The photoacoustic spectroscopic investigations of the surface preparation of ZnSe crystals with the use of the optimization methods

This paper shows results of the photoacoustic (PA) spectral studies, with the microphone detection, of a series of ZnSe crystals with differently prepared surfaces. All samples exhibited the surface absorption connected with defects states located on their surfaces. The quality of the surface preparation is expressed by the surface absorption coefficient spectra of the samples times the thickness of a damaged layer. In this paper both theoretical and experimental photoacoustic amplitude and phase spectra as also the corresponding computed surface and volume optical absorption coefficient spectra of the samples with differently prepared surfaces are presented and discussed. The procedure of computations of the volume and surface absorption spectra with the use of the optimization method is presented in the paper too.     

Numerical analysis of the photoacoustic spectra of silicon samples with differently treated surfaces

This paper presents results of the photoacoustic (PA) spectral studies of a series of silicon samples with differently prepared surfaces. The PA amplitude and phase spectra of the samples indicated existence of the damaged surface layers. In the paper the two layer mathematical model of a sample with a damaged surface layer, that was used for numerical interpretation of the amplitude and phase PA spectra of the investigated samples, is presented and discussed. This model comprises the Urbach edge contribution to the optical absorption coefficient spectrum and it enabled observation of its influence on the PA amplitude spectra of silicon samples.     

Numerical analysis of absorption and transmission photoacoustic spectra of silicon samples with differently treated surfaces

This paper presents results of the photoacoustic (PA) spectral studies, of a series of silicon samples with differently prepared surfaces, in two PA experimental configurations, so-called, absorption and transmission ones. The PA amplitude spectra of the samples indicated existence of the damaged surface layers. In the paper, the two layer mathematical models of a sample with a damaged surface layer that were used for numerical interpretation of the amplitude PA spectra of the investigated samples, are presented and discussed.     

Photoacoustic spectroscopy of surface defects states of semiconductor samples

This paper presents both theoretical and experimental issues connected with measurements and numerical analysis of the microphone amplitude and phase photoacoustic spectra of semiconductor samples exhibiting surface absorption connected with defects states located on their surfaces. The analytical model of surface absorption in semiconductors is described and the results of computations are compared with experimental amplitude and phase spectra for Zn_0.965Be_0.035Se crystal samples. This paper shows the importance of the phase spectra for the proper interpretation of the PA (photoacoustic) results.     

Transmission and absorption based photoacoustic methods of determination of the optical absorption spectra of Si samples — Comparison

This paper is a comparison of two photoacoustic methods of determination of the optical absorption coefficient spectra of semiconductors illustrated with results obtained from Si samples. It presents experimental transmission and absorption photoacoustic spectra of Si samples as also the appropriate models leading to the determination of optical absorption coefficient spectra. The idea and the experimental set-up of the analyzed methods are presented in the paper too. From the fitting procedure of theoretical characteristics to experimental transmission and absorption photoacoustic spectra and after computations of the optical absorption coefficient spectra three components of the optical absorption coefficient spectra of Si samples were identified i.e. band to band transitions, Urbach tail and free carrier absorption. Their parameters are given and discussed in the paper. At the end the advantages and disadvantages of both methods are discussed. To the best of our knowledge, no such proof of the correctness of the PA method of determination of optical absorption spectra has been done.     

Photoacoustic operation modes for determination of absorption spectra of SiGe mixed crystals

This paper presents comparison of two photoacoustic modes of determination of optical absorption spectra of semiconductors illustrated with the results obtained for SiGe crystals. Experimental transmission and absorption photoacoustic spectra of SiGe crystals as well as appropriate models for determination of optical absorption coefficient spectra are given. The idea and experimental set-up of the analyzed methods are presented too. From the fitting procedure of theoretical characteristics to experimental transmission and absorption photoacoustic spectra and after computations of the optical absorption coefficient spectra, three components of the optical absorption coefficient spectra of SiGe crystals were identified, i.e., band to band transitions, Urbach tail and free carriers absorption. Their parameters are given and discussed in the paper. At the end, the advantages and disadvantages of both methods are discussed. To the best of our knowledge, such a comparison of the two PA methods of determination of the optical absorption spectra has not been done before.     

Piezoelectric photoacoustic spectroscopy of surface states of Zn0.81Be0.04Mg0.15Se mixed crystals

This paper presents basics of the space selective piezoelectric photothermal spectroscopy method. This method is illustrated with the experimental piezoelectric amplitude and phase spectra of ZnBeMgSe(4%Be, and 15%Mg) samples and with the corresponding optical transmission spectra. The fitting of theoretical curves computed in the piezoelectric space sensitive spectroscopy method to experimental data indicated the presence of surface states located on both surfaces of the sample. From the fitting procedure the optical absorption coefficient spectra connected with the surface absorption on both sides of the sample were determined.     

Photoacoustic spectroscopy analysis of thin semiconductor samples

This paper is an analysis of determination possibility of the optical absorption coefficient spectra of thin semiconductor layers from their normalized photoacoustic amplitude spectra. Influence of multiple reflections of light in thin layers on their photoacoustic and optical absorption coefficient spectra is presented and discussed in detail. Practical formulae for the optical absorption coefficient spectrum as a function of the normalized photoacoustic amplitude spectrum are derived and presented. Next, they were applied for computations of the optical absorption coefficient spectra of thin In₂S₃ thin layers deposited on a glass substrate. This method was experimentally verified with the optical transmission method.     

Photoacoustic investigations of the optical absorption spectra of porous silicon layers on a silicon backing

This paper presents a series of experimental photoacoustic spectra of porous silicon layers on crystalline silicon and their numerical analysis performed in the proposed two-layer model. The goal of the analysis was to calculate the optical absorption spectra of porous silicon from the photoacoustic spectra of porous silicon layers on a silicon background. The experimental character of the observed absorption band associated with the porous silicon was revealed. This is the first attempt at a theoretical interpretation of the photoacoustic spectra of porous silicon on a silicon backing.     

Pulsed photoacoustic technique to measure the absorption coefficients of the highly transparent optical materials

A new technique of measuring the low optical absorption coefficient is described by using pulsed photoacoustic calorimetry. The frequency dependence of the photoacoustic signal is different owing to its main origin, either the bulk absorption or the surface absorption. The Fourier transform of the pulsed photoacoustic signal, generated by a pulsed CO₂ laser, is obtained as the frequency response of the photoacoustic signal. The ratio of the bulk absorption coefficient and surface absorption coefficient is acquired as 1:1.5.     

Determination of the low absorption coefficients of thick semi-conductor samples using rear side photoacoustic spectroscopy detection

Based on the Rosencwaig and Gersho theory, we have theoretically derived the photoacoustic signal in the gaz behind the unilluminated surface of thick samples and presented a simple analytical procedure for determining the low optical absorption spectra of these samples.The rear side photoacoustic spectroscopy (PAS) detection has been employed on thick samples of GaP (0,2-1mm) and optical absorption coefficients in the region between 15 to 200 cm^?1 were measured.Our results are discussed in comparison with those obtained by usual front side PAS detection and spectroscopic ellipsometry.     

Photoacoustic spectroscopy of solids immersed in transparent liquids

A method is developed to obtain the photoacoustic spectra of solids by immersing them in a liquid cell with a submersed tranducer and detecting the acoustic pulse generated due to bulk absorption of pulsed laser radiation in the solids. Proper choice of liquids enables spectra to be obtained which are independent of the optical properties of the solid surfaces of the surrounding liquid. This technique is compared to other established PAS methods.     

小麦品质的太赫兹波段光学与光谱特性研究

采用太赫兹时域光谱技术(THz-TDS),以储藏小麦为研究对象,研究了霉变、虫蛀、发芽等小麦与正常小麦样品在0.2～1.6 THz波段的光学与光谱特性,采用傅里叶变换得到被测样品的频域光谱,并计算获得THz吸收系数和折射率等光学参数。结果表明,不同品质小麦具有不同的折射率和吸收系数,其中正常小麦比霉变、虫蚀和发芽小麦的吸收系数和折射率都高,且吸收系数在有效波段随频率的增加而增加,进而可以根据其在THz波段的特征谱进行判别。THz-TDS在小麦品质检测中的应用,为该技术在储粮品质检测和分析中提供新的实验方法,具有重要的应用前景。     

基于低温光声光谱技术的高Tc超导材料Bi2Sr2CaCu2O8

在光声光谱技术基础上,将不同仪器组装成一套系统,并成功测量出碳黑的光声光谱。利用低温检测系统测定高温超导材料Bi2Sr2CaCu2O8在室温和液氮温度下的光声光谱,发现室温时在598nm和695nm有峰值,液氮温度时在466nm出现峰值。以吸收系数近似为1的碳黑为参照,利用归一化方法得到了Bi2Sr2CaCu2O8相对吸收系数谱图,并进行了初步的探讨,得到了该超导材料的一些信息,为利用低温光声光谱技术,研究超导材料的超导特性提供了一种可行的途径。     

Optical properties of xenon implanted CuInSe2 by photoacoustic spectroscopy

A theoretical relation is derived for the normalized photoacoustic amplitude signal of a gas-coupled cell for the case of double-layer solid samples with particular application given to ion implanted semiconductors. Numerical estimates for a solar cell of the type CdS/CuInSe₂ based on experimental measured data of these compounds are given to illustrate the photoacoustic effect originating from double-layer samples. In application to ion implanted semiconductors, we show that the absorption coefficient of the implanted layer can be very easily extracted by photoacoustic spectroscopy if the absorption coefficient of the untreated substrate is known. We also present the optical properties results obtained from the analysis of the effect of xenon implantation into CuInSe₂ single crystals with the energy of 40 keV and a dose of 5×10¹⁶ ions/cm².     

土壤的中红外光声光谱研究

红外光声光谱是基于光声理论的新型数据采集方式,与传统红外光谱相比,其吸收系数大,适合高吸收和高散射的土壤分析。以中国三种典型土壤为试验材料,研究了这三种土壤(红壤,潮土和水稻土)的中红外光声光谱特征。结果表明,土壤的中红外光声光谱的测定快速方便,土壤样品不需前处理,光谱吸收值适中,具有更丰富的吸收,且土壤主要组成成分的中红外光声光谱也具有明显不同的吸收特征,因此中红外光声光谱能更好地适用于土壤分析;利用主成分分析处理土壤中红外光声光谱时,第1和第2主成分包含了光谱98.17%的信息;利用这两个主成分作二维散点分布图,结果表明该分布能对这三种土壤进行有效分类,这为土壤鉴定提供了快捷的新手段,并使中红外光声光谱在进一步的土壤定量分析中将具有潜在的应用前景。     

聚丁二炔Langmuir—Blodgett薄膜的光声谱研究：（Ⅰ）结构表征与光声？…

本在用Ｘ－射线小角衍射聚合与转载先后次序不同的ＰＤＡ ＬＢ膜进行结构表征的基础上,不同厚度的ＰＤＡ ＬＢ膜的光声新斩波频率效应说明,随着ＰＤＡ ＬＢ膜厚度增加,ＬＢ膜的热学性质逐渐明显。此外,还探讨了如何从ＰＤＡ ＬＢ膜的光声谱求得光声吸收系数问题,本的研究结果表明,光声谱技术是研究ＬＢ膜热学特性的有效手段。     

Features of different honeys identified by acoustic method

In this paper a series of experimental piezoelectric spectra of Zn_1-x-yBe_xMn_ySe (y = 0.05, x = 0.05, 0.10, 0.15) crystals are presented and discussed. Three groups of samples exhibiting different composition with different surface treatment: grinded, polished and etched were prepared. The influence of a different surface treatment on piezoelectric amplitude spectra are discussed with in model taking into account the presence of defects located on the surfaces of the samples.     

聚丁二炔Langmuir-Blodgett薄膜的光声谱研究(Ⅰ)结构表征与光声吸收系数

本文在用Ｘ－射线小角衍射对聚合与转载先后次序不同的ＰＤＡＬＢ膜进行结构表征的基础上,不同厚度ＰＤＡＬＢ膜的光声斩波频率效应说明,随着ＰＤＡＬＢ膜厚度增加,ＬＢ膜的热学性质逐渐明显。此外,还探讨了如何从ＰＤＡＬＢ膜的光声谱求得光声吸收系数问题,本文的研究结果表明,光声谱技术是研究ＬＢ膜热学特性的有效手段。     

Study of light collection as a function of scintillator surface roughness

The variation of pulse-height spectra was observed under the consecutive treatment of CsI:Tl plane scintillators by different abrasives – with increase of the abrasive grain size the double peaks of the total absorption transferred into the single peaks with acceptable resolution. The light collection simulation of the differently treated surfaces was performed to interpret the experimental results. In simulation the surface relief was represented as a set of micro-facets with slope distribution functions extracted from the experimentally measured reflectance distribution functions. The behavior of the simulated pulse-height spectra in the vicinity of the total absorption peak under the assumption of uniform scintillation distribution in the scintillator volume was in a good agreement with experimental results for different surface treatment conditions. From pulse-height spectrum simulations for different positions of the point light source it was determined that the double peaks in experimental and simulated spectra had been caused by the scintillations in different scintillator areas. The decrease of the light output and the resolution improvement occurred under the input surface treatment of the plane scintillator by the larger abrasive was caused by the increase of the average pass length of light to the output detector window and by the decrease of the difference of this value for the various scintillator areas, respectively.