Munich Physicists have developed a
novel electron microscope that can visualize electromagnetic fields oscillating
at frequencies of billions of cycles per second.
Temporally varying electromagnetic
fields are the driving force behind the whole of electronics. Their polarities
can change at mind-bogglingly fast rates, and it is difficult to capture them
in action. However, a better understanding of the dynamics of field variation
in electronic components, such as transistors, is indispensable for future
advances in electronics. Researchers in the Laboratory for Attosecond Physics
(LAP), jointly run by Ludwig-Maximilians-Universität (LMU) and the Max Planck
Institute of Quantum Optics (MPQ), have now taken an important step towards
this goal – by building an electron microscope that can image high-frequency
electromagnetic fields and trace their ultrafast dynamics.
The electronic devices we have become
so familiar with and use every day are – without exception – powered by
changing electromagnetic fields. These fields control the flow of electrons in
components such as 'field-effect' transistors, and are ultimately responsible
for the manipulation, flow and storage of data in our computers and
smartphones. A better understanding of electromagnetic waveforms and their
ultrafast reconfiguration in individual components will help to shape the
future of electronics. The LMU and MPQ physicists who belong to the research
group in Ultrafast Electron Imaging have now developed an electron microscope
that is specifically designed for the analysis of rapidly varying
electromagnetic fields.
This instrument makes use of ultrashort
pulses of laser light, each of which lasts for a few femtoseconds (a
femtosecond equals one millionth of a billionth (10-15) of a
second). These laser pulses are used to generate bunches of electrons made up
of very few particles, which are then temporally compressed by the action of
terahertz (1012 Hz) near-infrared radiation. The Munich team first
described this strategy earlier this year in the journal Science (Science
22. April 2016, DOI: 10.1126/science.aae0003),
and demonstrated that it can generate electron
pulses that are shorter than a half-cycle of the optical field.
The researchers now show that these
ultrashort electron pulses can be used to map high-frequency electromagnetic
fields. In the experiment, the pulses are directed onto a microantenna that has
just interacted with a precisely timed burst of terahertz radiation. The light
pulse excites surface electrons in the antenna, thus creating an oscillating
optical (electromagnetic) field in the immediate vicinity (the so-called near
field) of the target. When the electron pulses come under the influence of the
induced electromagnetic field around the antenna, they are scattered, and the
pattern of their deflection is recorded. On the basis of the dispersion of the
deflected electrons, the researchers can reconstruct the spatial distribution,
temporal variation, orientation and polarization of the light emitted by the
microantenna.
"In order to visualize electromagnetic fields oscillating at optical frequencies, two important conditions must be met", explains Dr. Peter Baum, who led the team and supervised the experiments. "The duration of each electron pulse, and the time it takes to pass through through the region of interest, must both be less than a single oscillation period of the light field." The electron pulses used in the experiment propagate at speeds approximately equal to half the speed of light.
"In order to visualize electromagnetic fields oscillating at optical frequencies, two important conditions must be met", explains Dr. Peter Baum, who led the team and supervised the experiments. "The duration of each electron pulse, and the time it takes to pass through through the region of interest, must both be less than a single oscillation period of the light field." The electron pulses used in the experiment propagate at speeds approximately equal to half the speed of light.
With their novel extension of the
principle of the electron microscope, the Munich physicists have shown that it
should be feasible to precisely detect and measure even the tiniest and most
rapidly oscillating electromagnetic fields. This will allow
researchers to obtain a detailed understanding of how transistors or
optoelectronic switches operate at the microscopic level.
The new technology is also of interest
for the development and analysis of so-called metamaterials. Metamaterials are
synthetic, patterned nanostructures, whose permeability and permittivity for
electrical and magnetic fields, respectively, deviate fundamentally from those
of materials found in nature. This in turn gives rise to novel optical
phenomena which cannot be realized in conventional materials. Metamaterials
therefore open up entirely new perspectives in optics and optoelectronics, and
could provide the basic building blocks for the fabrication of components for
light-driven circuits and computers. The new approach to the characterization
of electromagnetic waveforms based on the use of attosecond physics brings us a
step closer to the electronics of the future.
emporally varying electromagnetic
fields are the driving force behind the whole of electronics. Their polarities
can change at mind-bogglingly fast rates, and it is difficult to capture them
in action. However, a better understanding of the dynamics of field variation
in electronic components, such as transistors, is indispensable for future
advances in electronics. Researchers in the Laboratory
emporally varying electromagnetic
fields are the driving force behind the whole of electronics. Their polarities
can change at mind-bogglingly fast rates, and it is difficult to capture them
in action. However, a better understanding of the dynamics of field variation
in electronic components, such as transistors, is indispensable for future
advances in electronics. Researchers in the Laboratory for Attosecond Physics
(LAP), jointly run by Ludwig-Maximilians-Universität (LMU) and the Max Planck
Institute of Quantum Optics (MPQ), have now taken an important step towards
this goal – by building an electron microscope that can image high-frequency
electromagnetic fields and trace their ultrafast dynamics.
emporally varying electromagnetic
fields are the driving force behind the whole of electronics. Their polarities
can change at mind-bogglingly fast rates, and it is difficult to capture them
in action. However, a better understanding of the dynamics of field variation
in electronic components, such as transistors, is indispensable for future
advances in electronics. Researchers in the Laboratory for Attosecond Physics
(LAP), jointly run by Ludwig-Maximilians-Universität (LMU) and the Max Planck
Institute of Quantum Optics (MPQ), have now taken an important step towards
this goal – by building an electron microscope that can image high-frequency
electromagnetic fields and trace their ultrafast dynamics.
EmoticonEmoticon