Chromatic compensation of broadband light diffraction: ABCD-matrix approach

Parallel laser micromachining based on diffractive optical elements with dispersion compensated femtosecond pulses

We experimentally demonstrate multi-beam high spatial resolution laser micromachining with femtosecond pulses. The effects of chromatic aberrations as well as pulse stretching on the material processed due to diffraction were significantly mitigated by using a suited dispersion compensated module (DCM). This permits to increase the area of processing in a factor 3 in comparison with a conventional setup. Specifically, 52 blind holes have been drilled simultaneously onto a stainless steel sample with a 30 fs laser pulse in a parallel processing configuration.

Debye representation of dispersive focused waves

We report a matrix-based diffraction integral that evaluates the focal field of any diffraction-limited axisymmetric complex system in the paraxial regime. This diffraction formula is a generalization of the Debye integral, here accommodated to broadband problems. The Fresnel number is reformulated to guarantee that the focal region is entirely within the region of validity of the Debye approximation when this parameter largely exceeds unity. Several examples are examined in detail, one of them exhibiting in-focal-plane compensation of the spatial dispersion. This simple formalism opens the door for the analysis and design of focused beams with arbitrary angular dispersion.

Chromatic compensation in the near-field region: shape and size tunability

We report a diffractive-lens triplet with which to achieve wavelength compensation in the near field diffracted by any aperture. On the one hand, the all-diffractive triplet allows us to tune, in a sequential way, the Fresnel-irradiance shape to be achromatized by changing the focal length of one diffractive lens. On the other hand, we can adjust the scale of the chromatically compensated Fresnel diffraction field by shifting the aperture along the optical axis. Within this framework, we present an extremely flexible white-light Fresnel-plane array illuminator based on the kinoform sampling filter. A variable compression ratio and continuous selection of the output pitch are the most appealing features of this novel application.