Ultrashort pulse laser cutting of glass by controlled fracture propagation

International audienceLaser induced controlled fracture propagation has great potential in cutting brittle materials such as glass or sapphire. In this paper we demonstrate that the use of ultrashort pulse laser sources may be advantageous since it allows to overcome several restrictions of the convenient method

Transient waveguiding effects during glass processing by bursts of ultrashort laser pulses

We have used bursts of femtosecond laser pulses for bulk modification of glasses. The small time interval of 25 ns between subsequent pulses causes transient thermal waveguiding effects resulting in high aspect ratio volume modifications

Improved laser glass cutting by spatio-temporal control of energy deposition using bursts of femtosecond pulses

We demonstrate the advantage of combining non-diffractive beam shapes and femtosecond bursts for volume laser processing of transparent materials. By redistribution of the single laser pulse energy into several sub-pulses with 25 ns time delay, the energy deposition in the material can be enhanced significantly. Our combined experimental and theoretical analysis shows that in burst-mode detrimental defocusing by the laser generated plasma is reduced, and the non-diffractive beam shape prevails. At the same time, heat accumulation during the interaction with the burst leads to temperatures high enough to induce material melting and even in-volume cracks. In an exemplary case study, we demonstrate that the formation of these cracks can be controlled to allow high-speed and high-quality glass cutting

Material Processing by fs Laser Pulse Trains: Experiments vs. Simulations

The use of femtosecond (fs) trains of pulse is now well established as an efficient technique to modify dielectric materials. Through numerous experimental parameters, it is possible to adjust the amount of deposited energy into the material with a great accuracy. When an intense fs laser pulse is focused inside a dielectric material, here soda-lime glass, electrons get promoted from the valence band (VB) to the conduction band (CB) by photo-ionization processes. After the fs pulse interaction, electrons in the CB transfer their energy to the lattice through collisional processes, and heat diffusion towards the surrounding cold matter of the focal point sets in. Due to the low heat diffusion coefficient (a few microseconds for micron-size volume), and by using a few hundreds kilohertz repetition rate (RR), one can achieve pulse-to-pulse accumulation of temperature. For sufficiently large number of pulses, it is possible to exceed the annealing temperature, and the dielectric material gets modified permanently. Our approach to simulate this phenomenon is based on the separation of the different timescales of the key physical processes. To this end, the laser pulse propagation is simulated by a paraxial Forward Maxwell code taking into account key nonlinear effects, in order to compute the single pulse energy deposition in the material. Thermal diffusion is taken into account by the heat equation, where we use the (repeated) single pulse energy deposition as heat source. Finally, reaching the annealing temperature is used as a threshold to get the dimensions of the permanent modification of the matter. Simulations and experiments were performed in soda-lime glass for a train of 300 fs pulses with an incident energy of 1.3 µJ per pulse. The laser beam, with a wavelength centered around 1030 nm, was focused into the glass bulk by a 10× objective. The theoretically predicted dimensions of the glass transition temperature zone are confronted with the dimensions of the experimental modifications of the glass. We note a threshold-like behavior for the onset of measurable modifications between 100 and 200 kHz, in the experiments as well as in the simulation results. The experimental dimensions are well reproduced by our model, despite a slight deviation in the predicted length for 200 and 300 kHz. We attribute this discrepancy to changes in the propagation dynamics due to successive material modification which is not (yet) taken account in this work

Modeling dielectric material modifications by trains of fs laser pulses

We show that by taking into account nonlinear pulse propagation effects, heat diffusion, and heat accumulation, it is possible to explain size and shape of dielectric material modifications induced by trains of fs laser pulses

Femtosecond laser cutting of glass by controlled fracture propagation

We present the use of a compact femtosecond laser with 300-fs pulse duration and pulse energy on the order of 10s of µJ for the cutting of glass by controlled fracture propagation

Effects of burst mode on transparent materials processing

We investigated the effect of burstmode with nanosecond (ns) time delay between subpulses on sodalime glass volume machining. We observed in tight focusing configuration that the use of burstmode with ns time delay between subpulses does not increase the absorption efficiency and does not bring a significant effect on the heat affected zone diameter with respect to single pulse mode. On the contrary in loose focusing configuration the use of burst mode allows increasing the aspect ratio of the heat affected zone without extra energy absorption. This effect is highly interesting for filamentation glass cutting applications

Femtosecond laser pulse train interaction with dielectric materials

We investigate the interaction of trains of femtosecond microjoule laser pulses with dielectric materials by means of a multi-scale model. Our theoretical predictions are directly confronted with experimental observations in soda-lime glass. We show that due to the low heat conductivity, a significant fraction of the laser energy can be accumulated in the absorption region. Depending on the pulse repetition rate, the material can be heated to high temperatures even though the single pulse energy is too low to induce a significant material modification. Regions heated above the glass transition temperature in our simulations correspond very well to zones of permanent material modifications observed in the experiments