ER-Doped Laser Transmitter for a 1.6µm-CO2 Differential Absorption LIDAR: - Er-doped laser crystals (Subproject A) - Fiber lased pumped, high-power, pulsed, single-frequency Er-doped laser transmitter for 1.6 µm-CO2DIAL (Subproject B)

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Subproject A:The goal of this subproject is to achieve diode laser pumped solid-state lasers which directly operate at the required lidar wavelengths near 1600 nm (1572 nm, 1579 nm, 1603 nm or 1609 nm) for C02. This way, simple and efficient laser systems can be realized and further investigated with respect to their scalability for lidar applications. Efficient new laser crystals for the proposed C02 lidar applications will be grown and optimized with respect to laser wavelength, active ion doping concentration, and optical quality. The crystals will be fully characterized with respect to their laser parameters and laser performance. Especially, Er-doped mixed garnet crystals and Er-doped sesquioxides are particularly most interesting candidates to address the lidar wavelengths and to achieve the goal of efficient, compact, and reliable diode pumped high power laser sources. Further interesting crystal candidates for wavelengths near 1.6 µm are Er-doped vanadates. These crystals exhibit high cross sections, high gain, and a versatility of laser wavelengths in the regions of interest. The most suitable Er-doped crystals realized in this project will be used for high power operation by the related subproject B of IPM ( Erbium laser transmitter ).Subproject B:A high-power, pulsed, single-frequency laser transmitter based on an Er-doped laser crystal shall be developed for a new CO2 differential absorption lidar (DIAL) system. Laser crystals with excellent quality will be grown and characterized within Subproject A. The laser will be pumped by a unique laser source, two cw 40-W average-power Erbium fiber laser units, which recently became commercially available. An extraordinary efficiency of the Er-laser transmitter can be expected by in-band pumping at about 1530 nm so that the laser will operate with a very small quantum defect. A special ring resonator in combination with the small thermal lensing of the Er-laser will ensure operation with an average power of more than 10 W at a repetition rate of about 1kHz as well as with high stability and reliability. By injection-seeding of frequency-stabilized, single-frequency diode lasers in the ring cavity, single-frequency and spectrally pure operation of the Erlaser will be achieved with a frequency stability of 10 MHz. Highly reproducible online/offline frequency switching required for DIAL measurements will be accomplished by two injection-seeders in combination with a fiber switch. It will be demonstrated that this system fulfills all requirements for accurate, range-resolved CO2-DlAL measurements.