Laser physics: A phase it's going through

When we observe laser light, we typically measure its intensity, and so wave amplitude. The phase, which encodes further details of the laser's internal workings, was obscure — but fresh light is being shed on it. Laser radiation is usually measured with detectors that determine frequency and intensity, but gather no information about the phase of the radiation. By measuring the phase it would become possible to gain insights in the dynamic processes of optical amplification and attenuation underlying laser operation. Kroll et al. have now developed a way of measuring amplitude as well as phase of laser radiation from so-called quantum cascade lasers, which operate in the terahertz regime. The technique, which could be extended to other types of lasers, can be used to study effects leading to optical losses — useful information to improve the laser performance.