Photonic crystal spatial filters fabricated by femtosecond pulsed Bessel beam.

We propose and experimentally demonstrate femtosecond direct laser writing with Bessel beams for the fabrication of photonic crystals with spatial filtering functionality. Such filters are mechanically stable, of small (of the order of a millimeter) size, do not require direct access to the far-field domain, and therefore are excellent candidates for intracavity spatial filtering applications in minilasers and microlasers. The proposed technique allows the fabrication of photonic crystal filters in inorganic glass, with a narrow angle (∼1°) nearly 100%-transmission passband between a broad angle (∼10°) nearly 0%-transmission angular stopbands.