2 September 2009
Light measurements just got stronger
A new, highly sensitive, low-cost technique for measuring light in the near-infrared range is now under development that may apply to areas from forensics to quantum communications.
This new technique can measure the spectrum of the specific wavelengths of near infrared light used widely in telecommunications as well as the very weak infrared light at single-photon levels given off by fragile biomaterials and nanomaterials, said researchers at the National Institute of Standards and Technology (NIST).
A single photon detector is the key device needed to build highly sensitive instruments for measuring spectra.
For the past 30 years, researchers made progress increasing the efficiency and sensitivity of visible and ultraviolet photon detectors while methods for detecting elusive single photons in the near-infrared (NIR) range have faltered. The current methods are too static-laden, inefficient and slow, or depend on superconducting detectors, which require expensive, low-temperature operating environments. NIST researchers looked to develop a way to use existing detectors such as avalanche photodiode detectors (APD), which work well for detecting visible light and see wide usage, but are ineffective for the detection of NIR.
Their approach was to adapt a technique developed two years ago for quantum cryptography that “up converts” photons at one frequency to a higher frequency. The technique promotes the infrared photons up to the visible range using a strong, tunable laser. During the frequency conversion process, the narrow-band pump laser scans the infrared signal photons and converts only those that have the desired polarization and wavelength to visible light. Once converted to visible light, the signal photons are easy to detect by commercially available APDs. NIST researcher Xiao Tang said the new system enables the measurement of spectra with sensitivity of more than 1,000 times that of common commercial optical spectral instruments.
“Our key achievement here was to reduce the noise, but our success would not have been possible without the many years of work by others in this field,” Tang said. “We hope that our discovery will open doors for researchers studying diseases, pharmaceuticals, secure communications, and even solving crimes. We are very excited to make this technology available to the larger scientific community.”
For related information, go to www.isa.org/manufacturing_automation.
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