelength. BBO crystal was used for second harmonic generation, and output pulses with the 30 uJ energy and 34 ns length were generated at 373.5 nm wavelength.

Self-similarity is a ubiquitous concept in the physical sciences used to explain a wide range of spatial- or temporalstructures observed in a broad range of applications and natural phenomena. Indeed, they have been predicted or observed in the context of Raman scattering, spatial soliton fractals, propagation in the normal dispersion regime with strong nonlinearity, optical amplifiers, and mode-locked lasers. These self-similar structures are typically long-time transients formed by the interplay, often nonlinear, of the underlying dominant physical effects in the system. A theoretical model shows that in the context of the universal Ginzburg-Landau equation with rapidly-varying, mean-zero dispersion, stable and attracting self-similar pulses are formed with parabolic profiles: the zero-dispersion similariton. The zero-dispersion similariton is the final solution state of the system, not a long-time, intermediate asymptotic behavior. An averaging analysis shows the self-similarity to be governed by a nonlinear diffusion equation with a rapidly-varying, mean-zero diffusion coefficient. Indeed, the leadingorder behavior is shown to be governed by the porous media (nonlinear diffusion) equation whose solution is the well-known Barenblatt similarity solution which has a parabolic, self-similar profile. The alternating sign of the diffusion coefficient, which is driven by the dispersion fluctuations, is critical to supporting the zero-dispersion similariton which is, to leading-order, of the Barenblatt form. This is the first analytic model proposing a mechanism for generating physically realizable temporal parabolic pulses in the Ginzburg-Landau model. Although the results are of restricted analytic validity, the findings are suggestive of the underlying physical mechanism responsible for parabolic (self-similar) pulse formation in lightwave transmission and observed in mode-locked laser cavities.

The modeling and characterization of simple semiconductor wafers of GaAs, InP, etc. as passive laser modulators that give burst of Q-switched pulse and Q-switched mode-locking pulses train will be present in detail. Various simple and inexpensive semiconductor wafer pieces were used to passively modulate the Nd:hosted solid state laser systems, and the mechanism of saturable absorption that give burst of Q-switched pulse and Q-switched mode-locking pulses were studied theoretically and experimentally. We have established complete passive laser saturable absorber model, and the numerical derivation results are quite coincident to the experimental results.

A frequency-doubled Nd:YAG laser was used to pump the RbTiOAsO₄(RTA)/AgGaSe₂ (AGSE) cascade optical parametric oscillator (OPO) to generate the 5.764 μm IR pulses, which correspond to the main absorption band of cholesterol. A maximum average output power of 40 mW was regularly obtained at 30 Hz and a pump power of 2.5 W with a long-term pulse-to-pulse fluctuation of ±10%.

We report here a laser induced transient dip in the electrical conductivity of some crude toxic samples of organic origin prepared in liquid base. The electrical conductivity variation of the samples under laser exposure indicates to the occurrence of phenomenon similar to Optogalvanic effect in liquid. In the Optogalvanic effect the current of a discharging gas varies (may increase or decrease) as the discharge cavity is irradiated by a resonant electromagnetic field. This phenomenon, which has thoroughly been investigated both theoretically and experimentally for last few decades, has not been reported so far in liquid medium. In our work the samples in liquid base were placed between the electrodes of a conductivity tester and their respective electrical conductivities were measured. Once the laser was switched on in the cavity between the electrodes of the tester, the conductivity went down nearly by an amount ranging from 0.2% to 0.5% of the original values. The dip in conductivity was temporary and disappeared as soon as the laser source was removed. The experimental results are being explained in the light of Optical Nutation of the dipole moments of the molecules caused by the resonant nonlinear interaction of the molecules with the electric field of the laser. As an extension of F. Bloch's work on nuclear induction to optical frequency, we have shown that the Nutation of the dipole vectors of the interacting molecules cause a dephasing among them. This dephasing, which the key to our observation, leads to a decrease in the electrical polarizability of the medium, which finally decreases the ion production rate between the electrodes and the detector shows a dip in conductivity.

K_1-x(NH₄)_xH₂PO₄ mixed crystals were grown using low temperature solution growth method. [100] and [101] faces growth rates were investigated using an in-situ optical method. It was found that the growth rate of K_1-x(NH₄)_xH₂PO₄ with x=o.1 and 0.9 along [101] is faster than that along [100]. FTIR spectra of the mixed crystals with selected composition values confirmed the presence of both the salts in the grown crystals.

Large built-in piezoelectric fields in nitride nanostructures, because of their wurtzite structure, induce a spatial seperation between confined electrons and holes and lead to formation of electric dipoles. This paper investigates the effects of exciton-exciton interaction as a dipolar interaction in a GaN/Al_xGa_1-xN microdisk. We show how this interaction result in biexciton binding energies in the meV energy range. Also we study the effect of disk radius on exciton binding energy. Results show that the exciton binding energy in smaller disks, is larger than the bigger one.