3-dimensional imagery is democratized at a very short distance in industrial control or video games. At long distance, in the altimetric domain (structure of buildings and forests), its access is already open via LIDAR scanning systems. In the meteorological field, 3D imagery is very limited to simultaneously achieve large distances, high resolutions in voxels and sufficient precision on the measured variables: wind speed, temperature, absorption of trace gases, etc.
To overcome these limitations, technological barriers must be lifted on different axes:
- Increase the energy capacities of high-speed lasers, especially in the near infrared, where you can benefit from maximum eye safety (1.5-2 µm)
- Improve the sensitivity of detectors in this same spectral domain and design matrix detectors integrating advanced reading circuits
- Design ultrafast scanning systems
Research on atmospheric CO 2 has motivated the LIDAR group's interest in the various technological barriers mentioned above. In preparation for a CO 2 lidar space mission , the group has produced a new 2 µm laser source for the European Space Agency (ESA). This is the PHLAC project (2014-2018), “2-µm pulsed holmium laser for atmospheric CO 2 ”, with the LMD-ONERA-LEONARDO consortium . The laser source produced is based on a MOPA (Master Oscillator - Power Amplifier) configuration double pulse, double wavelength single mode. The source delivers 11/40 mJ energy pulses at 300 Hz with very good frequency stability (<150 kHz @ 10 s).
The spectral purity is 99.98%. An industrial application of this type of development concerns the monitoring of anthropogenic emissions to verify inventories of CO 2 emissions over a dedicated site (city, industrial zone, CO 2 capture and storage site ). The CARE-CO 2 project , “Mapping CO 2 atmospheric emissions by lidar”, aims to integrate the laser source described above into a mobile lidar that can be deployed in the field.
Photograph of the PHLAC laser developed at LMD for a CO 2 space lidar application
Mechanical and thermal integration for applications - space and industrial lidar as part of the CARE-CO 2 project
In parallel, close collaboration between LMD, CEA-Leti and CNES has enabled the development of a prototype of an HgCdTe 2 µm avalanche photodiode. A complete direct detection module integrating this type of detector has been successfully tested at LMD as part of Arnaud Dumas' thesis [Dumas these, 2016; AO 2017] . This work made it possible to lift the technological lock on the lidar detection in the infrared where no detector amplified internally and very low noise existed until now. The H2020 HOLDON project (2018-2021), “HgCdTe APD Optimization for Lidar Detection of greenHouse gases”, aims at the technological maturity of this type of detector for lidar (see holdon-h2020.eu project). As part of the 3-D observation of thermodynamic meteorological variables and greenhouse gases, the lidar group is also developing scanners with large openings (ø 50 cm) for COWI and TERA lidars .
Prototype HgCdTe avalanche photodiode detector produced at CEA-Leti (Grenoble) and tested in a DIAL lidar configuration at LMD
Large honeycomb mirror made for COWI and TERA scanners