SMART 3D ultrafast Laser fabrication of embedded optical functions in chalcogenide materials using self-improving spatio-temporal adaptive control: Applications in integrated spectrometry concepts for IR astrophotonics applications – SMART_LASIR

Building on partners expertise, the program follows different axis of innovation (materials-fabrication-design-performance tests-devices) which defines the actions of the project. It includes: -Material elaboration -Fundamental investigation of laser structural changes, definition of control factors -Development of diagnostic methods for rapid feedback -Adaptive beam engineering for parallel processing and beam corrections -Design, fabrication and testing 3D complex functions validating SWIFTS concept.

We address the possibility of developing 3D optical functionalities in MIR for validating concepts of integrated spectrometry in astronomy. The impact is in fabrication with a strong component of adding to the present state of knowledge. A performant 3D ultrafast laser photoinscription technology in chalcogenide glasses will be developed. The approach is based on ultrafast laser techniques with self-adjusting spatio-temporal capabilities for upgraded optimal interaction. Achieving control on matter transformation by energetic beams has beneficial consequences for material processing and results are anticipated in areas like fundamental knowledge, new processing methods, development of micro and nanosystems with optical functions. We target specifically optical materials that respond in the MIR range astronomy bands, enabling concepts of optical integration in astrophotonics instrumentation. Impact is expected concerning laser functionalization of bulk optical infrared chalcogenide materials as well micro and nano-structuring approaches integrated in new productive processes. These techniques are conceived to generate new matter properties based on synergies with material response, unfolding perspectives for “intelligent”, feedback-assisted processing of materials.

Achieved results:
-Material elaboration. Definition of Chalcogenide glasses with high laser-generated index contrast
-Definition of an automated photoinscription setup with spatio-temporal control.
-Optical design of large mode area guides and MIR guiding.

The scientific and technical benefits lie in solutions that are time-effective, yet precise and reconfigurable to material and optical design, with impact in material elaboration, processing and optical design. The method is a unique and potentially efficient method for 3D optical functionalization in bulk materials. The extrapolation towards MIR ensures a tremendous scientific and technological potential for material processing.

Articles:

1. Cheng et al. Opt. Lett.38, 1924 (2013)
2. Bai et al. Appl. Opt. 52, 7288 (2013)
3. R. Stoian Opt. Mat. Express 3, 1756 (2013) –invited review
4. K. Mishchik et al. J. Appl. Phys. 114, 133502 (2013) - review
5. X. Long et al. Opt. Lett. 37, 3138 (2012)
6. A. Mathis et al, Appl. Phys. Lett., 101,071110 (2012)

Conferences:
1. R. Stoian Conference on Laser Ablation, Ischia 2013
2. R. Stoian Femtomaching Workshop, Cargese, 2013 [invited]
3. R. Stoian Seminaire CEA-DAM [invited]
4. F. Courvoisier et al, CLEO/Europe 2013, Munich, Germany (12-16th May 2013), talk CM5.5 (2013) [invited]

Strong demand exists today in astrophotonics for advancing optical functions and accessibility in mid infrared ranges. This concerns astronomy and space sensing particularly tracking molecular organic tracers. The effort towards miniaturization targets specifically the area of multiplexed spectroscopy in 3D, imposing a depart from current planar technologies. The possibility of fabricating integrated microoptical functions for spectroscopy is considered a major breakthrough, with a specific interest in IR chalcogenide glasses opening MIR down to 14µm. One particular example is the Stationary-wave integrated Fourier transform spectrometer (SWIFTS), an interferometric fringe tracking apparatus for detection in astrophysical thermal MIR ranges. Its compact conception requires the development, transport, and real-time reading of a stationary modulated field carrying the spectral information, i.e. several optical functions embedded on the same chip. This essentially implies designing light transport functions at arbitrary positions and, equally, diffusive points to access the evanescent field. To this, 3D ultrafast laser processing of optical components by bulk modification of transparent materials offers unique perspectives. Localized refractive index changes allow to add specific functions (light guiding, dispersion, diffraction) in compact optical devices. The embedded nature without movable parts provides intrinsic phase stability. The nowadays fabrication challenges impose several conditions: throughput, accuracy, flexibility, efficient light delivery with optimal material response, according to complex optical system designs, but also performance upgrade. Particularly the optical performance is linked to the optimal balance between index contrast, profile, and dimension. That means that the physical interaction and its dimensionality have to be accurately controlled.
The project proposes an advanced ultrafast laser 3D fabrication technique in bulk IR materials with adaptive, self-adjusting characteristics in space and time, coupling the 3D flexibility with high throughput parallel approaches in optimally-controlled interaction conditions. Grouping expertise in material elaboration, laser fabrication, optical design and metrology, we aim at the optimal 3D processing of chalcogenide materials for astrophotonic applications, particularly for integrated miniaturized spectrometry designs. The objective is to design upgraded structural modifications with guiding or diffusive properties, targeting optical functions in the MIR, particularly light transport in SWIFTS device with improvements in design, scale and efficiency. The approach gives the possibility of regulating the physical result of interaction on flexible patterns and irradiation geometries with ultimate accuracy achieved by involving adaptive irradiation systems. Three major advantages can be identified: The smart control of energy delivery regulated in adaptive loops has the potential to achieve a significant upgrade in quality. Depth-invariant, constant conditions can be established using corrective beam propagation approaches. The result is to be seen in well-balanced index contrast, positive and negative index changes, and trace dimensions that allow efficient low-loss single mode guiding in flexible patterns. Additionally efficient fabrication recipes can be developed using high throughput multibeam parallel processing and non-diffractive concepts based on adaptive spatial tailoring. Dedicated design and performance tests accompanying the production process are proposed for the fabricated devices in relation to their spectroscopic use. The goal is to achieve a high degree of control over material modifications for refractive index engineering by correlating irradiation and material properties in a synergetic manner for optimal processing applications. This is a strong move towards fabrication of performant embedded systems.