July 2nd, 2007
A new nanowire light source
Californian researchers have created a bio-friendly nano-sized light source capable of emitting coherent light across the visible spectrum. According to the researchers, this is ‘the first electrode-free, continuously tunable coherent visible light source that’s compatible with physiological environments.’ When the technology becomes available, maybe in 10 years, our computers might be thousands of times faster than our today’s tools. Other applications are envisioned, such as single cell endoscopy and other forms of bio-imaging.
This development in nanophotonics has been led by chemist Peidong Yang and biophysicist Jan Liphardt, who both worked with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, and the University of California at Berkeley. You can see on the left a detailed set-up for the single-beam optical instrument they used to trap single potassium niobate — KNbO3 — nanowires. (Credit: Yang and Liphardt)
Here are some details about the technique used. The “nanowires of potassium niobate were synthesized in a special hot water solution and separated using ultrasound. The wires were highly uniform in size, several microns long, but only about 50 nanometers in diameter. A beam from an infrared laser was used to create an optical trap that allowed individual nanowires to be grabbed and manipulated. Because of potassium niobate’s unique optical properties, this same beam of infrared laser light also served as an optical pump, causing the nanowires to emit visible light whose color could be selected. In a demonstration of the technique’s potential, these nanowire light sources were used to generate fluorescence from specially treated beads.”
Besides faster computers and networks, what could be some applications of these nanowire light sources? “Bio-imaging may be the field in which this nanowire light source technology has its biggest impact. Optical or visible light microscopy remains at the forefront of biological research because it allows scientists to study living cells and tissues. However, whereas the resolution of optical microscopy is limited by diffraction, through subwavelength techniques it becomes possible to visualize features smaller than visible light wavelengths.”
This research work has been published by Nature under the name “Tunable nanowire nonlinear optical probe” (Volume 447, Number 7148, pages 1098-1101, June 28, 2007). Here is the beginning of the editor’s summary, Down to the Nanowire. “Nanophotonics, dealing with the properties of light on a nanometre scale, could revolutionize the fields of telecommunications, computing and sensing. A newly developed nanowire frequency-tuneable light source described in this issue could contribute to the advance of nanophotonics, especially in bio-imaging applications, as it can function in physiological conditions and ensures a minimum of damage to the sample.”
And here are two links to the abstract and to the full paper (PDF format, 5 pages, 1.48 MB) from which the above illustration has been extracted. Here is an excerpt from the introduction. “Here we report the development of an electrode-free, continuously tunable coherent visible light source compatible with physiological environments, from individual potassium niobate (KNbO3) nanowires. These wires exhibit efficient second harmonic generation, and act as frequency converters, allowing the local synthesis of a wide range of colours via sum and difference frequency generation. We use this tunable nanometric light source to implement a novel form of subwavelength microscopy, in which an infrared laser is used to optically trap and scan a nanowire over a sample, suggesting a wide range of potential applications in physics, chemistry, materials science and biology.”
So far, these applications are not ready yet. for example, “Liphardt compares it to where atomic force microscopy was some 10 years ago. He also says that this technology is not intended to replace existing microscopy technologies, but will enable researchers to do things that cannot be done with current technology.”
Sources: Lawrence Berkeley National Laboratory news release, June 28, 2007; Nature, June 28, 2007; and various websites
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