FOCUSIS · Focal volume Control Using Structured Illumination Sources

Focal volume Control Using Structured Illumination Sources

One of the challenges in materials processing with lasers is the modification of materials with highest spatial resolution. In this quest, the role of optics is to provide new methods to increase the resolution close to or beyond the natural diffraction limit of the optical system. In most laser-based micromachining techniques, the spatial resolution is increased by using high numerical aperture lenses in combination with short laser wavelengths, effectively shrinking the focal volume and thus the minimum feature size that can be inscribed. An alternative approach is based on near-field optical methods due to the extraordinary properties of the optical near field at extremely short scales, where the field is evanescent rather than propagating, allowing it to be concentrated to smaller volumes. Moreover, beam shaping techniques are powerful complementary strategies that offer new control parameters to define how light propagates and ultimately interacts with matter. In order to meet the challenge of processing materials with highest spatial resolution, the project FOCUSIS developed and applied a specific optical system composed by dielectric microspheres as focusing lenses placed on the material combined with advanced beam shaping employing a spatial light modulator. The goal was to shape femtosecond laser pulses incident onto the microspheres in order to achieve maximum resolution as well as axial and lateral positioning control of the modifications inscribed. The overall objective required a complete control and characterization of the laser pulses implemented, in order to be able to modify and optimize the intensity distribution at user defined locations. Importantly, for the FOCUSIS project, user defined locations mean also axial positioning. This feature should be highlighted, since in this project we demonstrate that it is possible to modify how and where the maximum intensity is located by means of phase control over the incident laser beam, without requiring mechanical movement of the optical elements or the irradiated sample. This achievement has the potential to contribute to a resolution increase of well-established ultrahigh resolution imaging and marking techniques. At the same time, the advantage of allowing lateral and axial positioning control can be exploited in near-field point scanning microscopy techniques. In short, the findings obtained from the project FOCUSIS offer new approaches for controlling how light can be shaped to alter matter at will and benefit areas of science and applications including optics, biology, medicine, and materials science, to name a few.

Data: CORDIS, © European Union