Comment
Within four decades, the applications of lasers have changed our life, as Nicolaas Bloembergen comprehensively illustrates in this lecture. However, this happened quite differently from “what excited the military and the people in the newspapers” when the first lasers were operated in the early sixties. “The incredible laser which was going to be used in star war concepts and death rays” was always far from reality, as well as the presentation of laser beams in James Bond movies, Bloembergen reminds his audience, and quotes the inscription on the door to Arthur Schawlow’s lab in Stanford: “For credible lasers see inside”. Even if widespread military applications have emerged, such as laser range finders in tanks or laser target designation techniques, lasers have primarily proven beneficial to mankind, concludes Bloembergen who had shared one of the Nobel Prizes in Physics 1981 with Schawlow. “More than percent 80 percent of laser expenditures are for civilian purposes.”
Bloembergen exemplifies these peaceful applications with a lot of concrete examples: In the shipbuilding industry, lasers drill holes in heavy metal plates, cut through them or weld them together. They even drill holes in diamonds, which is very important for the wire producing industry where steel wires are drawn through a diamond hole to continuously produce miles and miles of wire. In the car industry, moving laser spots are ideal tools to shape and harden the surface of cylinder walls and gears. Within a microsecond, they heat and melt defined surface areas of complex metal work pieces. As soon as the laser spot moves on, the just treated area immediately re-solidifies. Thus, the stability of the entire piece is not endangered.
In ophthalmology, laser pulses can be focused and fine-tuned to such a degree that they shape the cornea and correct shortsightedness and other visual disorders. In surgery, laser scalpels work sharper than the best metal scalpels: “The sharpest knife you can make has a knife edge of 10 microns, a laser can be focused to one micron”. In addition, when lasers cut through a blood vessel, their heat automatically closes them again, so that blood losses can be avoided.
Beams from small semiconductor lasers that are shone on a disc that contains photo resist material are pulsed by the “little dimples” in the disc and thus retrieve and read out this digitized information: Laser on means yes, laser out means no. “You can almost put the content of the Encyclopedia Britannica on one disc today and read out 10 to the 10 pulses per second.” Moreover, one can send this information via optical fibers, which are thinner than a human hair, over distances of 10.000 kilometers. “That is why we can communicate by email and have access to the World Wide Web.” If an optical fiber is equipped with erbium-doped amplifiers, it transports a terabit per second, which is equivalent to 78 million simultaneous telephone conversations. Finally Bloembergen mentions an optical fiber network between Europe and South-East Asia, operated by 92 carriers, with a length of 39.000 kilometers and 410 landing points in 63 countries. “This makes our world more unified.”
At the beginning of this lecture, referring to a panel discussion at the Lindau meeting, Bloembergen briefly deals with the distinction between pure and applied physics and the implication that the latter is less pure. “A hierarchy of an increasing lack of purity is damaging to science”, he says and elucidates this warning with two examples from his own career. To alleviate the controversy a bit, he says, the US funding agencies now talk about curiosity-driven or goal-oriented research. So the best option, Bloembergen advises young researchers, might be “to follow your curiosity but present it to the funding agency as goal-oriented”.
Joachim Pietzsch
