Temperature field in a two-layer plate heated by a surface source

An examination is made of the problem of temperature distribution in a two-layer plate heated by a constant-power surface source.     

Unsteady-state temperature field in a semi-infinite body heated by a disk surface heat source

The paper deals with a three-dimensional axisymmetric problem on temperature field in a semi-infinite body heated by a time-constant heat flux distributed uniformly within a circular region on a free surface. Exact formulas are obtained for the unsteady-state temperature on the edge of the heating zone and for the average temperature within the region being heated. A non-obvious property of radial inversion of the value of average temperature is revealed. A new expression for unsteady-state temperature field, which is convenient for use in numerical calculations, is derived in an integral form on a circular cylindrical surface which is a continuation of the boundary of the heating zone. A general analytical solution of the problem is found in a closed form for the steady-state mode. The steady-state temperature field is expressed in terms of a combination of elliptic integrals. Particular cases are treated, in which the general expression derived for temperature assumes a simpler form. The decrease in the degree of concentration of heat flux with increasing depth is calculated. Fields of isotherms are constructed for both steady-state and unsteady-state cases, and the pattern of their distribution is analyzed. The asymptotics of the obtained dependences at low and high values of dimensionless time and in the vicinity of and away from the region being heated are studied. The range of validity of the adopted model of linear heat conduction is identified.     

Krypton fluoride laser pulse shortening by stimulated thermal scattering on a liquid surface

Pulse shortening of the backscatter of a KrF excimer laser beam focused on the surface of n-hexane is reported. Simultaneous measurements of the backscattered beam, a Fresnel reflected beam, incoherent scattered photons from a liquid surface, and a transmitted beam are performed. The results show that the surface reflected beam disappears followed by beam expansion and the transmitted beam is reduced to form a filamentlike structure with the onset of backscatter. The pulse width of the backscattered beam shows a clear dependence on the focal position in the liquid. Incoherent scattering is sharply enhanced when the laser beam is focused at the liquid surface where the backscattered beam is especially short. The observed phenomena indicate that stimulated thermal scattering is the pulse shortening mechanism.     

Thermal radiation of nanoparticles occurring at a heated flat surface in vacuum

The most general expression for the rate of radiative heating (cooling) of an electrically neutral nanoparticle occurring in vacuum near a flat surface of a homogeneous polarizable medium is obtained for the first time. The magnetic polarizability of a conducting nanoparticle radically influences the rate of heat exchange between this particle and a metal surface. The rate of radiative cooling is several orders of magnitude higher than the power density of thermal radiation from a blackbody of the same size. This ratio is retained for micron size particles occurring at a distance of several hundred microns from the surface.     

On the homogeneity of a conductor heated by electric current pulse

A simple criterion is suggested for selecting a proper regime of electric explosion of a thin cylindrical conductor heated by a high-power current pulse. The selected regime ensures homogeneous heating of the conductor, which is necessary for investigating various physical processes and studying thermal and electrical properties of liquid (including refractory) metals at high temperatures.     

Heat flux measurement by the temperature field of a heated surface. 1. Uniform flux

Calculation formulas are suggested for solving the three-dimensional inverse problem of reconstruction of the heat flux by the temperature of a heated surface. For the special case where the heat flux is uniformly distributed over the heating surface, a numerical experimental on reconstruction of the heat flux is performed for various boundary conditions of heating.Institute of the Optics of the Atmosphere, Siberian Branch of the Russian Academy of Sciences, Tomsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 67, Nos. 3–4, pp. 275–280, September–October. 1994.     

The thermal inertia of materials heated with a laser pulse faster than relaxation time

The nonlocal hyperbolic heat conduction equation is used to describe the thermal inertia of thin metal films (TMF) heated with femtosecond laser pulses. It is shown that for TMF the signatures of thermal inertia are (i) the delay of the heating process and (ii) the strong localization of the thermal energy in TMF.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Phase transformations of carbon heated by a high-power current pulse

The phase trajectories of carbon heated in various regimes by a high-power electric current pulse have been theoretically calculated. It is shown that diamond can be synthesized from a liquid phase in the regime of high-energy electric explosion.     

Response of a fiber ring cavity to chirped Gaussian pulse laser injection

In this paper, the response of a fiber ring cavity to chirped Gaussian pulsed laser injection is investigated theoretically, and the expression of the field intensity out of the ring cavity is derived in the time domain. Numerical results demonstrate that different microwave and millimeter signals can be achieved, such as in the case of chirp parameter C?=?5 and input pulse width of 80?ps, the frequencies of generated microwave and millimeter-wave signals are ～16.1?GHz, ～26.3?GHz, ～33.3?GHz, and ～50?GHz. The results have potential application in tunable microwave/millimeter-wave generation.     

Thermal flux distribution over the inside surface of a heated tube with a cylindrical groove on the outside

The heat conduction problem is solved for an electrically heated tube with a cylindrical groove on the outside surface. The thermal flux over the inside surface is calculated as a function of the geometrical parameters.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 2, pp. 325–330, February, 1972.     

激光诱导硅基Al-Ti金属膜构建各向异性表面及其浸润特性

利用脉冲激光在Si表面刻蚀微米级四方柱,通过多靶磁控溅射镀膜机在其表面上沉积Al-Ti双层金属膜,然后利用激光诱导金属涂层形变,在四方柱的硅基底上形成定向微渠道,通过测量水与定向微渠道表面的接触角(前进角和后退角)研究各向异性表面浸润性特性.结果表明,在硅基底上构建的Al-Ti金属膜各向异性表面表现出水滴的前进角和后退角都较大,各向异性结构对其浸润性有明显的影响.因此,利用激光可以在固体表面制备各向异性表面, 控制表面的润湿行为.     

Thermal energy transfer by plasmon-resonant composite nanoparticles at pulse laser irradiation

Heating of composite plasmon-resonant nanoparticles (spherical gold nanoshells) under pulse laser illumination is considered. The numerical solution of the time-dependent heat conduction equation accounting for spatial inhomogeneities of absorbed laser radiation is performed. Important features of temperature kinetics and thermal flux inside nanoparticles are analyzed. Possible applications of the observed effects in nanotechnology and medicine are discussed.     

The melting wave in a metal fast heated by a high-power current pulse

The region of a solid-liquid phase transition, which propagates at a finite velocity into a cylindrical conductor under the conditions of slightly inhomogeneous heating by a current pulse, is considered as a melting wave. The results of numerical simulation of the melting wave in a tungsten wire heated by a nanosecond high-power current pulse are presented. It is shown that the melting wave in this system cannot be treated as an infinitely thin transition region between solid and liquid metal phases.     

Mode-locked ring laser with output pulse width of 0.4 ps

The output pulse width of a mode-locked ring laser composed of an erbium-doped fiber amplifier, Mach-Zehnder optical modulator, and optical band-pass filter depends largely on the repetition frequency and the wavelength characteristics of these optical circuit elements. In previous experiments, the output pulse width was in the order of 5 ps at a repetition frequency of 5 GHz. The principal reason was that the narrow passage band of the optical circuit elements made it extremely difficult to generate an ultra-short optical pulse. Consequently, we examined how to narrow the optical pulse width by flattening the wavelength characteristics of these optical circuit elements. Furthermore, we drove the optical modulator in the cavity using a frequency multiplier to operate at an effectively higher frequency By widening the wavelength passage band of all the devices in the optical circuit, we achieved an output pulse width of 0.4 ps at a repetition frequency of 5 GHz; the pulse peak power was more than +23 dBm, and the time-bandwidth product was 0.34. We successfully tested an ultra-short optical pulse source with an output pulse width of 0.4 ps with no external pulse compression using a mode-locked ring laser     

Dynamic target ionization using an ultrashort pulse of a laser field

Ionization processes under the interaction of an ultrashort pulse of an electromagnetic field with atoms in nonstationary states are considered. As an example, the ionization probability of the hydrogen-like atom upon the decay of quasi-stationary state is calculated. The method developed can be applied to complex systems, including targets in collisional states and various chemical reactions.     

Two-dimensional unsteady temperature field on the surface of a semiinfinite body subject to heating by an annular pulse

The development of an unsteady temperature field on the surface of a semiinfinite body is studied in the case where the body is heated by rectangular heat pulse through an annular region.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 2, pp. 287–294, August, 1986.     

Measurement of glitter-point velocities on the sea surface using circular scanning with a collimated narrow laser beam

Alaser device (lidar) for remotely measuring the parameters of the glitter-point motion on the sea surface has been developed. The system employs a He-Ne laser to provide the probe beam. Circular scanning was performed by means of a piezoelectrically controlled mirror that had a frequency of rotation of 2 kHz. The positions of glitter-point echo pulses were compared with the reference signal of the mirror controller to trace the time evolution of the glitter-point coordinates on the circumference of the circular laser beam track. The measurements yielded the velocity distribution of the glitter points. The results were obtained under natural conditions and indicate an anisotropy of the glitter-point motion that is related to the sea conditions and the wind direction.     

Formation of an electret structure by exposure of a dielectric to a laser pulse in an electric field

The appearance of mechanical stresses on the surface of a dielectric exposed to a laser pulse is considered.N. E. Bauman Moscow State Technical University, Russia. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 6, pp. 926–929, November–December, 1996.