High harmonic lasers unlock a resolution boost for optical microscopy
Physicists at the Australian National University say that optical microscopes should get a huge boost in magnification, after their discovery of a new high harmonic laser illumination technique, using a tiny cylinder 1/50th the width of a human hair.
These tiny cylinders, made of aluminum gallium arsenide, are able to take a burst of high-powered infrared laser light and convert it to higher harmonics, making its wavelength up to seven times shorter and sending it into the visual and ultraviolet parts of the spectrum. The result: extremely bright, tunable laser radiation all the way up to the X-ray range, in extremely short attosecond bursts (less than one trillionth of a second).
Before this work, high harmonics of this kind were typically generated using relatively large volumes of gas or plasma. The ANU team's cylinders offer a solid-state, ultra-miniaturized way to achieve this effect – provided you can aim your invisible infrared laser precisely enough to target the exact center of a tube that's about one thousandth of a millimeter wide.
But unlocking these extreme wavelengths opens up a potential way to get past the resolution barrier that caps optical microscopes at a maximum magnification of about 1,000 times. While the optics allows greater magnification levels, the wavelength of visible light means that anything smaller than about 20 nanometers simply can't be distinguished.
“Tiny sources of high harmonics should bring optical microscopy to a completely new level,” said lead researcher Anastasiia Zalogina, who recently completed a PhD in the Nonlinear Physics Centre, in a press release. "With such light sources we will be able to see in the optical microscope much tinier things, like individual viruses, or monitor in real time fabrication of nanometer-scale semiconductor chips for computers and smartphones. We will also be able to trace dynamics of electron clouds of atoms and molecules in real time.”
Previously, the only way to look at things at this scale has been in the black and white world of electron microscopy.
“High harmonic generation has promising prospects in exploring the area of nonlinear optics and photonics, and applications in bio-imaging due to higher penetration depth and reduced photobleaching,” Zalogina continued. “The development of high harmonic generation also can connect quantum optics and strong laser-field physics: quantum theory of extreme nonlinear optics suggests non-classical light sources based on generated harmonics could be valuable for quantum communication, information, and computation.”
The research is available in the journal ACS Publications.