Pulse-by-pulse optical observation of laser-irradiated thin glass substrate using oil-immersion microscopy

To study the formation mechanism of laser-induced periodic surface structures, we carried out a pulse-by-pulse optical observation of laser-induced surface morphological changes on thin glass substrates. We adopted oil-immersion microscopy, which has a higher spatial resolution than dry microscopy, and the laser was irradiated from the air side. A thin transparent substrate of coverslip was used as the sample. When a scratched coverslip was irradiated with focused subnanosecond laser pulses of 1.064 µm wavelength, periodic structures occasionally appeared in the flat region near the focus, with a period of about 0.55 μm.