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Gallium phosphide is irradiated with 150fs–7ns duration laser pulses at a wavelength of 800nm. After irradiation with 150fs pulses, periodic surface structures (ripples) are observed on the GaP surface, exhibiting near-wavelength and substantially subwavelength spatial periods depending on irradiation conditions. As the pulse duration increases, near-wavelength ripples become a more dominant feature, completely replacing subwavelength ripples for pulse lengths beyond 80–130ps. Overall the results show that subwavelength ripples can be generated for a wide range of pulse durations, and their formation is quite insensitive to pulse intensity.

We present cross-sectional transmission electron microscopy studies of laser induced periodic surface structures (LIPSS) formed on gallium phosphide after irradiation with ultrashort laser pulses with a pulse duration of 150fs and centered at a wavelength of 800nm. LIPSS with spatial periods (∼165nm) substantially smaller than the incident wavelength are found to have vertical profiles as high as ∼960nm measured from the crest to the trough. The present observations provide important insights into the formation mechanisms of subwavelength LIPSS.

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