Cladding waveguides have been realized in Nd:YAG by direct writing with a femtosecond-laser beam. A classical
method that inscribes many tracks around the waveguide circumference with step-by-step translations of the laser
medium, and a new technique in which the laser medium is moved on a helical trajectory and that delivers waveguides
with well-defined walls were employed. Laser emission on the 1.06 μm <sup>4</sup>F<sub>3</sub>/2→<sup>4</sup>I<sub>11/2</sub> transition and at 1.3 μm on the
<sup>4</sup>F<sub>3/2</sub>→4I<sub>13/2</sub> line was obtained under the pump with a fiber-coupled diode laser. Thus, laser pulses at 1.06 μm with energy
of 1.3 mJ for the pump at 807 nm with pulses of 12.5-mJ energy were recorded from a circular waveguide of 100-μm
diameter that was inscribed in a 5-mm long, 0.7-at.% Nd:YAG single crystal by the classical translation technique. A
similar waveguide that was realized in a 5-mm long, 1.1-at.% Nd:YAG ceramic increased the 1.06-μm laser pulse energy
to 2.15 mJ for the pump pulses of 13.1-mJ energy. Furthermore, a circular waveguide of 100-μm diameter that was
inscribed in the Nd:YAG ceramic by the helical-movement method yielded pulses at 1.06 μm with increased maximum
energy of 3.2 mJ; the overall optical-to-optical efficiency was 0.24, and the laser operated with a slope efficiency of 0.29.
The same device outputted laser pulses at 1.3 μm with energy of 1.15 mJ.
Nonlinear optical phenomena which dominate the interaction of tightly focused femtosecond laser beams with materials are discussed. Different femtosecond laser based techniques for material processing such as laser ablation, two-photon photo-polymerization, and material surface nano-structuring are described. For the computer controlled micro-processing of materials, near-infrared Ti:sapphire femtosecond lasers, with nano-Joule/micro-Joule pulse energy, were coupled with direct laser writing workstations. Laser fabricated micro-nanostructures and their applications are presented.