The main characteristics of accelerated aluminum targets, which are the target velocity, the uniformity of the acceleration and the backside temperature have been studied in laser experiments performed at wavelength 0.26,um with an absorbed flux of a few 1013 W / cm 2 , in 400- ps pulse duration by using the double-foil technique and an optical pyrometry diagnostic: The

ablation pressure was inferred from the velocity measurements. The uniformity of the acceleration was shown to be controlled by the hot spots in the focal spot, and the importance of studying the smoothing of laser inhomogeneities for accelerated targets with large ablated fractions was emphasized. The observed dependence of the backside temperature as a function of the initial foil thickness is discussed in the light of shock wave heating and radiative heating. The process of ablation by laser irradiation, as a method of acceleration of the imploding shell, is of considerable in­ terest in laser fusion. The accelerated target has to require several constraints: the efficiency and the uniformity of ac­ celeration, as well as the level of preheating have to be known. There has been recently a great interest in using shorter wavelengths for ablative compression: the coupling of shorter laser wavelength to the target is indeed very good. I • 2 • 3 But the achievement of uniform acceleration 4 in direct iHumination at shorter wavelength is a major issue for the goal of very symmetric implosion. More, little data exist actually on the mechanisms and level of the preheating of the accelerated targets with ultraviolet irradiation. In this paper, we present the first experimental results obtained at 0.26,um on accelerated targets, using the experi­ mental techniques of double foils 5 and optical pyrometry6 developed these last years at the Naval Research Laborato­ ry. These experiments were realized at 0.26 pm laser wave­ length, with an intensity ofa few 10 13 W/cm2, a pulse width of 400 ps, and rather large focal spot ( - 260 ,urn half energy diameter). The target velocity, the uniformity of its accelera­ tion and the rear-side temperature were measured for our given experimental conditions as a function of the initial tar­ get thickness. These points are respectively presented and discussed in Sects. HI, IV, and V. The experimental arrange­ ment is described in Sec. II. iI. EXPERIMENTAL ARRANGEMENT A. Target chamber