Zygmunt Kleszczewski

Elastic constants of the lithium tantalate crystal in the hypersonic range

Elastic constants of the lithium tantalate LiTaO3 crystal were determined in the hypersonic range by the use of the Brillouin laser light scattering method. Obtained values show variation with respect to ultrasonic measurements. Results are interesting because the same effects are qualitatively different in isomorphic lithium niobate LiNbO3 crystal.

Fabry-Perot interferometer in Brillouin scattering experiments

The Fabry–Perot interferometer has become a standard spectroscopic tool in scientific laboratories for the study of Brillouin scattering. This article examines some basic properties of the Fabry–Perot interferometer with the student or beginning user in mind in order to demonstrate why it is especially useful for this application. Single and complex Fabry–Perot systems in use for Brillouin scattering studies are discussed starting from elementary equations to show, in particular, how the half‐width of the transmission function depends upon the instrumental configuration. The primary results are summarized in graphical form.

Elastic constants of the SrLaAlO4 and SrLaGaO4 crystals measured at ultrasonic and hypersonic acoustic frequencies

Elastic constants measured by Brillouin light-scattering experiments were compared with results estimated from the pulse-echo-overlap method for the ultrasonic frequency to find dispersion in their values. In this way Brillouin hypersonic experiments complete the ultrasonic results. The present investigation includes a careful analysis of the accuracy of the results. The measured values of elastic constants suggest a weak dispersion in acoustic wave velocities. However, given the magnitude of the experimental errors, it is difficult to conclude about the dispersion.

Photothermal measurements for plates

Basing on a 1D model of heat propagation in gas-sample-gas structure, a method for determining thermal properties of plat-like samples is proposed. The method assumes photodeflection detection of photothermal signal. In the method, a signal frequency dependence is measured. It is shown that in high frequency limit, the signal depends only on thermal properties of gas. Excluding the gas contribution to the measured dependence a signal part connected with the sample can be calculated. Fitting theoretical curves to obtained data, one can estimate thermal diffusivity of the sample. Methods for determining thermal diffusivity of gas and distance between a probe beam and the sample surface are also proposed. A good agreemnt between theory and experiment is obtained.

Photoacoustic imaging of ion-implanted semiconductor samples

Abstract A short description of a measuring technique concept which makes use of the photothermal effect is given. An analysis of applications of the technique for testing semiconductors and semiconductor structures is made, and an experimental apparatus for photoacoustic imaging is described. Results of an investigation of ion-implanted silicon wafers are presented, which show the possibilities of photoacoustic imaging of ion-implanted regions in semiconductors. Alterations of sample properties caused by technological processes, such as annealing, can be observed using the method. The main advantage of the method is its non-destructive character.

Solid state photoacoustics with laser pulse: mathematical model and experimental data filtering

The first part of this paper presents theoretical analysis of the response of typical photoacoustic cell excited with a laser pulse absorbed by the sample located inside the cell and causing changes of temperature in the whole system. Pressure response curves provide information about optical and thermal properties of the sample. System of 1D heat conduction differential equations for each region of the cell has been solved. Changes of solid sample temperature, resulting from absorption of a laser beam warm up gas surrounding the sample. Changes of gas temperature are transferred into changes of its pressure, in result of thermodynamic processes in the gas filling photoacoustic cell and are detected with a microphone in a typical photoacoustic experiment. In the second part of the article a review of application of wavelet analysis for PT signal filtering is presented. The wavelet method is compared with Fourier transform and signal subtraction and seems to be very promising.

Photothermal Determination of the Thermal Conductivity of Superhard Thin Films

The nondestructive method is proposed for determination of the thermal conductivity of transparent, thermally thin coating on opaque, thermally thick substrates. The sample is heated by intensity modulated, unfocused laser beam. The photodeflection detection is used for signal registration and the “mirage” signal dependence on modulation frequency is measured.. The method is based on 1-D model of heat propagation in layered structure. The light interference in coating layer is taken into account. Two geometries of photothermal experiments are considered. The modulated light may illuminate the coated surface of sample or the opposite one. It is shown that the ratio of signals measured in these geometries does not depend on parameters of the probe beam. The proposed method is verified experimentally for silicon wafers coated with DLC. Obtained results are very promising.

Acousto-optical Bragg interaction in an isotropic medium under uniaxial stress condition

The basic topic of this work is the theoretical analysis of external stress field influence on the geometry and effectiveness of acousto-optic interaction in isotropic solids. An external field causes changes of mediums optical properties, that is, changes of dielectric permeability tensor components. Because of such changes, an isotropic medium becomes a uniaxial on.e Detailed calculations have been carried out for a BK7 glass in the 104-109 Hz frequency range, for stress of values of 103-107 N/m. The results of calculations are presented in the form of graphs.

Photoacoustic imaging of semiconductor structures

In the report an experimental apparatus for photoacoustic imaging is described. Results of testing measurements and investigation of ion-implanted silicon wafer were presented. Obtained results show possibilities of photoacoustic imaging of ion-implanted regions in semiconductors with good resolution. Strong dependence of the resolution on frequency was demonstrated.