Recording stars

August 2007 was the “silver” anniversary of the compact disc (CD). Hard to believe these ubiquitous silver discs have been around for only 25 years. Royal Philips Electronics of the Netherlands manufactured the first one (starring the group ABBA) on Aug. 17, 1982, in Langenhagen, Germany, although CDs were not actually marketed until later that year (in Japan) after about 150 titles had been made. Introduction in Europe and the USA followed in early 1983. In terms of [laser] units sold, the optical disc represents far and away the single largest application of lasers. The earliest CDs were typically mastered with ion or HeCd lasers and the players used 780 nm diode devices. Today, the family of optical discs has grown to include an “alphabet soup” of different formats centered around media for digital entertainment as well as (computer) data storage. In 1996 Shuji Nakamura demonstrated the first gallium-nitride-based blue-violet laser diodes, paving the way for further development of the optical disc. Most recently these blue laser diodes have enabled higher capacity disc formats like the Blu-ray Disc and HD-DVD. In the meantime, Nakamura and his group have been busy trying to improve the performance of blue-diode technology, investigating the performance of nonpolar gallium nitride devices (see page 79). And while all this has been going on, some 200 billion CDs have been sold over the past quarter century.

While it may not be their silver anniversary, today’s infrared focal-plane arrays used in astronomy are an enormous improvement over the first two-dimensional IR imaging arrays produced in the 1980s. The consequent extended capabilities of both land- and space-based telescopes have resulted in beautiful images of the stars like the one on our cover of the Orion Nebula (see page 75). Other developments, like adaptive optics, can improve such images even further-to the point that some ground-based systems can image with quality as good as space-based systems (see page 42).