Abstract

Recent outcomes from photonics research have yielded the advent of continuously tuneable semiconductor laser sources offering high optical power output and excellent spectral purity. Quantum cascade lasers (QCLs) can be tailored to emit laser radiation from 4 m to 150 m in a robust and extremely compact package. They provide an excellent opportunity to develop new highly sensitive and compact instrumentation for atmospheric research both for in situ and remote monitoring.

A novel passive remote sensing instrument based on a mid-infrared QCL operating at 9.7 m will be presented: a ground-based prototype laser heterodyne radiometer (LHR) has been developed within the Space Science and Technology department of the Rutherford Appleton Laboratory. Principles, advantages, and key elements of the instrument will be discussed. Measurements on carbonyl sulphide have been used to assess the performance of the LHR in the laboratory, and a detection limit equivalent to three times the ultimate shot noise limit has been observed. Results from solar occultation atmospheric transmission measurements targeting ozone will be presented, including ozone profiles retrieved using the optimal estimation method. Measurement information content and retrieval errors will also be discussed. This first atmospheric measurement campaign has shown that ozone mixing ratios up to an altitude of 35 km may be retrieved with an average vertical resolution of 4 km. This initial deployment of the ground-based prototype LHR has been highly successful and has demonstrated the potential of laser heterodyne radiometry to deliver excellent sensitivity at high spatial and spectral resolution in an unprecedented compact package.

To conclude an outline of methods to improve instrument performance and the current developments being undertaken will be given.