This paper compares sub-micro/nano structure formation on polished silicon surface irradiated by nanosecond laser pulses in ambient air and distilled water. Surface cluster density and optical reflectivity of silicon surface (at a typical wavelength of λ = 632 nm) were studied in terms of number of laser pulses and laser fluence. The surface density and optical reflectivity give information on clusters filling factor and clusters height respectively. The results show that the values of surface cluster density and clusters height strongly depend on laser pulse numbers and interacting ambient. Comparing to air, distilled water as an interacting ambient can affect more significantly the clusters height.
