Femtosecond-laser micromachining (also known as inscription or writing) has been developed as one of the most efficient techniques for direct three-dimensional microfabrication of transparent optical materials. In integrated photonics, by using direct writing of femtosecond/ultrafast laser pulses, optical waveguides can be produced in a wide variety of optical materials. With diverse parameters, the formed waveguides may possess different configurations. This paper focuses on crystalline dielectric materials, and is a review of the state-of-the-art in the fabrication, characterization and applications of femtosecondlaser micromachined waveguiding structures in optical crystals and ceramics. A brief outlook is presented by focusing on a few potential spotlights.

Light beams carrying orbital angular momentum, such as Laguerre-Gaussian beams, give rise to the violation of the standard dipolar selection rules during the interaction with matter yielding, in general, an exchange of angular momentum larger thanh per absorbed photon. By means of ab initio 3D numerical simulations, we investigate in detail the interaction of a hydrogen atom with intense Gaussian and Laguerre-Gaussian light pulses. We analyze the dependence of the angular momentum exchange with the polarization, the orbital angular momentum, and the carrier-envelope phase of light, as well as with the relative position between the atom and the light vortex. In addition, a quantum-trajectory approach based on the de Broglie-Bohm formulation of quantum mechanics is used to gain physical insight into the absorption of angular momentum by the hydrogen atom.

Intense laser ionization expands Einstein's photoelectric effect rules giving a wealth of phenomena widely studied over the last decades. In all cases, so far, photons were assumed to carry one unit of angular momentum. However it is now clear that photons can possess extra angular momentum, the orbital angular momentum (OAM), related to their spatial profile. We show a complete description of photoionization by OAM photons, including new selection rules involving more than one unit of angular momentum. We explore theoretically the interaction of a single electron atom located at the center of an intense ultraviolet beam bearing OAM, envisaging new scenarios for quantum optics.

We report on the fabrication of depressed cladding waveguide lasers in Nd:YAG (neodymium doped yttrium aluminum garnet, Nd:Y3Al5O12) ceramics microstructured by femtosecond laser pulses. Full control over the confined light spatial distribution is demonstrated by the fabrication of high contrast waveguides with hexagonal, circular and trapezoidal configurations. The confocal fluorescence measurements of the waveguides reveal that the original luminescence features of Nd3+ ions are well-preserved in the waveguide regions. Under optical pump at 808 nm, cladding waveguides showed continuous wave efficient laser oscillation. The maximum output power obtained at 1064.5 nm is ~181 mW with a slope efficiency as high as 44%, which suggests that the fabricated Nd:YAG ceramic waveguides are promising candidates for efficient integrated laser sources.

An analysis of the influence of the magnetic field of an intense, high-frequency laser pulse on the stabilization of an atomic system is presented. We demonstrate that at relatively modest intensities the magnetic field can significantly alter the dynamics of the system. In particular, a breakdown of stabilization occurs, thereby restricting the intensity regime in which the atom is relatively stable against ionization. Counterpropagating pulses do not negate the detrimental effects of the magnetic field. We compare our quantum mechanical results with classical Monte Carlo simulations. PACS numbers: 32.80.Fb, 32.80.Rm, 42.50.Hz Theoretical studies of atoms interacting with highfrequency intense laser pulses have predicted a significant decrease in the ionization probability with increasing laser intensity. This phenomenon is referred to as atomic stabilization, and has been extensively studied over the past decade [1]. Many aspects of this phenomenon can be understood by performing a Kramers-Henneberger (KH) transformation to the rest frame of a classical electron in the laser field. In particular, by developing a highfrequency Floquet theory in the KH frame [2], stabilization can be seen to have its origin in the rapid quiver motion of the atomic electron in the laser field. This allows the electron dynamics to be described by an effective potential that, on average, localizes the electron away from the vicinity of the nucleus. Subsequent ab initio Floquet calculations confirmed that ionization rates decrease with increasing intensity in a high-frequency field [3]. By directly integrating the time-dependent Schrödinger equation numerically, simulations in one [4] and three dimensions [5] demonstrated reductions in the ionization probability with increasing laser intensity when an atom interacts with realistic laser pulses having a finite duration. Further work has been carried out in order to elucidate the effects of the pulse shape and duration [6,7]. We also note that evidence of atomic stabilization of Rydberg states has been observed experimentally [8].In the above-mentioned theoretical studies, the magnetic component of the laser pulse was neglected. However, as the laser intensity increases, relativistic effects that alter the stabilization dynamics become important. Classical Monte Carlo simulations have indicated that the magnetic field pushes the electron in the laser pulse propagation direction, reducing the degree of stabilization [9]. Relativistic wave equations have also been considered within the context of reduced dimensional models [10,11]. However, it is also of interest to study the effects that are neglected in the dipole approximation by using the fully space-and time-dependent vector potential in the nonrelativistic Schrödinger equation [12]. For atomic hydrogen, this results in the cylindrical symmetry of the system being broken, thereby requiring a fully three-dimensional calculation to be carried out for extremely high laser intensities. This is a computationally demanding task. Howev...