P. Cavaliere

Soret effect in forced Rayleigh scattering

In forced Rayleigh scattering of mixtures or suspensions the temperature gratings generate, by the Soret effect, concentration gratings that may be very important since they produce both a phase and an amplitude grating superimposed on the principal one. The experimental evidence of their influence was given by Thyagarajan and Lallemand using a mixture of carbondisulfide and ethanol. In this paper we study the temporal behaviour of the concentration grating versus the sample properties and its effect on the detected diffracted beam. Explicit expressions are given for the output intensity taking into account both the generated amplitude and phase gratings.

Spatial filtering in the detection of transverse phase modulation through a nonlinear thin film

Abstract In thermal lens spectroscopy, improvement of the signal to background ratio can be achieved by the introduction of a circular stop operating as a spatial filter. In this communication we introduce a mathematical model for the signal interpretation and show its validity by comparison with experimental data and, where available, with an analytical solution.

Laser induced thermal profiles in thermally and optically thin films

The temperature field generated by the weak absorption of a gaussian laser beam in an optically and thermally thin film bounded by two transparent plates is discussed. An analytical solution of the problem is presented together with an algorithm for the numerical integration. The influence of the finite thermal conductivity of the plates is shown in an example.

Ideal nonfocusing concentrator with fin absorbers in dielectric rhombuses

Two ideal concentrators with fin absorbers in dielectric rhombuses are described. Expressions for the design, height, and mirror length are derived. The devices have a concentration factor (n/sin ?(M)) that is clearly higher than the traditional air-filled ideal concentrators. They do not require more mirrors or space and, when such easily available dielectrics as glass and water are used, offer useful configurations for purposes such as the collection of solar energy.

Laser heating of optically thin samples

SummaryA mathematical model able to describe the temperature profiles generated in a thin film by the steady-state illumination by a Gaussian laser beam is presented. The film is supposed to be made by a weakly absorbing liquid sample bounded by two parallel transparent plates, the cell walls, whose thermal exchange to the surrounding ambient may be assumed to be linear with the temperature difference. An analytical solution of the problem is presented in form of Hankel transform and a matrix numerical approach to the computation of the temperature profiles is reported. It is particularly well suited to a computer implementation and allows one to get very accurate results in very short computing times. The influence of the heat exchange coefficient to the ambient is shown in an example. A check of the method accuracy is performed by comparison with literature results in the particular case of infinite heat exchange coefficient.RiassuntoSi presenta un modello matematico che esprime i profili di temperatura generati in un film sottile dall’illuminazione stazionaria con un fascio laser gaussiano. Si suppone che il film sia costituito da un liquido quasi trasparente racchiuso fra due lastre parallele trasparenti, le pareti della cella, per le quali il flusso di calore verso l’ambiente può essere assunto lineare con la differenza di temperatura. Si presenta una soluzione analitica del problema sotto forma di trasformata di Hankel ed inoltre si introduce un approccio numerico che utilizza delle matrici per il calcolo dei profili di temperatura. Tale approccio è particolarmente adatto all’implementazione su computer e permette il conseguimento di risultati con notevole precisione ed in tempi di calcolo molto brevi. In un esempio si mostra l’influenza del coefficiente di scambio termico. Un controllo della precisione del metodo é mostrato mediante confronto con risultati disponibili in letteratura nel caso particolare di coefficiente di scambio infinito.РезюмеПредлагается математическая модель для описания температурных профилей, образованных в тонкой пленке при стационарном облучении гауссовым лазерным пучком. Предполагается, что пленка образована слабо поглошаюшим жидким образцом, ограниченным двумя параллельными прозрачными пластинками (стенки ячейки). Предполагается, что теплообмен пленки с окружающей средой линейно зависит от разности температур. Прдлагается аналитическое решение проблемы в виде преобразования Ганкеля и описывается матричный численный подход к вычислению профилей температур. Этот подход оказывается удобным для комьютерных вычислений и позволяет получить довольно точные результаты с малыми затратами компьютерного времени. На примере рассматривается влияние коэффициента теплообмена на окружающую среду. Оценивается точность метода путем сравнения с данными, имеющимися в литературе.

Free-space laser beams with pulsing on-axis intensities

SummaryWe present a family of laser beams with spatially pulsing on-axis intensity. They are obtained by summation of nondiffracting Bessel beams. They are shown to be able to realize, with good approximation, any spatial periodic on-axis intensity in the period limits set by the frequency of the monochromatic source of light used.

Heat Transfer Studies By Microholographic Interferometry

A set up for real-time and double-exposure microholographic interferometry has been assembled to determine temperature distribution in very small volumes of transparent mediums traversed by a laser beam. The axisymmetric refractive index distribution was evaluated from experimental data by means of a suitable mathematical model for the interpretation of the microinterferograms. Computer model calculations for the temperature distributions were also developed and compared with the experimental data.

Experimental confirmation of a laser-induced temperature field model by means of microholographic interferometry

SummaryThe experimental validation of a mathematical model of the temperature field generated by the laser irradiation of a sample is shown. The test was performed on water, a material with well-known thermodynamic parameters. The experimental data were obtained by means of holographic interferometry. The validated model, in connection with the microholographic method, can be used to determine the thermodynamic properties of different materials.RiassuntoSi presenta la validazione sperimentale di un modello matematico dei campi di temperatura generati dall’irraggiamento laser di campioni. Il test è stato eseguito sull’acqua, un materiale dai parametri termodinamici ben noti. I dati sperimentali sono stati ottenuti mediante interferometria microolografica. Il modello validato, congiuntamente al metodo microolografico, può essere usato per la caratterizzazione termica dei materiali.РезюмеЭкспериментально докаэывается справедливость математической модели температурного поля, образованного при лазерном облучении образца. Проверка проводилась на воде, т.е. материале с хорошо известными термодина-мическими параметрами. Экспериментальные данные получены с номощью голографической интерферометрии. Предложенная модель может быть использована для определениа термодинамических свойств различных материалов.