21 Apr 2005
A look at some of the innovations in optics unveiled this month.
Amnon Yariv's group at the California Institute of Technology has made an optical fibre-based refractive index sensor which boasts a sensitivity of 1.4x10-5. The so-called Fibre Fabry-Perot Interferometer sensor consists of two Fibre Bragg Gratings (FBGs) that are separated by an etched section of fibre. "These highly flexible sensors add the function of refractive index sensing to the established repertoire of FBG sensing techniques and can be applied to many fields including biomechanical sensing and environmental monitoring," report the authors in their paper. (Applied Physics Letters 86 151122)
An optical molecular clock with an instability of 1.2x10-13 in 1 s has been demonstrated by a US-Russian partnership. The apparatus, based on a HeNe laser operating at 3.39 microns and the Methane F2 line, serves as a highly accurate optical frequency standard in the near and mid-infrared. It was developed by scientists from the National Institute of Standards and Technology in Colorado, the Lebedev Physical Institute in Moscow, and Massachusetts Institute of Technology. "Our setup represents a compact, reliable clock with high stability and exceedingly low phase noise, which can in principle be operated for long (>24 hr) periods," say the researchers. (Optics Letters 30 570)
Scientists in the US and Russia have placed dye-doped cholesteric liquid crystals (CLCs) between glass plates to create a laser that can be tuned by illuminating it with ultraviolet light. The team from Queens College of the City University of New York, US, Fordham University, US, and Moscow State University, Russia found that the lasing wavelength of Nd:YAG-pumped, dye-doped CLCs was shifted by 15-20 nm at low UV irradiation levels. Significantly, the lasing wavelength returns back to its original wavelength of around 620 nm after the UV radiation is turned off. “The observation of reversible tuning of the lasing wavelength opens new possibilities for the design of optically tunable linear and non-linear optical devices using the isomerization of novel chiral azo-dyes,” say the authors in their paper. (OPTICS EXPRESS 13 2358)
An optical sensor that can detect trace vapours of the explosives TNT and DNT has been made by a team at Massachusetts Institute of Technology, US. The sensor is based on monitoring the lasing action of a semiconductor organic polymer (SOP). The explosive gases cause the lasing to cease by introducing non-radiative pathways that compete with the stimulated emission. According to the team, the technology "promises to deliver sensors that can detect explosives with unparalleled sensitivity." (Nature 434 876)