共查询到20条相似文献,搜索用时 15 毫秒
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2.
An explicit thermoelastic model is developed to describe
the photothermal deformation of a coated sample excited by a cw modulated
laser beam with a top-hat profile. The surface displacement obtained with
this explicit model is compared to that obtained by an approximate model
developed by Reichling and Gr?nbeck (J. Appl. Phys. 75, 1914 (1994)).
Both thermoelastic models are then applied in a Fresnel diffraction based
surface thermal lens (STL) theory. Numerical calculations are performed to
investigate the differences between the explicit and approximate models in
both surface displacement and STL signal. The simulation results show that
the approximate model over-estimates the surface displacement and the
corresponding STL signal amplitude. A decrease in the thermal diffusion
length reduces the differences between the results obtained with the two
thermoelastic models. 相似文献
3.
Surface thermal lens (STL) signal produced by a cw
modulated top-hat beam excitation is detected by an obliquely-incident probe
beam. The dependence of the STL amplitude on the incident angle θ of the
probe beam is experimentally investigated. The STL amplitude as a function
of the detection distance is measured at different angles of incidence. The
results show that the maximum STL amplitude and the optimum detection
distance, where the maximum STL amplitude is obtained, decrease by
cosθ as the incident angle increases. These experimental dependences are well
explained by a simple theoretical model. 相似文献
4.
A theoretical model, based on the Fresnel diffraction integral, is developed to describe the thermal lens (TL) signal in a mode-mismatched collinear configuration, which is optimized for a near field detection scheme and excitation by a cw modulated laser beam with a top-hat profile. The TL amplitudes obtained with both top-hat and Gaussian beam excitations are numerically computed and compared, and the dependence of the TL amplitude on the experimental parameters is discussed. Numerical results show that the top-hat beam TL instrument is more sensitive than the Gaussian beam TL instrument, with a potential doubling of the sensitivity. The use of the top-hat beam excitation with TL detection is a significant improvement because a top-hat beam can be easily obtained with a low-cost, wide-spectral emission white-light source. The use of incoherent light sources as the excitation sources would substantially expand the applicability of the TL technique to the general area of chemical analysis.This revised version was published online in March 2005. In the previous version, the published online date was missing 相似文献
5.
N. G. C. Astrath F. B. G. Astrath J. Shen J. Zhou C. E. Gu L. C. Malacarne P. R. B. Pedreira A. C. Bento M. L. Baesso 《Applied physics. B, Lasers and optics》2009,94(3):473-481
A complete theoretical model is presented for the thermal mirror technique under top-hat laser excitation. Considering the
attenuation of the top-hat excitation laser intensity along the thickness of a sample due to its optical absorption coefficient,
we calculate the laser-induced temperature and surface deformation profiles. A simplified theoretical model for a high absorption
sample is also developed. The center intensity of a probe beam reflected from the thermal mirror at a detector plane is derived.
Numerical simulation shows that the thermal mirror under the top-hat laser excitation is as sensitive as that under Gaussian
laser excitation. With top-hat laser excitation, the experimental results of thermo-physical properties of opaque samples
are found to be well consistent with literature values, validating the theory. 相似文献
6.
本文给出了聚焦激光束加热时脉冲光热偏光谱的理论,考虑了加热束传输特性和探测束有限尺寸的影响,比较了各种理论模型及其适用范围,并对紧聚焦激光束加执焊脉冲光热偏转光谱的各项结构参数进行了优化。 相似文献
7.
Astrath NG Astrath FB Shen J Zhou J Pedreira PR Malacarne LC Bento AC Baesso ML 《Optics letters》2008,33(13):1464-1466
Thermal lens spectroscopy is a highly sensitive and versatile photothermal technique for material analysis, providing optical and thermal properties. To use less expensive multimode non-Gaussian lasers for quantitative analysis of low-absorption materials, this Letter presents a theoretical model for time-resolved mode-mismatched thermal lens spectroscopy induced by a cw laser with a top-hat profile. The temperature profile in a sample was calculated, and the intensity of the probe beam center at the detector plane was also derived using the Fresnel diffraction theory. Experimental validation was performed with glass samples, and the results were found well consistent with literature values of the thermo-optical properties of the samples. 相似文献
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9.
S. I. Yun Ki-Dong Oh Kwon-Sang Ryu Chang-Geon Kim H. L. Park H. J. Seo Chae Kum 《Applied physics. B, Lasers and optics》1986,40(2):95-98
We have used a modified photothermal probe beam deflection system with a back pumping configuration for the measurements of the temperature-dependent thermal diffusivity of atmospheric air. The results are consistent and reasonably well agree with the literature values. The measured thermal diffusivity values are the same for the same measuring temperature regardless of the beam offsets and the deflecting surface temperatures. For the gas with known temperature-dependent thermal diffusivity, this method can be used to deduce the temperature of a gas from the measured thermal diffusivity value. 相似文献
10.
《Infrared physics》1987,27(3):181-191
A single-beam dispersive photothermal beam deflection (PBD) spectrometer system usable in the IR range is described. A Nernst glower along with a severely modified Perkin-Elmer Model 421 monochromator were used to illuminate a solid sample with modulated monochromatic IR radiation. The resulting photothermal effect generated at the sample's surface caused modulated changes in the refractive index of the air over the sample, causing a probe laser beam grazing the surface to be deflected. The deflections were measured with a bi-cell silicon photodetector. Experiments and analysis of the deflection system showed that lenses used to focus the probe beam at the sample were not needed, and that an improvement in the PBD signal could be obtained by increasing the sample-to-detector distance, but only until a certain sample-detector separation was attained. The dispersive PBD instrument is less sensitive than one based on an interferometer but can be profitably used for studies requiring control of the modulation frequency. Useful spectra of solids were recorded over the 4000-550 cm−1 region using IR excitation in the approximately 5 × 10−6−5 × 10−7W range. 相似文献
11.
Drawing on interferometry and Fourier analysis, this paper describes the use of a two-beam thermal lens technique for measuring thermo-optical properties in optical materials. The procedure consists of yield interference patterns deformed by a localized photothermal effect. The photothermal phase shift is locally induced by the pump beam focused on a tested sample located on an on-axis probe beam, which is the first arm of a Mach-Zehnder interferometer. The plane where the effect is localized is imaged onto a CCD camera. Then two interferograms are recorded: one without effect and the other one with the induced photothermal phase. Fourier analysis performed on these interferograms allow us to plot the thermal lens map and, therefore, to estimate thermo-optic constant of Malachite Green in water solution. The method is applied to measure low linear absorptions of a diluted sample of Rhodamine B in water solution at 633 nm, showing that the proposed technique allows to measure photothermal phase shift as low as 3.1 mrad at 8 mW of input power in diluted materials. 相似文献
12.
Jyotsna Ravi S. Lekshmi K.P.R. Nair T.M.A Rasheed 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,83(2):193-202
A modified amplitude method to analyze the photothermal probe beam deflection signal for the determination of low thermal diffusivity values of materials is proposed. This simple theoretical model, which is an extension of the amplitude method proposed by Quelin et al., takes into account the dependence of the photothermal signal on the height of the probe beam above the sample surface which affects mirage measurements when the thermal diffusivity of the coupling medium is greater than that of the sample. The present work is similar to the modification to the phase method proposed by Bertolotti et al. for determination of low thermal diffusivity. The method can be applied irrespective of whether the sample is optically transparent or optically opaque and is independent of thickness. 相似文献
13.
Photothermal deflection spectroscopy is combined with a Sagnac interferometer to enhance the sensitivity of the absorption measurement by converting the photothermal beam deflection effect into the light intensity change by the interference effect. Because of stable light interference due to the common path, the signal intensity can be amplified without increasing the noise by extending the optical path length between a sample and a photodetector. The sensitivity is further improved by the use of focusing optics and double-pass geometry. This makes photothermal deflection spectroscopy applicable to any kind of material in the whole visible region with a xenon lamp for excitation and water or air as a deflection medium. 相似文献
14.
P. Castellini G. M. Revel L. Scalise R. M. De Andrade 《Optics and Lasers in Engineering》2000,32(6):525-581
In this paper it has been described part of the research devoted to the development of a complete non-intrusive experimental modal analysis procedure based on laser techniques both for excitation and for measurement. In particular, attention has been focused on the thermal effects generated by laser pulses on the excited structure. An analytical model of the energy exchange between the light pulse and the target surface is proposed together with a finite element model of thermal and mechanical behaviour of the structure under excitation. Both the models (analytical and numerical) have been experimentally validated by measuring the thermal and the vibration responses induced by the laser pulses. The experimental part of the study has been performed on a cantilever beam excited with laser pulses from an Nd : YAG source (532 nm, 100 mJ/pulse) using an high-speed infrared camera and a scanning laser Doppler vibrometer. Results from this work can be used to improve understanding concerning the features of laser excitation and to establish a mechanical equivalent system of forces and moments, useful in order to increase the accuracy in the measurements of modal parameters when laser pulses are used as excitation sources. 相似文献
15.
Photothermal deflection microscopy for imaging sub-micronic defects in optical materials 总被引:2,自引:0,他引:2
Photothermal deflection is widely used to study defects in optical coatings and role of these defects in laser damage. Because defects responsible for laser damage are assumed to be nanometer-sized and lowly absorbing, both high spatial resolution and high sensitivity are required to detect them. In this work we theoretically and experimentally explore the capability of collinear photothermal deflection to give micronic resolution by reduction of the pump beam diameter. Thanks to a model describing temperature distribution and photothermal deflection, we have studied the effects of pump beam focusing on photothermal deflection. Then, we have developed a high resolution, high sensitivity microscope based on the photothermal deflection of a transmitted probe beam. The setup is characterized and the theoretical predictions are checked. We present a test of lateral spatial resolution obtained on specially prepared absorbing resolution targets and show that a lateral spatial resolution of 1 μm is reached on non-isolated defects. In case of single defects, we expect that 10 nm sized defects could be detected. 相似文献
16.
A form of optical modulation at low pulse rates is reported in the case of surface plasmons excited by 1.55-microm photons in a thin gold foil. Several visible-photon energies are shown to be pulsed by the action of the infrared pulses, the effect being maximized when each visible beam also excites surface plasmons. The infrared surface plasmons are implicated as the primary cause of thermally induced changes in the foil. The thermal effects dissipate in sufficiently small times so that operation up to the kilohertz range in pulse repetition frequency is obtained. Unlike direct photothermal phenomena, no phase change is necessary for the effect to be observed. 相似文献
17.
In this work the surface temperature oscillation of
multilayered cylindrical samples which are uniformly heated by a modulated
light beam is calculated using the thermal quadrupole method. This
temperature is compared with that calculated in cylinders with continuously
varying in-depth thermal conductivity. Following this theoretical approach,
photothermal techniques can be used for the quantitative thermophysical
characterization of hardened steel wires, tubes and nails. 相似文献
18.
Solid state laser (SSL) powers can be realistically scaled when pumped by a real, efficient and multimode pulse. In this work,
a fourth-order super-Gaussian pulse was assumed as a pump for SSL’s and a complete analytical expression for the thermal phase
shift is given. Moreover, the focal length of thermal lens in paraxial ray approximation regime was studied. The results when
applied to a Ti: sapphire crystal show an appreciable correction for abberation compared to a top-hat pulse. 相似文献
19.
The thermal diffusivity h of a thin film on a substrate is measured by using the mirage technique. The photothermal deflection of the probe beam is caused by the heat field and the substrate, heated by the pump beam. From the experimental data a two-dimensional algorithm is proposed to obtain the measurements of the diffusivity of film and substrate in one set of mirage detection. 相似文献
20.
XIAO Liantuan LI Changyong ZHANG Linjie ZHAO Yanting JIA Suotang ZHOU Guosheng 《Chinese Journal of Lasers》2000,9(6):538-544
1 Introduction Thermaldiffusivitymeasurementisparticularlyimportantformaterialsofnewconceptioninordertocontroltheirmanufacturingprocess .Atthesametime ,thedeterminationofliquidthermaldiffusivityisalsoimportantwhentheliquidisusedasacoolantforhigh powera… 相似文献