Exceeding the Rayleigh Limit

Optical resolution is the ability of an imaging system to distinguish between closely spaced objects. The picture shows two points separated by the Rayleigh's limit, as observed in the experiment. (Source: M. Paúr / Palacký Univ.)

Optical resolution is the ability of an imaging system to distinguish between closely spaced objects. The picture shows two points separated by the Rayleigh’s limit, as observed in the experiment. (Source: M. Paúr / Palacký Univ.)

The reso­lution of an optical system is limited by the Rayleigh criterion. An inter­national team, led by Complutense University of Madrid, has broken this limit, showing that it is not a funda­mental curse. This opens the door to considerable improve­ment in reso­lution and could force the revision of optics textbooks.

An ideal optical system would resolve a point perfectly as a point. However, due to the wave nature of light, dif­fraction occurs, caused by the limiting edges of the system’s apertures. The result is that the image of a point is a blur. This limits the resolution of any imaging system, including micro­scopes, tele­scopes, and cameras. The quanti­tative formu­lation of this pheno­menon is the Rayleigh’s limit. Rayleigh’s curse limits the minimum distance that can be distin­guished with visible light: on the order of 0.1 micrometer, “which is a great limi­tation to our ability to see finer details,” says Luis Sánchez Soto, Professor at the Faculty of Physics at Complu­tense University of Madrid (UCM).

In coope­ration with scientists from Palacký University in Olomouc (Czech Republic), the physicist has managed to break this limit, reaching reso­lutions up to 17 times lower than those purported by Lord Rayleigh. “Textbook optics should be recon­sidered and Rayleigh’s limit placed in a broader context,” says Sánchez Soto, who is also a researcher at the Max-Planck Institute for the Science of Light in Erlangen, Germany. The research is the culmi­nation of a thrilling race between four teams of scientists around the world. Everyone wanted to prove the vio­lation of this limit, but the group led by the Spanish was the first to achieve it.

The experiment shows that Rayleigh’s curse is not inherent, but a conse­quence of not having chosen a good detec­tion strategy. “So far, all our tele­scopes or micro­scopes directly observed inten­sity. Here, we propose a scheme that optimizes the infor­mation ob­tainable and can exceed the Rayleigh limit,” says the physicist. (Source: UCM)

Reference: M. Paúr et al.: Achieving the ultimate optical resolution, Optica 3, 1144 (2016); DOI: 10.1364/OPTICA.3.001144

Links: Dept. de Óptica, Facultad de Física, Universidad Complutense, Madrid, Spain • Dept. of Optics, Palacký University, Olomouc, Czech Republic

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