When did lasers start being used for less lethal devices, and why has their use expanded so greatly over the past few decades?
Nieuwsma: Other uses for lasers started to take off in the 1970s, probably because there was a lot of government money put into the technology in the 1960s to do the core research. But, as scientists, we liked to look at different types of applications. One of the early uses was taking laser targeting technology and using it to make pictures, [the origin of what would become] laser light shows. By 1974, they were doing laser scanning of bar codes. They were doing early medical work with lasers in 1962. Raytheon developed the first laser welder in 1965, which was significant not only for welding but also for emphasizing the power of lasers and the safety issues of lasers to the government. Ophthalmology became an obvious use of lasers, using light to spot-weld the retina inside the eye. You don't want to cut the eye because it doesn't heal well. Dentistry, too, uses lasers for drilling. You can tune the laser so that it's absorbed by a dark cavity and not the white of the tooth.
What major breakthroughs enabled lasers to be used in so many other technologies, including CD players, medical equipment and fiber optics?
Byren: The first real revolution was in the number and types of lasers available [to inventors]. The semiconductor laser [also called a laser diode], developed at General Electric in 1962, allowed lasers to be scaled down in size into something very small, like what you find today in a CD player. Another innovation was the use of a number of different types of materials to make different kinds of lasers, whether they are gas lasers, free-electron lasers or solid-state lasers.
A second revolution was diode pumping, which is when you store the energy used to create the laser beam in the laser's diode crystal. Diode pumping enabled you to cut down on the amount of power needed to operate the laser and reduced the amount of heat generated, which can cause the laser to move out of alignment. Lasers became more portable because you could run them on batteries rather than a larger power source.
A third revolution was fiber lasers, which spawned the long-distance fiber optics industry. These lines contain the laser inside a flexible cable.
What are some of the hurdles that researchers are trying to overcome in developing the next generation of lasers?
Nieuwsma: The military wants every soldier to have a laser the size of a cell phone that they can use for a number of different things, such as finding distances accurately, identifying objects at a distance better, or illuminating targets on the ground that can be destroyed via unmanned aircraft. The challenge is getting enough power out of a device that small to run the laser long enough to do the job, where we are trying to take advantage of advances in energy storage and batteries made by computers and cell phones. That's kind of the low end. The high end is putting a laser into space, where it can observe the Earth very accurately to identify military targets, measure changes in the ice pack or atmosphere to observe the climate and biosphere, or even to help protect against ballistic missiles. One of the challenges there is that lasers depend, often in very subtle ways, on having an atmosphere around it, or a direction for the force of gravity, and they are often harmed by the natural radiation in space. To date, lasers have been boxed up to simulate the Earth when launched into space. Both the military and NASA would like a true space-qualified laser that does not depend on being in a protected box.
Byren: A laser [that can be positioned outside the Earth's atmosphere] certainly requires a close look at how you make the laser's different components and assemble them because once you put a laser in space, you have a long way to go to fix it if it breaks.