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.”