Holographic Raman and Rayleigh lidar

Summary form only given. Thermometric lidar systems exploiting either Raman or Rayleigh scattering have been operating for many years. In the majority of these systems, the critical components of the return signal are isolated using conventional multilayer filters. In the case of Raman lidar, the filters are used to isolate two discrete parts of the rotational Raman scattering (RRS) spectrum. Since the spectrum shape is temperature dependent, the relative photon count through each filter gives a measure of the temperature of the air molecules. This method, however, suffers from inaccuracies due to unknowns in the filter profile and central wavelength due to thermal effects. This, along with the low throughput of the required ultra-narrowband filters has restricted the range and accuracy of these systems. In our system, a holographic optical element (HOE) has been constructed, which simultaneously disperses and focuses the backscattered light. Individual lines of the nitrogen RRS spectrum can be extracted with high efficiency making it possible to obtain more accurate temperatures, at much higher altitudes than previously possible. Furthermore, with the simple addition of another collection fiber, the Rayleigh signal can be extracted for temperature measurements at much higher altitudes.