Daniel C. McCarthy
Emitting at 2.94 µm, Er:YAG lasers offer some very promising solutions for a broad range of medical applications. Because of their wavelengths' very high absorption by water, these lasers enable "cold ablation" of biological material while minimizing heat deposition in the surrounding tissues. Cold ablation applies also to tissues with very low water content, such as tooth enamel, making Er:YAGs a topic of interest in dental circles.
This capability comes at a price, however. Because the absorption by water molecules is so intense, Er:YAG laser energy can easily destroy dielectric coatings if any moisture remains following the manufacture of lenses.
"It is our experience that resonator mirrors will get damaged first," said Marko Marincek, a project manager at Fotona. "This is due to the fact that all the components in the resonator are exposed to higher intensities." Fotona dd, whose product lines include industrial and medical lasers, found a solution for its Er:YAGs with mirrors and beam delivery lenses made by Rocky Mountain Instrument Co.
Because of their high absorption by water, Er:YAG lasers enable cold ablation of biological tissue -- including dental tissue. However, Er:YAG energy can also destroy dielectric coatings if any moisture remains following the manufacture of lenses.
The main reason Fotona selected Rocky Mountain's optics sprung from a comparison study of optics from different suppliers, Marincek said. The study indicated that the company's optics carried a higher damage threshold.
The solution is in the way the optics are manufactured. "We had to control moisture all the way through to polishing and coating," explained Debbie Hunt, sales director for Rocky Mountain. "But it also helps that we're in Colorado, where it's a dry climate." Once finished, the calcium fluoride and zinc selenide optics are packed in desiccant for shipping.
"We were able to reduce the number of [customer] service procedures after choosing RMI's optics, and also increase the output energy of the laser and therefore the speed of the [medical] procedures," said Marincek.
The improved output enabled Fotona's lasers to increase ablation efficiency by delivering a shorter pulse with the same energy density. Improving resistance to damage also could make Fotona's Q-switched Er:YAG lasers more reliable, which could achieve more precise cutting with a significantly reduced thermal load.