The detailed theoretical and experimental investigations of the self-reconstruction of the structure of Bessel beams in various scattering media, including biological tissue, have been carried out. Also the self-reconstruction of Bessel beam after shadowing with single obstacle is studied. Using conical beams, the peculiarities of speckle contrast imaging of subsurface targets embedded into highly scattering media have been investigated.

We present our results of the development of some schemes for nondestructive optical profilometry of cylindrically shaped surfaces by using spatially matched conical light beams. A theoretical model is elaborated which describes profilometers with Bessel beams. A special feature of the profilometers proposed is the possibility to control their sensitivity and resolution. To this end, a scheme of tuning the cone angle of the Bessel beam over a wide range is incorporated. The operation regime of the profilometers is characterized by a nonzero spatial frequency of output signal. It allow us to apply a new algorithm for the interpretation of the output signal. This algorithm consists in the calculation of the azimuth spectrum which characterizes the deviation of tested profiles from the circular ones

The possibility of the formation of zero-order Bessel light beams using a uniaxial crystal with cylindrical electrodes is investigated. It is shown that, if a given polarization distribution is provided in the incident beam, a Bessel light beam with the cone angle controlled by an external electric field is formed. It is proposed to use this result for the matching of the axicon parameters and creation of conical lenses with an adjustable cone angle

We present an optical method for determining the hardness of metals, based on the correlation between the thermal diffusion coefficient and the hardness of the material. Spatial and temporal modulation localized in the nonstationary thermal wave profiles is transferred to the surface of the metal, where the time evolution of the speckle images produced by a probing laser beam is recorded by a CCD camera. A special algorithm for processing the speckle images allows us to determine the thermal diffusion coefficient. Experimental studies on steel samples confirmed the workability of the proposed method.Introduction. Widely used methods for measuring the hardness of metals and alloys, based on resistance of the sample to mechanical indentation (see, for example, [1]), do not meet the growing demands of modern industry. The problem is mainly that these are destructive contact methods. There is also the problem of testing on curved surfaces and the difficulties of measuring the hardness profile vs. depth. Nondestructive testing of the mechanical properties of steels based on use of a magnetic method [2] is applicable only for ferromagnetic materials. Therefore it is very important to develop nondestructive contactless methods for measuring both the hardness itself and the profile while hardening the surface layer of a part during its production.The physical basis for thermooptic and elastooptic nondestructive testing and diagnostic methods is the use of weakly damping acoustic waves and nonstationary thermal fields for probing the surface and interior regions of metals.Spatial and temporal modulation, localized in the amplitude and phase profiles of the acoustic or thermal waves, is transferred to the surface of the metal and the information is read using a laser beam. For example, in [3], laser infrared photothermal radiometry was used to measure thermophysical properties (thermal diffusion and conductivity) of coatings deposited on the metal. In [4], for the first time a flash method was used to measure the thermal diffusivity, heat capacity, and thermal conductivity coefficient of metals (copper, silver, iron, nickel). A high-power light pulse was absorbed by the front surface of a thermally insulated sample, and the temperature variation over time was measured by a thermocouple on the rear surface.Basis for the Method. We know that a correlation can be established between mechanical hardness and the thermophysical characteristics of a metal. Thus in [5], IR photothermal radiometry was used to establish the hardness profile for the surface of tempered steels. A good correlation was observed between the thermophysical parameters, their time variation, and the mechanical hardness profiles, and this correlation is suitable for assessing the transverse inhomogeneity in the hardness of the tempered layer. In the photothermal method for determining the hardness of steel [6], it has been shown that the thermal diffusion coefficient k can be used as one such thermophysical characteristic. This coefficient determines in part...

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