Yuri N. Kulchin

Adaptive interferometry with photorefractive crystals

This work presents a review of progress and development in the field of adaptive laser interferometry. This method enables highly precise and reliable measurement of various physical parameters under unstable environmental conditions, which makes it very attractive for numerous industrial applications.

Silicatein genes in spicule-forming and nonspicule-forming Pacific demosponges.

Silicatein genes are known to be involved in siliceous spicule formation in marine sponges. Proteins encoded by these genes, silicateins, were recently proposed for nanobiotechnological applications. We studied silicatein genes of marine sponges Latrunculia oparinae collected in the west Pacific region, shelf of Kuril Islands. Five silicatein genes, LoSilA1, LoSilA1a, LoSilA2, and LoSilA3 (silicatein-α group), LoSilB (silicatein-β group), and one cathepsin gene, LoCath, were isolated from the sponge L. oparinae for the first time. The deduced amino acid sequence of L. oparinae silicateins showed high-sequence identity with silicateins described previously. LoCath contains the catalytic triad of amino acid residues Cys-His-Asn characteristic for cathepsins as well as motifs typical for silicateins. A phylogenetic analysis places LoCath between sponge silicateins-β and L-cathepsins suggesting that the LoCath gene represents an intermediate form between silicatein and cathepsin genes. Additionally, we identified, for the first time, silicatein genes (AcSilA and AcSilB) in nonspicule-forming marine sponge, Acаnthodendrilla sp. The results suggest that silicateins could participate also in the function(s) unrelated to spiculogenesis.

Ion-beam assisted laser fabrication of sensing plasmonic nanostructures

Simple high-performance, two-stage hybrid technique was developed for fabrication of different plasmonic nanostructures, including nanorods, nanorings, as well as more complex structures on glass substrates. In this technique, a thin noble-metal film on a dielectric substrate is irradiated by a single tightly focused nanosecond laser pulse and then the modified region is slowly polished by an accelerated argon ion (Ar+) beam. As a result, each nanosecond laser pulse locally modifies the initial metal film through initiation of fast melting and subsequent hydrodynamic processes, while the following Ar+-ion polishing removes the rest of the film, revealing the hidden topography features and fabricating separate plasmonic structures on the glass substrate. We demonstrate that the shape and lateral size of the resulting functional plasmonic nanostructures depend on the laser pulse energy and metal film thickness, while subsequent Ar+-ion polishing enables to vary height of the resulting nanostructures. Plasmonic properties of the fabricated nanostructures were characterized by dark-field micro-spectroscopy, Raman and photoluminescence measurements performed on single nanofeatures, as well as by supporting numerical calculations of the related electromagnetic near-fields and Purcell factors. The developed simple two-stage technique represents a new step towards direct large-scale laser-induced fabrication of highly ordered arrays of complex plasmonic nanostructures.

Adaptive correlation filter for stabilization of interference-fiber-optic sensors

A type of adaptive correlation filter for processing the speckle pattern emerging from an interference fiber-optic sensor is proposed. This filter is simple and self-adjustable, operating on the base of the photorefractive fanning effect. Experiments carried out with a Bi12TiO20 crystal and multimode optical fiber demonstrate high sensitivity and long-term stability of the sensor.

Occurrence of a Silicatein Gene in Glass Sponges (Hexactinellida: Porifera)

Silicatein genes are involved in spicule formation in demosponges (Demospongiae: Porifera). However, numerous attempts to isolate silicatein genes from glass sponges (Hexactinellida: Porifera) resulted in a limited success. In the present investigation, we performed analysis of potential silicatein/cathepsin transcripts in three different species of glass sponges (Pheronema raphanus, Aulosaccus schulzei, and Bathydorus levis). In total, 472 clones of such transcripts have been analyzed. Most of them represent cathepsin transcripts and only three clones have been found to represent transcripts, which can be related to silicateins. Silicatein transcripts were identified in A. schulzei (Hexactinellida; Lyssacinosida; Rosselidae), and the corresponding gene was called AuSil-Hexa. Expression of AuSil-Hexa in A. schulzei was confirmed by real-time PCR. Comparative sequence analysis indicates high sequence identity of the A. schulzei silicatein with demosponge silicateins described previously. A phylogenetic analysis indicates that the AuSil-Hexa protein belongs to silicateins. However, the AuSil-Hexa protein contains a catalytic cysteine instead of the conventional serine.

Fabrication of porous metal nanoparticles and microbumps by means of nanosecond laser pulses focused through the fiber microaxicon

We present a novel optical element - fiber microaxicon (FMA) for laser radiation focusing into a diffraction-limited spot with Bessel-like profile as well as for precision laser nanostructuring of metal film surfaces. Using the developed FMA for single-pulse irradiation of Au/Pd metal films on quartz substrate we have demonstrated the formation of submicron hollow microbumps with a small spike atop as well as hollow spherical nanoparticles. Experimental conditions for controllable and reproducible formation of ordered arrays of such microstructures were defined. The internal structure of the fabricated nanoparticles and nanobumps was experimentally studied using both argon ions polishing and scanning electron microscopy. These methods reveal a porous inner structure of laser-induced nanoparticles and nanobumps, which presumably indicates that a subsurface boiling of the molten metal film is a key mechanism determining the formation process of such structures.

Sensing of multimode-fiber strain by a dynamic photorefractive hologram

We present a strain sensor in which a multimode fiber is used as a sensitive element. High sensitivity to dynamic strains is achieved by means of vectorial wave mixing in a photorefractive CdTe:V crystal. It was found that the largest source of noise in our sensor is related to the instability of the polarization state of speckles emerging from the fiber. This noise is significantly diminished in fiber with a core of large diameter (550 microm).

Photorefractive vectorial wave mixing in different geometries

We analyze vectorial wave mixing in a photorefractive crystal of cubic symmetry in different geometries of beam interactions--reflection, transmission, and orthogonal. It is shown that orthogonal geometry in contrast with others supports an efficient phase demodulation of a depolarized object wave in linear mode without using any polarization-filtering elements. As a result adaptive interferometers based on the orthogonal geometry can provide a higher signal-to-noise ratio due to lower noise and lower optical losses.

Fast photogalvanic response of a Bi12SiO20 crystal

A photoelectric response of a Bi12SiO20 crystal grown in an argon atmosphere on a linearly polarized light (which is referred to as the linear photogalvanic effect) is reported for the first time in the nanosecond-time domain. Optimal geometry for detection of the photo-induced current concerning the orientation of the polarization state of the incident light in respect to the crystallographic axes of a sample was determined considering both the natural optical activity and light absorption of sillenite crystals. Spectral dependence of the photogalvanic current was measured in the visible part (410 - 610 nm) of the spectrum. Temporal shape of light-induced electric-current pulses observed at different experimental conditions is discussed. Obtained results are believed to show that sillenite crystals are very prospective for development of different ultra-fast optoelectronics devices.

Photorefractive correlation filtering of time-varying laser speckles for vibration monitoring

We proposed and experimentally studied a technique of vibration object monitoring. The technique is based on self-diffraction of the speckle pattern on the adaptive correlation filter recorded in photorefractive Bi12TiO20 crystal. This filter is recorded owing to the light-induced scattering known as fanning effect. The proposed technique is as sensitive as interferometric systems and it is very simple for implementation: neither reference nor readout beam is needed for operation. It is shown that the system has a linear response on the lateral displacement of the object surface and its dynamic range can be easily varied depending on experimental conditions.