Bogumił B.J. Linde

Improvement in performance of a TeO2 acousto-optic imaging spectrometer

This paper concerns the problem of the optimization of parameters in acousto-optic image processing systems. The optimization was carried out with the purpose of obtaining the best performance and minimum driving power. A choice of optimal geometry of acousto-optic interaction in the crystal is discussed. Longitudinal aberrations in the device caused by dispersion of refractive indices of acousto-optic media are studied. Calculations prove that a specific choice of distances between optical elements in the device can reduce the aberration to a value less than the focal depth of a filtered image. Spectral analysis of radiation reflected from artificial test objects demonstrates operationaal capability of the imager.

Acousto-optic interaction in a non-homogeneous acoustic field excited by a wedge-shaped transducer

The article is devoted to theoretical analysis of light diffraction in a non-homogeneous acoustic field created by a wedge-shaped piezoelectric transducer. Relationships describing electrical, acoustic and acousto-optic properties of the acousto-optic cell are derived in the approximation of a small thickness of the piezoelectric plate. Principal characteristics of acousto-optic interaction are examined such as dependences of the light diffraction efficiency on the phase mismatch and the acoustic wave amplitude. It is shown that the acoustic field has a complicated amplitude-phase structure changing with the acoustic frequency. It is demonstrated that the diffraction efficiency in the Bragg regime can approach 100% in spite of a noticeable phase mismatch. The appropriate optimal values of ultrasound power and incidence angles of light are found.

Modal parameters of two incomplete and complete guitars differing in the bracing pattern of the soundboard

Similarities and differences in vibrational behavior of two guitars having a symmetric Torres bracing pattern and an asymmetric pattern forming a lattice on a soundboard are investigated by means of the modal analysis technique and laser Doppler vibrometry (LDV) measurements. Instruments are investigated before and after a bridge and strings assembling (i.e., they are incomplete or complete). The bracing pattern and the absence/presence of the bridge and strings have some effect on modal frequencies and mode shapes. The bracing pattern does not affect the sequence of at least first three low frequency mode shapes of incomplete/complete instruments but affects their modal frequencies. Depending on frequency, the bridge behaves either as a rigid or a flexible structure.

The effect of bond saturation in five-membered heterocyclic compounds upon their acoustic properties – VT energy migration rate

Abstract Acoustic investigations were carried out for a series of cyclic and heterocyclic compounds, with particular regard to the dependence of acoustic parameters on chemical structures. Several interesting regularities were found among five-membered cyclic compounds, a few of which have been previously described by Linde et al. [1] , but the rest were observed for the first time. In the present paper, the results of investigations in six five-membered heterocyclic compounds are discussed. These compounds are furan, 2,3-dihydrofuran, 2,3-dihydrofuran, tetrahydrofuran, thiophene and tetrahydrothiophene. The acoustic relaxation observed in all the compounds was found to result from Knesers processes (vibrational relaxation). As can be seen from pressure-dependent acoustic measurements in tetrahydrofuran, both propagation velocity and absorption of ultrasonic waves decrease with increasing pressure. The values of the acoustic absorption coefficient in the low frequency range were several times higher and relaxation times markedly longer than those observed in non-saturated compounds, similarly to the previously considered cyclic and heterocyclic compounds 1 , 2 , 3 , 4 , 5 . It was found that the changes in acoustic parameters, and hence in the rate of the energy transfer between vibrational and translational degrees of freedom (VT transition), can be accounted for by the effect of the compounds aromaticity. Comparison of the changes in the parameters of furans and thiophenes, with adiabatic compressibility being maintained, shows that acoustic parameters strictly depend on the internal molecular structure. This problem is also dealt with in the present paper. Being unequivocal for the group of six five-membered compounds, the interpretation becomes less obvious in the case of other cyclic compounds, e.g. six-membered substances.

Acoustical Method for Investigation of Pressure Influence on Absorption in Liquids

Abstract In this paper, the set-up for measurements of ultrasound velocity and absorption, as a function of pressure, is described. There are also presented some results of such research in liquid tetrahydrothiophene.

COMPARISON OF SINGLE AND DUAL-PHASE LOCK-IN AMPLIFIERS FOR PHOTOACOUSTIC SPECTROSCOPY

Dual phase lock-in is usually used in photoacoustic research because it allows precise projection of the measured spectra. In this article, double and single phase lock-in amplifiers were used and the advantages and disadvantages of both were compared. Two liquid crystals were studied in this work: ethylo- and penthylo-cyanobiphenyl in cyclohexane, tetrahydrofuran, and acetonitrile. The red-shift of the maximum related to the polarity of solvents and a bigger shift for 4-penthylo-4′-cyanobiphenyl relative to 4-ethylo-4′-cyanobiphenyl were observed. In order to investigate the usefulness of the single-phase device, compared to the more expensive double-phase device, the frequency dependence measurements and photoacoustic spectra were recorded and compared. Small differences were observed (within the limit of error) in spectra obtained using the single and the double lock-in amplifier. The simpler single-phase lock-in device can be used to reliably measure frequency spectra without any loss of information.

Observation of acousto-optic interactions in liquid nematic crystals

Abstract The purpose of this research was to investigate the reaction of an optically uniaxial liquid nematic crystal ordered by a magnetic field, to disturbances caused by a high‐frequency ultrasonic field. The measurements were carried out for PCB, OCB, and Merck4 by an optical orthoscopic method.

Influence of the frequency‐range broadening for the value of the acoustic vibrational relaxation time

This paper deals with the many acoustical investigations, provided by some scientists (Rapuano et al.), in two liquid compounds: benzene C6H6 and carbon disulfide CS2. These compounds are typical liquids where one can observe the acoustical relaxation combined with Kneser processes—energy transfer between translational and vibrational degrees of freedom. Acoustical values, a characteristic of the compounds, were different in many papers and the goal was to try to explain these discrepancies and show how it is possible to avoid these mistakes. The main problem in experimentally determining the relaxation time from the dependence of absorption and frequencies was the narrow frequency range.

Photo-acoustic and ultrasonic investigation of the mixtures of water and several glycols

In the paper the results of the ultrasonic velocity and absorption measurements were presented, as well as the thickness in water mixtures of some glycols. The experiments were provided in the temperature range from 291.15 to 303.15 K for whole molar fraction. Adiabatic compressibilities were calculated from Laplaces equation based on the experimental results obtained. Variations of these values with concentration and temperature were studied. Structural interactions and the formation of a compact pseudostable structure at very low concentrations of ethylene glycol and polyethylene glycols were observed. The plots of the adiabatic compressibility versus the mole fraction of PEG and EG display two characteristic points at low concentrations: the intersection of the isotherms and their minimum. Such relations between adiabatic compressibility, concentration and temperature are usually attributed to the formation of pseudo-stable molecular structures. To formulate a model of local structures present in the ...

Ultrasonic and photoacopustic investigations of water mixtures with dioxanes 1‐3 & 1‐4

Ultrasonic velocities, densities and thermal eusivity dependence on concentration were measured in the mixtures of water with dioxanes 1-3 and 1-4. in the temperature range from 291.15 to 303.15 K. Adiabatic compressibilities were calculated from Laplace’s equation based on the experimental results obtained. Variations of these values with concentration and temperature were studied. Structural interactions and the formation of a compact pseudo-stable structure at very low concentrations of these liquids were observed. The plots of the adiabatic compressibility versus the mole fraction of these molecules display two characteristic points at low concentrations: the intersection of the isotherms and their minimum. Such relations between adiabatic compressibility, concentration and temperature are usually attributed to the formation of pseudostable molecular structures. To formulate a model of local structures present in the investigated molecular systems it is indispensable to get an insight into hydration of molecules and the formation of hydrogen bonds. Therefore, the attention was focused particularly on these problems.