Light detection, the basis of many modern technologies, is relatively simple in visible spectrum (region of the electromagnetic spectrum perceived by the human eye) and in the near infrared. However, detection is complicated when the wavelength gets longer and shorter (and the frequency lower) and we move towards the mid infrared and beyond in the range of terahertz.
The reason is that light carries very little energy in these spectral bands compared to ambient heat at room temperature. This ambient ‘noise’ obscures infrared light unless specialized detectors operating at very low temperatures are used, which is expensive and consumes a lot of energy.
These new nanoantennas and nanotechnology convert invisible infrared light into visible infrared light, more accessible to conventional detectors, which opens the door to new systems for environmental monitoring and observation of the universe.
O Polytechnic University of Valencia (UPV), with its Center for Nanophotonics Technology (NTC), has participated together with researchers from the United Kingdom, Switzerland and other countries in the development and validation of new technology with which they were able to convert infrared light into visible, a range in which it can be detected with systems conventional ones.
The experiments were carried out within the scope of the European project THOR and the results are published this week in the magazine. Science.
“The basic idea is that matter vibrates at very high frequencies, on the order of tens of terahertz. Thus, we can use molecules as mixers and be able to convert the frequency of incident infrared radiation into visible light”, he explains. Alejandro Martinez, researcher at NTC and professor at UPV.
For now, these results open the doors to new detection systems for application in thermal imaging, observation of the universe, detection of pollutants and greenhouse gases, as well as in chemical and biological analyses. Also, being able to detect light at frequencies where it is not easy to do so can lead to unforeseen applications.
Room temperature operation
“This technology will allow us to inspect a frequency regime in which today we practically detect nothing, because current detectors are inefficient, slow, bulky and need to operate at cryogenic temperatures”, emphasizes Martínez. Infrared detectors now introduced, however, operate at room temperature.
Their experimental validation was arduous: they needed dual nano antennas working in very different spectral regimes and able to efficiently collect incident infrared light and locate visible light in the nanometric regions where the molecules are located.
The key is to use gold nanostructures, which allow us to capture and localize light in regions the size of the molecule.
Alejandro Martínez (UPV)
“The key is to use gold nanostructures, which allow us to capture and locate light in regions the size of the molecule”, explains Martínez, who participated in the two independent groups of scientists who are now publishing their results in Science.
The difference between the two experiments is the nanoantenna used: in one carried out in the Federal Polytechnic School of Lausanne (Switzerland) placed the gold nanoparticle inside a nanometer groove in one gold film while in another Cambridge University (United Kingdom) placed on a precious metal disk. In both cases, the molecules of biphenyl-4-thiol in the middle.
“Our next goal is to reach lower frequencies, in the terahertz band, where there are no efficient detectors that work at room temperature, and for that what we will do is change the molecule”, explains Martínez, who concludes: “We also want to implement it on a silicon chip, so the technology would be very cheap and compatible with microelectronics”.
References:
W. Chen et al.: “Continuous-Wave Frequency Upconversion with a Molecular Optomechanical Nanocavity.” A. Xomalis et al.: “Detection of mid-infrared light by molecular frequency upconversion with dual wavelength hybrid nanoantennas”. Science, 2021
Rights: Creative Commons.
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