Grating Reflectors Enabled laser Applications and Training

Project Information

GREAT

Grant agreement ID: 813159

DOI

10.3030/813159

Project closed

EC signature date 17 August 2018

Start date 1 March 2019

End date 31 January 2024

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 4 058 697,24

EU contribution

€ 4 058 697,24

Coordinated by

UNIVERSITY OF STUTTGART
Germany

Periodic Reporting for period 2 - GREAT (Grating Reflectors Enabled laser Applications and Training)

Reporting period: 2021-03-01 to 2024-01-31

Summary of the context and overall objectives of the project

Improving the control of the properties of lasers has led to their rapid commercial adoption, through high-value manufacturing in the automotive and consumer electronics markets, in digital communications for increased bandwidth, to medical applications with enhanced biological imaging and surgical techniques.
The overall research objectives of GREAT are to conceive and produce Grating Waveguide Structure GWS which are responding to the end-users’ needs and products.
Another overarching objective of this Innovative Training Network was to provide a balanced portfolio of skills development to a cohort of fifteen early-stage researchers (ESRs). These ESRs were trained under three main target areas: firstly, specific expertise, which underpinned their PhD project work and research; secondly, additional scientific training, covering the entire fabrication chain from design to implementation of GWS devices; and lastly, complementary skills that included communications and entrepreneurial training.
A key outcome of the project has been that 15 newly trained people have been prepared for future careers in the highly technical field of precision photonics. In a time where it is increasingly difficult to find qualified people capable of doing highly skilled work in this field, either in industry or academia, this is a major achievement for the GREAT ITN and the MSCA scheme in general. These skilled ESRs have already started finding their places in premiere academic and industrial institutions across the globe.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The first mapping, definition, and development tasks have put together the fabrication resources in the consortium and allow for establishing such fabrication chains that utilize the strengths of each institute, both in infrastructure and know-how. Therefore, for the fabrication of the devices the needed lithography and etching processes were determined for each application also regarding the final design of the first generation of GWS, which resulted in a comprehensive list with all available processes (thin film deposition, patterning, and etching) and process flows.
Furthermore, extensive simulation and design routines were conducted. Selected designs were fabricated to provide the 1st generation of GWS addressing all applications.
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The qualification and laser results obtained with generation 1 GWS (56 samples) allowed gaining strong insights in the behaviour of the developed GWS.For instance, GWS with efficiency as high as 99% were successfully demonstrated. .
More than 30 GWS were produced for 2nd generation GWS. Optical characterization, LIDT qualification and laser experiments of selected 2nd generation GWS confirmed their advanced performances.
Training in specific, scientific, and complimentary skills was provided to the ESR cohort, encompassing direct doctoral supervision at the host institutes for each, two three-day ‘school style’ scientific tutorial events, and over 70 hours’ worth of transferable skills workshops. In addition, where possible, the majority of the cohort carried out secondments at partner institutes to augment their studies with related activities. Typically, these were on-the-job training, based around one of the four primary activities of the project, i.e. Design Concepts, Fabrication Methods, Characterization and Qualification, and Implementation and Validation. Severe disruption to the planned secondments was caused by the pandemic and subsequent restrictions imposed on mobility and access to facilities. Nevertheless, a majority of the planned activities were successfully undertaken, during the ESRs’ tenure or even post the end of contract for some.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

A key overarching aim of the GREAT ITN was to train a cohort of early-stage researchers to create a reliable and reproducible production capability for the fabrication of highly efficient, low-cost grating waveguide structures. In striving to advance the state-of-the-art for GWS, the complete development chain from design, fabrication, to implementation was conducted within GREAT. Robust designs of GWS for the different applications were developed together with characterization tools that allowed for reproducible and reliable evaluation of the fabrication processes and performance when in use, which were used in a feedback loop to optimize the entire development chain processes.
The results achieved by the GREAT ESR cohort have advanced the fabrication processes for a variety of devices with GWS, showing great potential: in power scaling polarized and narrow-bandwidth 1 µm thin-disk lasers with crystalline substrate GWS; with the ability to spectrally combine multiple lasers into single laser beams with demonstrations with both diode-laser and thin-disk laser architectures; in producing structured vector beams with radial (or azimuthal) polarization characteristics in a power-scalable laser architecture; and identifying key limitations in developing large scale GWS for highly efficient pulse compression for wavelengths in the 1 µm as well as the 2 µm region with suitably high damage thresholds that are needed for advancing the average power performance in extreme peak-power lasers.
There have been several key outcomes achieved during the GREAT project, of which we highlight a few here.
• Identification of key materials and fabrication processes to raise the damage threshold limits of GWS. A critical issue that needed to be addressed for realisation of pulse-compression optics for the advancing power levels of ultra-short-pulse lasers.
• The development of a new generation of GWS with enhanced power-handling capability through exploitation of crystalline substrates, leading to a ~fifty-fold reduction in the heating rate of these optics compared to previous state-of-the-art devices.
With the knowledge developed within the GREAT project, we are better placed to realise a next generation of GWS that will lead to more efficient laser systems with beyond the state-of-the-art control of the spectral, polarization, and output power and brightness characteristics, which will address a variety of applications benefitting society. These laser systems will be the underpinning tools for; greener and advanced manufacturing, enabling new parameters for medical diagnosis and procedures, to realising new operating regimes for future experiments in fundamental sciences.
Another key outcome of the GREAT ITN was the development of a cohort of trained scientists. Additional sets of skills developed by the ESR cohort were how to communicate their research to others and to undertake scientific research with rigour and attention to detail. The success of which was demonstrated by the number of scientific papers published in highly regarded peer-reviewed journals. Moreover, more than 40 conference presentations were accepted at the premiere international conferences in the field, of which the majority were selected for Oral Presentation. This is a mark of the technical quality of the submissions.
A final demonstrable impact of the GREAT ITN is that each of the ESRs who started earlier in the project and for whom the pandemic-restrictions did not delay their doctoral studies significantly, have found follow-on positions practically immediately. These candidates are already making an impact in their new professions/positions. We expect the remainder of the cohort will also move onto the next phase of their careers’ as quickly once they are able to complete their PhDs.

Silicon master for Nanoimprint Lithography (NIL) of GWS for pulse compression

Grating waveguide output coupler (GWOC) for the generation of beams with radial polarization

Leaky-mode GWS: Grating waveguide mirror for the generation of beams with radial polarization

GWS as polarization converter for 1-micron wavelength

GWS operating in Littrow incidence for polarization and wavelength selection and stabilization

Crystalline GWS for polarization and wavelength selection and stabilization