Temperature sensing using defects in diamonds

Japanese scientists have developed a method for monitoring temperature using the naturally occurring atom-like defects in diamonds, finding that increased heat led to reduced intensity of the nonlinear harmonic generation of light. Their results, published in the journal Optics Letters, may lead to highly accurate nanosized thermometers.

Nanotechnology is playing an increasingly important role in new devices, and the ability to measure temperatures at small scales grows ever more vital. Conventional thermometers are often too large or not practical for many applications that involve length scales smaller than a few hundred nanometres; thus, new approaches are needed for tiny, non-contact temperature sensors. Now, researchers from the University of Tsukuba and the Japan Advanced Institute of Science and Technology have taken advantage of the nonlinear optical properties of a particular kind of defect in diamonds, which are made of carbon atoms arranged in a diamond cubic lattice.

Nitrogen-vacancy (NV) defects are naturally occurring flaws in diamonds in which two adjacent carbon atoms have been replaced by a nitrogen atom and a hole. They have attracted a great deal of attention because they are easy to obtain and have unusual quantum and nonlinear optical properties, including the ability to combine two or even three photons together into a single high-energy photon in a process called harmonic generation. Using infrared ultrashort pulse laser stimulation, the researchers found that the harmonic generation decreased with temperature over the range of 20–300°C.

“This study presents an efficient and viable way for creating diamond-based nonlinear optical temperature sensing,” said Tsukuba’s Dr Aizitiaili Abulikemu, first author on the study. This temperature-dependent change was explained by mismatch due to the speed of different colours of light in the diamond. That is, as the atomic lattice heats up, the difference in the index of refraction between the original light and the higher energy light created by harmonic generation grows larger, which decreases the efficiency of harmonic generation.

“Diamonds can be processed into a tiny tip for a probe as part of a nanometre-scale temperature sensor,” added senior author Professor Muneaki Hase, also from Tsukuba. Future applications might even include a thermometer small enough to fit inside a living cell, which could be detected remotely with a laser.

Image credit: ©stock.adobe.com/au/htoto911

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