In this paper, we studied nonlinear absorption of infrared (IR) (1250 nm) femtosecond pulses and visible photoluminescence (PL) excited by them in liquid-crystal (LC) polymer films with embedded CdSe/ZnS core-shell type quantum dots (QDs). The dependence of nonlinear transmission on incident intensity indicated three-photon absorption in the films, with the three-photon absorption coefficient for the QD-LC polymer composite comparable with the one for bulk CdSe. The spectrum of PL excited by IR pulses coincides with one-photon excited PL spectrum. Dependence of the PL signal on the IR laser radiation power is cubic with further saturation for the spectral region from 2.10 to 2.25 eV, with saturation intensity decreasing with lower PL photon energy. The presence of the second-harmonic signal in the up-conversion spectrum results in its variation with an excitation power increase.

New azochromophores (ACh) with terminal nitrile group have been synthesized. All compounds are crystalline at room temperature. Their melting points were measured by differential scanning calorimetry. The AСh containing carboxyl group have very high melting points. In this respect, carboxyl-free derivatives were preferred as azochromophoric additives to liquid crystal (LC) matrices. Blend compositions of the synthesized ACh with low molecular and polymer liquid crystals have been prepared and studied. From the point of view of homogeneity, the optimal content of ACh in low-molecular LC-matrices is 10 wt. %, whereas in polymer matrices, the ACh content does not exceed 5 wt. %. The thermal properties of the LC blend compositions, which were capable to the melt into isotropic phase due to LC order disruption caused by photoisomerization, have been studied. The ability of some blend compositions to undergo a UV-photoinduced isotropic phase transition at temperatures below the melting point of nematic matrix has been demonstrated. The times of UV-irradiation required for the implementation of trans-cis isomerisation and the times of visible light irradiation needed for recombination process have been assessed. The irradiation times were estimated by polarized optical microscopy.

Chalcogenide vitreous semiconductors (ChVSs) find application in rewritable optical memory storage and optically switchable infrared photonic devices due to the possibility of fast and reversible phase transitions, as well as high refractive index and transmission in the near- and mid-infrared spectral range. Formed on such materials, laser-induced periodic surface structures (LIPSSs), open wide prospects for increasing information storage capacity and create polarization-sensitive optical elements of infrared photonics. In the present work, a possibility to produce LIPSSs under femtosecond laser irradiation (pulse duration 300 fs, wavelength 515 nm, repetition rate up to 2 kHz, pulse energy ranged 0.03 to 0.5 μJ) is demonstrated on a large (up to 5 × 5 mm2) area of arsenic sulfide (As2S3) and arsenic selenide (As2Se3) ChVS films. Scanning electron and atomic force microscopy revealed that LIPSSs with various periods (170–490 nm) and orientations can coexist within the same irradiated region as a hierarchical structure, resulting from the interference of various plasmon polariton modes generated under intense photoexcitation of nonequilibrium carriers within the film. The depth of the structures varied from 30 to 100 nm. The periods and orientations of the formed LIPSSs were numerically simulated using the Sipe–Drude approach. A good agreement of the calculations with the experimental data was achieved.

The efficiency of silicon nanoparticles (SiNPs) formation via picosecond laser fragmentation of silicon micropowder in water suspension was analyzed. We carried out numerical simulations of propagation of a single focused laser pulse with energy of 16 mJ in suspensions of silicon microparticles (SiMPs) with diameter of 5 μm accounting for temperaturedependent thermal and optical properties of the media under study. The simulations were performed for SiMP mass concentrations varied from 0.5 to 12 mg/mL and irradiation wavelengths of 1064 and 532 nm. To estimate the efficiency of the fragmentation process we calculated the mass of the silicon melted by the laser pulse. The fragmentation process as well as mass of silicon undergone phase transitions were demonstrated to depend significantly on SiMPs mass concentration and wavelength of the laser radiation. For irradiation at 1064 nm the mass of melted silicon varies nonmonotonically with increase of SiMPs mass concentration decreasing to minimum at 5 mg/mL and increasing an order of magnitude with a further increase in SiMPs mass concentration. When using radiation at a wavelength of 532 nm, the mass of melted silicon increases up to two orders of magnitude in comparison with the case of 1064 nm, while the mass of melted silicon rose with increase of the SIMP concentration.

The possibility of manufacturing silicon nanoparticles by picosecond laser fragmentation of silicon microparticles in water is analysed. It is shown that for fragmentation duration of 40 min, the dependence of the average sizes of particles on the initial mass concentration of the micropowder varied in the range of 0.5 – 12 mg mL −1 is nonmonotonic, with the maximum average size of 165 nm being achieved at a concentration of 5 mg mL −1 . To explain the obtained result, the simulation of propagation of a focused laser beam in a scattering suspension of silicon microparticles is performed for their different mass concentrations. It is demonstrated that at concentrations not exceeding 5 mg mL −1 , fragmentation occurs in the paraxial region of the beam when it propagates deep into the cuvette with a suspension, while at higher concentrations it occurs primarily in the superficial layer owing to strong extinction. Calculations results allow the experimental features of the formation of silicon nanoparticles to be explained. Spectrophotometry measurements on suspensions of nanoparticles obtained at the initial concentration of microparticles of 12 mg mL −1 are compared with the theoretical estimates of the absorption and scattering coefficients obtained in the framework of the Mie theory. Measured optical properties indicate the potential of using fragmented nanoparticles as scattering and/or absorbing contrast agents in optical imaging of biological objects.

Pulsed laser ablation and fragmentation of porous silicon, silicon nanowires and silicon microparticles in water and ethanol allowed to fabricate crystalline silicon nanoparticles with mean sizes 25 - 200 nm. Such particles are promising both in fluorescence and scattering bioimaging techniques and in photohyperthermia of tumors.

Femtosecond laser treatment allows to fabricate periodic structures at amorphous hydrogenated silicon surfaces on areas more than a square millimeter. The period of the structures is near the laser wavelength and determines by the nonequilibrium electrons concentration at high power laser excitation. The obtained structures possess a pronounced electrophysical anisotropy.

Femtosecond laser-modified amorphous silicon (a-Si) films with optical and electrical anisotropy have perspective polarization-sensitive applications in optics, photovoltaics, and sensors. We demonstrate the formation of one-dimensional femtosecond laser-induced periodic surface structures (LIPSS) on the surface of phosphorus- (n-a-Si) and boron-doped (p-a-Si) amorphous silicon films. The LIPSS are orthogonal to the laser polarization, and their period decreases from 1.1 ± 0.1 µm to 0.84 ± 0.07 µm for p-a-Si and from 1.06 ± 0.03 to 0.98 ± 0.01 for n-a-Si when the number of laser pulses per unit area increases from 30 to 120. Raman spectra analysis indicates nonuniform nanocrystallization of the irradiated films, with the nanocrystalline Si phase volume fraction decreasing with depth from ~80 to ~40% for p-a-Si and from ~20 to ~10% for n-a-Si. LIPSS’ depolarizing effect, excessive ablation of the film between LIPSS ridges, as well as anisotropic crystalline phase distribution within the film lead to the emergence of conductivity anisotropy of up to 1 order for irradiated films. Current–voltage characteristic nonlinearity observed for modified p-a-Si samples may be associated with the presence of both the crystalline and amorphous phases, resulting in the formation of potential barriers for the in-plane carrier transport and Schottky barriers at the electric contacts.

Ge2Sb2Te5 (GST225) looks to be a promising material for rewritable memory devices due to its relatively easy processing and high optical and electrophysical contrast for the crystalline and amorphous phases. In the present work, we combined the possibilities of crystallization and anisotropic structures fabrication using femtosecond laser treatment at the 1250 nm wavelength of 200 nm thin amorphous GST225 films on silicon oxide/silicon substrates. A raster treatment mode and photoexcited surface plasmon polariton generation allowed us to produce mutually orthogonal periodic structures, such as scanline tracks (the period is 120 ± 10 μm) and laser-induced gratings (the period is 1100 ± 50 nm), respectively. Alternating crystalline and amorphous phases at the irradiated surfaces were revealed according to Raman spectroscopy and optical microscopy studies for both types of structures. Such periodic modulation leads to artificial optical and electrophysical anisotropy. Reflectance spectra in the near infrared range differ for various polarizations of probing light, and this mainly results from the presence of laser-induced periodic surface structures. On the other hand, the scanline tracks cause strong conductivity anisotropy for dc measurements in the temperature range of 200–400 K. The obtained results are promising for designing new GST225-based memory devices in which anisotropy may promote increasing the information recording density.

Biodegradable and low-toxic silicon nanoparticles (SiNPs) have potential in different biomedical applications. Previous experimental studies revealed the efficiency of some types of SiNPs in tumor hyperthermia. To analyse the feasibility of employing SiNPs produced by the laser ablation of silicon nanowire arrays in water and ethanol as agents for laser tumor hyperthermia, we numerically simulated effects of heating a millimeter-size nodal basal-cell carcinoma with embedded nanoparticles by continuous-wave laser radiation at 633 nm. Based on scanning electron microscopy data for the synthesized SiNPs size distributions, we used Mie theory to calculate their optical properties and carried out Monte Carlo simulations of light absorption inside the tumor, with and without the embedded nanoparticles, followed by an evaluation of local temperature increase based on the bioheat transfer equation. Given the same mass concentration, SiNPs obtained by the laser ablation of silicon nanowires in ethanol (eSiNPs) are characterized by smaller absorption and scattering coefficients compared to those synthesized in water (wSiNPs). In contrast, wSiNPs embedded in the tumor provide a lower overall temperature increase than eSiNPs due to the effect of shielding the laser irradiation by the highly absorbing wSiNPs-containing region at the top of the tumor. Effective tumor hyperthermia (temperature increase above 42 °C) can be performed with eSiNPs at nanoparticle mass concentrations of 3 mg/mL and higher, provided that the neighboring healthy tissues remain underheated at the applied irradiation power. The use of a laser beam with the diameter fitting the size of the tumor allows to obtain a higher temperature contrast between the tumor and surrounding normal tissues compared to the case when the beam diameter exceeds the tumor size at the comparable power.

Embedding quantum dots (QDs) into an organic matrix of controllable order requires the identification of their structural characteristics. This analysis is necessary for the creation of anisotropic composites that are sensitive to external stimuli. We have studied the QD structures formed during the single-step synthesis of CdSe/ZnS QDs and their transformations after the initial ligand's substitution for another ligand. This single-step process leads to the formation of the core/shell structure. We detect the presence of two oleic acid residues ionically connected to Zn and Cd. At the same time, the amount of Cd oleate at the surface is very small. We observe the ligand exchange process at the surface of the core/shell QDs. The oleic acid residues are substituted by terphenyl-containing (TERPh-COOH) aromatic acid residues. The reaction between CdSe/ZnS carrying TOP and oleic acid residues ionically bound with QDs and terphenyl-containing acid leads to the coexistence of multiple ligands on the QD surface at a ratio of 11:6:33 for TOP/OA/TERPh-COOH.

One-dimensional periodic surface structures were formed by femtosecond laser irradiation of amorphous hydrogenated silicon (a-Si:H) films. The a-Si:H laser processing conditions influence on the periodic relief formation as well as correlation of irradiated surfaces structural properties with their electrophysical properties were investigated. The surface structures with the period of 0.88 and 1.12 μm were fabricated at the laser wavelength of 1.25 μm and laser pulse number of 30 and 750, respectively. The orientation of the surface structure is defined by the laser polarization and depends on the concentration of nonequilibrium carriers excited by the femtosecond laser pulses in the near-surface region of the film, which affects a mode of the excited surface electromagnetic wave which is responsible for the periodic relief formation. Femtosecond laser irradiation increases the a-Si:H films conductivity by 3 to 4 orders of magnitude, up to 1.2 × 10−5 S∙cm, due to formation of Si nanocrystalline phase with the volume fraction from 17 to 28%. Dark conductivity and photoconductivity anisotropy, observed in the irradiated a-Si:H films is explained by a depolarizing effect inside periodic microscale relief, nonuniform crystalline Si phase distribution, as well as different carrier mobility and lifetime in plane of the studied samples along and perpendicular to the laser-induced periodic surface structures orientation, that was confirmed by the measured photoconductivity and absorption coefficient spectra.

Raman spectroscopy is often considered as a powerful tool for chemical sensing and imaging and in the times of COVID- 19 pandemic is frequently suggested as the way to identify the presence of viral particles in solution. In this report, we evaluate the ability of Raman spectroscopy to quantitatively assess the presence of nanoparticles in colloidal solutions. © 2021 SPIE. All rights reserved.

The feasibility of photohyperthermia treatment of nodular basal cell carcinoma (BCC) in presence of silicon nanoparticles is studied by numerical simulations employing Monte-Carlo and finite element methods.

The efficiency of using silicon nanoparticles, produced by laser ablation of porous silicon in liquids, as agents for hyperthermia of tumours using laser radiation with wavelengths of 633 and 800 nm is evaluated. Using the optical parameters of the nanoparticles suspensions determined earlier by the spectrophotometry measurements, the heating of tumour tissue with embedded nanoparticles is numerically modelled. The heat transfer equation is solved by the finite element method which considers the volumetric distribution of the absorbed light power, calculated by the Monte Carlo technique, as a distributed heat source. The simulations performed indicate that embedding silicon nanoparticles with a concentration of up to 5 mg mL −1 into a tumour allows its maximum temperature to be increased by 0.2–4 °C in comparison with heating the tumour without nanoparticles depending on the irradiation wavelength and intensity.

In this Letter, we report on the circular anisotropy of third-harmonic (TH) generation in an array of silicon nanowires (SiNWs) of approximately 100 nm in diameter tilted to the crystalline silicon substrate at an angle of 45°. Numerical simulations of the scattering at the fundamental and TH frequencies of circularly polarized light by a single SiNW and an ansatz structure composed of 13 SiNWs used as a geometrical approximation of the real SiNW array indicate asymmetric scattering diagrams, which is a manifestation of the photonic spin Hall effect mediated by the synthetic gauge field arising due to the special guided-like mode structure in each SiNW. Despite strong light scattering in the SiNW array, the experimentally measured TH signal demonstrated significant dependence on the polarization state of incident radiation and the SiNW array spacial orientation in regard to the wave vector direction.