A 10‐nsec pulsed ruby laser was used to prepare atomically clean silicon surfaces in UHV. With picosecond Nd:YAG laser pulses at 532 amd 266 nm, the amorphous patterns formed on the atomically clean silicon surfaces in UHV were compared with those formed in air and other ambient conditions. Results show that the picosecond laser‐induced phase transition of silicon does not depend on the ambient conditions or on the native surface oxide layer of silicon.