Microchip Laser Aims at Argon-Ions

Michael D. Wheeler

A microchip laser developed as a compact excitation source for Raman spectroscopy should have laser manufacturers green with envy. The 532-nm laser produces 8 mW, and it may evolve into a suitable replacement for solid-state and argon-ion lasers.

Scientists employ solid-state lasers as excitation sources because they have smaller footprints and demand less power and maintenance than traditional Raman spectroscopy sources. However, they suffer from other limitations, including a high price. And although ir-cooled argon-ion lasers avoid the costs, their fans introduce mechanical vibrations.

Researchers from the University of Central Florida and II-VI Inc.'s VLOC division in Port Richey, Fla., looked into an alternative for their lab: microchip lasers.

The lasers, also known as monolithic crystal assembly lasers, incorporate a laser gain material such as Nd:YAG or Nd:YVO₄ and a nonlinear crystal such as KNbO₃ or KTP. Because the components are optically bonded in the laser cavity, they are less complex and less costly than solid-state devices. Moreover, the crystals are produced using conventional growth methods and yield quantities large enough for wide-scale commercial production.

Another important advantage is size. The research team, led by Alfons Schulte, put a premium on finding an excitation source that would fit easily within the small footprint of the Raman setup it was developing. The microchip, which is pumped by a 0.5-W near-infrared laser diode, measures 3 × 3 × 3.5 mm. The complete optical setup fits on a 1×1-ft breadboard.

Unlike most solid-state devices, producing blue light at subwave-number linewidth also was relatively simple for the microchip laser. By using thin-film coatings and KNbO₃ for intracavity conversion, and by permitting laser oscillation at discrete neodymium lines, the team achieved stable blue-green emission.

The researchers suggested that the devices will find applications in quality control and materials analysis, but there are no plans to commercialize this particular laser. "The point here was to show that they are a viable excitation source for Raman spectroscopy," Schulte said. "This was a prototype for use in our laboratory. However, all the components are simple and readily available."

Details of the team's work appeared in the May issue of Applied Spectroscopy.