A good way to control a laser's intensity and color quickly

What is it about?

I show that with a few simple design tricks and a mildly laborious one-time characterization, the cheap and simple approach of controlling laser diodes by the current passing through them is as good, and sometimes much better, than common external means in precisely controlling both the light intensity and color on nanosecond timescales. The basic ideas are well established, old even, yet devices of this design type almost never show up in investigations of quantum technologies. The paper serves both as a public service announcement that this approach is well worth the effort, e.g. for photon based experiments suffering from laser light contamination, and as guide to assembling and characterizing something similar.

Featured Image

Photo by mk. s on Unsplash

Photo by mk. s on Unsplash

Why is it important?

Lasers are generally the tools that grant those working in optics and all the different things that can be cast under the umbrella of light-matter interaction precise control over their experiments and devices. This is a natural result of lasers' favorable properties - they are bright, only one color, their light follows a narrow beam path, and so on. The ability to control these properties often sets the technical capabilities along two axis, precision and speed. There are many different standard techniques to do so, and often there is a trade-off between these axis. The system described here addresses an evident gap in standard approaches optimized to the routine but rarely met needs of fast experiments involving both high laser powers and single photons. Particularly investigations into quantum technologies, including memories, light sources, and processors, are regularly limited by the quality and speed of laser switches. While not a panacea, for there is no perfect universal tool, in the crucial feature of extinguishing an intense beam these devices deliver vastly superior performance to the best external modulation systems over nanoseconds. In shifting color and accuracy of operation they also hold their own. For comparison, a nanosecond is the equivalent time scale of gigahertz rate processing and gigabit/s volume communication, and therefore of prime technological interest.