New Solution Advances Fiber Stub End Pumping

Michael D. Wheeler

A new pumping technology for solid-state lasers incorporates fewer optical elements and a simpler assembly at the same time that it promises greater conversion efficiency and better beam quality.
Dubbed fiber stub, the technology could be the cornerstone for compact, semiconductor end-pumped solid-state lasers used in ophthalmology and dermatology.
In recent years, engineers have worked to refine end-pumping designs because of the disadvantages of side pumping -- namely, lower pump efficiency.
While end-pumped lasers appeared to be a better choice in some circumstances, their design posed a major problem: It is difficult to focus an array of diodes to a small spot at the end of a laser. To overcome this, engineers at companies such as Spectra-Physics Lasers Inc. incorporated special optics and mirrors.
Researchers at Light Solutions Corp., also in Mountain View, proposed another solution. They coupled several single semiconductor diodes through separate optical fibers. The fibers were bundled and butt-coupled to the crystal -- without a coupling lens, a fiber jumper or other specialized optics.
Extra advantages
Unexpectedly, they found pumping the laser with a dispersed source excited the solid-state laser more efficiently, increased the output power and produced better beam quality.
The end-pumping design offered other advantages:

Its robust architecture made it insensitive to tilt and misalignment
of the pump laser.

The end-pumped laser also was free of the high degree of stress
and thermal lensing induced in other configurations.
One of its biggest advantages, however, is the compact size of the laser. "We're trying to compete against argon-ion laser technology, and we really had to push to reduce the components and the cost," said Larry R. Marshall, president of Light Solutions.
Marshall's company expects to have fiber stub end-pumped lasers ready for the medical industry in the next few months, selling for about $25,000 to $30,000 -- about $5000 less than laser systems now on the market. Besides dermatology and ophthalmology, the system's compact size and air-cooling could make it attractive to the laser marking industry.