11 Sep 2008
Developers of argon-ion lasers and their rivals take note, researchers in France have unveiled a new challenger.
Argon-ion lasers emitting around 490 nm have a new competitor thanks to work being carried out in France by Oxxius and researchers at the University of Paris-South. The team's laser employs intracavity sum-frequency mixing and emits 155 mW continuous wave at 491 nm, which it says suits biological applications such as fluorescence microscopy. (Optics Letters 33 1632)
"We demonstrate that it is possible to develop diode-pumped solid-state laser sources around 490 nm with standard commercial laser crystals," François Balembois of the Solid-State Lasers and Applications Team at the Institut d'Optique told optics.org. "The goal is to replace the argon-ion in a large number of applications, and in particular in biology."
In the past few years, numerous research groups and companies have sought to replace the argon-ion laser with a compact and efficient alternative. Approaches have included optically-pumped semiconductor (OPS) technology, direct frequency doubling of diode lasers and frequency mixing in Nd:doped crystals.
The idea exploited by Balembois and colleagues involves pumping a Nd:GdVO4 crystal at 808 nm, which produces light at 912 nm, and then using this 912 nm emission to pump the 1064 nm transition in an Nd:YVO4 crystal, a process known as cascade pumping. The 1064 nm cavity is completely enclosed in the 912 nm cavity. In the final step, intracavity sum-frequency mixing at 912 and 1064 nm via a BiBO crystal produces light in the blue part of the spectrum.
"This is an elegant way to have only one pump source for two crystals emitting at two different wavelengths," explained Balembois. "The other benefit is that the second laser crystal is pumped by a TEM00 beam, so the overlap is fully optimized."
Comparing his design with OPS technology, Balembois believes a key factor is the commercial availability of components. "For OPS, the semiconductor chip is not commercially available, so only a few companies can commercialise OPS at 490 nm," he said. "The second advantage with respect to OPS is the ability to support passive losses. OPS is a very low gain media and it is rather complicated to design a low-loss cavity with second harmonic generation. In the case of Nd:vanadate cascade pumped, the gain is much more important and the sensitivity to intracavity losses is strongly reduced."
Now that this first proof-of-concept design has proved successful, the team will try to improve the laser's performance. "Higher brightness laser diodes should help to improve the performance significantly," said Balembois. "One could also think about an integrated setup where all the optical pieces are in contact, with the appropriate coatings in between."
Jacqueline Hewett is editor of Optics & Laser Europe magazine.
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