New applications emerging for new and old lasers
For years after its invention, the laser was spoken of as a solution without a problem. That reputation soon disappeared as lasers found uses in a variety of industries. But now several new lasers, particularly solid state instruments that operate at ultraviolet wavelengths and those based on nonlinear materials, are finding uses in emerging areas. Computing, telecommunications, and, in particular, medicine, stand to benefit from the unique qualities of these new or improved systems.
Figure 1. Before and after pictures of the removal of a butterfly tattoo by a Q-switched medical laser. Image courtesy of the Dermatology and Laser Center of Louisiana (www.derm-laser.com).
The new applications run the gamut from drilling minuscule holes in PC boards to removing cavities on teeth. Lasers that operate at ultraviolet wavelengths have shown particular commercial promise in recent years. "Ultraviolet has been one of the key areas of improvement for commercial interest," said Jeffrey Pierce of Aculight Corp. Pierce will be chairing the Nonlinear Materials, Devices, and Applications II conference at Photonics West (20-26 January, San Jose), which will help focus attention on new uses of lasers.
Another Photonics West conference, Solid State Lasers X, will have a similar focus. Chaired by Richard Scheps of the Space and Naval Warfare Systems Ctr. in San Diego, the conference will highlight the development of new laser sources, including such topics as ytterbium-doped lasers, upconversion lasers, and solid state dye lasers.
Why are the new applications emerging now rather than in earlier years? "Lasers have taken a long time to really mature in terms of their applications, partly because the lasers available in the 1970s were so large," Scheps said. "It wasn't possible to take a device sitting in someone's laboratory and put it in a truck to be driven around."
Solid state lasers have become increasingly important in the past few years. "In the solid state laser program we've emphasized solid state dye lasers. This novel technology hasn't had much exposure outside these conferences," Scheps said. "We have a number of papers that will look at the photochemistry, stability, technology, and applications for solid state dye lasers, which are unique in their ability to cover the visible spectrum."
The combination of solid state and dye technologies also offers the advantage of safety. "Dyes are considered hazardous and they may be toxic," Scheps said. "They are also flammable. A solid state hose avoids the possibility of leaks, spills, and the need to touch the dyes. And by agreeing to dispose of the dyes, manufacturers relieve users of another task."
Another advantage of solid state lasers is their longevity. Scheps said an argon ion laser lasts about 2000 hours, and a new tube costs about 60 percent of the cost of the entire system. A doubled YAG laser, by contrast, lasts about 100,000 hours and doesn't require huge amounts of power for cooling. "Ytterbium lasers are fairly interesting," he said. "Dye-pumped YAG and FAG lasers have very high doping densities and extremely high power."
Ultraviolet lasing will also attract plenty of attention at Photonics West, and beyond. One particular area of interest involves the nonlinear borate crystal CLBO (a compound of cesium, lithium, boron and oxygen).
"CLBO is very new and extremely difficult to work with," Pierce said. "But it has impressive power in the fourth harmonic and even the fifth, where it works quite well. Lasers based on CLBO are very difficult to handle, but they can generate unprecedented power in the deep ultraviolet."
The nonlinear material opens up new applications in the ultraviolet. In the past, Pierce said, "ultraviolet applications have always relied on excimer lasers, which are cranky, unruly beasts that nobody wants but that generate more power than solid state systems ever will. But there are things that solid state lasers can do very well that excimers can't."
While new technologies such as CLBO crystals are making possible some entirely new uses of lasers, most of the recent new applications stem from adaptations of existing technology. "You're now looking not at developing a new laser, but at adapting a laser to fit a technology to new applications -- such as putting a laser in a solider's backpack, or putting it in a doctor's office to do procedures usually carried out in hospital. It's development rather than research," Scheps said.
The new and adapted laser systems are showing promise in a number of areas, including industrial applications. "One of the big applications is in machines that drill PC boards," Pierce said. "Because of tighter specs, the holes are getting smaller and smaller, down to 30 µm. Try doing that with a mechanical drill.
"You need high repeat rates, high average powers, and relatively small pulse energies, which solid state laser technology does very well," he added.
Work on photoresists in preparing integrated circuits also stands to benefit from new versions of lasers. "The flagship of all diode-pumped lasers is the neodymium YAG lasers," Scheps said. "Its third and fourth harmonics are both in the ultraviolet, at 355 and 246 nm. There has been a 2-watt ultraviolet laser on the market to work on photoresist at 355 nm. A number of applications in fluorescence detection have driven that market."
On the other hand, Pierce does not see solid state lasers making an impact in lithography. "They are okay for interferometers and items like that, but it's too hard to get enough power for production lithography," he said.
Lasers show the most promise for new applications in medicine, which is a field that, in some ways, is playing catch-up. "Lasers had a slow start in medicine," Scheps said. One of the few early areas of use involved cosmetic treatments using the CO2 laser. Now, with the emergence of new and adapted lasers, the uses have expanded. "Whatever you can do with metals you can do with skin," Scheps said. "In dermatology, lasers are being used to remove tattoos. Lasers have possibilities for seeing through subsurface media, therefore making it thinkable to diagnose cancers before they become visible. They also have the potential for treating skin cancers before they become dangerous."
Elsewhere, manufacturers are looking at applications in ophthalmology. "Obviously ophthalmology is the first place it's taken hold, as excimer lasers paved the way," Pierce said. The excimer laser was critical in photorefractive keratectomy (PRK), a procedure in which a surgeon uses a computer-controlled laser to sculpt the surface of the cornea, thereby changing its shape and the way in which light is refracted through it to the retina. According to Pierce, solid state lasers have significant advantages over excimer lasers for PRK procedures. "All the players in the industry are working on developing systems," he said.
One other medical area -- dentistry -- is beginning to benefit from laser technology. Dentists have now started using lasers to remove small cavities. And the technology is beginning to find its way into the cosmetic end of the profession. "It's now possible to improve patients' smiles by using a laser to move very small amounts of gum," Scheps said.
