Local melting of glass material and its application to direct fusion welding by Ps-laser pulses

Abstract

Fusion welding of glass by picosecond laser pulses is reported where laser energy absorbed by nonlinear absorption is utilized as a heat source for local internal glass melting. Laser pulses with 10ps duration with repetition rates up to 500kHz were focused within borosilicate glass, Schott D263, by an objective lense of NA 0.7. The nonlinear absorptivity of the laser pulses was determined at different pulse energies, repetition rates, traveling velocities and depth of the focus position. The transient and time-averaged temperature distribution in fusion welding of glass was calculated using a thermal conduction model where heat is instantaneously deposited at different repetition rates in the rectangular solid moving linearly at a constant velocity. The experimental dimensions of the melt features agreed well with the calculated values in a velocity range of 1~100mm/s. Excellent seam welding of two glass plates is demonstrated without cracking and thermal distortion. 10ps laser pulses provided higher melting and joining efficiencies than sub-ps pulses due to the higher nonlinear absorptivity by the larger contribution of the avalanche ionization, and also provided the highest efficiencies in the existing fusion welding techniques.