Ablation of an optically homogeneous absorbing medium by scattered pulsed laser radiation

We have studied the ablation of an aqueous CuCl₂ solution in a pulsed Nd:YAG laser field featuring a speckle-patterned structure characterized by spatial radiation energy fluence fluctuations. This leads to a nonuniform distribution of the energy absorbed in the bulk of the sample being irradiated and causes local overheating centers to form, wherein ablation is observed to take place at laser energy fluences below the threshold value found in experiments with a homogeneous laser beam. This effect should be manifest in the laser irradiation of biotissues which, as a rule, scatter light strongly.     

在1341.4 nm激光波长对生物组织折射率的测量

根据全反射原理,设计一个由准直宽光束和双棱镜构成的测量装置用于测量生物组织的折射率.在波长632.8 nm通过对几个样品测量,证明该方法用于测量生物组织的折射率具有可靠、精确和简单易行的特点.第一次测得了某些生物组织在1341.4 nm 的折射率,也为在1341.4 nm激光波长测量人体组织的折射率提供了一种有效的方法.     

Laser polarimetry of pathological changes in biotissues

The possibility of using laser polarization techniques to diagnose the appearance and development of pathological changes in the morphological structure of biotissues is analyzed.     

Principles of fluorescence laser tomography of strongly scattering media

The propagation of laser radiation and fluorescence excited by it in a strongly scattering medium are analyzed in the diffusion equation approximation. The possibility of applying efficient algorithms of the tomographic reconstruction with the use of mean paths of photons in biotissues to fluorescence laser tomography is substantiated.     

Laser-induced photodissociation of oxyhemoglobin: Optical method of elimination of hypoxia (oxygen deficiency in biotissue)

We consider the effect of laser-induced in vivo photodissociation of blood oxyhemoglobin on gas exchange in biological tissues. An optical method of laser-induced oxygenation of biotissues is developed and proposed. We show that, in the region of the action of the laser radiation, the degree of oxygenation of a tissue increases. We experimentally confirm that the phenomenon of laser-induced in vivo photodissociation of oxyhemoglobin opens up a new possibility of controlling the local concentration of free molecular oxygen in tissues, eliminating tissue hypoxia, and stimulating aerobic metabolism of cells. We show that the efficiency of the proposed method of laser-induced oxygenation of biotissues proves to be comparable with the efficiency of the hyperbaric oxygenation, but has the advantage of the locality of the action. The proposed optical method of local oxygenation of biotissues will make it possible to eliminate the problem of hypoxia in cancerous tumor tissue and to considerably increase the efficiency of photodynamic, radiation, and chemotherapy in modern oncology.     

Doppler velocimetry and backscattering spectroscopy according to a homodyne scheme using a single-mode Er fiber laser

The prospects for the homodyne recording of backscattered radiation of an Er fiber laser in measuring velocity and in Doppler spectroscopy are investigated. The sensitivity and accuracy of measuring velocity are estimated. It is shown that this method can be used to control laser-induced hydrodynamic flows that form upon the laser evaporation of biotissues.     

Scattering of laser radiation by multifractal biological structures

Scattering of laser radiation by structured biotissues—histological mounts of bony and muscular tissues and skin, are studied.     

An analysis of thermal effects resulting from laser radiation interaction with a multilayered biotissue

Initial data for solving the problem of heating biological tissues by laser radiation are the optical characteristics of the tissues determining light regimes after irradiation, and their thermal-physical properties determining heat transfer as functions of time and depth of penetration into the medium. Based on an analysis and generalization of literature data and results of our investigations, we suggest a model of the optical and thermal-physical characteristics of the biotissues. The finite-element method is used to solve the problem of thermal conductivity. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 90–94, October, 2006.     

Determination of the Diffusion Coefficient of 40%-Glucose in Human Gum Tissue by Optical Method

Optics and Spectroscopy - The problem of increasing the depth of light penetration in biotissues, which is solved by the use of immersion agents, including hyperosmotic ones, such as glucose, is...     

The biomedical effect of laser-induced photodissociation of oxyhemoglobin in vivo

It is demonstrated that the photodissociation of oxyhemoglobin in cutaneous blood vessels and capillaries allows additional extraction of molecular oxygen, prevents hypoxia, and stimulates aerobic metabolism of cells. On the basis of the studied phenomena, a new optical technology of local oxygenation of tissue directly in the zone of laser irradiation has been developed. It is shown that the efficiency of the proposed method for laser-induced oxygenation of biotissues is comparable with the efficiency of hyperbaric oxygenation, with local action being an additional advantage. Various aspects of the applications of the new technology in modern medicine in which the elimination of local hypoxia is needed are discussed. The proposed optical method for local oxygenation of biotissues makes it possible to solve the hypoxia problem in malignant tissue and substantially increase the efficiency of photodynamic, radiation, and chemical therapy in modern oncology.     

Comparative studies of infrared laser and radio-frequency action on in vitro biotissues by the method of polarization sensitive optical coherence tomography

We make comparative studies of structural changes of in vitro biotissues subject to the infrared (IR) laser radiation and the radio-frequency field. Noninvasive diagnostics and monitoring of microstructural changes of biological tissues are performed using optical coherent tomography.     

Laser ablation of absorbing liquids

We have studied experimentally the formation of microdroplets upon the ablation of an aqueous CuCl₂ solution by pulsed laser radiation. Laser fluence dependences are obtained from the number of droplets formed and from their statistical size distribution. The experimental data obtained can be explained within the framework of our acoustical microfragmentation model providing for excitation and interference in the field of laser acoustic waves of random phases. The ablation mechanism suggested is of universal character and manifests itself particularly in the laser ablation of biotissues.     

Technique for interaction of optical fields with turbulent medium containing particles

We develop a method for transmission of stochastic fields through turbulent media (atmosphere, ocean, biotissues) containing randomly distributed particles. The method is based on the angular spectrum representation of stochastic, statistically stationary, scalar fields, the Rytov perturbation series for propagation in weakly fluctuating media, and the first Born approximation for weak scattering from particulate media. The results for transmission of the deterministic (laser) field may be obtained from our general results as a limiting case.     

Effects of transient local heating of spatially and spectrally heterogeneous biotissue by short laser pulses

Summary A new laser method for the spectroscopy of locally absorbing microvolumes much smaller than the radiation wavelength in size is discussed. Such an absorption is characteristic of biotissues and other biological media. The method allows data to be obtained on the size of local microvolumes absorbing at the radiation wavelength. It is based on the possibility of transient overheating of the microvolumes by means of an ultrashort pulse with a duration much shorter than the time it takes to heat to diffuse from the microvolumes. The pulse-heated microvolumes must have an altered refractive index leading to an additional scatter of another probe laser pulse, that is made to irradiate the medium under study after some delay. Besides, the locally heated microvolumes will have temperature-altered fluorescence induced either by the heating laser pulse or by an additional probe pulse at another wavelength more suitable for fluorescence excitation. Due to the relevance of its scientific content, this paper has been given priority by the Journal Direction.     

Dynamic laser prototyping for biomimetic nanofabrication

Micronanofabrication technologies developed so far pursue faithful conversion from digital models to matter structures. This is vital for microdevices in optics, mechanics, and electronics, where device shape and size matter. However, biotissues grow under rich environmental factor interactions, as demands novel manufacturing approaches for biomimetic and biological fabrication. Here, a concept of dynamic laser prototyping is reported, which is based on a new finding of a multilayered three‐dimensional (3D) wrinkling phenomenon. The 3D wrinkling started with formation of a photocrosslinked hydrogel sheet by femtosecond laser direct writing. It was followed by spontaneous self‐bending of the sheet, caused by a purposely designed sheet–substrate stress mismatch. The flower blooming process has been successfully mimicked, indicating broader usages of the technology in biotissue‐growth‐related manufacturing.     

Control of optical properties of biotissues: I. spectral properties of the eye sclera

A method for computer modeling of transmission and diffuse reflection of a strongly scattering biotissue is described. Results of calculations of spectral characteristics for a model of the human eye sclera are presented and compared with experiments. The possibility to control optical properties of biotissues is theoretically substantiated and experimentally confirmed. Variations in color indices of biotissues are calculated using theoretical and experimental spectral characteristics obtained for the eye sclera.     

Features of applying fiber-optic sensors in spectral measurements of biological tissues

The fiber-optic sensor is a key element for in vivo spectral measurements of the diffusion reflection of biotissues. Its construction and geometry of the detection of light emerging from the biotissue have a significant effect upon the spectral composition of the detected light. This work presents the results of theoretical and experimental studies of the effect of the detection area on the spectral composition of diffusion reflection of skin. It was found that significant losses took place when detecting the light of the red and near-infrared light ranges if the dimensions of the detection area were comparable with the dimensions of the illuminated skin. The losses can be minimized with an increase in the detection area up to dimensions exceeding those of the illuminated skin by a factor of 3–4. In this case, losses during detection of the long-wavelength spectral range of light diffusely reflected by the skin are less than 5%.     

Reconstruction of object location for diffuse fluorescence tomography on the basis of hybrid models of light scattering in biotissues

We propose a new method for reconstructing the spatial distribution of fluorophore in a highly scattering object from its images obtained by the method of diffuse fluorescence tomography. This method is intended for diagnostics of the fluorophore-marked tumors and is based on the algebraic-reconstruction principle combined with a new theoretical model and simulation of light propagation in randomly scattering media, such as biotissues, by the Monte Carlo method. The model experiments show that for 18-mm thick objects, the developed method allows one to determine location of the geometric center of a fluorescent inhomogeneity and its transverse and longitudinal dimensions with accuracies of up to 0.5 and 1.5 mm, respectively.     

Stationary spectroscopy of biotissues in vivo: Fluorescent studies of some pathological states

The stationary spectra of autofluorescence, along with the reflection coefficient at the wavelength of excitation, are measured in vivo for some stomach tissues in the case of different pathological states (dysplasia, superficial gastritis, and cancer) using a nitrogen laser as the source of excitation (λ_rad=337.1 nm). The fluorescence spectra obtained are decomposed into Gaussian-Lorentzian components. It is found that, in development of dysplasia and tumor processes, at least seven groups of fluorophores can be distinguished that form the entire emission spectrum. The ratio between the fluorescence intensities of flavins and NAD(P)H is determined and the degree of respiratory activity of cells estimated for the states considered. The quantum yields of fluorescence of the biotissues under investigation are estimated.     

Spectrophotometric system for measuring the characteristics of light scattered by biological tissues and humoral media

The structure, assembly, and physical capabilities of a spectrophotometric system intended for studying biotissues and humoral fluids are described. It can be used to investigate all the characteristics of scattered light at wavelengths of 400–1000 nm that are of interest for various problems in biomedical optics. Examples of these problems include noninvasive diagnostics of the structural and biophysical parameters of human skin tissue, analysis of the hemoglobin composition, sizes and degree of aggregation of erythrocytes, and evaluating the depth of penetration of light into biotissue. Pilot experiments on measuring the characteristics of scattered light are conducted in order to select an optimum operating mode for the system, estimate its errors, and develop ways of minimizing these errors.