Anton S. Bychkov

Laser optoacoustic tomography for the study of femtosecond laser filaments in air

We propose to use optoacoustic tomography to study the characteristics of femtosecond laser filamentation in air and condensed matter. The high spatial resolution of the proposed system, which consists of an array of broadband megahertz piezoelectric elements, ensures its effectiveness, despite the attenuation of ultrasonic waves in air.

Laser-induced ultrasonic imaging for measurements of solid surfaces in optically opaque liquids [Invited]

The paper describes a novel laser ultrasonic profilometry method which uses pulsed laser radiation for imaging of the surface profile of solid objects in optically opaque liquids by scattering of ultrasonic waves. Algorithms for the construction of laser ultrasonic images and for profile segmentation are presented. An experimental setup for profile measurements is described. It allows reconstructing of laser ultrasonic images with a frame rate of 10 Hz and performing an automated 3D scanning of samples. The results of the experimental testing of laser ultrasonic profilometry on duralumin samples are presented. The approximation error of duralumin cylinder surface profile measurements in water is 15 μm. The results are compared to those obtained by x-ray tomography.

On the use of an optoacoustic and laser ultrasonic imaging system for assessing peripheral intravenous access

We describe a universal system for research in combined real-time optoacoustic (OA) and laser-ultrasonic (LU) imaging. The results of its testing on the task of needle insertion into the blood vessel model diagnostics are presented. In OA mode, where laser light is absorbed directly in the sample, the contents of blood vessel model is clearly visible. In LU mode, where the short ultrasonic probe pulse scattered on the sample is detected, the needle is clearly visible. The developed solution combining OA and LU imaging modalities due to the common detection system allowed real-time diagnostics of the position of medical needles (0.63 mm and 0.7 mm in diameter) inside blood vessel models (1.6 mm and 2.4 mm in diameter). Frame rate was 10 Hz. High longitudinal spatial resolution of the system − 0.1 mm − allows distinguishing the two walls of the vessel model and the position of the needle inside.

Laser optoacoustic diagnostics of femtosecond filaments in air using wideband piezoelectric transducers

New opportunities in ultrasound diagnostics of femtosecond laser filaments with wideband piezoelectric transducers are considered. Transverse spatial resolution better than 100 microns is demonstrated in the single and regular multiple filamentation regime making path toward 3D filament tomography. The simple analytical model of the cylindrical acoustic source fitted well with the experimental data.

A refraction-corrected tomographic algorithm for immersion laser-ultrasonic imaging of solids with piecewise linear surface profile

In this paper, a technique for reflection mode immersion 2D laser-ultrasound tomography of solid objects with piecewise linear 2D surface profiles is presented. Pulsed laser radiation was used for generation of short ultrasonic probe pulses, providing high spatial resolution. A piezofilm sensor array was used for detection of the waves reflected by the surface and internal inhomogeneities of the object. The original ultrasonic image reconstruction algorithm accounting for refraction of acoustic waves at the liquid-solid interface provided longitudinal resolution better than 100 μm in the polymethyl methacrylate sample object.In this paper, a technique for reflection mode immersion 2D laser-ultrasound tomography of solid objects with piecewise linear 2D surface profiles is presented. Pulsed laser radiation was used for generation of short ultrasonic probe pulses, providing high spatial resolution. A piezofilm sensor array was used for detection of the waves reflected by the surface and internal inhomogeneities of the object. The original ultrasonic image reconstruction algorithm accounting for refraction of acoustic waves at the liquid-solid interface provided longitudinal resolution better than 100 μm in the polymethyl methacrylate sample object.

Improvement of Image Spatial Resolution in Optoacoustic Tomography with the Use of a Confocal Array

The spatial resolution and size of the sensitivity area of tomographic systems are estimated by calculating sensitivity maps and spatial resolution maps in the image plane of complex arrays. The relation between the size of areas of high sensitivity and high spatial resolution for real-time oriented tomographic systems with confocal arrays is studied. It is shown that arrays with toroidal geometry significantly improve the diagnostic capabilities of optoacoustic and laser-ultrasound structural analysis of biological objects, rocks, and composite materials.

Study of the Internal Structure of Isotropic Pyrolytic Graphite by Broadband Ultrasonic Spectroscopy

As material for structural components, isotropic pyrolytic graphite (IPG) is widely used in such objects of critical infrastructure as nuclear fission reactors. There is the possibility of using IPG as a facing material for experimental thermonuclear facilities; this is currently being explored. Also, IPG is used as a sealing and anti-friction material in the aerospace industry. It is shown that X-ray tomography is not very suitable for studying the internal structure of IPG produced by chemical vapor deposition because its density is much the same as that of heterogeneities encountered in IPG, such as carbon black inclusions and anisotropic pyrographite crystallites. Broadband ultrasonic spectroscopy has been used to detect pores and carbon deposited layers in IPG samples, 2D images of the internal structure produced.

Toroidal sensor arrays for real-time photoacoustic imaging

Abstract. This article addresses theoretical and numerical investigation of image formation in photoacoustic (PA) imaging with complex-shaped concave sensor arrays. The spatial resolution and the size of sensitivity region of PA and laser ultrasonic (LU) imaging systems are assessed using sensitivity maps and spatial resolution maps in the image plane. This paper also discusses the relationship between the size of high-sensitivity regions and the spatial resolution of real-time imaging systems utilizing toroidal arrays. It is shown that the use of arrays with toroidal geometry significantly improves the diagnostic capabilities of PA and LU imaging to investigate biological objects, rocks, and composite materials.

Real-Time Laser Ultrasound Tomography for Profilometry of Solids

We studied the possibility of applying laser ultrasound tomography for profilometry of solids. The proposed approach provides high spatial resolution and efficiency, as well as profilometry of contaminated objects or objects submerged in liquids. The algorithms for the construction of tomograms and recognition of the profiles of studied objects using the parallel programming technology NDIVIA CUDA are proposed. A prototype of the real-time laser ultrasound profilometer was used to obtain the profiles of solid surfaces of revolution. The proposed method allows the real-time determination of the surface position for cylindrical objects with an approximation accuracy of up to 16 μm.

Laser-Ultrasound Imaging for the Investigation of Heterogeneous Media

The development of a laser ultrasonic imaging technique for diagnostics of heterogeneous materials involves solving the inverse problem of ultrasound scattering. The paper describes the back-projection algorithm for the reconstruction of laser-ultrasonic images of inhomogeneous media. To demonstrate the capabilities of laser ultrasonic imaging, an experiment was carried out to reconstruct the image of an orifice 1 mm in diameter in a duralumin half-cylinder with a radius of 65 mm.