Big Light: Optical Coherence Over Very Large Areas in Photonic-Crystal Distributed Feedback Lasers

摘要

High-power midwave-infrared (mid-IR) semiconductor lasers, emitting in the lambda = 3 - 5 microns wavelength range, are needed to jam heat-seeking- missile threats to U.S. planes and ships. Because of their potential for compactness and low cost, they are viewed as ideal long-term sources for infrared countermeasure (IRCM) systems. The most straight-forward way to scale up the output power is to widen the stripe of gain material that is lasing. However, this strategy is usually ineffective because optical coherence is generally lost once the stripe width exceeds a few wavelengths. The beam then tends to break into multiple modes, or filaments, that lase independently of one another, rather than maintaining optical coherence over the entire gain region. The result is a rapidly diverging output beam that becomes much too diffuse to be useful when it reaches a missile nose cone several kilometers away.