Lidar is a high-performance system for monitoring greenhouse gas emissions from space at a global scale. However, this type of instrument generally includes a complex laser system which has led in the past to significant delays of several European payloads (e.g. ADM-Aeolus, EarthCARE or MERLIN). HALLOA targets the development of a hybrid laser architecture, less complex than current free-space lasers, for greenhouse gas monitoring by Lidar. This laser architecture combines the advantages of fiber-based systems (compact and alignment-free) with those of free-space direct generation systems (high power). This development aims to reach the genuine optical performance for Lidar CO2/H2O monitoring from space and, for independency purpose, to use EU-only components/sub-systems. HALLOA will: 1- Develop new EU industrial capabilities and reach EU independency for two key critical sub-systems of the hybrid laser: the 2,05 m pulsed fiber amplifier and the high-power laser diode at 793 nm 2- Space qualify to TRL6, the pulsed fiber amplifier at 2.05m and the high-power laser pump diode at 793 nm 3- Demonstrate experimentally that a complete hybrid laser system, built with EU-only components/sub-systems, can meet the space-mission requirements for Lidar CO2/H2O monitoring. Finally, HALLOA will provide a technical roadmap to establish a European supply chain for the 2m hybrid-laser system for Lidar application, including a business plan for commercial exploitation of the pulsed fiber amplifier at 2m and a strategy for space mission insertion. The project involves 6 entities, including 3 non-profit research entities (ONERA, LMD, LZH), 2 industry key-players (KEOPSYS, LPI) and 1 SME (ERDYN). It will pave the way for building a cutting-edge and competitive European supply-chain. The TRL6 demonstration of a hybrid laser system in the eye-safe region for Lidar CO2 measurements will represent a major step forward for EU technological independence in this domain.