Green laser diodes

"The key technology is the optically pumped VECSEL, which resembles the geometry of a solid-state laser while retaining the wavelength versatility offered by semiconductor gain media," says Mircea Guina of Tampere University's Optoelectronics Research Centre, project manager of the EU funded NATAL project. A VECSEL (vertical external-cavity surface emitting laser) is a semiconductor laser that produces a high-quality beam of light perpendicular to the surface of the chip. The geometry also makes it easier to dissipate waste heat and so work at higher power. Research in NATAL has focused on producing red, green and blue wavelengths by developing new nanomaterials to provide gain in a VECSEL – including quantum dot structures that have not been used in a VECSEL before, and using frequency doubling. Among the highlights from the project are high-power VECSELs operating directly in red light and frequency doubled infrared VECSELs that can emit in the sought after green gap, as well as in the amber-orange-red part of the spectrum. The red lasers can be frequency doubled to emit ultraviolet light. "One of the partners, the Institute of Photonics at the University of Strathclyde, has for the first time demonstrated direct-emission red VECSELs pumped with commercially available blue diode lasers," Guina added. "Another significant outcome of the project was a full 3D VECSEL simulation software that takes into account the laser geometry as well as optical and thermal properties of the laser." Industrial uses for compact, mass-produced lasers are likely to be numerous. Two NATAL partners, OSRAM Opto Semiconductors and EpiCrystals, are in the process of developing the green laser for projection technologies. A third industrial partner, TOPTICA Photonics, is working on scientific applications. " The amber-orange-red lasers could be used for photodynamic therapy and to make artificial guide stars for telescopes by exciting sodium atoms high in the atmosphere. The work on quantum-dot VECSELs is being continued in the FastDot project funded under the EU's Seventh Framework Programme.