Evolution of periodic structures on InP (100) surface irradiated with femtosecond laser

• Subwavelength ripples were developed on InP surface with orientation parallel to the laser polarization.
• Grooves with periods of a few micrometer were superimposed on ripples and perpendicular to the laser polarization.
• The results shed light on the mechanism of groove formation.

Single crystalline InP was irradiated in air with p-polarized Ti:sapphire femtosecond laser at a fixed laser fluence of 274 mJ/cm2. Ripples parallel to the laser polarization direction were found to form preferentially for small number of laser pulses ranging from 50 to 300 or at positions far from the center of laser spot, whereas grooves with the direction perpendicular to the laser polarization appeared to be superimposed on ripples for larger number of laser pulses or at positions close to the center of laser spot. Results reveal that ripple formation is a precursor for the formation of grooves and pattern evolution is dependent on the laser fluence used.