Standoff spectroscopy via remote generation of backward lasing and/or gain swept superradiance in air

Abstract form only given. 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 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 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.