Optics & Photonics News - February 2010

History of

Gas
Lasers
Gas

Ask anyone to name the most important application of lasers, and they will probably point to their clini- cal use—for example, lasers that reshape the cornea of the eye to correct vision defects, as explored in this month’s cover article on “Lasers in Ophthalmology” (p. 28). The laser that has made corneal reshaping possible is the argon fluoride (ArF) excimer laser, which operates at 193 nm. It is a rare gas halide (RGH) excimer laser, a type that burst on the scene in 1975. Because of its very short wavelength and its ability to propagate in air, the ArF laser has also become the key light source for microlithography—which allows scientists and engineers to produce features of size less than 100 nm on semiconductor chips. This is the largest application for this type of laser, and a driving force in electronic technology. Without it—or its KrF analogue—much of today’s computer technology would not be possible. But the excimer laser was not created in a vacuum. There is a considerable history of pulsed gas lasers that precedes it. Here, following Jeff Hecht’s January feature on continuous wave gas lasers, I explore how pulsed gas laser systems came to be.

Part 2: Pulsed
Gas Lasers

In this second article of a two-part series, Colin Webb explores the origins of pulsed gas lasers, which made possible many critical applications of laser technology, including corneal reshaping and microlithography.

The nitrogen laser—a DIY project

Among the very earliest of the purely pulsed gas lasers is the molecular nitrogen system, which operates in the near ultraviolet on the C—>B band of the N2 molecule at wavelengths around 337 nm. H.G. Heard at Energy Systems discovered this laser in 1963. Its performance in terms of pulse energy (typically a few mJ), and pulse repetition frequency ( typically 2-20 per second), are by no means impressive by today’s standards. Nevertheless, it is of great significance in the history of lasers, not only because its output was (and still is) used to pump tunable dye lasers covering the near-ultraviolet and visible regions, but because it was so simple to construct and operate.

In fact, many thousands of these lasers have been built as science projects in colleges and domestic garages all around the world. Scientific American’s Amateur Scientist column published do-it-yourself instructions in 1974. This has been the inspiration for myriad designs. In 1973, Jim Piper and I built our own nitrogen laser to be used for atomic physics experiments at the Clarendon Laboratory at Oxford.