Electro-Mechano-Optical NMR Detection

This silicon nitride membrane is linking the three electro-mechano-optical systems. (Source:
Kyoto U., K. Takeda)

An inter­national research project led by Kazuyuki Takeda of Kyoto Univer­sity and Koji Usami of the Univer­sity of Tokyo has developed a new method of light detec­tion for nuclear magnetic resonance by up-con­verting NMR radio-frequency signals into optical signals. This new detection method has the potential to provide more sensi­tive analysis compared with conven­tional NMR. Its possible utili­zation in higher-accuracy chemical analysis, as well as in magnetic resonance imaging tech­nology, are also of interest.

NMR is a branch of spectro­scopy where scientists measure the spin of an atom’s nucleus in order to determine its identity. Atomic nuclei subjected to a magnetic field induce radio-frequency signals in a detector circuit. Since different atoms cause signals at different frequencies, scientists can use this infor­mation to deter­mine the compounds contained in a sample. The most well-known appli­cation of this is in MRI-based imaging, such as CT scans.

“NMR is a very powerful tool, but its measure­ments rely on amplifi­cation of electrical signals at radio-fre­quencies. That pulls in extra noise and limits the sensitivity of our measure­ments,” explains Takeda. “So we developed an experi­mental NMR system from scratch, which converts radio-frequency signals into optical ones.” The principle behind this up-conver­sion is a new hybrid quantum con­version tech­nology.

The team worked to integrate this system into NMR, even­tually building a device that connects elec­tronics to mechanics, and then to optics. The material linking all three systems is an elastic membrane of silicon nitride. “We constructed a capacitor by vacuum-depositing a metal layer onto the silicon nitride membrane,” explains Usami. Using this with an inductor, they built a reso­nator to detect NMR signals, and next con­structed an optical cavity using the metal layer as a mirror. “The incoming electric NMR signal shakes the membrane, causing motion that is detected by an optical inter­ferometer.”

The team believes that the success of this optical detec­tion can push the spectro­scopy method even further, with the hope that this increased accuracy in detection and characteri­zation of materials can be utilized in multiple scientific disciplines. Takeda concludes, “Various methods for optical NMR detection have been reported, and while some are highly sensitive, they have so far lacked wide­spread appli­cability. Our new scheme has proven to be both ver­satile and appli­cable to a wide range of materials.” (Source: Kyoto U.)

Reference: K. Takeda et al.: Electro-mechano-optical detection of nuclear magnetic resonance, Optica 5, 152 (2018); DOI: 10.1364/OPTICA.5.000152

Link: Div. of Chemistry, Graduate School of Science, Kyoto Univ., Kyoto, Japan

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