Computer-generated microcooled reflection holograms in silicon for material processing with a CO(2) laser

Achromatic optical system with diffractive-refractive hybrid lenses for multifocusing of ultrashort pulse beams

We report an achromatic cascade optical system for multifocusing ultrashort pulse beams with a diffractive beam splitter. Distortion compensation requires the removal of pulse front distortions from arrayed pulses, which originate from beam-radius-dependent group delay dispersions. The inclusion of hybrid diffractive-refractive lenses can effectively manage system dispersions. Simple design formulas are derived using the ray-matrix analysis and the designed system is evaluated using 20-fs pulses. We confirm that the hybridized system can remove not only chromatic aberrations but also pulse front distortions, hence improving the system spatio-temporal focusing resolutions. The proposed pulse delivery technique enhances the practicality of materials processing with ultrashort pulses.

Grey-scale silicon diffractive optics for selective laser ablation of thin conductive films

Laser beam shaping can play a crucial role in improving many laser processes, especially in selective laser patterning of thin films for display devices and solar cells. Typical Gaussian spatial energy distributions can increase damage to the substrate and lead to large crater edge ridges, which are sub-optimal for typical industrial thin film processes. We report on the design, fabrication, and testing of reflective silicon diffractive optics developed for spatial beam shaping at a wavelength of 355 nm. The application of the elements for laser-selective removal of 20 nm indium tin oxide thin films on glass substrates is demonstrated. The design of the phase profile is first generated using the numerical method of computer-generated holography. The phase profiles are realized on a silicon substrate using a novel two-step fabrication technique consisting of a calibrated focused ion beam and an inductively coupled plasma etch. This results in truly grey-scale, blazed diffractive optics, which were analyzed using white light interferometry and atomic force microscopy. Using the diffractive elements with 355 nm nanosecond pulses shows excellent focused spot profiles with a good reproduction of the intended design with a first-order off-axis diffractive efficiency of approximately 80% at a 45 deg angle of incidence.

Multi-level diffractive optical elements produced by excimer laser ablation of sol-gel

Material ablation by excimer laser micromachining is a promising approach for structuring sol-gel materials as we demonstrate in the present study. Using the well-known direct etching technique, the behaviour of different hybrid organic/inorganic self-made sol-gel materials is examined with a KrF* laser. Ablated depths ranging from 0.1 to 1.5 microm are obtained with a few laser pulses at low fluence (< 1 J/cm(2)). The aim is to rapidly transfer surface relief multi-level diffractive patterns in such a substrate, without intermediate steps. The combination with the 3D profilometry technique of coherence probe microscopy permits to analyse the etching process with the aim of producing multi-level Diffractive Optical Elements (DOE). Examples of four-level DOEs with 10 microm square elementary cells are presented, as well as their laser reconstructions in the infrared.