ClosedLoop-LM

Ultrafast Laser Closed-loop Manufacturing using mid-IR Spectroscopy
Background and main goal
Lasers can be found in numerous manufacturing processes. To date, the vast majority of these processes are performed open-loop: Laser processing parameters are pre-selected to accommodate for inherent variations during production, following step-and-repeat approaches. These methods become rapidly inefficient when it comes to processes requiring a high level of precision and/or having a high level of complexity, for instance, when two-dimensional planar problems are turning into three-dimensional ones.

In the ClosedLoop-LM project closed-loop control strategies will be investigated and adapted to ultrafast laser and non-ablative 3D laser processes. Mid-infrared dual-comb spectroscopy will be used to perform in-situ, ultrafast monitoring of structural changes in the material being exposed to the laser. In addition, X-ray experiments at the Swiss synchrotron and free-electron laser sources will be used to gain fundamental information on the dynamic transformation of the material and to guide the sensing and control-loop methodologies.
Idea and approach
The ClosedLoop-LM project aims at investigating ultrafast laser-feedback control based on in situ structural material information acquired in real-time, leveraging recent progress in mid-infrared dual comb spectroscopy.
 
From fundamental processes to operando conditions and correlation of IR fingerprints with X-ray investigations:
  • Gain in-depth understanding of the physical and physicochemical processes in femtosecond laser processing on a microscopic to a macroscopic level with state-of-the-art X-ray tools.
  • Link the fundamental insights from the X-ray investigations to specific signatures in the IR spectra.
 
Compact mid-infrared dual comb sensing:
  • Develop quantum cascade laser combs specially for their application in the fast acquisition of dual comb spectra in the relevant frequency band of the project that will comprise mainly the second atmospheric window around 2’200 cm-1.
  • Generation one and two of the devices will be based on state-of-the art technology and incorporate the newest developments such as tapered waveguide and RF injection capabilities.
  • Generation three will be based on an integrated optics approach that combines molecular-beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) grown active and “passive” waveguides, enabling the combination of different functionalities such as dispersion compensation, in-situ optical frequency reference and non-linear optics in the same device.
Demonstrator
Portable, desktop-sized laser platform for manufacturing and in-situ observations

The demonstration platform will consist of three axis moving stages capable of moving the specimens under a stationary laser beam. A single reflective objective will focus the mid-infrared sensing and the machining probe into the specimen. Third-harmonic signals are used for locating precisely the specimen substrate surface.

The demonstration platform will be evaluated using three representative laser-induced structural transformations:
  1. localized densification, self-organized nanogratings,
  2. laser-induced amorphization, and
  3. laser-induced crystallization in glass systems.
Technical challenges
Implementing closed-loop control strategies implies that relevant information from the machining site is retrieved. Here, the main challenges are:
  1. to select the pertinent physical information to be retrieved with respect to the process objective, and
  2. to implement a sensing scheme capable of measuring the selected properties at a sufficient rate and at the laser site.
Consortium
Involved and supporting industry partners
Key project data 
Project Duration:
July 2021 – June 2025 (48 months)
Project Funding:
1.99 million CHF
Linked scientific publications
An initiative of the ETH Board
Participating Institutions of the ETH Domain
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