Fusion Welding of Glass Using Femtosecond Laser Pulses with High-repetition Rates

Laser energy of femtosecond pulses absorbed by the nonlinear process is utilized as a heat source for fusion welding of glass. A femtosecond fiber laser, IMRA America, FCPA Jewel D-400l, with variable repetition rates between 100kHz and 5MHz, was focused with a lens of NA0.65 into borosilicate glass (Schott D263) at different pulse energies, repetition rates and traveling velocities for local melting. The temperature distribution was calculated using a thermal conduction model where instantaneous heat is periodically deposited in a moving rectangular solid. The nonlinear absorptivity of the femtosecond laser pulses increased significantly as the repetition rate increased by the contribution of avalanche ionization caused by the increase in temperature at the laser-irradiation region. The calculated values agreed well with the experimental melt dimensions in a velocity range of 0.5~200mm/s, when the experimental values of the nonlinear absorptivity and the dimensions of the nonlinear absorption region were used for temperature calculation. The fusion welding of glass by femtosecond laser provided much higher melting and joining efficiencies than existing laser welding of metals.