Nonlinear crystal only ‘made in China’

FUJIAN, CHINA--A potentially very important nonlinear optical crystal, potassium beryllium fluoroborate (KBBF), can be fabricated in only one laboratory in the world--and that laboratory is in mainland China.

FUJIAN, CHINA--A potentially very important nonlinear optical crystal, potassium beryllium fluoroborate (KBBF), can be fabricated in only one laboratory in the world--and that laboratory is in mainland China. As reported by David Cyranoski in Nature magazine (Volume 457, pgs. 953–955, February 19, 2009), Chuangtian Chen and his group at the Fujian Institute of Research on the Structure of Matter began looking in 1988 at hundreds of potential nonlinear optical compounds to produce shorter UV wavelengths, first discovering KBBF, then figuring out a practical way of making and using the crystal. Not only does KBBF facilitate the production of nonlinearly generated light with wavelengths less than 200 nm, but the resulting light has a vary narrow bandwidth.

While it has already proven invaluable for physics research, for example the determination of energy levels in superconductors, KBBF, if made thick enough, could possibly allow diode-pumped solid-state lasers to replace excimer lasers in at least some applications in semiconductor lithography and in the medical world. The Chinese government is funding Chen’s R & D efforts and is not allowing Chen to distribute any of the crystals without the government’s permission.

In 2008, Chen’s institute had the capacity to produce only 15 KBBF crystals, but is ramping up to produce 50 in 2009 and 100 in 2010, according to Cyranoski. Other projects funded by the Chinese government include the integration of KBBF into applications such as photoemission spectrometers, Raman-scattering spectrometers, and scanning-tunneling microscopes. The output of Chen’s institute may be increasing, but because the demand within China is increasing as well, it may well be that all KBBF produced within the next couple of years will be used within China.

Chen himself has experience in nonlinear crystals dating back to the 1970s, and can count the development of barium borate and lithium triborate as just two of his achievements. Cyranoski notes that along with its huge head start and large funding, Chen’s laboratory is 70 people strong. Such momentum means that the group’s successes in pushing KBBF toward practicality will likely continue.

The decades of work put into KBBF development within China have included creating safety procedures and equipment for working with the poisonous, cancer-causing element beryllium; the characteristics of beryllium are a hurdle to setting up KBBF research laboratories in the U.S. and elsewhere. For now, the rest of the world has to make do with the few KBBF crystals that are outside China, and with other nonlinear crystals that have lesser properties.

--John Wallace

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