Periodic Reporting for period 2 - FOCUSIS (Focal volume Control Using Structured Illumination Sources)
Reporting period: 2022-03-01 to 2023-02-28
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.
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.
The project started in 2020 at Princeton University, in Princeton, New Jersey, USA, under the supervision of Prof. Craig B. Arnold. In his laboratory, experiments implementing optically trapped dielectric microspheres for the near-field irradiation of materials took place. Then, a secondment period at FEMTO-St, in Besançon, France under the supervision of Dr. François Courvoisier. Here, different microlens fabrication methods were developed, consisting in the selective melting of glass fibers. Importantly, experience with the use of Spatial Light Modulators was acquired during this phase. The final incoming phase at the home institution, starting in 2022, the Spanish National Research Council, in Madrid, Spain, under the supervision of Prof. Jan Siegel. It was here where the culmination of the project took place, allowing the demonstration of actual lateral and axial control in an optical system based on a spatial light modulator and a microsphere as last focusing element.
The project outcome includes 7 peer-reviewed publications, 1book for scientific dissemination, 2 book chapter contributions and 1 US patent application. Moreover, 20 scientific contributions were presented at different international conferences in the field of laser materials processing, optics and photonics. 2 of these contributions were invited talks and 1 prize was received for best paper. Strong emphasis was put on dissemination activities to non-scientific audiences in form of 4 seminars and participation in 3 outreach actions in USA, France and Spain.
The project outcome includes 7 peer-reviewed publications, 1book for scientific dissemination, 2 book chapter contributions and 1 US patent application. Moreover, 20 scientific contributions were presented at different international conferences in the field of laser materials processing, optics and photonics. 2 of these contributions were invited talks and 1 prize was received for best paper. Strong emphasis was put on dissemination activities to non-scientific audiences in form of 4 seminars and participation in 3 outreach actions in USA, France and Spain.
The axial focusing control on a direct-laser write system usually is limited by the focusing optics. Fortunately, when using dielectric microspheres in combination with spatial light modulators, it is possible to modify the position of the focus axially and transversally without significantly compromising lateral spatial resolution. It is therefore important to identify the experimental parameters and theoretical constrains and understand under which conditions this effect takes place. The obtained results underline the innovation potential for high resolution modification techniques for the marking of materials, and potentially for the imaging of micro and nano-metric structures.