Noise-induced local heatings in beam irradiation

In every kind of beam irradiation, a part of the incident power is eventual ly dissipated within the irradiated sample, leading to a heating which has to be evaluated, in order to be sure that thermal effects (such as diffusio n, phase transitions, etc.) are under control. Expanding on usual thermal e stimations 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 w hite noise induces an extra heating whose relative influence increases as t he distance to the center of the beam decreases. Relying on the physical re sults derived for white noise, a simple method is proposed to extract the m ain aspects of these extra heatings from experiments where the autocorrelat ion 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].