We investigate the temperature and size distribution of Ag, Ge, CdSe and ZnS nanoparticles undergoing UV excimer laser pulses. A two laser pulse experiment is designed to monitor nanoparticle size before and after laser interaction. We study HRTEM images and measure the ablation and fluorescence spectra of particles before and after evaporation. Results show that the nanoparticle mean radius decreases from 3.4 ± 0.2 nm to 2.6 ± 0.2 nm, from 4.3 ± 0.1 nm to 3.5 ± 0.1 nm, and from 3.1 ± 0.2 nm to 2.6 ± 0.2 nm for Ag, Ge and CdSe, respectively. No ZnS nanoparticle size reduction was observed. Theoretical models for nanoparticles undergoing laser heating show that temperatures above the bulk and nanoparticle material melting point reduce the nanoparticles size by a factor of 0.3 and suggest recondensation before collection. For CdSe nanoparticles collected on dry substrates and solvents, blue shifted fluorescence (PL) peaks support the size reduction. / text