The maximum probing depth is of considerable interest in the characterization and optimization of an optical coherence tomography (OCT) system when used for imaging in highly scattering tissue. In this paper, we calculate the maximum obtainable probing depth based on the design variables of the OCT system, the detector characteristics, and the optical properties of the tissue. The calculation of the maximum probing depth is based on the minimum acceptable signal-to-noise ratio and a new analytical model of the OCT technique, which is valid in both the single and multiple scattering regimes. The new model is based on the extended Huygens-Fresnel principle and the use of mutual coherence functions. The so-called shower curtain effect, which manifests itself in standard OCT systems, is an inherent property of this model. We demonstrate the utmost importance of including both multiple scattering and the shower curtain effect when calculating the maximum probing in tissue. Furthermore, we show how the maximum probing depth depends on the design variables of the OCT system and the optical properties of the tissue including the reflection characteristics of the probed discontinuity. Finally, experiments are presented verifying the validity of the model used in the calculations.

In order to understand better the imaging contrast of OCT, Monte Carlo technique is applied to simulate the OCT signal form turbid medium with various optical properties. In the simulation, least scattered photons and multiple scattered photons in relation to the desired target depth are scored separately to show the limit of OCT imaging depth. The results show that multiple scattered photons are responsible for the decrease of contrast of the OCT image and their contributions become more significant as the depth increase. The anisotropy parameter of the turbid medium plays a significant role in the OCT imaging contrast. With the scattering coefficient fixed, the higher the g values, the deeper the depth of OCT imaging capability, but the lower the OCT signal magnitude. The lower the g value, the more the multiple scattered photon contribute to the OCT signal reducing the imaging capability.

Photon migration through skin tissue leads to a poorly defined 'sampling volume' so that the optical signal represents a spatial average over cell layers 1 mm deep or more. This problem is well known in the field of Laser Doppler Flowmetry. The current work is to theoretically investigate to what extent we can localize the sampling volume of reflectance spectroscopy to the upper layers of skin. The results of Monte Carlo simulation of the degree of photon spatial localization for different kind of optical probes are given. Such localization is very important for the clinical interpretation of the results, as capillary loops are responsible for the delivery of nutrients to the epidermis, whereas deeper vessels are primarily thermo regulatory in function.

In the later years, a great effort has ben put into simulation of the geometry of an optical coherence tomography (OCT) system. Recently, a new analytical model of the OCT geometry has been developed based on the extended Huygens-Fresnel (EHF) principle. Although advanced, the result of the model are surprisingly simple and easy to handle for e.g. system optimization. To validate this model, new features have been added to the Monte Carlo (MC) simulation program MCML, which is widely used and recognized for its credibility. We have incorporated the true shape of a focused Gaussian beam including the finite size of the beam waist, which previously has been approximated by a point. This enables us to do high-resolution comparison of the intensity distribution in the focus plane and excellent agreement is found between the EHF model and the MC simulations. Results are also compared with previously published modeling result and it is shown that there are substantial differences. We emphasize the importance of the so-called shower curtain effect (SCE), which is an inherent - but often overlooked - effect in light propagation through random media. Finally, we calculate the OCT signal using MC simulation. This is done by keeping track of the path length traveled by each photon packet and restricting its access back into the OCT system from the sample using the antenna theorem. The degradation of the detected signal due to scattering is determined, and compared with the EHF model and experiments. The comparison of MC simulations with EHF allows us to show that the SCE is an inherent effect in MC simulation, and that for common tissue parameters, the EHF model yields the same results as the MC simulation but with faster computation time and with field and phase information available.

The least scattered photons that arrive at a detector through the highly scattering tissues have the potential for imaging internal structures, functions and status with high imaging resolution. In contrast optical diffusing tomography is based on the use of the late arriving photons, which have been diffusely scattered, leading to very low imaging resolution. A good model of the early arriving photons, i.e. the least scattered photons may have a significant impact on the development of imaging algorithms and the further understanding of imaging mechanisms within current high resolution optical imaging techniques. This paper describes a vertex/propagator approach, which attempts to find the probabilities for least scattered photons traversing a scattering medium, based on analytical expressions for photon histories. The basic mathematical derivations for the model are outlined, and the results are discussed and found to be in very good agreement with those from the Monte-Carlo simulations.

Different configurations are presented which allow simultaneous acquisition and presentation of OCT en-face images from different depths. If a sufficient number of slices are collected, 3D rendering of the object in real time is made possible. Results using two configurations to produce simultaneously two such images are presented, as a hardware version towards 3D imaging. Rendering of a 3D profile of the retina is also shown, as a software version, using slices obtained at different depths collected by a single channel en-face OCT instrument.

'Spectral radar' combines a white light interferometer with a spectrometer. It is an optical sensor for the acquisition of skin morphology based on OCT techniques. The scattering amplitude along one vertical axis from the surface into the bulk can be measured within one exposure. We will discuss some essentials of signal formation and a new method of signal evaluation that significantly reduces artifacts from some source imperfections. We will further demonstrate new measurements.

The most straightforward interferometer for optical coherence tomography (OCT) is a simple Michelson interferometer. A low-coherence source illuminates the interferometer. The light is split by a 50/50 beamsplitter into a sample and a reference path. Light retro reflected from the reference and the sample is recombined at the beamsplitter and half is collected by a photodetetor in the detection arm of the interferometer. Half of the light is returned towards the source, where it is lost. In addition, the reference arm light is typically attenuated by orders of magnitude in order to improve signal to noise ratio. Thus, using this typical configuration, virtually 75 percent of the optical power supplied by the source is not used for image formation. We present a family of novel interferometer designs incorporating optical circulators, unbalanced couplers, and/or balanced detection which are designed to optimize optical power efficiency and circulators, unbalanced couplers, and/or balance detection which are designed to optimize optical power efficiency and system signal to noise ratio. We evaluate the expected performance of the novel interferometers as compared with the standard Michelson interferometer. We review signal and noise sources important for the design of OCT interferometers, and specify the design equations for evaluation and optimization of signal to noise ratio. This analysis, based on sound, experimentally verified literature, predicts improved sensitivity for all of the new interferometer designs.

In optical coherence tomography (OCT), mapping the polarization state of the reflected light provides additional information about tissue structure and prevents polarization induced image artifacts. As OCT is increasingly used with subjects in vivo, demands on the imaging system and data acquisition rates increase. We present a fiber- based, rapid scanning, polarization-sensitive OCT system capable of acquiring image data at the rate of 20K pixel/s. To achieve high scan rates, a rapid-scanning optical delay line generates a reference arm group delay while a waveguide-based phase modulator generates a suitable, stable carrier frequency for the detection electronics. Group delays up to 4.5 mm are obtained at frequencies approaching 1 kHz. The group delay and carrier frequency are independently controllable, which has the advantage that either the lateral or the axial scan direction may be chosen as the fast axis. Tomographic images corresponding to the intensity and polarization components of the Stokes vector describing the back scattered light are obtained by analyzing the interference signals from two orthogonally polarized channels in the detection arm for each of four polarization states incident on the sample. Polarization images of human skin taken in vivo are shown.

Chirp optical coherence tomography (Chirp OCT) has been introduced as an alternative solution for imaging scattering media or biotissues. The basic principle of Chirp OCT is well-known by the FMCW radar technique and is adapted to the optical regime. This method uses a frequency modulated laser source in the near IR frequency range. Fast imaging can be performed by an electrical tuned diode laser without the disadvantage of any mechanical moved elements but retaining the properties of optical tomographic tools for contact less, non-ionizing, non-invasive and high depth resolved scanning. The demand of high resolution imaging for media application requires a large frequency tuning range. Covering the whole lasing bandwidth of an external cavity laser by the frequency Chirp, non-linear terms as well as mode-hopping reduce the depth resolution and the dynamic range, if equidistant sampling in the time domain is performed. To restore the resolution given by the Chirp bandwidth a reference detector has been implemented, which allows the detection of mode-hopping quantitatively and the correction of the non-linearity. The reference detector can be used for real-time laser frequency measurements and offers the possibility to determine the location of discrete reflectors more accurate. Images with a high dynamic range demonstrate an increased penetration depth.

Differential phase contrast optical coherence tomography can image small phase differences occurring between beams that penetrate a sample at closely spaced areas. Such phase differences can be caused by regions of slightly varying refractive index. We report on two recent improvements of this technique: we demonstrate depth resolved differential phase imaging in a transparent multi-layer sample. Furthermore, we report on a modified setup designed for phase imaging in scattering samples and demonstrate first results.

Optical tomography and imaging techniques using coherence domain methods are widely studied for biomedical applications. Most optical tomographic images are reconstructed using the intensities of transmitted or reflected lights. In highly scattering media such as biological tissues, the exponential attenuation of the coherence-gated transmitted light beyond an optical thickness of 20 scattering mean free paths is small when compared to attenuation in a relatively transparent media. Tomographic image reconstruction of optical thicker scattering media using the intensity of emergent photons results in images of low resolution and contrast. Here, we report transillumination optical computed tomography (CT) of highly scattering media using the laser spectral linewidth broadening, instead of the transmitted light intensity. We demonstrate that quantitative scattering linewidth broadening CT images. Our method could provide novel information on biomedical applications of thick tissues, where the differences in the scattering coefficients or dynamic properties can not be quantitatively determined from the images reconstructed with the intensity of transmitted light.

Noninvasive quantitation of blood flow in the retinal micro circulation may elucidate the progression and treatment of ocular disorders including diabetic retinopathy, age-related degeneration, and glaucoma. Color Doppler optical coherence tomography was recently introduced as a technique allowing simultaneous micron-scale resolution cross-sectional imaging of tissue micro structure and blood flow in the human retina. Here, time-resolved imaging of dynamics of blood flow profiles was performed to measure cardiac pulsatility within retinal vessels. Retinal pulsatility has been shown to decrease throughout the progression of diabetic retinopathy.

The blood flow velocity registration method using an optical coherent photo detection in a diode laser is presented. The dependence of signal on distance and non-conventional self- mixing interferences has bene discussed. Also, an experimental device with pigtail laser diode is developed. This device is able to measure blood flow velocity or velocity of liquid suspension containing particles with size of erythrocytes. During experiments the liquid suspension containing polymer micro spheres with spheres diameter 7.0 microns and density 1.05 g/cc was used instead of real blood. The basis of the registration is the self-mixing that occurs in diode laser cavity when the radiation scattered back by the particles into the laser interferes with the field inside it and causes a changes of a laser pump current. National Instruments software LabView for Windows is used for output signal digitalization and pre-processing purposes. There is good correlation between calculated and measured with proposed device values of different velocities. Described device as application of self-mixing method highlighted the significant advantages of simplicity, compactness, and robustness as well as the self-aligning and self-detecting abilities of such methods when compared with the use of conventional interferometric methods.

We report here first results of measurements of the pathlength distribution of scattered photons by low- coherence Doppler interferometry. Laser Doppler Flowmetry (LDF) is used to non-invasively monitor the blood micro circulation in biological tissue. On the other hand, the LDF response is also affected by the optical properties of the tissue itself, which complicates the problem of the exact evaluation of the blood perfusion. In a scattering medium like skin photons travel along different paths of variable length. The longer the pathlength, the higher the change for the photon to be scattered by a blood cell. An aqueous suspension of Intralipid is used to mimic the most important properties of the skin. Using a free beam Michelson interferometer we measure the AC component of the intensity of the pattern formed by interfering the scattered light with a coherent component from the reference channel. In each measurement the mirror in the reference channel is kept fixed while the AC component arises due to the Doppler effect in light scattered by the micro-particles experiencing Brownian motion. The pathlength distribution is extracted from the dependence of the detected signal on the reference mirror position.

Laser Doppler microscopy was used to study the effect of multiple scattering on Doppler spectra in the experiments with concentrated suspension flows imbedded into a multiply scattering medium. A suspension of latex particles was used to model biological fluids and diluted suspension of Intralipid-20 percent at different concentrations - to model tissues. The shape of Doppler spectra and the signal-to- noise ratio were used to characterize the feasibility of laser Doppler measurements.

Basing on such fundamental optical phenomena as elastic and quasi-elastic light scattering, diffraction, and interference of optical fields we have designed coherent optical methods offering much promise for biomedical applications. The scope of research includes the development of photon-correlation spectroscopy, speckle-interferometry, coherent micro-topography of living tissues, and study of optical images contrasting due to reduction of scattering properties of surrounding medium using immersion liquids.

A theoretical framework is proposed for the description of the photodetector signal generated by Doppler-induced speckle fluctuations. The theory allows for predicting the power of the photo current fluctuations. It is valid for a detector of arbitrary size. The input data required for application of the theory are the angular distribution of the detected light, the fraction of Doppler shifted photons and the active detector size. The theory is based on the time domain approach to the statistics of dynamic speckle patterns on the photodetector. An experiment has been carried out to validate some aspects of our theory. The consequences of the speckle dynamics for the various modes of laser Doppler Flowmetry are discussed. As one of a practical application of the theory the fraction of Doppler- shifted photons in light back scattered from human skin has been measured in vivo. .

Cilia are finger like organelles present throughout the epithelium of the human respiratory tract. Typically 5-6 micrometers long, with a density of around 8/micrometers ², they 'beat' at frequencies of 10-20Hz and propel an overlying mucus layer. The mucus traps airborne particulars providing an essential respiratory cleaning/infection control mechanism. A novel method for measurement of ciliary beat frequency in-vivo is presented. Homodyne mixing of scattered coherent light promises a relatively large signal with minimal sensitivity to vibrational when compared with existing methods: Vibrational susceptibility is minimized since all scattered pathlengths are similarly affected, while phase discrepancies introduced by the muco-ciliary surface produce high contrast speckle giving good signal quality. The need to illuminate a relatively small area of epithelium to give large speckle has been addressed using a 'shortened' gradient index rod as a combined delivery/focusing device. Results are good when the ciliary surface reflectivity is increased. However the relatively low reflection co-efficient of the unprepared surface allows homodyne mixing from deeply scattered light giving a speckle structure too small to resolve and consequent signal loss. Evidence is presented that demonstrates how a source with limited temporal coherence might be used to suppress the interference from these 'longer pathlength' photons.

We show that standard tissue phantoms can be sued to mimic the intensity and polarization properties of tissue. Polarized light propagation through biologic tissue is typically studied using tissue phantoms consisting of dilute aqueous suspensions of microspheres. The dilute phantoms can empirically match tissue polarization and intensity properties. One discrepancy between the dilute phantoms and tissue exist: common tissue phantoms, such as dilute Intralipid and dilute 1-micrometers -diameter polystyrene microsphere suspension, depolarize linearly polarized light more quickly than circular polarized light. In dense tissue, however, where scatterers are often locate din close proximity to one another, circularly polarized light is depolarized similar to more quickly than linearly polarized light. We also demonstrate that polarized light is depolarized similar to or more quickly than linearly polarized light. We also demonstrate that polarized light propagates differently in dilute versus densely packed microsphere suspensions, which may account for the differences seen between polarized light propagation in common dilute tissue phantoms versus dense biologic tissue.

Various functions of biological membranes are closely related to phase transition of phospholipid bilayers. However, there has been no possible method for in vivo measurement to detect the phase transition of biological membranes. In this paper, we demonstrate a novel method for detection of biological membranes using the low coherence interferometry. In the experiment, rat mesentery was used as the sample of biological membranes, and the refractive index of the mesentery was measured precisely as the sample temperature was changed. Abrupt change in both the index and transmission of the mesentery can be found in the temperature range of 38 percent C to 42 percent C, which is good agreement with the temperature range for the gel-to- liquid phase transition of the artificial membrane. Our method does not require any treatments, including fragmentation and centrifugation, for extraction of phospholipid bilayers form biological membranes. It, therefore, is a useful method for in vivo measurement and analysis of the membrane functions.

A new method is described for analyzing the penetration of drugs and cosmetic products into the skin. This method combines the tape stripping procedure with UV/VIS spectroscopic measurements to determine the amount of corneocytes on the tapes removed by their scattering properties. The UV/VIS spectroscopic measurements were made using a Perkin Elmer Lambda 20 double beam spectrophotometer, which had been modified to obtain a rectangular beam diameter of 10 times 10 mm². The absorbance measured at 430 nm was taken as measure for the mass of the corneocyte aggregates placed on the individual tapes. It was proven by weighing, laser scanning microscopy and spatial-spectral density analysis, that the absorbance in the visible range is better suited than the weight to quantify the amount of corneocyte aggregates removed by a single strip. This novel combination method permits to determine the actual position of sunscreen components in the stratum corneum.

The laser-tissue interaction code LATIS is used to analyze photon scattering histories representative of optical coherence tomography (OCT) experiments performed at Lawrence Livermore National Laboratory. Monte Carlo photonics with Henyey-Greenstein anisotropic scattering is implemented and used to simulate signal discrimination of intravascular structure. An analytic model is developed and used to obtain a scaling law for optimization of the OCT signal and to validate Monte Carlo photonics. The appropriateness of the Henyey-Greenstein phase function is studied by direct comparison with more detailed Mie scattering theory using an ensemble of spherical dielectric scatterers. Modest differences are found between the two prescription for describing photon angular scattering in tissue. In particular, the Mie scattering phase functions provide less overall reflectance signal but more signal contrast compared to the Henyey-Greenstein formulation.

The speckle pulse-analyzer is used to measure the human resonant mechanovibrations under pulsating magnetic influences, to conduct their Fourier-spectra analysis and dynamical processes documentation. The fast coherent response of organisms on super weak ultra-low-frequency magnetic field was recorded on coherent cells vibrations. Possible biophysical mechanisms are suggested and proved on experiments with blood cells. In particular, gradient steady magnetic fields could reveal the vibrational potency of cells in pulsating magnetic fields provided of the appearance of cellular magnetic sign-difference and anisotropy under pathological situations in organism. From the disturbances oxidative process in cells which give the paramagnetic shift of cells magnetic susceptibility relatively the normal state, the single cells or certain parts of organs become more paramagnetic than other native tissue. Arising magnetic vectors of living system appear oscillations in pulsating magnetic fields.

Optical Coherence Tomography (OCT) is a noninvasive optical imaging technique that allows high-resolution cross- sectional imaging of tissue microstructure. We have recently developed a system for endoscopic OCT (EOCT) to examine the gastrointestinal tract of humans in vivo. Compared to endoscopic ultrasonic devices it offers a higher resolution and does not require coupling gels or fluids. EOCT may lead to a versatile tool for biopsy site selection or optical biopsy itself. The EOCT unit is comprised of an interferometer unit with a high speed scanning reference arm and an endoscopically compatible radially scanning probe as the sample arm. Fast data acquisition allows real-time display. Temporal averaging for speckle reduction and a transformation to correct nonlinear scanning were included in the EOCT control software, both in real-time. During in vivo clinical trials, we have observe the structure of the mucosa and submucosa in several gastrointestinal organs as well as glands, blood vessels, pits, villi and crypts. The purpose of this study was to correlate images acquired in vitro with EOCT to corresponding histological sections. EOCT images were obtained on fresh specimens, which were then fixed in formalin and submitted for standard histology. Tissues examined were normal specimens, which were then fixed in formalin and submitted for standard histology. Tissues examined were normal specimens of stomach, ileum, colon and rectum. It was shown that he thickness of the mucosa correlates well with the first bright layer in EOCT. The R²-value was determined to be 0.69. The submucosa and the muscularis propria could be identified. Furthermore, we were able to show the effect of pressure on the tissue on the visible details in the EOCT images.

Vascular stents and grafts have many proven and promising clinical applications, but also a large number of complications. A focus of current research is the development of biocompatible implants. Evaluation of these devices generally requires a large number of animals due to the need for explanation and histological evaluation of the implant at several time intervals. It would be desirable to use instead a high resolution, in situ assessment method. An in vitro study was performed to determine if OCT could image cell proliferation and thrombus formation on vascular stents and grafts. First, images were taken of explanted stents. The implants were locate din peripheral vessels of a porcine model of atherosclerosis. The images clearly show the vessel response to initial damage, the materials of the implant, extent of intimal cell hyper proliferation, and small platelet aggregates. Next, a tissue engineered graft, which had been sodded with smooth muscle cells and incubated in a bioreactor, was evaluated. Cross-section images showed the pores of the polymer material and the layer of smooth muscle cells beginning to invade the graft material. For comparison, in vitro 20 MHz IVUS images of the same grafts were obtained. A catheter was designed for intravascular imaging. The 2.3 mm diameter catheter contains a fiber with GRIN lens and right angle prism, a monorail guidewire, and a novel positioning wire that can be protruded to push the catheter against the vessel wall, potentially eliminating the need for saline flush. Preliminary in vitro results with this catheter are encouraging.

We used a novel phase-resolved optical Doppler tomographic (ODT) technique, with very high flow velocity sensitivity and high spatial resolution, to image blood flow in port wine stain (PWS) birthmarks in human skin. The variance of blood flow velocity is used to locate the PWS vessels in addition to the regular ODT images. Our device combines an ODT system and laser so that PWS blood flow can be monitored in situ before and after treatment. To our knowledge, this is the first clinical application of ODT to provide a fast semi-quantitative evaluation of the efficacy of PWS laser therapy in situ and in real-time.

Burn depth determination is a critical factor in the treatment of thermal injury. We have developed a technique, polarization sensitive optical coherence tomography (PS- OCT), to assess burn depth non-invasively. Thermal injury denatures collagen in human skin. PS-OCT is able to measure the resulting reduction in collagen birefringence using depth resolved changes in the polarization of light propagated and reflected from the sample. In a previous study, we used a free space PS-OCT system at 850 nm to image in vivo the skin of rats burned for various amounts of time. Using a high-speed system at 1.3 micrometers has the advantages of greater depth penetration and reduction of motion artifacts due to breathing and small movements of the animal. Stokes vectors were calculated for each point in the scans and the relative birefringence was determined using different incident polarization states. Birefringence was correlated with actual burn depth determined by histological analysis. Our results show a marked difference between normal tissue and even the slightest burn, and a consistent trend for various degrees of burns.

The photometric readings are obtained by ektacytometry over several millions of shear elongated cells, using a home-made device called Erythrodeformeter. This time series is used to study the fractal behavior of erythrocyte viscoelastic properties. We have only a scalar signal and no governing equations. Therefore the complete behavior has to be reconstructed in an artificial phase space. We used the technique of time delay coordinates by Takens. A numerical method based on self-affine Brownian motion is proposed to analyze sensitive dependence on initial conditions. We hypothesize that this photometric temporal series, could be modeled as a system of bounded correlated random walk. Hence, two phase spaces n-dimensional are generated, and used to distinguish chaotic from white noise behavior. We have applied modified methods of Grassberger and Procaccia not only on our photometric readings but also on a pseudo- aleatory series in order to check their results. It was found that while the pseudo-aleatory series is high- dimensional, our series are low-dimensional. The role of random noise and the number of data points are discussed. Finally, our results, allow us to conclude that these methods could be used to evaluate the predictability and clinical aspects of erythrocyte rheological properties.

As a branch of scanning probe microscopy, near field scanning optical microscopy (NSOM) has been the most intensively developed for the past few years. A wide variety of types of NSOM have been created of recent years. However, a versatile NSOM that allow to investigate a same with different near field microscopy is not worked out up to now. In our lab a new versatile NSOM for biological application have been developed. The microscope can be operated in all known modes, viz., scanning optical, photon tunneling and aperture less photon tunneling modes. The basic element of the NSOM design is a coarse adjustment unit on which various scanners and sample holders are mounted. The maximal displacement of the coarse adjustment unit is 1 mm the approach step is about 50 micrometers . The NSOM scanner consists of a mechanical scanner with large displacement range on which is mounted a fine piezoscanner with t a scanning range about 2 micrometers . The maximal scanning range of the NSOM is about 1 mm laterally and 4 micrometers in perpendicular to sample surface direction with rough selection of area for study in the total are about 3 X 3 mm under conventional optical microscopy observation. As a sample holder are used either a glass prism in photon tunneling mode or a flat glass in scanning optical mode. The microscope has a digital control unit connected with IBM PC through a parallel interface. Different biological samples were investigated by means of the NSOM with resolution better than 15 nm. The NSOM high rigidity makes it possible to operate in ordinary laboratory without any additional vibration isolation devices.

In the work the medium inhomogeneities are considered as the optical parameter deviations from a certain mean values and represented by a random spatial 'pulse' process. These 'pulses' are supposed to have arbitrary geometrical forms, random parameters and random locations and orientations in space. We obtain the general analytical representation for the characteristic functional, autocorrelation function and Wiener-Khinchin's spectrum of the modeling process, that are applicable to various geometry of scattering objects and may be easy calculated. The corresponding relations contain statistical moments of geometrical and optical parameters of scattering centers and their spatial density. As an example the obtained relations are written for the medium with the spheroidal irregularities. The introduced model of the random continuous scattering medium may be useful in the classification of the solutions of the inverse problem of light interactions with homogeneous medium and in the noninvasive diagnostics.

The comparison method of color coordinates measurements for estimation of the optical anisotropy of tissue is suggested. The anisotropy of form of fibrous tissue was measured, it makes (Delta) n equals 0.001 for both types of studied tissues. We have suspected that optics of the muscle tissue is similar to optical properties of a uniaxial crystal, which optic axis is parallel to fibrils of a tissue. Due to more complicated structure scleral tissue optics is similar to optics of a biaxial crystal. The estimated value of an optical anisotorpy of the clarified sclera allowed us to evaluate the mean length of collagen fibrils of about 2 mm at mean radius of fibrils of 50 nm.

In this paper, we described our results of computer simulations of light propagation in a multi-layered biological tissue, such as the human brain and the skin. This report includes optical clearing simulations and light propagation researches at small distances. As well as we described light beam deformation in a multi-layered tissue and general principles of our algorithms construction.

Modeling of skin burns has been realized in this study. Autocorrelation functions of intensity fluctuations of scattered light were measured for two-layered turbid media. The first layer served as a model of motionless scatterers whereas the second one simulated dynamic light scattering. This medium was used as a model of skin burns. A theory related quasi-elastic light scattering measurements to cutaneous blood flow was used. The dependencies of statistical properties of Doppler signal on the properties of skin burns as well as on the velocity of cutaneous blood flow has ben investigated. Predictions were verified by measurements both of dynamic and stationary light scattering in model media. Experimental results might be used as a basis for blood micro circulation diagnostics as well as for precise measurements of a depth of burned skin.

We present recent results on development of superluminescent diodes (SLEDs) at spectral range from 680 nm to 1300 nm, that are able to deliver 10-30 mW singlemode fiber-coupled non-coherent light. It is shown that optimization of SLED structure and facet protection/antireflection coating procedures allows to get very flat spectrum at very high fiber outputs, with very small parasitic Fabry-Perot resonances. It is also shown, that by optimization of SLED structure it is possible to widen output spectrum considerably. At 940 nm band, 70 nm FWHM spectrum is demonstrated with 5 mW SM fiber output. Coherence function of different SLEDs, and impact of residual spectral modulation and minor structure non-regularities on secondary coherence effects are discussed. The results show that SLEDs are capable to deliver same and even higher outputs than fluorescent fiber doped sources. We also discuss some SLED parameters that are important for OCT applications, like optical feedback sensitivity and SLED noise and its subtraction. Finally, some possibilities on SLED power increasing and spectrum broadening are discussed.