The first technical step consisted in the full definition of the specifications of the HOLDON detection chain (expected performances of the hybrid detectors and the acquisition chain) by the technical Partners, based on different ground-based and space LIDAR scenarios. These specifications were slightly updated (completed) during the second period.
Based on these specifications, the following main developments were made for the hybrid detectors:
-A CTIA architecture was used for the ROIC, offering a large dynamic range and a dual-operation mode (continuous mode or on-chip-sampling mode). The ROIC was designed and a CMOS batch with 200mm wafers was processed. Electrical pre-tests in a probe station showed that the ROICs had nominal characteristics with high yield.
-Two technological batches of APDs based on epitaxy-grown HgCdTe wafers were realized, and allowed getting APD variants with a gain quite above 100 (at low temperature) and suitable for the demonstrators.
- Specific cold PCBs were designed and manufactured.
- Hybrid components (APDs+ROIC) were bonded to the cold PCB and integrated into the LN2 or cryocoolers cryostats to form the detection modules.
The results obtained from the characterization of the modules showed that the HOLDON objectives for the detector modules have globally met the performance of the KPIs when characterized within the laboratory equipment. In particular, the high sensitivity, down to single photon level, combined with an ultra-high dynamic range and low recorded persistence. This performance should represent a guarantee that the HOLDON detector will find use in future atmospheric Lidar missions. Unfortunately, all the partners could not test the detectors within their Lidar setups. These characteristics are also expected to open a new horizon of applications in fields beyond the field of atmospheric Lidar.
Laboratory test results of the detector were presented at the ICSO2022, IAC2022 conferences and at a workshop held in Paris by CNES the 20/10/2022.
Regarding the control and acquisition chain:
- 5 back-end electronics systems (each system comprising 3 boards) were fabricated and validated.
- The FPGA building blocks (for pre-processing, timing and fast data transfer to a custom user) were validated through system integration.
In parallel, for laboratory tests, a Lidar Echo Emulator (LEE) was designed and implemented. The equipment can emulate signals at NIR, VIS, and UV wavelengths, for short-pulsed or long echoes, and can be controlled through a dedicated user interface.
Most of the measured parameters were in line with the expectations.
It is foreseen to present HOLDON results at the infrared detection for space applications workshop to be held in June 2023 in Toulouse, co-organized by CNES and ESA.
In view of the laboratory and field measurement of atmospheric methane, a test plan has been prepared to evaluate the new HOLDON detection module within 1.64 µm IPDA systems.
The opto-mechanical integration for the detection chain was partially completed up to the integration of the detection module.
For CO2 DIAL, a 2-µm laser source has been developed and the key performances of the 2-µm laser source have been assessed especially for pulse energy (>40 mJ), spectral purity (99.986%) and frequency stability (<70 kHz at 10s). Then, an optical detection chain, which will integrate the HgCdTe APD, has been built and now ready for the Lidar integration.
Lidar system has been tested in coherent detection. CO2 measurements from DIAL and in situ sensor agreed within the error bars and coherent detection will be used to check direct detection performances. Measurements with the APD detection module could not be carried in the timeframe of the project.
The dissemination activities are well on-going, with public communications through the website (
http://holdon-h2020.eu(se abrirá en una nueva ventana)) social media, and conferences/publications/posters. HOLDON is still attracting new people. The progress of the technical program has been delayed with the outbreak of the covid-19 virus but has regained its momentum.
