This PDF file contains the front matter associated with SPIE Proceedings Volume 11026, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

The mid-infrared spectral range is unique in many ways. Within this region, electromagnetic radiation can resonate with the most intense signature molecular bands, thus drastically enhancing the coupling between the field and molecular motions. Electrons driven by intense ultrashort mid-IR field waveforms acquire unusually high pondermotive energies within a fraction of the field cycle, giving rise to new regimes of high-field nonlinear optics. The λ² scaling of phasespace mode volume with radiation wavelength λ translates into the λ² dependence of the self-focusing threshold, allowing much higher peak powers to be transmitted in a single laser filament in the mid-IR range without losing beam continuity and spatial coherence. Recent breakthroughs in ultrafast photonics in mid-IR help understand complex interactions of high-intensity ultrashort mid-IR pulses with matter, offer new approaches for x-ray generation, enable mid-IR laser filamentation in the atmosphere, facilitate lasing in filaments, give rise to unique regimes of laser−matter interactions, and reveal unexpected properties of materials in the mid-IR range. Motivated and driven by numerous applications and long-standing challenges in strong-field physics, molecular spectroscopy, semiconductor electronics, and standoff detection, ultrafast optical science is rapidly expanding toward longer wavelengths. Experiments reveal unique properties of filaments induced by ultrashort laser pulses in the mid-infrared, where the generation of powerful supercontinuum radiation is accompanied by unusual scenarios of optical harmonic generation, giving rise to remarkably broad radiation spectra, stretching from the visible to the mid-infrared. Generation of few- and even single-cycle midinfrared field waveforms has been demonstrated within a broad range of peak powers and central wavelengths. Belowthe- bandgap high-order harmonics generated by ultrashort mid-infrared laser pulses are shown to be ideally suited to probe the nonlinearities of electron bands, enabling an all-optical mapping of the electron band structure in bulk solids. As a part of a bigger picture, laser-induced filamentation in the mid-infrared and intraband high-harmonic generation using ultrashort mid-infrared pulses offer important physical insights into the general properties of the nonlinear-optical response of matter as a function of the wavelength. Unlike their near-infrared counterparts, which can be accurately described within the framework of perturbative nonlinear optics, mid-infrared filaments often entangle perturbative and nonperturbative nonlinear-optical effects, showing clear signatures of strong-field optical physics.

We demonstrate a novel approach of femtosecond laser pulse spectral-temporal control under filamentation in a wide range of pressures from 5 bar up to supercritical state. We showed that laser-induced processes such as supercontinuum generation and pulse self-compression could be tuned both by pressure and by energy adjustment due to the nonlinear refractive index alteration via pressure change. Thanks to the high pressure-controlled nonlinearity, a broadband (from 250 to 2500nm) supercontinuum with total efficiency more than 50% of energy can be generated in supercritical Xe and CO₂. It was also demonstrated that the femtosecond laser pulse can be compressed in Xe in the femtosecond monofilamentation mode by 3.5 times with efficiency as high as 60%.

When near infrared femtosecond Bessel laser beam (fs-BLB) is obliquely incident on the silica surface, annular beams (ABs) with bandwidths of several tens of nanometers and different peak wavelengths in visible range are generated simultaneously. It is considered that four-wave mixing (FWM) and corresponding cascaded parametric processes are responsible for the generation of multi-wavelength ABs. It has also been found that the generation efficiency is significantly enhanced by the resonance absorption of the silica glass. Since the diffraction angles of these colorful ABs mainly depend on their wavelengths and is insensitive to the input laser energy, this technique may find important applications where multi-wavelength ultrashort pulses are needed, such as multidimensional multiplexing optical communications, optical sensing, and pump-probe measurements. Besides, they are also expected to be used as heralded photon source integrated into the quantum information system.

We report on a new experimental technique aimed to investigate femtosecond filamentation process in transparent condensed dielectrics. The proposed method is based on a highly resolved shadow photography and wideband (about 100MHz) photoacoustic imaging. We demonstrate, that combination of these techniques allows conducting comprehensive filament investigation by retrieving the value of the energy deposition into a medium, plasma electron density and the size of the filament formation region. Moreover, applying these techniques we studied the dependence of filament properties on a filamentation regime.

The appeal of on-chip broadband supercontinuum generation (SCG) comes from its potential to pave the way to full integration of various ultrafast optics applications in frequency metrology, wavelength division multiplexing, and sensing. However, the generation of octave-spanning supercontinuum requires either the use of exceedingly short femtosecond pulses or large footprints. One promising method to achieve broadband supercontinuum is to exploit the high-order soliton fission. Bragg solitons leverage the large anomalous dispersion at the photonic band edge of nonlinear Bragg gratings, therefore they can facilitate high-order soliton fission in much shorter waveguide lengths and significantly lower powers. Soliton dynamics, especially fission, on CMOS-compatible platforms have been limited due to the nonlinear losses such as two-photon absorption and free carrier effects in silicon or low optical nonlinearities in traditional silicon nitride. We use compositionally engineered ultra-silicon-rich nitride (USRN) that possesses a large Kerr nonlinearity in the absence of two-photon absorption. Utilizing ideal nonlinear properties of USRN platform in conjunction with our monolithically integrated cascaded grating-waveguide design, we experimentally demonstrate × 4 spectral broadening enhancement, from 79 nm in the 7 mm long reference waveguide to 311 nm at the cascaded Bragg grating and waveguide device of the same footprint, using input pulses of 1.68 ps FWHM. This result is promising for generating wide supercontinuum, without the need to use sub-picosecond pulses or increasing the device footprint, by exploiting the high-order soliton dynamics availed through the simple photonic chip design consisting of a nonlinear Bragg grating and nonlinear waveguide.

Optical activity, i.e. the ability to rotate the polarization state of light, can also occur in structures that are not chiral at all, a property of fundamental importance for the diagnostic applications. This effect can be artificially obtained by means of metasurfaces, i.e materials surface with suitable nanostructures under appropriate light injection. In addition it is possible to obtain an optical response from metasurfaces that exhibits a nonlinear response such as second- order circular dichroism thanks to the recent successes in nanotechnology, opening the way to new functionalities on a spatial scale of few hundred on nms. In what follow we describe some properties of chiral metasurfaces.

We investigate the impact of different substrates on the radiation efficiency of nonlinear processes from dielectric nanoantennas. Several approaches have been considered to optimize the nonlinear radiation efficiency from these structures, but all the strategies have generally failed at limiting the amount of radiation at the harmonic frequencies that is lost in the substrate. It is well known that epsilon-near-zero (ENZ) materials, namely material showing a zero-crossing for the real part of the dielectric permittivity, have peculiar linear properties, such as their ability to realize perfect electromagnetic tunneling and re-direct antennas electromagnetic radiation. Here we first compare the second harmonic signal radiated from a cylindrical AlGaAs nanoantenna placed over different materials, including an ENZ substrate and found that the ability to re-direct the electromagnetic radiation is particularly favored when the ENZ condition occurs at the second harmonic frequency. These results let us foresee a novel approach to improve nonlinear processes at the nanoscale and the possibility to realize novel functionalities, such as beam steering and tailored antenna directivities thanks to the tunability of ENZ materials.

We study the dynamic behavior and switching of optical pulses in the PT - symmetric structure with the additional periodic modulation of the Kerr nonlinearity. In such structure the change of a refractive index by an intense optical radiation causes the change of the PT - symmetry breaking threshold while the gain/loss value is constant. As the result the system can move from the full PT - symmetry state to the broken PT - symmetry or vice versa. It is shown that despite the self-pulsation instability these transitions can be observed in the switching of long enough optical pulses. Furthermore, such active structures allow to control the amplitude enhancement of the transmitted pulses.

Here, we analytically study optical activity of chiral semiconductor gammadions whose chirality arises from the nonuniformity of their thickness. We show that such gammadions distinguish between the two circular polarizations upon the absorption of light, unlike two-dimensional semiconductor nanostructures with planar chirality. Chiral semiconductor gammadions of inverse conical shape are found to exhibit the highest dissymmetry of optical response among the nanostructures of the same size. The results of our theoretical study can be used in future applications of semiconductor gammadions in biomedicine and optoelectronics.

At present, laser sources are widely used in many fields. Not only in laboratories, but also in sphere of medicine, manufacturing and military. Lasers are potentially dangerous to the eyes or sensitive optical devices, therefore it is necessary to develop optical limiters. One of the significant properties of carbon nanotubes is their optical limitation of laser radiation. Many works of scientific groups are devoted to materials for limiters, which include carbon nanotubes. However, they still have an increased interest. A particular role is given to such mechanism of nonlinear attenuation as scattering and absorption. Moreover, it is important not only their combined effect to increase the effectiveness of the limiters as a whole, but also the contribution of each of them with their combined effect. It is equally important to accurately determinate the concentration in which there is a strong attenuation of high-intensity laser radiation and minimal attenuation at low intensity. The nonlinear and linear optical properties of water-dispersed media with different concentrations of single-walled carbon nanotubes (SWCNTs) were obtained by optical density spectra, experimental Zscan data with an open aperture and a fixed location of the limiter. Radiation in single mode with duration of 16 ns at wavelength of 1064 nm from Nd:YAG laser was used. The linear transmittance of the prepared water dispersions of the SWCNTs ranged from 60% to 70%. Limiter with such working substances had attenuation coefficient 10 and 14 for the concentration of nanotubes 3.125 mg/l and 6.25 mg/l, respectively.

The photosensitive protein bacteriorhodopsin (bR) has been shown to be a promising material for optoelectronic and photovoltaic applications, but it cannot effectively absorb and utilize light energy in the near-infrared (NIR) region of the optical spectrum. Semiconductor quantum dots (QDs) have two-photon absorption cross-sections two orders of magnitude larger than those of bR and can effectively transfer the up-converted energy of two NIR photons to bR via the Förster resonance energy transfer (FRET). In this study we fabricated a hybrid material in the form of an aqueous solution of electrostatically bound complexes of QDs and purple membranes (PMs) containing bR. Efficient FRET from QDs to bR was observed in these complexes under selective two-photon excitation of QDs. Then, we fabricated a photoelectrochemical cell operating in the NIR spectral region. Measurement of the photoelectrical signals from the cell containing pure PMs, or QD–PM hybrid material has shown that the light conversion in the QD-PM hybrid material with 3:1 bR-to-QD molar ratio is more efficient than in the material with 20:1 bR-to-QD molar ratio. The results of this study may extend the use of bioinspired hybrid materials in optoelectronics, holography, and bioenergetics under the conditions of nonlinear excitation.

The features of the nonlinear absorption of CdSe/CdS core-shell nanocrystals based on 5 monolayer (ML) CdSe nanopletelets (NPLs) in the case of one-photon excitation of the exciton transitions by means of ultra-short laser pulses (non-stationary regime) were investigated. CdSe NPLs were synthesized by colloidal method at the temperature of 210 oC. Optical absorption spectrum of as prepared CdSe NPLs showed narrow excitonic absorption bands at 463 and 436nm corresponding to hh-e and lh-e, respectively, which indicates that the CdSe NPLs have 5ML thickness. The CdSe/CdS core-shell NPLs were obtained using method of colloidal atomic layer deposition (c-ALD). The c-ALD method allows obtaining core-shell NPLs with thickness control at the atomic monolayer level. The obtained CdSe/CdS core-shell NPLs showed narrow and pronounced hh-e and lh-e transitions characteristic for cadmium chalcogonide NPLs, which indicates their high uniformity in terms of thickness. Resonant excitation of heavy hole and light hole excitons was realized for 5CdSe/CdS, 5CdSe/2CdS, correspondingly, and non-resonant excitation both heavy hole and light hole excitons was carried out for 5CdSe/3CdS NPLs. Excitation of colloidal solution of NPLs was carried out by the second harmonic of passively Q-switched Nd3+:YAG laser (2w, λ=532 nm, the pulse duration is 30 ps). Nonlinear transmission spectra evolution was measured while changing pumping intensity. The variation of excitation intensity was realized by neutral optical filters. The increase in transmission of the exciton transitions at the excitation wavelength was observed for all three samples. This feature of nonlinear change in transmission is attributed to phase space filling effect. The greater induced bleaching was discovered for resonantly excited sample. The saturation intensity of all samples were measured about 50 MW/cm2 for non-stationary excitation regime. The transmission increases in absolute value ΔT=T-T0≈30%, with relative change in transmission ΔT/T0≈50% in the case of resonant excitation of excitons, and ΔT≈15%, ΔT/T0≈35% in the case of resonant excitation. The role of up-conversion and down-conversion processes were defined.

Nowadays the generation of terahertz pulses using the mechanism of optical rectification is intensively studied both theoretically and experimentally. If the group velocity of an optical pulse is equal to the phase velocity in the terahertz range of a medium with quadratic nonlinearity, then a two-component optical-terahertz temporal soliton can be formed. In the present work, we study the possibility of forming an optical-terahertz spatiotemporal soliton (optical-terahertz bullet) in a gradient focusing waveguide. If the duration of the input optical pulse lies in the femtosecond region, then when generating a terahertz signal, the nonlinearity dispersion is important. This also leads to the influence of the phase modulation of the optical pulse on the generation process. We take this circumstance into account when considering the formation of optical-terahertz bullets. The system of related equations for the complex envelope of the optical pulse and the electric field of the THz pulse is solved numerically. The original conservative nonlinear finite-difference scheme is realized with the help of a pseudo-spectral method. We find the conditions under which it is possible to trap an optical terahertz pulse into a focusing waveguide with the formation of optical-terahertz bullets.

Imaging with terahertz (THz) waves has great potential for applications, such as in nondestructive testing, tumor detection, and biodetection. However, due to its millimeter-scale wavelength, using conventional imaging method, one cannot get THz images within spatial resolution better than sub-millimeter, which hinders from resolving smaller objects. Sensing evanescent waves in near field (<<λ) is a feasible path to realize sub-diffraction imaging. Raster scanning object’s surface pixel by pixel via a sub-wavelength-sized metallic aperture or an extremely tiny probe tip have been used to realize THz sub-diffraction imaging, while both mechanical-scan methods have disadvantages, such as invasive effects on sample, inflexible setups, and low source energy efficiency. Another technique called electrooptic (EO) near-field microscope driven by intense THz pulsed field achieves THz sub-diffraction images using a thin EO crystal (LiNbO3). It not only needs strong THz pulsed field but also suffers from thickness of the EO crystal. More recently, a novel scheme based on single-pixel imaging (SPI), which reconstructs the image by sequentially measuring correlations between the object and a set of prearranged masks, has been demonstrated in THz regime in far field and near field based on dynamic spatial THz wave modulator. In this work, we proposed and experimentally demonstrated a novel THz wave near-field ghost imaging with spatial resolution of ~4 μm (over λ0/100 at 0.5 THz) using single-pixel compressive sensing enabled by femtosecond-laser (fs-laser) driven spintronic nonlinear near-field THz wave emitter. By fs-laser exciting a few-nm-thick metallic ferromagnetic/nonmagnetic (FM/NM) heterostructural (Pt/Fe/W) thinfilm with a couple of digital micromirror devices, we generate spatially encoded array of near-field THz wave emitter. With single-pixel Hadamard detection of the emitted THz waves, we reconstructed the THz wave near-field ghost image of an illumined object at near-field from a serial of encoded sequential measurements, yielding improved signal-to-noise ratio by one-order magnitude over raster scanning technique. Further, we demonstrate the acquisition time was compressed by a factor of over four with 90% fidelity using total variation minimization algorithm. The proposed terahertz wave near-field ghost imaging technique enabled by nonlinear spintronic terahertz emitter inspires new and challenging applications, such as cellular imaging.

We report on the numerical investigation of the generation of THz short pulses by two-color laser pulses in ionized gas plasma in ambient air. One of the major aspects of this study is to find the ideal conditions of second harmonic pulse generation in a suitable nonlinear crystal, where the generated THz pulse is the most intense at given input pulse parameters. We found that an optimal thickness can be found depending on the input pulse parameters, which is defined by two opposing phenomena, the frequency conversion and the linear dispersion. On one hand, a thick crystal can generate energetic second harmonic, but group velocity mismatch spoils the temporal overlap, while on the other hand, a thin crystal does not have enough conversion efficiency. The optimal thickness of one of the most common nonlinear material, BBO was investigated between 1 μm and 500 μm in regards two of the major laser pulse parameters, the pulse duration from 25 fs up to 100 fs and the fluence from 1 Jcm^-2 up to 5 Jcm^-2. Our investigation concluded that the optimal thickness increases with the pulse duration and decreases with the fluence.

Asymmetric nanostructures can mimic a chiral response when circular polarized light interacts with the structures under particular angle of incidence [1]. This phenomenon is called ‘extrinsic chirality’ and usually is present under linear optical investigation with low visibility. Due to the fact that optical second harmonic generation is possible only in samples with some degree of asymmetry, this can be used in order to investigate the extrinsic chirality with a background free technique, thus inducing a high visibility of the artificial circular dichroism [2,3]. Here we present the second harmonic generation (SHG) measurements obtained on samples composed by GaAs nanowires grown on silicon. The wires present resonant leaky modes around 800nm and at 400nm due to the high refractive index contrast ratio between wires and air, even if these wavelengths lie on the absorption band of GaAs [4]. The measurements performed on this sample present good SHG signal due to the second order nonlinear term of GaAs, but did not present any circular dichroism (SHG-CD). By coating the sample with a 20nm thin layer of gold deposited asymmetrically, by evaporating the metal only from one side of the nanowires, the symmetry of the structure is broken, thus induced high SHG-CD. The SHG-CD is measured by shining the sample with circular polarized pump light at the fundamental wavelength of 800nm and by revealing the second harmonic signal at 400nm in s or p polarization, as a function of sample rotation. Four samples were measured with GaAs wires of about 5 micron in length with different diameters ranging from 140nm to 200nm. In this case it is possible to explore different resonance conditions and different SHG-CD is revealed. For each sample, the measured were carried out before and after the asymmetric gold layer deposition, thus allowing direct comparison of the results. References [1] A. Belardini, M. C. Larciprete, M. Centini, E. Fazio, C. Sibilia, D. Chiappe, C. Martella, A. Toma, M. Giordano, and F. Buatier de Mongeot, Phys. Rev. Lett. 107, 257401 (2011). [2] A. Belardini, M. Centini, G. Leahu, D. C. Hooper, R. Li Voti, E. Fazio, J. W. Haus, A. Sarangan, V. K. Valev, C. Sibilia, Sci. Rep. 2016, 6, 31796. [3] G. Leahu, E. Petronijevic, A. Belardini et al., Adv. Optical Mater. 2017, 1601063 (2017). [4] G. Leahu, E. Petronijevic, A. Belardini, M. Centini, R. Li Voti, T. Hakkarainen, E. Koivusalo, M. Guina, C. Sibilia. Sci. Rep. 7, 2833 (2017).

In this work we present results of our study of light bullets in inhomogeneous media with quadratic nonlinearity. We consider the second harmonics generation by few-cycle pulses having about 3 – 5 oscillations under the envelope. We give reasons to apply “slowly varying envelope approximation” in this case. The self-consistent system of nonlinear equations for the envelopes of both harmonics is substantially modified in comparison with the case of quasimonochromatic signals. This system is supplemented by a third order group dispersion and by a dispersion of nonlinearity. The diffraction terms are also modified. The appropriate system of parabolic equations for the envelopes of both harmonics is obtained. To solve an arising 2D+1 system numerically we construct an original nonlinear finitedifference scheme based on the Crank-Nicolson and pseudo-spectral methods preserving the integrals of motion. We discuss different regimes of pulse propagation depending on the competition among nonlinearity, diffraction, temporal dispersion and waveguide geometry.

By means of numerical simulation we investigate vortex solitons comprised of coupled pulses with phase singularity under conditions of second harmonic generation. They are usually known for their low stability. We carefully examine homogeneous or inhomogeneous media. Our principal interest is to obtain a stable two-component bullet at normal dispersion. We demonstrate that such bullet can form if spreading tendencies compete with the proper focusing waveguide geometry.

We demonstrate second harmonic generation from a GaAs substrate, well-below the absorption edge. The pump is tuned in the transparency range, at 1064 nm, while the SH is tuned in the opaque spectral range of GaAs, at 532 nm. We work far from the phase matching condition and we find that the phase locked component of the second harmonic propagates trough the opaque material. As expected, we find that the polarization of the generated SH signal is sensitive to the polarization of the pump. We demonstrate different surface and bulk contributions to the SH transmitted signal and we show that the surface-generated SH components can be more intense than bulk-generated SH signals. The experimental results are contrasted with numerical simulations that include these two factors, using a hydrodynamic model, accounting for all aspects of the dynamics, including surface and bulk generated harmonic components.

We have studied generation of stable and low-noise de-chirped ultrashort solitons in bound states and we have experimentally demonstrated the formation multi-bound solitons with the controllable number of bound states 7 < N < 17 by pump power variation. A numerical simulation of the influence of various types of fluctuations on the generation mode was also carried out.

Moving the polarization of the incident wave along a meridian of the Poincaré sphere, experimentally we show that the coupling with the fundamental Bloch’s surface waves of the mode, provide a spatially coherent, macroscopic spinmomentum locked propagation along the symmetry axes of the PhCM. This novel mechanism of light-spin manipulation enables a versatile implementation of spin-optical structures that may pave the way to novel strategies for light spin technology and photonic multiplatform implementations.

Intraoperative margin assessment during Mohs micrographic surgery (MMS) is clinically critical. Currently, frozen pathology is the gold standard of assessing Mohs excisions for signs of remaining cancerous lesions; however, it is still considered time-consuming and sometimes misses the real margins. In this study, we demonstrate nonlinear microscopy imaging of hematoxylin-eosin (H&E) stained whole-mount skin tissues with a sub-femtoliter resolution through third-harmonic- generation (THG) and three-photon-excited-fluorescence (3PF) by using 1260 nm Cr:forsterite-laser-based nonlinear microscopy, which also enables virtual biopsy for preoperative margin assessment. Without the physical sectioning procedure and with a simplified staining process, real margins were preserved and time before microscopic examination was potentially saved three times shorter than frozen pathology. By exactly stained by H&E, the compatibility allows the adjunction to frozen pathology if further examination is needed. Virtual-sectioning imaging of H&E stained skin tissues is displayed real-time and can be post-processed analogously to conventional H&E histology, facilitating pathologists for diagnosis.

Recently the numerical and experimental results of optical self-written waveguides (SWWs) has been demonstrated intensively in the photopolymer media. In order to further understand the mechanism of self-written net-waveguide in photosensitive polymers, light-induced material response is analyzed. Optical netwaveguide trajectories formed using solid bulk of acrylamide/polyvinyl alcohol (AA/PVA) photopolymer material. As part of this work presents a studying of non-linear optics in photopolymer systems to form a net-waveguides. Which deals with the nonlinearity behaviors of transmitted light in photopolymer media, during refractive index changed throughout the optical self-propagating process. The self-interactions of crossing beams inside photopolymer material during SWWs process are studied. It is shown that there is good agreement between the numerical simulation results and experimental observations. These are confirmed the validity of the numerical model that was used to simulate these experiments.

The deposited energy density (DED) serves as a key parameter in the process of the femtosecond laser pulse energy delivery into the bulk of transparent dielectrics. The laser-induced micromodification can be created if the value of DED exceeds a certain threshold, which is specific for each material and does not depend on the laser wavelength. In this contribution, we present a comprehensive study of the DED evolution with the driving pulse energy and wavelength under femtosecond microstructuring of transparent dielectrics. To precisely determine the laser impact area we applied for the first time a real-time diagnostic of microplasma based on third harmonic generation. This technique gives submicron spatial resolution and is extremely sensitive to the free electron density (about 10^-5 of the critical electron density). We found out that the threshold DED equals to approximately 2.5 kJ/cm³ for fused silica and roughly corresponds to excess of glass transition temperature. The highest DED is achieved for the shortest wavelength (620 nm) and equals to 16 kJ/cm³.

As of today, one of the milestones in quantum theory testing is obtaining of macroscopic quantum states, for which very low temperatures are necessary. Such low energies can be present during optical and optomechanical cooling of nanostructures. Here we investigate the deep cooling of ytterbium-doped fluorite nanocrystal via coherent population transfer techniques. We consider two main approaches towards coherent transfer, namely, Raman pulses and stimulated Raman adiabatic passage, and search for the most efficient cooling parameters. Optimization of the process of deep nanocrystal cooling opens up possibilities for various applications and technologies.

High-intensity nanosecond Nd:YAG laser pulses were used to induce crystallization in saturated solutions of the nitrate salts; sodium nitrate (NaNO₃), potassium nitrate (KNO₃) and calcium nitrate [Ca(NO₃)₂] to produce small micro-meter in size crystals. The crystallization of nitrate salts has been specifically chosen to study as these salts have tremendous applications over a wide spectrum of industries such as food, agriculture, dyes, and solar cells production. The induced crystallization in the nitrate salts solutions was mainly triggered by shock waves produced in the solution by directly focusing the laser pulses of 80 mJ pulse energy and 532 nm wavelength into nitrate salts solutions for a period of time ranging from 1 to 15 minutes. The yielded small crystals were characterized using different techniques, namely; x-ray diffraction (XRD), polarized light microscopy (PLM) as well as scanning electron microscope (SEM). A comparison has been drawn between crystals formed conventionally without photochemical intervention versus crystals formed by laser-induced shock wave crystallization mechanism. Finally, the grown crystals size and size distribution were related to laser irradiation time and energy in the three solutions.

This work presents the dependences of the absorption intensity of acid-soluble chitosan biopolymer films in the infrared region of the spectrum on the concentration of silver and gold nanoparticles of different morphology. The interaction mechanisms in the vibrational spectra overlapping area of silver nanoparticles and chitosan molecules (2500-3500 cm^-1) were observed. The influence of metal nanoparticles on dipole moments of OH- , CH - chitosan molecule oscillation groups was established. This interaction leads to a linear increase of the infrared absorption intensity with an increase of the silver nanoparticles concentration, synthesized by citrate and borohydride methods. The presence of silver and gold ablative nanoparticles in the chitosan films demonstrates the infrared absorption intensity exponential decrease with metal nanoparticles concentration.

The linear and nonlinear chiro-optical properties of chiral molecules are typically investigated by employing a few sensitive to optical activity spectroscopic methods, such as circular dichroism (CD), optical rotation, infrared absorption and vibrational circular dichroism (VCD). In this study, the spectra of differential absorption between left-and right circularly polarized light of carvone’s R and S mirror-image configurations of enantiomers in vapor and solution phases are presented for both electronic (CD) and vibrational (VCD) energy levels. Furthermore, well-resolved ultraviolet, visible and infrared absorption spectra of carvone’s individual enantiomers in vapor and solution phases are also reported and thoroughly discussed. Lastly, a comparison will be drawn between the R and S enantiomers linear versus nonlinear optical activity.

We analyze the solutions of integro-differential generalized nonlinear Shrodinger equation, which was introduced recently to describe intense optical pulse propagation in gas-filled hollow core photonic crystal fibers. With the help of moment method, we have derived system of equations for pulse parameters, which allows to explain nonlinear phenomena connected with red and blue frequency self-shift.

In this work, we investigated the generation of THz short pulses by two-color mid-infrared laser pulses induced gas plasma in ambient air by numerical analysis. In the simulation, the central wavelength of the input laser varied from 2.5 μm up to 4.0 μm. Our result indicates that the generated THz pulse intensity increases at longer wavelengths significantly. In our simulations, the fundamental pulse intensity and duration were kept fixed yielding no significant difference between the generated electron densities indicating that the asymmetry of the electric field has a major role in the THz generation efficiency by increasing the velocity of electrons. Our results also show that the fundamental pulse and the THz pulse can spectrally overlap, which makes it difficult to separate them spectrally. The possibility of the relative phase control between the fundamental and the second harmonic pulses with a single plate is also examined. Our calculations show that the best materials are the fluorides for controlling the relative phase.

Optical properties of layered composite materials consisting of plasmonic nanostructures and semiconductor quantum dots (QDs) have been investigated both experimentally and theoretically. It was demonstrated that in the case of spectrally overlapping bands of plasmonic absorption and fluorescence of alloyed QDs placed directly onto silver island film, the fluorescent intensity increases. While in other samples with alloyed QDs the fluorescence was not sensitive to silver nanoparticles or even quenched by silver nanoparticles for core-shell QDs. That was explained by resonant and non-resonant interaction of QDs with the near fields of plasmonic structures. Measuring the fluorescence decay time, we observed a clear correlation between the fluorescence intensity of alloyed QDs and reducing fluorescent lifetime in the case of resonant interaction or the Purcell effect. The interaction between excitons in semiconductor material and plasmons in metal nanoparticle was explored also in the Zn-ZnO system via numerical modeling. This system is interesting because metal films may be easily created via magnetron sputtering on silica glass substrates and then fully or partially oxidized in the course of thermal annealing in air. Thus a core-shell nanostructure consisting of a semiconductor shell with promising chemical sensor properties (ZnO) and metallic core with the plasmon resonance in the same spectral region (Zn) will be created.

We report on numerical modeling of the spectral dynamics of telecom range laser pulse of moderate power in a silica fiber with a flattened dispersion and longitudinally varying diameter. In the simulation experiments, the optimal fiber profile has been proposed for more than 60% energy transfer from the initial telecom range pulse to subpicosecond pulse at 2.2-2.3 μm. Another option of the fiber diameter profile provides flat radiation spectrum in the range 2-2.5 μm.

Dynamics of light bullets in the Raman active and ionizing gas was analyzed with the help of moment method. Analysis of this system shows that quasi-stable regime take place as a result of balance between dispersion and nonlinearity, photoionization and stimulated Raman self-scattering. Explicit formulas for the parameters of light bullet were proved by numerical simulation.

Semiconductor quantum dots (QDs) have high two-photon absorption cross-sections and long photoluminescence (PL) lifetimes, which make them a promising photosensitive part for fabrication of QD-based hybrid materials for two-photon bio-imaging, bio- and optoelectronics. In these areas, mode-locked femtosecond lasers are often used for two-photon excitation of QDs because of the high peak intensity of the laser pulse. However, the QD radiative lifetime usually exceeds the period between the laser pulses of such laser systems, which can affect the absorption and PL properties of QDs. In this work, we investigated the PL properties of CdSe/ZnS QDs under two-photon excitation. We have shown that using femtosecond laser excitation at a wavelength of 790 nm with a pulse repetition rate of 80 MHz and a peak intensity of more than 10 GW/cm², the two-photon absorption in QD is saturated. However if QDs were in complexes with purple membranes (PM) containing the photosensitive protein bacteriorhodopsin (bR), saturation was not observed up to an intensity of about 27 GW/cm². It was concluded that the difference in the saturation of two-photon absorption between QDs and QD-PM material is associated with the Förster resonance energy transfer from QD to bR and the corresponding shortening of the PL lifetime. The results obtained will allow to optimize the two-photon excitation regime of QD-PM nano-bio hybrid material which will expand the possible areas of its application in bio-imaging, bioand optoelectronics.

New possibilities to use the zircon-type YVO₄ and GdVO₄ Raman-active crystals for extreme SRS-radiation pulse shortening higher than 30 times down to the inverse value of the vibrational Raman line width in a synchronouslypumped crystalline Raman laser with combined long (ν₁) and short (ν₂) shift Raman conversion have been found. It is caused by strong broadening of the short-shift bending vibration ν₂ line in the spontaneous Raman spectrum of these crystals. We report characteristics of all-solid-state extracavity Raman lasers based on the 16-mm long a-cut YVO₄ (ν₁ = 889 cm^–1, ν₂ = 376 cm^–1) and GdVO₄ (ν₁ = 882 cm^–1, ν₂ = 382 cm^–1) crystals under synchronous pumping by a 1063-nm 35-picosecond Nd:GdVO₄ laser. Lasing was obtained in the YVO₄ (GdVO₄) Raman laser at not only the ν₁- shifted first Stokes wavelength of 1173 nm (1174 nm), but also at the (ν₁ + ν₂)-shifted Stokes wavelength of 1228 nm (1228 nm) with slope efficiency of 5.8 % (5.0 %) and output pulse energy up to 11 nJ (10 nJ) at 1228 nm. At 50 μm positive detuning of the external cavity length the strongest 30-fold and 42-fold shortening of the (ν₁+ν₂)-shifted Raman radiation pulse down to 1.2 ps and 850 fs in the YVO₄ and GdVO₄ crystals, respectively, has been achieved. These values are close to the inverse values of the ν₂ line widths of 11 cm^–1 and 24 cm^–1, respectively.

In this paper, the characteristics of synchronously pumped picosecond Raman laser based on the 36 mm long SrWO₄ crystal at the shifts of ν₁ = 921 cm^–1 and ν₂ = 336 cm^–1 under 36-ps extracavity pumping are presented. The first Stokes at the wavelength of 1178 nm, corresponding to the Raman shift of ν₁, with the slope efficiency of 45.1%, output energy of up to 40 nJ, and pulse duration of 33 ps, respectively, was achieved for the output coupler reflectivity of 89%. In the case of setup with the higher cavity Q-factor at 1178 nm, we obtained not only usual ν₁- shifted Raman radiation at 1178 nm, but also the unusual line at the wavelength of 1227 nm (ν₁ + ν₂). This additional line was achieved with the slope efficiency of 18.1 % and the output energy of 15 nJ with the output coupler reflectivity of 96.5% at 1227 nm. Strong pulse shortening from 36 ps down to 1.4 ps at the wavelength of 1227 nm was observed at +50 μm positive detuning of the external cavity length. This value is close to the inverse value of the ν₂ line.

Parametric four-wave mixing of frequency components in a crystalline Raman laser allowed generation of a collimated beam of not only Stokes, but also anti-Stokes components of the Raman radiation. Recently, to widen the angular tolerance of four-wave mixing and to obtain high conversion efficiency into the anti-Stokes wave, we have developed new schemes of the parametric Raman anti-Stokes lasers at 503 nm and 954 nm with tangentially phase-matched collinear beam interaction of orthogonally-polarized Raman components in a CaCO₃ crystal under 532 nm and 1064 nm laser pumping. Now we use not only the CaCO₃ crystal, but also other Raman-active crystals with different birefringence for the tangentially phase-matched parametric Raman laser under green (532 nm) pumping. We have theoretically and experimentally studied characteristics of tangential phase matching of Stokes <–< anti-Stokes interaction for different negative and positive uniaxial crystals with high and low birefringence. We have developed and experimentally realized the extracavity parametric Raman anti-Stokes lasers based not only on highly-birefringent uniaxial negative CaCO₃ (1086 cm^–1, 503 nm) and positive GdVO₄ (882 cm–1, 508 nm) crystals, but also on a low-birefringent uniaxial positive SrWO₄ crystal (921 cm^–1, 507 nm). Cyan anti-Stokes radiation was generated from green (532 nm), 5-ns, 1-mJ pump radiation. While high-birefringent crystals require probe-pump technique of double beam excitation, the low-birefringent crystal parametric Raman laser can be developed in the simplest system of single beam excitation. The green-to-cyan anti-Stokes conversion efficiency higher 1% was achieved in all the laser schemes.

The technology of modification of the CNT array on a silicon substrate using laser radiation of nanosecond duration has been developed. The energy regime of irradiation of the array is determined with the aim of aligning the nanotubes perpendicular to the substrate. Structuring of CNTs at a given area using impulse nanosecond radiation moving using a galvanometric scanner system is obtained. Patterning was carried out using pulsed laser radiation with a wavelength of 1064 nm, which was moved by means of galvanometric mirrors over the area of the CNT array. The spatial profile of the beam was Gaussian. The energy density of the pulse was in the range 0.4-2.2 J/cm². In order to obtain a homogeneous region of the CNT array after irradiation, the following parameters were set: the pulse duration was 100 ns, the radiation frequency was 30 kHz, at which the overheating of CNTs was minimized. The diameter of the laser beam at the focus of the laser was 20 μm. The moving rate of the laser beam of 500 mm/s was chosen in such a way so that individual pulses formed a continuous line with a laser beam overlap to compensate the changing in laser spot power along the diameter. Thus, the processed square 5×5 mm was formed by parallel lines 5 mm long, consisting of individual pulses located at a distance of 17 μm from each other. It is shown that the following effects are possible: CNT ablation, the effect of CNT alignment (straightening), singling, and “splicing” of individual CNTs in a single structure, as well as changing the morphology of the array itself. Nanotubes are less defective after laser modification. This is proved by Raman spectroscopy. The effect of CNT array structuring can be used to create new sensitive elements of photodetectors, solar cells, chemical sensors, temperature and pressure sensors, probes in microscopy and emitters.

Photoluminescence (PL) features and nonlinear transmission of Cu-doped CdSe colloidal quantum dots (QDs) under nanosecond laser pulses excitation were investigated. Strong difference of the pump intensity dependent behavior of basic exciton transition and Cu dopants associated PL was revealed. The presence of exciton-phonon interaction and its strong influence on the PL and nonlinear properties of Cu-doped colloidal CdSe QDs are proved by the simultaneous linear growth of basic excitons PL, the growth of the Stokes shift and significant decrease of absorption at the basic exciton transition wavelength with the increase of pump intensity [1].

Interaction of laser radiation with gold metal film deposited onto the lithium niobate substrate was investigated by means of piezoelectric resonance spectroscopy. Such metal-dielectric heterostructure has eigenmodes which can be excited by application of the probe radiofrequency electric field due to the piezoelectric nature of lithium niobate. Frequencies of these piezoelectric resonances are extremely sensitive to the temperature. During interaction with laser radiation the temperature of the film is determined as a solution of the nonstationary heat conduction equation relying on the experimentally measured induced shifts of piezoelectric resonance frequencies, which were preliminary calibrated in uniform heating conditions.

Solar panels are devices that can generate electrical energy directly from the solar irradiation. This devices are one of the renewable energy sources. Therefore, big solar plants are being created on the outskirts of cities. Micro solar plants are considered by developers last days. Solar panels which consist of few modules are positioned on the roofs of buildings. Sometimes to increase amount of energy generated by the solar panel, solar tracking systems are used. In highly urbanized places the partial shading can appear on the surface of the solar panel. This is an indeterministic phenomena which is observable especially if the solar tracker is used. Partial shading reduces power generated by the system and, in the worst cases, can damage the solar panel. Therefore, the bypass diodes connected with each module or even with some part of module are used. These diodes reduce the negative impact of partial shading but can cause appearance of the local maximum power points (LMPP) on the solar panel characteristics, and only one of them is the global maximum power point (GMPP). The regular maximum power point tracking (MPPT) algorithms can track only one of the local maximum power points that are close to the current working point.

Solar panels have nonlinear output characteristics. Therefore, there must be used a special device called the maximum power point tracker to track the voltage or the current value where the output power of the solar panel is highest. This point is called the maximum power point (MPP). Additionally, the panel consists of few parallel or series connected solar modules. To avoid negative impact of partial shading conditions, bypass diodes are used. This can complicate the detection of the maximum power point in partial shading conditions. When a solar panel is illuminated irregularly on the output characteristics the local maximum power points appear. Only one of them is the global maximum power point. There are plenty of maximum power point tracking (MPPT) algorithms in literature which are different in complexity or principle of operation. Most of commonly used methods can track only one point that is close to the current working point. There are some hybrid methods that can track the global maximum power point. These methods use the regular maximum power point tracking algorithm combined with an additional sub-procedure to calculate the position of the global maximum power point.

Usually a laser is considered as a system that delivers a particular temporal dynamic generation regime, which can be tailored by means of cavity parameters or power. By introducing a concept of PT-symmetry, one can achieve different types of stationary regimes, for example, single-mode operation. In the present work we consider a coupled Raman fiber lasers interconnected by means of Mach-Zender interferometer. We numerically investigate such coupled fiber lasers within a full dynamical model based on nonlinear Schrödinger equation. Firstly, we show that nonlinearity induced phase stochasticity does not destroy PT-symmetry, but makes PT-symmetric regimes to exist in narrower region of parameters. We study dynamical properties of the generation regimes and find that depending on parameters (pump power and phase shift), different dynamical regimes have different parity-time properties. We show that by varying PT-properties one can switch between different dynamic regimes. We also show that if the pump power is fixed, and phase shift is changed from zero (a case of fully uncoupled cavities) to the maximum value, the laser transits from generation in PT-broken regime to a PT-symmetric generation. At the same time, the laser exhibits a simultaneous reverse transition from a turbulent to a laminar generation.

Cylindrical microresonators based on the surface of optical fibers (SNAP structures) appear to be a promising platform for a variety of photonic devices. It turned out that the manufacturing accuracy of standard telecommunication optical fibers and the smoothness of their surface may be high enough to excite high-quality whispering gallery (WGM) modes in their cladding. Here we consider the question of the quality of resonances obtained on the surface of optical fibers, and the possibility of using them to create high-finesse optical filters. We used standard telecommunication fiber SMF-28 with a silica cladding diameter of 125 microns as samples to excite whispering gallery modes. We found that annealing with fire allows to obtain quality factors up to Q∼10⁷. Corresponding decay time in the microcavity was measured to be τ∼15 ns. We also discussed different schemes of optical filters that may be based of cylindrical microresonators.

We have used a nanosecond pulsed laser to study the dynamics of laser- induced breakdown with traditional optical detection on both nanosecond time scale and at later stages. Experiments on the induction of optical breakdown in the volume of liquid were performed using an Nd:YAG laser. It is shown that the optical breakdown in the liquid in the ultrasonic field is accompanied by an increase in the intensity of the spectral lines of potassium and oxygen with an increase in the amplitude and frequency of ultrasound. It was found that the effect of ultrasound on the intensity of the lines varies depending on the time of the breakdown evolution. Along with the optical spectra, the acoustic emission accompanying the pulsations of the cavitation bubble formed at the late stages of liquid breakdown source was studied. It was shown that the acoustic emission varies significantly with different ultrasound parameters. It is shown that an excited signal at its own switching frequency has a sufficiently high amplitude for its registration under typical experimental conditions. It is shown that the saturation effect is observed at frequencies above 200 kHz and at high ultrasound power, when the growth of the intensity of spectral lines slows down sharply. This effect indicates the possibility of using relatively small ultrasound powers for the implementation of the identified optoacoustic effects and spectroscopic properties in the laser breakdown in the liquid.

Aimed at remote sensing product validation, such as leaf area index (LAI), a new sampling strategy based on Taylor expansion method (TEM) and computational geometry model (CGM) is proposed in this paper. Firstly, a correlation index (CI) is calculated based on TEM using high-resolution LAI image to choose the field points of in-situ reference data. Secondly, based on the selected field measurements, the CGM model is established for simulating low-resolution LAI image. Thirdly, the points of in-situ reference data are decided according to the gaps between the simulated LAI and the aggregated LAI from high resolution. If the gap is accepted, the sampling strategy is finally established for field measurement. Otherwise, the field measurements should be re-selected and analyzed until the gap is accepted. Finally, the new sampling strategy is analyzed and compared with traditional sampling strategies, and the results indicate that the sampling strategy proposed in this paper is more stable and efficient.