The versatility of the laser synthesis method has been improved during the last few years. In this paper we present the synthesis of amorphous, nanosized Si/C/O powders obtained via ultrasonic injection of aerosol droplets into the beam of a high-power tunable CO 2 laser, using (CH 3 ) x Si(OC 2 H 5 ) 4 - x (0 ≤ ≤ 3) and hexamethyldisiloxane as alkoxysilane precursors. All these precursors strongly absorb the CO 2 laser emission between 9 and 11 μm. The addition of precursors containing Al or Ti in tetraethoxysilane (x = 0) leads to Si,Al or Si,Ti oxide composite powders. The evolution of the powders (chemical composition, crystallization, morphology) during heat treatment under air, argon or nitrogen is studied by infra-red absorption, thermogravimetric analysis, transmission electron microscopy and X-ray diffraction. Silica powders with specific surface area up to 500 m 2 g - 1 are obtained when heating in air.