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Disk laser challenges orange emitters

14 Jan 2004

A semiconductor disk laser that emits 610 nm could replace traditional sources of orange light.

Researchers at the University of Ulm in Germany have developed a semiconductor disk laser that emits 30 mW at 610 nm. Based on a simple frequency-doubling scheme, the team says its laser could replace expensive and power-hungry sources of orange light such as diode-pumped solid-state and dye lasers. (Journal of Applied Physics 94 7379)

“The main advantages of our device are its excellent beam quality, high-output power and the possibility to scale the power by enlarging the optical pumped surface of the disk laser,” said research leader Peter Unger.

The Ulm laser is based on intracavity frequency doubling of a layered semiconductor structure that emits at 1220 nm. At present, there are no semiconductor materials available which can produce orange wavelengths directly so frequency doubling is the only option.

“The frequency doubling of semiconductor lasers in a conventional setup usually requires an optical isolator and may require a sophisticated optical design together with regulation electronics,” explained Unger. “Intracavity frequency doubling does not have these disadvantages.”

The semiconductor chip within Unger’s laser consists of a gain region made up of GaAsSb quantum well layers and a Bragg mirror fabricated from layers of AlGaAs and AlAs. Once grown, the chip is mounted on a heat sink in the laser cavity.

The laser cavity is formed by the Bragg mirror and an external concave mirror. A lithium-triborate crystal sits inside the cavity and performs the second harmonic generation.

Pumped by a 805 nm broad-area laser diode, the disk laser’s fundamental wavelength is 1220 nm which is doubled to 610 nm. According to Unger, the laser emits 30 mW of 610 nm light at -15°C and 12 mW of 610 nm light at room temperature.

“We want to optimize the epitaxial structure with the goal to improve the output power and to access other wavelengths,” said Unger. “A longer term goal is to develop compact, cheap and speckle-free RGB laser sources (at 630, 530 and 460 nm respectively) based on the concept of a semiconductor disk laser with intracavity frequency doubling.”

This work is funded by the German Federal Ministry of Education and Research.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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