S.E. Svyakhovskiy

Mesoporous silicon photonic structures with thousands of periods

In this work, we present the results on the fabrication and characterization of the structural and optical properties of thick mesoporous silicon-based 1D photonic crystals (PC) containing up to 2500 periods (400 μm thick) made by electrochemical etching in the hydrofluoric acid solution. The composition of multilayered structures with good spatial periodicity up to thousands of layers and with good reproducibility of porosity of alternate layers is demonstrated that is proven by SEM measurements. Comparative studies of the reflectivity spectra from the front and back sides of a thick free-standing PC also testify a good periodicity of the multilayer structure which manifests itself by the appearance of the photonic band gaps. We demonstrate that the main mechanism that restricts the fabrication of thick porous silicon-based photonic crystals is the local decreasing of the HF concentration in pores.

Carbon nanowalls: the next step for physical manifestation of the black body coating

The optical properties of carbon nanowall (CNW) films in the visible range have been studied and reported for the first time. Depending on the film structure, ultra-low total reflectance up to 0.13% can be reached, which makes the CNW films a promising candidate for the black body-like coating, and thus for a wide range of applications as a light absorber. We have estimated important trends in the optical property variation from sample to sample, and identified the presence of edge states and domain boundaries in carbon nanowalls as well as the film mass density variation as the key factors. Also we demonstrated that at much lower film thickness and density than for a carbon nanotube forest the CNWs yield one order higher specific light absorption.

Polarization effects in diffraction-induced laser pulse splitting in one-dimensional photonic crystals

The polarization effects in the diffraction-induced pulse splitting (DIPS) observed under the dynamical Bragg diffraction in the Laue geometry in linear one-dimensional photonic crystals (PCs) are studied theoretically and experimentally. It is demonstrated that the characteristic length of the laser pulse path in a PC, or splitting length, used to describe the temporal pulse splitting, as well as the number of the outgoing femtosecond pulses, are influenced significantly by the polarization of the incident laser pulse. We have observed that the characteristic splitting time in porous quartz PCs for the s-polarized probe pulse is approximately 1.5 times smaller as compared with that measured for the p-polarized radiation. These results are supported by the theoretical description and ensure that the polarization sensitivity of the DIPS effect is due to a large lattice-induced dispersion of the PC. It is also shown that the number of output pulses can be varied from two up to four in both transmission and diffraction directions depending on the polarization of incident femtosecond pulses.

Controllable Laser Reduction of Graphene Oxide Films for Photoelectronic Applications

This article presents a new simple method of creating light-absorbing carbon material for optical devices such as bolometers. A simple method of laser microstructuring of graphene oxide is used in order to create such material. The absorption values of more than 98% in the visible and more than 90% in the infrared range are achieved. Moreover thermal properties of the films, such as temperature dependence and the thermal response of the samples, are studied. The change in resistance with temperature is 13 Ohm K-1, temperature coefficient of resistance (TCR) is 0.3% K-1, and the sensitivity is 0.17 V W-1 at 300 K. Thermal conductivity is rather high at ∼104 W m-1 K-1 at 300 K. The designed bolometer operates at room temperature using incandescent lamp as a light source. This technique suggests a new inexpensive way to create a selective absorption coating and/or active layer for optical devices. Developed GO and rGO films have a large surface area and high conductivity. These properties make carbon coatings a perfect candidate for creating a new type of optoelectronic devices (gas sensors, detectors of biological objects, etc.).

Optical pendulum effect in one-dimensional diffraction-thick porous silicon based photonic crystals

We present the realization of the multiperiodic optical pendulum effect in 1D porous silicon photonic crystals (PhCs) under dynamical Bragg diffraction in the Laue scheme. The diffraction-thick PhC contained 360 spatial periods with a large variation of the refractive index of adjacent layers of 0.4. The experiments reveal switching of the light leaving the PhC between the two spatial directions, which correspond to Laue diffraction maxima, as the fundamental wavelength or polarization of the incident light is varied. A similar effect can be achieved when the temperature of the sample or the intensity of the additional laser beam illuminating the crystal are changed. We show that in our PhC structures, the spectral period of the pendulum effect is down to 5 nm, while the thermal period is about 10 °C.

Experimental demonstration of selective compression of femtosecond pulses in the Laue scheme of the dynamical Bragg diffraction in 1D photonic crystals

We present the experimental results of diffraction-induced temporal splitting of chirped femtosecond optical pulses under the dynamical Bragg diffraction in the Laue geometry. For the experiments we made a transparent, high quality porous-quartz based 1D photonic crystal composed of 500 layers. We demonstrate that a selective compression of pulses is observed in this case, that is only one pulse from the pair is compressed, while the second one is broadened. This selective compression effect is determined by the sign and the value of the chirp parameter of the input pulse, in agreement with the theoretical description.

Quasiperiodic one-dimensional photonic crystals with adjustable multiple photonic bandgaps

We propose an elegant approach to produce photonic bandgap (PBG) structures with multiple photonic bandgaps by constructing quasiperiodic photonic crystals (QPPCs) composed of a superposition of photonic lattices with different periods. Generally, QPPC structures exhibit both aperiodicity and multiple PBGs due to their long-range order. They are described by a simple analytical expression, instead of quasiperiodic tiling approaches based on substitution rules. Here we describe the optical properties of QPPCs exhibiting two PBGs that can be tuned independently. PBG interband spacing and its depth can be varied by choosing appropriate reciprocal lattice vectors and their amplitudes. These effects are confirmed by the proof-of-concept measurements made for the porous silicon-based QPPC of the appropriate design.

Enhancement of Nonlinear Optical Effects in Porous Composite Plasmonic Structures

A method for formation of bulk plasmonic structures based on porous quartz with silver nanoparticles in pores has been proposed and implemented. The spectroscopy of their optical and nonlinear optical properties has been performed by methods of second harmonic generation and two-photon absorption. A significant increase in the nonlinear absorption coefficient has been detected in the plasmon resonance region. The enhancement of the second optical harmonic has been observed with the shift by tens of nanometers from the plasmon resonance position toward the long-wavelength region.

Giant Goos-Hanchen effect and focusing of Gaussian light beam by one-dimensional photonic crystal with modulated band gap

We present the theoretical and experimental studies of the giant Goos-Hanchen effect and the effect of focusing of light beam in one-dimensional photonic crystals with spatial modulation of photonic band gap position. We show that the photonic crystal with slow exponentially modulated band gap applies the second-order phase modulation to the reflected light and can focus or defocus the light beam.

New type of nanocomposite material for SERS

We experimentally observe effects of second harmonic generation, nonlinear absorbtion in porous quartz with metallic nanoparticles in order to find a possibility to make a new device for SERS-experiments.