Local Melting of Glass Material and Its Application to Direct Fusion Welding by Ps-laser Pulses

Abstract

New high repetition rate picosecond lasers offer possibility for high efficiency structuring of transparent conductors on glass and other substrates. The results of ablation of the indium-tin oxide (ITO) layer on glass with picosecond lasers at various wavelengths are presented. Laser radiation initiated ablation that formed trenches in ITO. Profile of the trenches was analyzed with a phase contrast optical microscope, a stylus type profiler, SEM and AFM. Clean removal of the ITO layer with the 266 nm radiation was observed when laser fluence was above the threshold of 0.20 J/cm 2 , while for the 355 nm radiation the threshold was higher, above 0.46 J/cm 2 . The glass substrate was damaged in the area where the fluence was higher than 1.55 J/cm 2 . The 532 nm radiation allowed getting well defined trenches, but a lot of residues in the form of dust were generated on the surface. Use of UV laser radiation with fluences close to the ablation threshold made it possible to minimize the recast ridge formation and surface contamination during the process. The latter was confirmed by the scanning Auger spectroscopy. The processing speed of up to 0.5 m/s was achieved when using high repetition rate picosecond lasers in the UV range.

Evaluation of nonlinear absorptivity in internal modification of bulk glass by ultrashort laser pulses

“…It was also reported that the region of the laser energy absorption extends toward the laser source at high pulse repetition rates [4,15], suggesting the absorbed laser energy distributes asymmetrically along the laser axis. The evaluation of the nonlinear absorptivity, however, still remains challenging, since the accuracy of the evaluated nonlinear absorptivity has not been shown, and no thermal conduction model to cope with asymmetrical distribution is available.…”

“…Since then the internal modification with heat accumulation has attracted interest due to its new possibility in internal modification process [7,8], and several authors reported thermal conduction models for internal modification in bulk glass at high pulse repetition rates [9,10]. In their models, however, the nonlinear absorptivity was simply assumed, and the distribution of the absorbed laser energy was assumed to be of spherical symmetry despite the modified structure extends asymmetrically along the optical axis [4,[8][9][10]. The laser energy absorbed in the laser-induced plasma has been also simulated based on the rate equation for free electrons at single pulse irradiation in distilled water [11][12][13].…”

“…Internal modification of transparent material by ultrashort laser pulses has been drawing much attention due to attractive applications such as formation of optical waveguide [1] and splitter [2], and fusion welding [3,4]. In the internal modification process, the laser energy is absorbed by nonlinear process with multiphoton ionization followed by avalanche ionization [5], and the absorbed laser energy in the free electrons is transferred to the lattice to provide the temperature field in bulk glass.…”

“…Recently, an experimental procedure to measure the nonlinear absorptivity of ultrashort laser pulses in bulk glass was developed [4], assuming the reflection and the scattering by the laser-induced plasma are negligible based on the measurement by Nahen et al [14], and the nonlinear absorptivity was shown to increase significantly with increasing pulse repetition rate at durations of 10ps [4] and 400fs [15]. It was also reported that the region of the laser energy absorption extends toward the laser source at high pulse repetition rates [4,15], suggesting the absorbed laser energy distributes asymmetrically along the laser axis.…”

The shorter, the better

“…Despite some exceptions, where ultra short pulsed lasers with very high repetition rates are used to weld glass and other sensitive materials [4] or to dope surface areas with different alloying elements through quasi-cw processes, the majority of applications are related to the removal of material. in general, one distinguishes into surface structuring, inside modifications and the complete cutting of parts.…”