The development, with researchers in Spain, the Netherlands and China, opens up a new class of compact sensors for thermal imaging and chemical or biological analysis.
The researchers at EPFL, Wuhan Institute of Technology, the Valencia Polytechnic University, and AMOLF in the Netherlands used a plasmonic nanocavity hosting a few hundred molecules to demonstrate optomechanical transduction of submicrowatt continuous-wave signals from the mid-infrared (32THz) onto the visible domain at ambient conditions.
The infrared light is directed to the 150nm diameter molecules where it is converted into vibrational energy. Simultaneously, a laser beam of higher frequency impinges on the same molecules to provide the extra energy and convert the vibration into visible light. To boost the conversion process, the molecules are sandwiched between metallic nanostructures that act as optical antennas by concentrating the infrared light and laser energy at the molecules.
The incoming IR light resonantly drives a collective molecular vibration, which imprints a coherent modulation on a visible pump laser. This results in upconverted Raman sidebands with an estimated 13 orders of magnitude enhancement in upconversion efficiency per molecule.
“The new device has a number of appealing features,” said Professor Christophe Galland at EPFL’s School of Basic Sciences, who led the study. “First, the conversion process is coherent, meaning that all information present in the original infrared light is faithfully mapped onto the newly created visible light. It allows high-resolution infrared spectroscopy to be performed with standard detectors like those found in cell-phone cameras. Second, each device is about a few micrometers in length and width, which means it can be incorporated into large pixel arrays. Finally, the method is highly versatile and can be adapted to different frequencies by simply choosing molecules with different vibrational modes.”
“So far, however, the device’s light-conversion efficiency is still very low,” said Dr Wen Chen, first author of the work. “We are now focusing our efforts in further improving it.”
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