Diode laser tunes in the blue

17 Jun 2002

Wavelength-tunable blue light is achieved from a frequency-doubled diode laser.

A novel concept that produces wavelength-tunable blue light from a laser diode could be adapted to contain no moving parts (Optics Letters 27 604).

Jörg Zimmermann and a team of colleagues based at Philipps University, Marburg, Germany, and Kaiserslautern University, Germany, used a fan-structured crystal of periodically-poled LiTaO₃ (PPLT) to frequency-double a laser-diode emission.

In the cavity set-up, light from a laser diode that emits across the 960 to 980 nm range is first directed towards a grating, before passing through an aperture and into the PPLT crystal. Owing to the linear dispersion of the grating, the wavelength of light incident on the PPLT crystal changes linearly with the position of the slit, which is placed in front of it.

Moving the aperture therefore allows tunability between 480 and 490 nm. Although output power in the blue region is only about 50 nW, the researchers say that their primary goal was not to produce a high output power.

They point out that this could easily be improved by adding antireflection coatings to the nonlinear crystal surfaces and using a periodically-poled lithium niobate crystal, which has a higher nonlinear coefficient.

By using a liquid-crystal array in place of the mechanical slit, wavelength tuning could be performed electronically, resulting in a tunable blue laser-diode with no moving parts.

Author
Michael Hatcher is technology editor of Opto & Laser Europe magazine.