Reconstruction of Optical Energy Deposition for Backward Optoacoustic Imaging

Visualizing optical properties, such as the optical absorption coefficient, helps us to obtain structural information of biological tissues. In this paper, we present an efficient reconstruction algorithm for optical energy deposition in backward optoacoustic imaging. Note that econstruction of optical energy deposition is the first step to imaging the optical absorption coefficient distribution. This algorithm is derived from the optoacoustic wave equations with line focusing, in which the focusing techniques were utilized to reduce the reconstruction problem from three dimensions (3-D) to one dimension (1-D). Simulations and experiments were conducted to verify efficacy of this algorithm. In the simulations, optoacoustic signals were generated based on the solution of the optoacoustic wave equations. In the experiments, a 3-D backward mode optoacoustic imaging system was built. The system consisted of a Nd YAG laser for optical irradiation and an acoustic detection system with a broadband hydrophone. A phantom was used to illustrate validity of the proposed algorithm. The results show that optical energy deposition can be efficiently reconstructed in both simulations and experiments.     

Application of the optoacoustic effect in optically pumped submillimeter lasers

The dependence of the optoacoustic signal generated in an optically pumped submillimetre laser system on gas pressure and modulation frequency has been studied experimentally and the results accounted for theoretically. With care an extracavity optoacoustic cell containing the laser gas diluted with air can be used to stablize the pump laser frequency to maximum absorption but this does not always optimise laser output.     

Methods of optoacoustic diagnostics of biological tissues

Acoustical Physics - Laser optoacoustic diagnostics is based on thermoelastic excitation of ultrasonic signals in a medium due to absorption of pulsed laser radiation. The pressure profile of such...     

Method for Measuring Multiphoton Absorption Cross Sections of Laser Pulses in Gases by Means of a Spectrophone

Optics and Spectroscopy - A method for measuring multiphoton absorption cross sections of Gaussian laser pulses in gases by means of an optoacoustic detector exhibiting temporal resolution...     

Multichannel optoacoustic spectroscopy of molecular gases with pulsed lasers

This paper contains a review of results of the experimental investigation of linear and nonlinear absorption of atmospheric gases using the methods of multichannel optoacoustic spectroscopy with pulsed visible and IR lasers.     

Experimental study using optoacoustic spectroscopy (OAS) on spherical gold nanoparticles

In this paper a spectroscopic characterisation method based on the optoacoustic technique has been used to investigate the optical properties of two separate spherical gold nanoparticle (SGNP) solutions where an absorption peak located at 520 nm has been observed. This analysis has been carried out over the visible wavelength range from 410 to 650 nm using a Q-switched Nd:YAG pumped optical parametric oscillator (OPO). To verify the reliability of optoacoustic spectroscopy (OAS), the results obtained have been compared to those from more standard and limited spectrophotometer and reference collimated optical transmission schemes, where good agreement is shown. The experimental procedure presented here demonstrates the potential of this technique for integration along with optoacoustic imaging methods to identify physiological information for non-destructive in-vivo applications.     

Some Aspects of Photoacoustic Tomography

A solution of the inverse problem of optoacoustic tomography is given in the present work within the framework of chronotomography under conditions of complex two-component absorption. The results of numerical experiments conducted with different model controllable and stochastic experimental errors are discussed.     

Optoacoustic effect in dense layers of oriented carbon nanotubes: Its use for measuring the optical absorption coefficient and the film thickness

The optoacoustic effect is used to measure the coefficient of light absorption at a wavelength of 0.53 μm by a dense layer of oriented carbon nanotubes on a quartz substrate. The value of the absorption coefficient is found to be equal to 3 × 10⁶ m⁻¹. This value is compared with the theoretical estimates and the estimate obtained from the reflection coefficient with the use of the Kramers-Kronig relation. With the coefficient of light absorption being known, the optoacoustic effect allows one to measure the film thickness at any point without destroying the film. Original Russian Text Sc I.S. Grudzinskaya, Z.Ya. Kosakovskaya, O.B. Ovchinnikov, I.A. Chaban, 2006, published in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 3, pp. 330–334.     

使用共振多程光声池的CO_2和SF_6的无多普勒饱和吸收光谱

本文使用共振多程池的光声探测法对CO_2和SF_6分子的无多普勒饱和吸收光谱进行了实验研究.测量CO_2的吸收凹陷约为2.5MHz,实验中观察到5个SF_6的吸收凹陷、凹陷深率约为1.9MHz.两种情况的分辨率均大于10~7.     

Nonlinear absorption of ultraviolet femtosecond laser pulses in argon

The optogalvanic and optoacoustic methods are used to determine the mechanisms of the nonlinear absorption of intense ultraviolet femtosecond laser pulses in gaseous argon. An increase in the nonlinearity of the absorption process from 3 to 4 with an increase in the laser radiation intensity in the range 0.03–12 TW/cm² is revealed. The possible physical mechanisms of this phenomenon are discussed.     

Optoacoustic laser spectroscopy of excited vibrational molecular states

A new detection method for absorption from excited vibrational states is suggested, based on optoacoustic detection of weak absorption in a heated gas. Using this method CO₂ laser radiation (λ=9.6 μm) absorption was investigated from excited vibrational states of CO₂, BCl₃, and BF₃ molecules.     

Optoacoustical studies in the spectral range 9–11μm of the absorption coefficients of aerosols originating from soils

A laser optoacoustic resonance spectrometer is described, and the results are given from a study of the radiation absorption coefficients for a number of aerosol samples in the suspended state.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 6–10, April, 1982.     

Time-resolved laser optoacoustic tomography of inhomogeneous media

The methods of time-resolved laser optoacoustic tomography of inhomogeneous media and related problems are reviewed. Time-resolved laser optoacoustic tomography allows one to measure the distribution of light absorption in turbid media with depth resolution up to several microns in real time. The theory of laser excitation of acoustic waves by absorbing of light in particles, dispersed in transparent, light-absorbing or scattering media, is developed. The distribution of light absorption can be obtained from the temporal course of acoustic pressure. Two schemes of acoustic wave detection — in the medium under testing (direct detection) and in transparent medium, coupled to the investigated one (indirect detection) — are discussed. In both cases the reconstruction of light absorption can be made by simple calculations. Test experiments with homogeneous and layered media confirm the proposed theoretical models and the possibility of using the proposed experimental schemes. Light absorption in homogeneous, inhomogeneous media and in absorbing particles dispersed in turbid media was investigated. The experimental setup allows one to measure the absorption coefficients over the range 1-500 cm^–1 with the depth resolution 10–15 m over the depth 1–1.5 mm.     

超快光声光谱技术的进展和前景

回顾了超快光声光谱学的发展过程并介绍了各种测量手段，论述了文章作者建立的飞秒时间分辨的光声光谱系统的工作原理及实验结果，并展望了超快光声光谱学的未来发展方向和应用前景。     

Frequency Stabilization of Waveguide CO2 Laser by a Digital Technique

In this work we present a simple technique for laser frequency stabilization, based on Digital signal processing. The technique is used to stabilize a waveguide CO₂ laser of wide tunability by using three kinds of reference signals: the CO₂ laser ouptut power, an infrared absorption optoacoustic signal and the output power of a Far-Infrared optically pumped molecular laser.     

液体光击穿阈值的研究

运用声学基础理论,讨论了激光入射到液体中,激光能量与声信号强度间的变化关系.发现激光能量与声信号强度之间存在着对数线形关系.根据液体中光声信号的连续性,得到了一种求取液体光击穿阈值的新方法.     

Control of tissue mechanics upon the repetitive-pulse laser heating of cartilage

The viscoelastic properties of laser-irradiated cartilages are studied with optoacoustic methods upon the thermal excitation of mechanical oscillations by repetitive-pulse laser radiation. The effect of laser power, pulse duration, repetition rate, and irradiation time on the shape of the optoacoustic signal is analyzed. It is demonstrated that the optoacoustic response of the cartilage to the repetitive-pulse radiation of a fiber laser depends on the softening of the tissue upon the variation in its shape. Under repetitive-pulse laser irradiation, the optoacoustic response of the cartilage depends on the mechanical characteristics of the biotissue (elastic modulus, hydraulic permeability, and thickness). A simple model that makes it possible to estimate the contribution of the viscoelastic properties to the formation of the optoacoustic response at various laser repetition rates is proposed.     

Periodic structure created by a CO2-laser pulse incident on an open water surface

Experiments on the effect of a CO₂-laser pulse on an open water surface are reported. They testify that the multilayer periodic structure of the resultant scattering region is due to the intensity modulation at the trailing edge of the pulse. The generation of optoacoustic pulses is studied at two different values of laser-pulse length. The shorter laser pulse is obtained through the trailing-edge absorption in a laser-spark plasma produced by focusing the radiation.     

Experimental and theoretical investigation of photoacoustic-signal generation by wavelength-modulated diode lasers

The dependence of photoacoustic spectra on different experimental parameters was investigated by both theoretical and experimental means. The experiments were carried out with an inexpensive resonant optoacoustic system based on near-infrared laser diodes, which allowed photoacoustic and direct absorption spectra to be recorded simultaneously. The experimental observations were compared to theoretical predictions. It was also demonstrated that source-frequency (wavelength) modulation at the resonance frequency of the cell provides superior signal to noise ratio compared to amplitude modulation and eliminates background drifts and fluctuations.     

布拉格光栅中微扰光声孤子

研究了布拉格光栅中光波和声波的相互作用. 利用多重尺度方法,将光声耦合方程约化为非线性薛定谔方程,并给出了单光声孤子和双光声孤子近似解析解. 进一步讨论了光声孤子抑制光速的机理和双光声孤子的相互作用性质. 关键词： 布拉格光栅 光声耦合 多重尺度方法 光声孤子