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We produce and characterize high-angle femtosecond Bessel beams at 1300-nm wavelength leading to nonlinearly ionized plasma micro-channels in both glass and silicon. With microjoule pulse energy, we demonstrate controlled through-modifications in 150-μm glass substrates. In silicon, strong two-photon absorption leads to larger damages at the front surface but also a clamping of the intensity inside the bulk at a level of ≈4 × 1011 W cm-2 which is below the threshold for volume and rear surface modification. We show that the intensity clamping is associated with a strong degradation of the Bessel-like profile. The observations highlight that the inherent limitation to ultrafast energy deposition inside semiconductors with Gaussian focusing [Mouskeftaras et al., Appl. Phys. Lett. 105, 191103 (2014)] applies also for high-angle Bessel beams. [ABSTRACT FROM AUTHOR]

Internal modification of silicon is important for wafer stealth dicing. In this paper, the authors report experimental and simulation results of three-dimensional modification inside silicon wafers using laser pulses with 1.55 μm wavelength and 3.5 ns pulse duration. Permanent modification is generated inside silicon by tightly focusing and continuously scanning the laser beam inside samples, without damaging the front and back surface. Cross sections of these modifications are observed after cleaving the samples and are further analyzed after mechanical polishing followed by chemical etching. The shape of the modification is found to depend on the input beam shape, laser power, and scanning speed. With proper conditions, a nearly circular modification is obtained, which has potential application for waveguide writing inside silicon. [ABSTRACT FROM AUTHOR]

Carrier kinetics in the density range of N = 1017 - 1020 cm-3 is investigated inside the bulk of crystalline silicon. Most conventional experimental techniques used to study carrier mobility are indirect and lack sensitivity because of charging effects and recombination on the surface. An all optical technique is used to overcome these obstacles. By focusing 1.3-µm femtosecond laser pulses in the volume, we inject an initial free-carrier population by two-photon absorption. Then, we use pump-and-probe infrared microscopy as a tool to obtain simultaneous measurements of the carrier diffusion and recombination dynamics in a microscale region deep inside the material. The rate equation model is used to simulate our experimental results. We report a constant ambipolar diffusion coefficient Da of 2:5 cm² s-1 and an effective carrier lifetime τeff of 2:5 ns at room temperature. A discussion on our findings at these high-injection levels is presented. [ABSTRACT FROM AUTHOR]

There are natural limits to the spatial resolution and the deposited energy densities that can be achieved in femtosecond laser dielectric modification. These arise because of the threshold-like nature of nonlinear absorption. We use two-pulse experiments to show that both limits can be exceeded by taking advantage of absorption seeded by free electrons or self-trapped excitons, depending on the pulse separation. [ABSTRACT FROM AUTHOR]