Abstract

The continuous monitoring of the atmosphere for traces of gases and pathogens at kilometer-scale distances is an important and challenging problem. We have demonstrated [1,2] that by tailored pairs of pulses of different colors (e.g., red and blue) it is possible to invert an ensemble of molecules such that lasing and/or gain-swept superradiance is realized in a direction toward the observer. In recent experiments, we have observed [3] strong backward lasing of oxygen-ionized molecules in air, thus enabling a transient gain for an optical field propagating toward the observer. This technique results in the generation of a strong, coherent, counter-propagating optical probe pulse. Such a probe, combined with a wavelength-tunable laser signal(s) propagating in the forward direction, provides a tool for various remote-sensing applications. The proposed technique can be enhanced by combining it with the gain-swept excitation approach as well as with beam shaping and adaptive optical techniques.

© 2011 Optical Society of America