Noise-induced local heatings in beam irradiation

In every kind of beam irradiation, a part of the incident power is eventually dissipated within the irradiated sample, leading to a heating which has to be evaluated, in order to be sure that thermal effects (such as diffusion, phase transitions, etc.) are under control. Expanding on usual thermal estimations based upon the coherent part of the incident power, we focus on the thermal effects due to the noisy (i. e., incoherent) part of the power. Starting from the autocorrelation of the beam, we show analytically that white noise induces an extra heating whose relative influence increases as the distance to the center of the beam decreases. Relying on the physical results derived for white noise, a simple method is proposed to extract the main aspects of these extra heatings from experiments where the autocorrelation function of the beam is not known a priori. Experimental data from MeV light ion microbeam are briefly presented as an example. (C) 1999 American Institute of Physics. [S0021-8979(99)04201-2].