Single-pulse perforation of thin transparent dielectrics by femtosecond lasers

A Strategy for Achieving Smooth Filamentation Cutting of Transparent Materials with Ultrafast Lasers

“…The VED bounds w1 and w2 in (12) correspond to some limits T1 and T2 for filament plasma temperature, T ≤ T1 or T ≥ T2, and:…”

“…where, as in (17), the VED w satisfies the condition (12). For comparison, in the opposite case, when Γ is large (e.g., about 10 or more), a known in the literature multifilament formation occurs, i.e., a filament branching into smaller and more curved filaments, but such a situation would be completely undesirable from the point of view of obtaining a better smoothness of cut walls.…”

“…A dimensionless conversion coefficient AP-H is an analogue of the surrounding material absorptivity, which describes the fraction of the filament plasma energy that actually passed into the energy for modification of material surrounding this filament for the relaxation time tE of the excited energy levels of the material. We put here that AP-H ≈ 0.9 taking into account that under the described above condition (12) of optimal choice of w only an insignificant fraction of energy (about 1 − AP-H ≈ 0.1) can be lost to the plasma emission in the mentioned above transparency region of the material surrounding the filament. This thermal emission leaves the modification zone and propagates for long distances (even can leave the material at all), thus not participating in the formation and expansion of this zone.…”

“…Other methods, such as diffraction optics, Bessel non-diffracting beams created with axicons, or intentionally astigmatic lenses (see, e.g., [11][12][13][14][15][16][17][18]), as well as the filament creation by a burst of pulses rather than by a single pulse [17,19], have also opened up a way where the total length of filaments, continuous or discontinuous, may be increased even by a single pass of the beam, thus allowing one to split materials of a greater thickness (up to few millimetres).…”

Methods of Interaction Field Extension for Precision Highspeed Femtosecond Laser Processing of Transparent Materials

“…The possibility of controlled formation of elongated micromodifications is promising tool for high-speed cutting and drilling of transparent dielectrics. Currently, several techniques are used to form elongated microcavities ( Figure 1), for example, the use of Bessel beams [6], Kerr filamentation [7], interface spherical aberration (ISA) [8], diffraction effects [9].…”