Theoretical and experimental investigation on enhanced thermal behaviour in chunk-shaped nano ZnO

Thermal properties of chunk-shaped ZnO nanostructures are studied for diffusivity, conductivity, and effusivity by photoacoustics (PA) and simulation methods. Thermal conductivity of nano ZnO was determined from simulation in the temperature range of 100–1000 K. Thermal conductivity of ZnO nanostructures at room temperature is approximately 52 and 128 times lower than that of bulk ZnO for PA and simulation, respectively. For simulation, Tersoff potential is used for the interatomic interaction. The velocity autocorrelation function and Green–Kubo relation are used to compute the thermal conductivity.     

Photoacoustic study of the thermal and optical properties of hippuric acid

Photoacoustic spectroscopy (PAS) is a recently developed, non‐destructive testing (NDT) tool, used for analyzing the physical properties of materials. This method is used here to determine the thermal diffusivity and conductivity of the gel‐grown single crystals of hippuric acid, a minor constituent of urinary calculi and also a non‐linear optical (NLO) material. Optical absorption of the specimen was studied using its PA spectrum and compared with UV‐visible absorption spectra. Second harmonic generation (SHG) conversion efficiency was also carried out. Characterization of the crystals was made using X‐ray powder diffraction and density determination. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nonlinear photoacoustic response of opaque media in gas microphone signal detection

We have theoretically studied the effect of thermal nonlinearity, due to the temperature dependence of the thermophysical and optical parameters for thermally thick opaque media, on the characteristics of the fundamental photoacoustic signal when the signal is detected by a gas microphone. We have shown that the dependence of the amplitude of the nonlinear component of the signal on the intensity of the incident radiation I₀ is expressed by means of the dependence of the temperature rise for the irradiated sample surface Θ₀ on I₀, and the thermal nonlinearity does not affect the phase of the photoacoustic signal. We propose a theory for generation of the second harmonic of the photoacoustic signal. We have established that the phase shift of the photoacoustic signal is equal to 3π/4, while its amplitude depends on the frequency (∼ω^−3/2) and the intensity (∼ I ₀ ² ). __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 2, pp. 170–176, March–April, 2006.     

IR Beam Deflection Spectroscopy with a Cold Source

In a photoacoustic¹ measurement, radiation is normally passed onto an absorbing sample, and one observes changes in the sample's properties or the effects they induce elsewhere. The sample itself is the prime sensor, and basically what is measured is the net energy transfer between sample and source. In practice, the source is made “hot,” i. e., a much stronger emitter than the sample. In principle, the source and detector are interchangeable, in terms of emittance or location, and also sometimes in practice. For example, infrared emission spectra of minerals were measured with hot (40°C) samples and a cold (30°C) detector² and also with cold (20°C) samples and a hot (24°C) detector³.     

Photoacoustic studies on the thermal properties of the NLO compound: L‐alaninium maleate

Studies on thermal and optical properties are very essential for a nonlinear optical material. Photoacoustics (PA) is a recently developed non‐destructive testing (NDT) tool for studying such properties. L‐Alaninium maleate (C₃H₈NO₂⁺·C₄H₃O₄^‐), an organic non‐linear optical (NLO) material was synthesized using submerged seed solution method and was characterized by single crystal X‐ray diffraction (XRD) and density. PA technique was used to determine the thermal parameters of LAM crystals. Moreover, possible phase transition analysis was conducted to ascertain the thermal stability. Scanning electron microscopic (SEM) studies were also carried out and crystal‐packing features discussed. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoacoustic and X‐ray Studies on H+ Ion Implanted n‐GaAs

Qualitative and quantitative analysis on the defects in H⁺ ion implanted (30keV with doses 10¹⁴, 10¹⁵, 10¹⁶ and 10¹⁷ ions/cm²) n‐GaAs are carried out here by Atomic Force Microscopy (AFM), XRD and Photoacoustic measurements, for various doses. The close agreement between these measurements reveal that even the microscopic strain parameter ∈₁ (from XRD) can be viewed microscopically with photoacoustics. Various thermal parameters are computed for the 30 keV H⁺ ion implanted n‐GaAs and reported for the first time.     

Construction of a Low Cost Photoacoustic Spectrometer for Characterization of Materials

During the past few years, another optical technique has been developed to study those materials, which cannot be studied, by the conventional transmission or reflection techniques. The present technique called Photoacoustic spectroscopy or PAS is different from the conventional techniques chiefly in that the interaction of the incident energy of the photons with the materials under investigation is studied not through subsequent detection and analysis of some of the photons, but rather through a direct measure of the energy absorbed by the material. The aim of this presentation is to highlight the construction of a simple Photoacoustic spectrometer which can easily be constructed even in high school and college laboratories with the available low cost but efficient components and use it for characterization of solid (opaque or transparent), liquid and gas samples under investigations. The essential parts of the photoacoustic spectrometer designed in the laboratory (MADURAI – PA SPECTROMETER), consists of three main components.The total cost comes around 900 Euros. It is an affordable cost for researchers working with paucity of funds and facilities and many constraints especially in the developing countries. In the next few years we aim to study material characterization using MADURAI –PA SPECTROMETER.     

生物医学光声成像

能够对组织体中的光学吸收体进行量化评估的光声成像（photoacoustic imaging）是一种有发展前景的医学成像模式.文章综述了处于快速发展阶段的光声成像技术.文章首先介绍光声成像的物理基础——光声效应.在此基础上,阐述光声成像技术的优势所在（与光学以及超声成像相比较）.然后讨论目前该领域的主要技术路线,包括扫描层析术、计算机层析术以及原位探测成像技术.最后简要总结了光声成像技术在生物医学领域中的主要应用.     

光声技术在固体材料热扩散率测量中的应用

光声（光热）效应是由于物质吸收一强度随时间变化的光束而被时变加热时所引起的一系列热效应和声效应,研究了这些热效应和声效应,可以获得物质的热学和学学性质,光声技术正是探测由于吸收光辐射后样品的微小温度变化所引起的周围气体压力变化,具有灵敏度高、操作方便、应用广泛等独特的优点,已成为研究物质光谱特性、热学性质等的独特有力手段,文章主要介绍了光声技术在固体热扩散率测量中的原理及常规应用方法。     

Photoacoustic study of the thermal properties of calcium carbonate – the major constituent of pancreatic calculi

The study of the thermal properties of condensed matter is very essential both for crystallizing and thermal energy induced fracturing of solid materials. Photoacoustic spectroscopy (PAS) is a recently developed, nondestructive testing (NDT) tool, used for analyzing the surface properties of materials. This method is used here to determine the thermal diffusivity and thermal conductivity of the gel grown single crystals of calcium carbonate (CC), which is the major constituent of pancreatic calculi. Characterization of CC was made using single crystal X‐ray diffraction and density determination. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)