Picosecond laser induced periodic surface structures on K9 glass

ABSTRACT In this paper, LIPSS (laser-induced periodic surface structures) are generated on the K9 glass surface by using an ultrashort pulsed laser with pulse width of 8 ps, wavelength of 532 nm and repetition frequency of 1 KHz. Two kinds of LIPSS are generated on the surface of K9 glass, in the laser fluence range from 1.52 J/cm2 to 9.38 J/cm2 and pulse number from 1 to 50, namely low space frequency LIPSS (LSFL) and supra-wavelength periodic surface structures (SWPSS). When the laser fluence is increased, LSFL (F = 1.9 J/cm2 ~ 9.38 J/cm2) can be generated on the surface of K9 glass. LSFL with a period in the range of 480 nm to 510 nm are found with 1 to 20 pulses when the laser fluences higher than 1.9 J/cm2. For low pulse numbers, the depth of the LSFL structures grows with increasing pulse number. It is noticed that when the laser fluence reaches the threshold of the LIPSS (LSFL), the formation of the LIPSS happened together with the removal of the material surface. In other words, the ablation craters are formed gradually at higher pulse numbers with the laser fluence above the LIPSS formation threshold. Furthermore, the depth of the ablation crater is increased with higher pulse numbers, and SWPSS appear at the bottom of the crater. The period of SWPSS is 1.2 μm to 1.5 μm. The LSFL found in this paper can be used to reduce the reflection coefficient of the K9 material from 4% to less than 2.2 % at wavelengths above 1.2 μm.