June 25, 2015

A novel microscope for nanosystems

LMU/MPQ-scientists can image the optical properties of individual nanoparticles with a novel microscope.

(June 25, 2015)  Nanomaterials play an essential role in many areas of daily life. There is thus a large interest to gain detailed knowledge about their optical and electronic properties. Conventional microscopes get beyond their limits when particle size falls to the range of a few ten nanometers where a single particle provides only a vanishingly small signal. As a consequence, many investigations are limited to large ensembles of particles. Now, a team of scientists of the Laser Spectroscopy Division of Prof. Theodor W. Hänsch (Director at the Max Planck Institute of Quantum Optics and Chair for Experimental Physics at the Ludwig-Maximilians-Universität Munich) has developed a technique, where an optical microcavity is used to enhance the signals by more than 1000-fold and at the same time achieves an optical resolution close to the fundamental diffraction limit. The possibility to study the optical properties of individual nanoparticles or macromolecules promises intriguing potential for many areas of biology, chemistry, and nanoscience (Nature Communications, DOI: 10.1038/ncomms8249, 24 June 2015).

Spectroscopic measurements on large ensembles of nanoparticles suffer from the fact that individual differences in size, shape, and molecular composition are washed out and only average quantities can be extracted. There is thus a large interest to develop single-particle-sensitive techniques. “Our approach is to trap the probe light used for imaging inside of an optical resonator, where it circulates tens of thousands of times. This enhances the interaction between the light and the sample, and the signal becomes easily measurable”, explains Dr. David Hunger, one of the scientists working on the experiment. “For an ordinary microscope, the signal would be only a millionth of the input power, which is hardly measurable. Because of the resonator, the signal gets enhanced by a factor of 50000.”

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