Nanosecond laser-induced filamentous modification in silicate glasses

Abstract

Laser-induced filamentous modification (LIFM) has been extensively studied in transparent materials and is widely used for cutting and drilling with a high aspect ratio. However, the discussion focuses on the domain of ultra-short pulses recently, such as picosecond and femtosecond pulses. In this work, a LIFM by a short pulse in silicate glasses is demonstrated, and the physical mechanism is investigated. In the soda-lime glass, a filamentous modification with a length of >650 μm was introduced by a nanosecond pulse with an energy of 0.86 mJ. The average length of LIFM is positively correlated with the pulse energy but is not affected by the focus depth significantly. Furthermore, LIFM is also observed in borosilicate glass and K9 glass, but not in fused silica glass. Theoretical analysis shows that the contribution of the self-focusing and optical error to LIMB could be ignored in soda-lime glass. An improved Laser-induced moving breakdown (LIMB) model is proposed to describe LIFM by a nanosecond pulse, and the thermal explosion (TE) model is used to explain the micro-structures. High-density defects dominate the LIMB of nanosecond pulses in silicate glasses, which provide seed electrons for laser-induced ionization and induce a thermal explosion through enhanced absorption. The estimation result of the TE model shows that the final temperature of thermal plasma exceeds 1 × 105 K, resulting in micro-explosion and forming micro-voids and micro-crack clusters. Based on the principle of LIFM, stealth cutting was implemented by a high-frequency nanosecond laser in soda-lime glass with a thickness of 2 mm, and the cutting speed reaches 3000 mm/s.