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First order phase transitions in metal induced by nanosecond laser pulse are studied here. The metal surface is irradiated through a layer of transparent dielectric-an optical glass. Such confinement con siderably increases the efficiency of pressure generation at the metal surface. This technique allows to obtain near critical states of metals-with temperatures ~10 4 K and pressures ~10 4 atm with table top equipment. At the same time the glass prevents the ablation plume formation-so the surface temperature can be mea sured using thermal radiation data. An experimental setup for simultaneous measurements of pressure, tem perature and reflectivity was assembled based on the elaborated method of experimental research. The pro cesses of melting of lead and boiling of mercury were studied. The onset of the phase transition process led to a considerable tightening of the pressure pulse. A substantial drop of surface reflectivity due to increase of temperature and decrease of density was observed.

This letter aims to experimentally demonstrate the possibility of measuring the temporal dependencies of the surface temperature of an aluminum film confined by a transparent dielectric in the range below and above the critical temperature of aluminum (from 2 kK to 14 kK). Such temperatures are achieved under the action of a powerful linearly-polarized laser pulse of one nanosecond in duration onto the film's surface. To find the temporal dependencies of the temperature of the aluminum film the nonlinear reflection coefficient of its irradiated surface is measured to determine the radiation of a Q-switched Nd:YAG laser at the fundamental wavelength.

This paper is a report on the novel experimental method of the study of the thermodynamic parameters of thin aluminum films in the critical point region. The controlled supercritical state of aluminum is achieved for the first time as a result of the heating of these films by the absorption of the powerful nanosecond pulse of Q-switched Nd:YAG laser at the fundamental wavelength. The possibility is demonstrated to find simultaneously the temporal dependencies of the temperature, of the pressure and of the density of aluminum during the experiment with the thin aluminum films confined at both sides by the quartz glass substrates. These dependencies are obtained taking into account the nonlinear dependence on the incident laser intensity of the light reflection coefficient from the irradiated surface of aluminum. For the first time the thermodynamic cooling cycle of aluminum after its heating by the powerful nanosecond laser pulse is plotted in the space of variables' temperature-pressure and temperature-density that get into the supercritical region.

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