Researchers have developed a temperature sensing method using naturally occurring atom-like defects in diamonds. The defects, known as Nitrogen-Vacancy (NV) defects, are naturally occurring flaws in diamonds (two adjacent carbon atoms replaced by a nitrogen atom and a hole). They are easy to obtain and have unusual quantum and nonlinear optical properties. Among them is the ability to combine two or even three photons into a single high-energy photon in a harmonic generation.
Using infrared ultrashort pulse laser stimulation, the team found that the harmonic generation decreased with temperature over the range of 20-300°C. The research presents an efficient and viable way for creating diamond-based nonlinear optical temperature sensing.
This temperature-dependent change occurs by mismatch due to the speed of different colors of light in the diamond. As the atomic lattice heats, the difference in the index of refraction between the original light and the higher energy light created by harmonic generation grows larger, decreasing the efficiency of harmonic generation.
Diamonds can be processed into a tiny tip for a probe as part of a nanometer-scale temperature sensing device. Future applications might even include a thermometer small enough to find inside a living cell, detected remotely with a laser.