One of the important tasks in optoacoustics today is the development of methods and tools for generating high-frequency ultrasound (above 1 MHz) in liquids and other media. To expand the frequency range of ultrasound, it was proposed to use coatings consisting of focusing spheres on a fiber tip. The methodology of calculating the ultrasound spectra depending on the sphere size, index of refraction, and parameters of laser radiation was developed. Two cases of small and large spheres in strongly and weakly absorbing media were simulated. The experimental results were analyzed in the approximations allowing a fairly accurate estimation of the spectrum and indicatrix of the generated ultrasound upon laser excitation through a converter based on a coating of transparent spheres. A good agreement between the model and experimental result was obtained.

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Light–heat converters are promising for further development of contact laser surgery. The simplest converter consists of an optical fiber with a strong absorbing layer at the tip. We studied the time dependence of the tip temperature at different CW laser powers and revealed that, in several seconds, the temperature evolution becomes almost power-independent. Mathematical modeling showed that laser ablation of the tip coating is the main reason for this phenomenon.

Purpose: evaluation of the efficiency of the “hot spot” method for the fragmentation of urinary stones. Materials and methods: A retrospective analysis of clinical records of 1666 patients with urolithiasis who underwent percutaneous nephrolithoextraction/tripsy and contact ureterolithotripsy/extraction in the period from 2014 to 2017 at the urology clinic was performed to assess the incidence of postoperative infectious and inflammatory complications. The research objects were postoperative urinary stones (n-78). The X-ray density and linear dimensions of the stones were determined. Stone fragmentation was performed with a continuous-wave diode laser operating at wavelengths of 0.81 μm, 0.97 μm, and 1.47 μm. An absorbing coating of micro-size graphite powder was applied on the working tip of the optical fiber. In vitro fragmentation was carried out in liquid. Results: A group of patients (224/1666) (13.4 ± 0.86%) was identified, who developed infectious and inflammatory complications after: percutaneous nephrolithotripsy, 123/361 (34.1 ± 2.5%) cases; percutaneous nephrolithoextraction, 59/240 (24.6 ± 2.78%); contact ureterolithotripsy, 23/294 (7.8 ± 1.57%); and ureterolithoextraction, 19/771 (2.5 ± 0.56%). In liquid, the “hot spot” technique made it possible to fragment stones with an X-ray density of up to 1000 HU at a laser wavelength of 0.81 µm, up to 1400 HU at 0.97 µm, and up to 1400 HU at 1.47 µm.

Transparent spheres in which the radius R of the sphere is larger than or equal to the wavelength λ of light have currently become of particular interest for quite a number of physical problems (2D colloidal crystal structures composed of transparent spheres, photonic crystals and meta-materials) and applications (laser lithography, fiber-optic systems, super resolution microscopy, biomedical applications, and others). The optical properties of a “full” sphere, when the light aperture r is of order R and the sphere is a natural spherical aberration, have not been investigated in ample detail yet. Strong spherical aberration makes focusing nontrivial. Usually, the exact solution of sphere optics is obtained using the Mie theory, the generalized Lorenz–Mie theory (GLMT), DFT, DDFT codes, which do not give much of a physical insight, as it requires summation of a large number of terms in a multipole expansion even for moderate sphere sizes. In this work we present an algorithm for describing the focusing properties of a transparent sphere using the Gaussian beam approximation that gives a good description of the field in the region of lens caustic. The algorithm developed for the spherical systems was used to create a code for calculating based on standard computation systems spheres with diameters ranging from ∼ λ to thousands of λ. The results obtained were compared with the data of some authors obtained earlier by more sophisticated methods.

Laser radiation sources of different wavelengths with a silica fiber output are widely used in engineering (surface clearing and scratching/engraving, and so on) and in medicine (effective low-invasive scalpels for treating various diseases). These applications are based primarily on direct exposure of the object to laser radiation. The properties of a converter of such a laser radiation to the radiation of a point (∼0.5 · 0.5 mm), high-temperature (∼2000 K) source with strongly absorbing coating (SAC) at the distal end of the silica fiber are considered in the presented work. The use of a converter expands the capabilities of laser instruments significantly. The temperature (∼2000 K) of the operating silica fiber tip with SAC at a laser pump power of 3–10 W (λ = 1.47 μm) and its time dependence in air atmosphere, in CO2 gas and in vacuum have been studied in experiment. The results of the studies and the physical properties of heat transfer and material stability in the converter design are considered. Recommendations on converter application as a scalpel with SAC for cutting soft and hard biological tissues are formulated.

One of the triggers of infectious processes developing in the kidney after contact laser lithotripsy is calculus disintegration followed the release of bacteria and toxins from the biofilm. Prevention urgency determines the search for new mechanisms and methods of laser calculus fragmentation without scattering of fragments and microbial dissemination into the pelvicalyceal system of the kidney. The aim of the study was to evaluate the possibilities of applying the technology of urinary calculus fragmentation with continuous-wave diode lasers of different wavelengths using fiber light guides with strongly heated distal tips for controlled fragmentation and minimization of traumatic effects on the adjacent tissues. Materials and Methods. To fragment postoperative samples of porous urinary stones (n=58), we applied standard certified continuous-wave diode 10 W lasers with fiber output to quartz light guides, their distal tips being coated with a layer of graphite microparticles in silicone varnish. The quality of stone fragmentation using lasers with wavelengths of 0.81 (n=17), 0.97 (n=22), and 1.47 mu m (n=19) and identical quartz light guides were evaluated. Control of laser-induced heating of the urinary tract tissues adjacent to the stone was carried out on the model medium with a thermocouple. Simulation of intraoperative errors (short contact with the ureteral wall as the result of the fiber slipping off the stone surface) was performed on the ureteral wall took post mortem. Tissue condition was assessed using histological sections stained with hematoxylin and eosin. Results. The average fragmentation time depended on calculus density and cross-sectional dimension and was 12-15 s. All selected stones, including those potentially infected, with X-ray density 119 to 1735 HU were fragmented effectively both in liquid and air. Assessment of temperature regimes provided by lasers with 0.81 and 0.97 mu m wavelengths showed that the stone surface temperature during fragmentation in the air reached 40 and 57 degrees C, respectively, and it was 25 and 33 degrees C in liquid. The obtained morphological and thermometric data suggest safety of lasers used for controlled fragmentation of potentially infected urinary calculi. Conclusion. The use of continuous-wave diode lasers with strongly heated distal fiber tips at 0.81 and 0.97 mu m wavelengths makes it possible to successfully fragment potentially infected urinary stones into size-controlled fragments, which may become a significant factor in prevention of systemic inflammatory response in the postoperative period.

New type of optoacoustic transducer containing monolayer of dielectric spheres is presented. Experiments of the ultrasound generation by the single nanosecond laser pulses (2nd harmonic of Nd: YAG) in a liquid absorbing ink were carried out. It was found that the irradiation of the liquid through a mask containing the monolayer of glass spheres result in the greater ultrasound intensity and the broader spectrum compared to the same setup without the mask. The effect is explained by the focusing of the laser light by the spheres. The laser intensity is being concentrated into the multitude of the 'hot spots' where the high-frequency ultrasound is generated.

The technology of applying a colloidal single-layer coating of transparent polystyrene (PS) Ø 1 μm spheres at the tip face of a quartz fiber has been proposed and tested. Such a coating plays, in a light absorbing liquid, the role of a converter of pulsed laser radiation into acoustic radiation. The generation of ultrasound in water using a converter based on a quartz fiber 1 mm in diameter with a 2D colloidal crystalline coating consisted of polystyrene spheres with a diameter of ~1 μm at the fiber end was investigated. When excited by laser radiation (λ = 1.064 µm), coating of polystyrene spheres created in the liquid a laser thermal microstructure with a characteristic size of fractions of ~λ and a maximum temperature up to 10−2 degree at an energy in a short laser pulse of ~0.005 J. This short-lived thermal microstructure generated sound pulses in the liquid in the approximately 0.2–4 MHz range. The results of the experimental study of this effect are reported. The proposed laser radiation converter with colloidal coating of the optical fiber distal tip by a single layer of transparent spheres can be used for the development of new laser microtools for studying, processing of various objects in microsurgery, microstructuring of the surface, spot cleaning and restoration of objects of art and history.

The development of nanosphere lithography relies on the ability of depositing 2D colloidal crystals comprising micro- and nano-size elements on substrates of different materials. One of the most difficult problems here is deposition of coatings on hydrophobic substrates, e.g. polymers, from aqueous colloidal solutions. We use UV photooxidation for substrate hydrophilization. We demonstrate a new method of producing a two-dimensional ordered array of polymer microparticles (polystyrene microspheres ∼1 μm in diameter) on a polymer substrate (PMMA). We show that implementation of the new deposition technique for directed self-assembly of microspheres on an UV irradiated surface provides an opportunity to obtain coatings on a hydrophilized PMMA surface of large area (∼5 cm2). UV irradiation of the surface through masks allows creating 2D patterns consisting of mesoscale elements formed by the deposited self-assembled microparticles owing to the fact that the colloidal particles are deposited only on the irradiated area leaving the non-irradiated sections intact.

Ensuring the complete removal of tumor tissue is the main challenge during resection operations. Recently, a technique of “indirect” contact laser surgery has been developed. In this study we assess the possibility of using such surgery for fluorescence image-guided tumor resection. Mouse colon adenocarcinoma CT-26 cells stably expressing the fluorescent protein mKate-2 was used as the tumor model. Resections of the tumor nodes were performed with either a scalpel blade, a laser scalpel with a bare tip, or a laser scalpel with a strongly absorbing coating on the fiber tip. Tumor-positive resection margins were detected using an IVIS Spectrum fluorescence imaging system. After tumor resection with the scalpel blade over half of the animals needed one additional resection to remove residual tumor cells. Animals in this group showed tumor recurrence within 7 days. Fluorescence imaging of the tumor bed, performed after resection to assess the presence of tumor cell clusters, was sufficiently effective only with a bloodless resection. The laser scalpels both with the bare tip and with the strongly absorbing coating on the tip provided such bloodless tumor resection in contact mode. Fewer animals required additional resections when the bare tipped scalpel was used and this also resulted in a reduction in tumor recurrence. After resections were carried out with the laser scalpel with the strongly absorbing coating on the tip, fluorescence was detected in the operative field and this led to undertaking additional resections, although subsequent investigation suggested that this was “false” fluorescence, resulting from the effects of the scalpel rather than the presence of residual tumor cells. The method of laser resection with a strongly absorbing coating on the tip therefore did not appear to demonstrate definite advantages over laser resection with a bare tip when removing tumors.

We present a theoretical model for laser cutting of biological tissue by a strongly heated fiber tip with a highly absorbing coating. A significant dependence of the cutting speed and cutting depth on the inclination angle of the scalpel to the surface when scattering exceeds absorption in the biological tissue is shown. Experimental evidences of this effect are presented. In the experiment, we used silica fiber with coating made of carbon and silicon organic varnish, the 0.97-µm wavelength laser and porcine skin. The additional opportunity to increase the efficiency of cutting by deposition of the absorbing layer on the tissue surface is considered.

A modified express method of contact angle measurement based on determining the diameter of a drop with a known volume has been elaborated.The method offers a number of advantages: it can be used in an express manner for in situ dynamic investigation and makes it possible to observe inhomogeneity and anisotropy of hydrophilicity.The method is convenient in comparative measurements and does not require any special equipment.Using the proposed method, the possibility of hydrophilic control of some materials (silicate glass, TiO 2 (anataze) and polymetilmetacrylate (PMMA)) by UV (ultra violet) and chloroform vapor treatment has been studied.In particular, hydrophilicity of PMMA after UV irradiation was observed, and it is shown that changes in hydrophilicity are connected with the surface oxidation of PMMA.The observed phenomenon of hydrophilicity control can be used in various technologies, such as liquid coating, printing, spray quenching, nanolithography, pharmacology and others.

The aim of the study was to evaluate the developed technique of contact lithotripsy using a strongly heated distal tip of a fiber providing controlled fragmentation of urinary stones.Materials and Methods. Postoperative kidney stones were used as research objects. For renal calculi fragmentation we applied a standard 0.97 mu m diode laser with a continuous wave laser regime, laser power 15 W. As a strongly absorbing coating ( SAC), we used a solution of graphite carbon microparticles in silicone varnish. SAC was localized at the distal end of the light guide of multimode quartz fiber, d=550 mu m. The contact zone of the light guide with a stone ( heated to 2000 degrees K) was smeared with a CO2 gas stream, which made it possible to optimize the high-temperature oxidation of graphite in the destruction of stones. Laser fragmentation was performed ex vivo in physiological saline and in liquid-free conditions by means of direct calculus contact.Results. Large calculus fragmentation was achieved through the carbonization with mechanical destruction of the surface by high temperature of an optical fiber tip. Calculus fragmentation time depended on stone density, cross-sectional dimension, and was from 10 to 80 s. Maximum cross-sectional dimension of calculi was from 6 to 21 mm, X-ray calculus density being 158-1,587 HU. Calculi with X-ray density of over 1,400 HU were unaffected by fragmentation in liquid, however, fragmentation in the atmospheric air proceeded successfully.Conclusion. The use of SAC of the laser fiber tip enables to develop new calculus fragmentation mechanism and provide the break of a stone along the marked line. The technique excludes small stone fragmentation, therefore enables to prevent intra-operative microbial dissemination of renal tissue from biofilms of potentially infected calculi. New opportunities enable to use various laser types as a lithotripter, and significantly simplify and cheapen the technology of their manufacture.

In the present communication, it is shown that a laser scalpel operating at the wavelength of 0.97 μm with a fiber tip having a strongly absorbing coating proves to be efficient for making contact incisions. At 6 W laser pump radiation, the temperature of silica glass on the cutting fiber tip during cutting is close to the silica glass softening point. The high fiber tip temperature allows bloodless resection with the cut depth of more than 1 mm and with high tissue cutting speed.

In this paper, we consider a method of laser resection using the silica glass core from which the cladding layer has been removed as the cutting part of a laser scalpel. An absorbing layer coating the silica fiber tip markedly alters its biotissue cutting characteristics. The results of histological studies of skin after exposure to a laser scalpel with and without a strongly absorbing coating (SAC) at a wavelength of 0.97[Formula: see text][Formula: see text]m show that resection using a coated scalpel is more sparing. When an uncoated scalpel was used, skin injury was more apparent in both its surface spread and the depth of structural damage, resulting in poorer tissue regeneration.

The paper presents the results of laboratory measurements of the acoustic nonlinearity parameter for a granite sample from the site of a conducted field experiment. This made it possible to completely confirm the results of the field experiment and explain the occurrence of a large scatter of values for the nonlinearity parameter in the field measurements. The size of the quadratic linearity parameter in granite rocks was determined, normalized to the volumetric concentration of fractures, which can be used for remote estimation of the fracture concentration.

UV irradiation of materials consisting of a polymer matrix that possesses precursors of different kinds can result in creation of nanoparticles within the irradiated domains. Such photoinduced nanocomposites are promising for photonic applications due to the strong alteration of their optical properties compared to initial non-irradiated materials. We report our results on the synthesis and investigation of plasmonic, excitonic and exciton-plasmonic photoinduced nanocomposites. Plasmonic nanocomposites contain metal nanoparticles of noble metals with a pronounced plasmon resonance. Excitonic nanocomposites possess semiconductor nanoclusters (quantum dots). We consider the CdS–Au pair because the luminescent band of CdS nanoparticles enters the plasmon resonance band of gold nanoparticles. The obtaining of such particles within the same composite materials is promising for the creation of media with exciton–plasmon resonance. We demonstrate that it is possible to choose appropriate precursor species to obtain the initially transparent poly(methyl methacrylate) (PMMA) films containing both types of these molecules either separately or together. Proper irradiation of these materials by a light-emitting diode operating at the wavelength of 365 nm provides material alteration demonstrating light-induced optical absorption and photoluminescent properties typical for the corresponding nanoparticles. Thus, an exciton-plasmonic photoinduced nanocomposite is obtained. It is important that here we use the precursors that are different from those usually employed.