Injection-seeded optical parametric oscillator for airborne water vapour DIAL

Any detailed understanding of the role of water vapour in the global climate system requires precise measurements in the atmosphere with high temporal and spatial resolution. A technique that is appropriate to deliver these data is airborne differential absorption lidar (DIAL) applied in the near-infrared spectral range. In order to accurately determine atmospheric water vapour concentrations by means of the DIAL technique tunability and spectral properties of the lidar transmitter are very important. It is demonstrated that the spectral and energy requirements are achieved using optical parametric oscillators (OPOs) that are line-narrowed by the technique of injection seeding with radiation from dye lasers or from laser diodes. When the OPO is unseeded its spectral width is broad enough to suffer only negligible absorption from the absorption lines. Therefore, the unseeded OPO radiation can be used for off-line measurement, which simplifies the DIAL set-up significantly. In addition, the laser diodes were employed to measure line parameters of a selected absorption line in the near-IR. Their precise determination is important in order to make accurate DIAL measurements.