The optical properties of a SiOx film rapid-thermal-annealed (RTA) by CO2 laser are primarily investigated. The microphotoluminescence (mu-PL) and high-resolution transmission electron microscopy (HRTEM) analyses indicate that the precipitation of random-oriented Si nanocrystals can be initiated when laser intensity (P-laser) is larger than 4.5 kW/cm(2). At P-laser of 6 kW/cm(2), the Si nanocrystal exhibits a largest diameter of 8 run and a highest density of 4.5 x 10(16) cm(-3), which emits strong PL at 790-825 nm. The microphotoreflectance of the CO2 laser RTA SiOx film reveals a volume density product dependent refractive index increasing from 1.57 to 1.87 as P-laser increases from 1.5 to 7.5 kW/cm(2). Nonetheless, the laser ablation of the SiOx film occurs with a linear ablation slope of 35 nm/kW/cm(2) at beyond 7.5 kW/cm(2), which terminates the enlargement of Si nanocrystals, degrades the near-infrared PL, and slightly reduces the refractive index of the CO2 laser RTA SiOx film.