Optical coherence tomography (OCT) is the novel method for producing three-dimensional images of the relatively thin (up to 2 mm) layers of the biological tissues. OCT is based on the interferometry of low-coherence light. The important factors, characterizing OCT, are the measurement speed and the quality of the obtained images. Both of these two factors actually characterize the amount of new information generated during the measurement with OCT. Using the Shannon's information theory; the quantitative characteristics of the information efficiency of OCT are introduced. Information capacities of OCT realizations based on scanning low-coherence interferometry and on spectral interferometry are defined and compared. It is shown that, image quality being the same, information capacity of spectral interferometry exceeds that of scanning low-coherence interferometry by a factor equal to the number of resolvable elements in a single in-depth scan. The speed of measurement and the image quality characterizing two methods are also compared.

Accuracy of some approximate ultra-fast algorithms, specially developed for real-time solution of direct and inverse problems of diffusion optical tomography of extra-large (with size about 1000 scattering lengths and more) objects, will be considered.

Interferometric imaging has the potential to extend the usefulness of optical microscopes by encoding small phase shifts that reveal information about topology and materials. At the Oak Ridge National Laboratory (ORNL), we have developed an optical Spatial Heterodyne Interferometry (SHI) method that captures reflection or transmission images containing both phase and amplitude information at a high rate of speed. By measuring the phase of a wavefront reflected off or transmitted through a surface, the relative surface heights and some materials properties can be determined. In this paper we briefly review a variety of application areas where this technology has been applied including semiconductor wafer inspection, photolithographic mask metrology and inspection, and we conclude with a discussion regarding future work to apply SHI to MEMS device characterization.

After more than 30 years since the first experiment we may say today that laser techniques are being widely employed by conservators and restorers as the best choice for the most important tasks: 1) diagnostics about the state of conservation; 2) restoration intervention in the crucial cleaning phase; 3) monitoring of the deterioration processes. Many important experiences have been carried out in Europe along these topics, with significant validation cases and sustainable technology transfer. In this paper the monitoring carried out by the EC Action COST G7 "Artworks Conservation by Laser" about the most advanced activities will be reported, showing how laser techniques in conservation of artworks are developing in Europe, providing a real change in the professional methods.

A new scanning lidar fluorosensor apparatus was developed for the diagnosis of stone samples and wall frescos relevant to the preservation and valorization of the Southern Italy and European cultural heritage. False color images retrieved from fresco investigation in the frame of the Advanced On-Site Laboratory for European Antique Heritage Restoration, held in Constanta (Romania), April 15-30, 2004, are presented.

A sample from the statue "Hercules and Telephus" by Le Sueur was analysed by Laser-induced Breakdown Spectroscopy (LIBS) in Pisa, Italy, in order to determine the quantitative composition of the bronze alloy.

We present herein a original concept of electro-optic (EO) probe for high frequency electric field measurements. This sensors is based on a thin organic layer of DR1-PMMA embedded in a high finesse Fabry-Perot cavity. The optimal orientation of DRl molecules, parallel to the face of the micro-cavity, has been obtained thanks to a lateral poling method. A r₃₃ of 2.5 pm/V has been reached for a 16 μm thick polymer layer. The final probe exhibits high sensitivity of 2V.cm^-1.Hz^-1/2.

We report on the implementation of novel, highly sensitive methods for strain measurements using FBG-based sensors, Basically, the strain detection technique rely on frequency modulation of a 1560-nm pig-tailed diode laser in the radio-frequency range with phase-sensitive detection of the FBG reflected signals. In one set-up, the power directly reflected by the fiber grating is demodulated at multiples of the sideband frequency. A different approach is based instead on using as a sensor an in-fiber Fabry-Pérot; cavity, made of an FBG pair with very high peak reflectivity (> 99 %). Static and dynamic deformation can be applied to the sensors in a controlled manner thanks to a piezoelectric actuator and a loud speaker. In the first case, a minimum detectable strain of the order of 100nε/Hz , in the quasi-static domain (0.5÷2 Hz), and 2 nε/Hz around 1 kHz. An FFT analysis of the output signals reveals the possibility of tracing dynamic strains up to 20 kHz, this limit being set only by the test device bandwidth. For the fiber interferometer set-up, similar tests have been performed using an electrical strain gauge as a reference probe. The diode laser, in this case, is actively frequency-locked to the FBG cavity, using the Pound-Drever-Hall technique. The resulting error signal is used as a monitor of strain suffered by the cavity fiber. We show that a sensitivity gain of at least one order of magnitude can be obtained with this scheme.

The direct problem of optoacoustics for the system, consisted of a metal film coating on a quartz substrate and immersed into a liquid is solved. The influence of a film coating thickness on an efficiency of optoacoustic (OA) excitation for two schemes of OA signal detection is investigated. In the forward mode a metal film is irradiated by laser pulses through the quartz substrate. In the backward mode (Fig. 1b) laser pulses irradiate the film through a liquid. The acoustic response of the system is determined in a liquid for both detection schemes. Experiments are carried out with the OA method in the forward mode using chrome films of different thickness and two immersion liquids: ethanol and acetone. Results of experiments coincide well with theoretical calculations, that allows one to determine the thickness of metal film coatings by the measured spectral transfer function of OA excitation. This method can be used also for measurements of thermophysical parameters of metal films.

Results on computer synthesis of kinoforms for pattern recognition by incoherent diffraction image correlator are presented. Gerchberg-Saxton and Fienup algorithms were used for kinoform synthesis. A correlation criterion was employed for error of synthesis estimation.

In this work we present the novel technique for z-distance measurement to an optically rough surface using dynamic speckles. The technique is based on the continuous frequency measurements of the power modulation of the spatially filtered scattered light. The dynamic speckle pattern is created when the laser beam scans the surface under study. The complete optical-electronic system was designed and fabricated for fast measurement of the speckles velocity, its recalculation into the distance, and further data acquisition into computer. The measured surface profile is displayed in a PC monitor in real time. Main advantage of the proposed technique is high scanning speed providing an extremely short response time below 1 μs. Important parameters of the system such as accuracy, range of measurements, and spatial resolution are analyzed. Limits of the spatial filtering technique used for continuous tracking of the speckle-pattern velocity are shown. Possible ways of further improvement of the measurements accuracy are demonstrated. Due to its extremely fast operation the proposed technique could find applications in such areas as online quality control of materials (paper thickness, rolled metal roughness, etc.) moving on production lines with high velocities (up to 20 m/s) or online control of the 3D-shape of complex objects (e.g., electronic circuits) during their assembling.

Aluminum dielectric permittivity has been determined for free-electron laser radiation of 1 10 micrometers by measuring surface electromagnetic waves (SEW) refractive index and propagation length. Both SEW's characteristics were measured using a newly developed double-beam surface-plasmon interferometer. The measurements were performed for clean aluminum surface and in the presence of a transparent germanium over layer.

The algorithms for screening singular points of the phase gradient vector field are developed, where vector field components can be measured with a Shack-Hartmann wavefront sensor or shearing interferometer. Special attention is focused on the singular points that allow localization of optical vortices (wavefront dislocations). Determination of the coordinates and the topological vortex charges is of special importance in optical vortex interferometry, in operation of optjcal communication devices that encode information by means of optical vortices, and for reconstruction of phase distribution of optical beams that propagate in a medium with dislocations. On basis of numerical modeling, accuracy of the algorithm is verified, comparison with other algorithms executed, and its advantages and drawbacks are analyzed. Performance results are presented of the singular wavefront recovery algorithm, whose operating requirement is preliminary detection of optical vortex dislocations.

The digital signal-processing method of fringe pattern extremal curves generation is presented. The method is based on 3D wavelet map computation. The correspondence between features of fringe pattern and 3D wavelet map of the same fringe pattern is described. For analysis, the Symmetrical Morlet wavelet is used. Wavelet map ridge detection algorithm is proposed. Fringe extremal curves obtained are used for fringe phase recovery that leads to possibility of 3D relief reconstruction.

The sensitive surface on the basis of fiber-optical measuring network with demodulation phase filters is offered. The purpose of the given work is further solution of actual fiber-optical tomography problem of spatial distribution reconstruction of the physical influences on the fiber-optical measuring networks. The problem of simultaneous reconstruction of the places and values of influences on fiber-optical measuring network from 4×4 dimension is described. For discussion of this problem were used the algebraic methods for solution of the system of linear algebraic equations with combinations of neural-like algorithms perceptron type. As the tomography data the integrated data coming from the fiber-optical measuring lines stacked on two and three directions on fiber-optical measuring network of researched area were used.

Design of functional modules of optically reconfigurable routing unit for fiber optical networks is proposed. The peculiarity of these devices consists in realization of optical data transport by means of transverse switching waves in bistable layer. The modules allow to develop gateway units with channel and packet routing of information flows at data rate of ~40 Gb/s and can be scaled up to systems with a higher throughput due to technology of wavelength division multiplexing (WDMDWDM).

Propagation of wide-band ultrasonic pulses in liquid-saturated printed paper samples of a various porosity soaked with liquids is studied. Three types of paper are used in experiments: "Zoom ultra" (Stora Enso, Finland) with surface specific gravity of 80 g/m² and 100 g/m² and "Data copy" (Mo Do, Sweden) with the surface specific gravity of 160 g/m². Two types of liquids (ethanol and transformer oil) are utilized for soaking of paper samples. The method of laser optoacoustic spectroscopy is employed both for excitation of ultrasonic pulses and its registration with a high temporal resolution. The phase velocity of ultrasound is measured in the frequency range of 5÷35 MHz for all types of paper samples. The absence of an appreciable frequency dispersion of the ultrasound phase velocity is proved in this frequency range. The possibility of the porosity measurement of paper based both on the theory of ultrasound propagation in a two-phase medium and the ultrasonic experimental data is demonstrated.

The laser ultrasonic method for nondestructive quantitative local evaluation of graphite-epoxy composites porosity is developed with only one surface of a sample or a product is available. The excitation and the registration of ultrasonic transients is carried out with the specially designed opto-acoustic transducer, which allows one to obtain both a temporal profile and a frequency spectrum of backscattered opto-acoustic signals. The empirical dependence of the volume content of pores (porosity) of a composite vs. the noise component power of a backscattered transient is obtained in the range of porosity of (0÷0,15). The experimental results prove the possibility to employ the laser opto-acoustic method for porosity evaluation of composite materials and products both during manufacturing and operation.

Ultimate spectral efficiency of information transmission of erbium-doped fiber amplifiers and lumped amplifier chains is considered on the basis of the number-state model for linear communication channel. For single amplifier the efficiency is about 12-14 bit⋅s^-1Hz^-1 at 1 μW⋅GHz^-1 input signal power density depending on pumping conditions. For long-haul communication lines it approximates 7-14 bit⋅s^-1 Hz^-1 for spectral density of input signal power of 1-100 μW⋅GHz^-1.

New variants of use of phase-conjugate feedback for content-addressable (associative) data retrieval by thin lensless Fourier holograms are considered: referenceless registration of interference pattern of mutually conjugated object waves, compensation of phase of initially diffracted by hologram wave and forming of second orders due to repeated, after phase conjugation, diffraction upon a hologram.

The problem of fast investigation of the structural properties of paper samples is of great interest nowadays. The existing methods for structural imaging of paper require long time for obtaining the final result or need changing the structure of the studied sample. One of modem high-promising non-invasive techniques for faster examination of paper structure is optical coherence tomography (OCT), based on the principles of low-coherence interferometry of light backscattered from the investigated object. In present paper we simulate OCT signals from different paper samples with planar and non-planar geometry of air-fiber boundaries implementing Monte Carlo method. OCT provides quality images of in-depth scanning for optically transparent low-scattering objects, however for high-scattering media the maximal scanning depth is quite small. In order to increase the scanning depth for such media different clearing agents are used. We consider ethanol, 1-pentanol, glycerol and benzyl alcohol as such agents applied to a paper sample. Obtained results show, that all agents under consideration provide better visualization of rear border of the studied sample, which is very important for precise paper thickness measurement. However, the agents, showing the best results for rear border visualization provide worse visualization of the inner structure of the sample.

Two highly dispersive devices of InGaAsP/InP integrated chirped pulse compressors are designed: a directional coupler and a uniform Bragg grating. Results of numerical analysis for the propagation of a chirped pulse in both devices are presented. Both devices present a good compression factor for device lengths useful for integration. The compression factor and the length of the two devices have been compared looking for an optimum behaviour for a monolithic implementation in a 40 GHz mode-locked diode laser.

The studies of luminescence of synthetic ruby, natural spodumene and natural IIa type diamond under the action of laser radiation at 222 nm and subnanosecond avalanche electron beam (SAEB) were carried out. It was demonstrated that SAEB parameters allow obtaining high-intensity luminescence of various crystals in the normal conditions without any vacuum equipment used. At the both types of excitation, ruby emission spectra were similar demonstrating luminescence of chrome only. It was shown that photoluminescence spectra of the spodumene and diamond samples contained some bands being absent in SAEB-initiated cathodoluminescence spectra.

A LIF fiber optic system for monitoring of ventilating ducts against harsh contaminations such are organic pathogen microorganisms and microbe toxins is described. Structures and requirements to main functional elements of the system are formulated and results of its power budget calculation are presented.

Exactly solvable profiles are found for a Bragg grating with amplitude or phase modulation. A simple formulas for reflection coefficient are derived. The shape of reflection spectrum in the case of amplitude modulation is trapezoidal in semi-logarithmic coordinates. In the case of phase modulation the solution is found for grating with the Gaussian chirp.

In this article, we propose a simple method to increase the pressure sensitivity of a typical fiber Bragg grating (FBG) while decreasing the temperature sensitivity. This method uses a typical FBG, which is coated with a thick layer of polymer with two symmetric air channels. By this method the pressure sensitivity can be increased (e.g. 1.1×10^-5 /MPa) while the temperature sensitivity is negligible (e.g. -0.174×10^-8/^oC) by proper selection of the geometrical parameters and material types of the sensor.