LMU/MPQ-scientists can image the optical properties of individual nanoparticles with a novel microscope.
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.”
In the microscope, built by Dr. David Hunger and his team, one side of the resonator is made of a plane mirror that serves at the same time as a carrier for the nanoparticles under investigation. The counterpart is a strongly curved mirror on the end facet of an optical fibre. Laser light is coupled into the resonator through this fibre. The plane mirror is moved point by point with respect to the fibre in order to bring the particle step by step into its focus. At the same time, the distance between both mirrors is adjusted such that the condition for the appearance of resonance modes is fulfilled. This requires an accuracy in the range of picometers.
For their first measurements, the scientists used gold spheres with a diameter of 40 nanometers. “The gold particles serve as our reference system, as we can calculate their properties precisely and therefore check the validity of our measurements” says David Hunger. “Since we know the optical properties of our measurement apparatus very accurately, we can determine the optical properties of the particles from the transmission signal quantitatively and compare it to the calculation”. In contrast to other methods relying on direct signal enhancement, the light field is limited to a very small area, such that by using only the fundamental mode, a spatial resolution of 2 micron is achieved. By combining higher order modes, the scientists could even increase the resolution to around 800 nanometers.
The method becomes even more powerful when both absorptive and dispersive properties of a single particle were determined at the same time. This is interesting especially if the particles are not spherical but e.g. elongated. Then, the corresponding quantities depend on the orientation of the polarization of light with respect to the symmetry axes of the particle. “In our experiment we use gold nanorods (34x25x25 nm to the 3) and we observe how the resonance frequency shifts depending on the orientation of the polarization. If the polarization is oriented parallel to the axes of the rod, the shift of the resonance is larger than if the polarization is oriented orthogonally, resulting in two different resonance frequencies for both orthogonal polarizations” explains Matthias Mader, PhD student at the experiment. “This birefringence can be measured very precisely and is a very sensitive indicator for the shape and orientation of the particle.”
“As an application of our method, we could think of e.g. investigating the temporal dynamics of macro molecules, such as the folding dynamics of proteins” says David Hunger. “Overall we see a large potential for our method: from the characterization of nanomaterials and biological nanosystems to spectroscopy of quantum emitters.” [OM/DH]
Matthias Mader, Jakob Reichel, Theodor W. Hänsch, and David Hunger
A Scanning Cavity Microscope
Nature Communications, DOI: 10.1038/ncomms8249, 24 June 2015
Dr. David Hunger
Max Planck Institute of Quantum Optics,
Schellingstr. 4 /III, 80799 Munich, Germany
Phone: +49 (0)89 / 21 80 -3937
Prof. Dr. Theodor W. Hänsch
Professor of Experimental Physics
Direktor at the Max Planck Institute of Quantum Optics
85748 Garching, Germany
Phone: +49 (0)89 / 32 905 -712
Dr. Olivia Meyer-Streng
Press & Public Relations
Max Planck Institute of Quantum Optics, Garching, Germany
Phone: +49 (0)89 / 32 905 -213
Dr. Olivia Meyer-Streng | Max-Planck-Institut für Quantenoptik
NASA laser communications to provide Orion faster connections
30.03.2017 | NASA/Goddard Space Flight Center
Pinball at the atomic level
30.03.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
30.03.2017 | Health and Medicine
30.03.2017 | Health and Medicine
30.03.2017 | Medical Engineering