For decades there has been interest in phonon lasers that emit quanta of vibrational energy - so called phonons - instead of light.
In solids, because of the short wavelength, the implementation of such a device would make it possible to achieve unprecedented resolution in imaging techniques like tomography. The experiment carried out at MPQ is still quite a bit away from these kinds of applications.
However, scientists of the Laser Spectroscopy Division of Prof. Theodor W. Hänsch in cooperation with Prof. Kerry Vahala of the California Institute of Technology (Pasadena, USA), at present guest scientist at MPQ, were able to demonstrate for the first time the effect of coherent phonon generation with a single magnesium ion cooled to a temperature of around 1 milli-Kelvin in an electromagnetic trap. Stimulus to this process is blue-detuned laser radiation.
As the scientists report in Nature Physics (Advance Online Publication 16 August 09, DOI: 10.1038/ NPHYS1367) this device represents a mechanical analogue to an optical laser that allows to investigate the fundamental dynamics of a phonon laser. The device in its present form could possibly be used as a sensor for extremely weak forces. The extension of the system to an ion chain or a two-dimensional ion array could perhaps make the breakthrough to possible applications.
The experiment starts with the preparation of a single magnesium ion in an electromagnetic so-called 'Paul-trap' that gets cooled down to temperatures of around one milli-Kelvin by laser cooling. This widely used technique exploits the fact that an ion irradiated with red-detuned (with respect to a suitable spectral line) laser light gets excited only when travelling towards the laser beam thus losing more and more kinetic energy. This setup represents a mechanical oscillator with adjustable quality factor, analogue to an optical laser resonator whose quality factor is given by the reflectivity of its mirrors.
Now a second laser comes into action, this time blue-detuned. Its purpose is to feed energy into the system, just like the energy source of an optical laser system. While in a series of experiments the intensity of the blue-detuned radiation is ramped up the centre-of-mass motion of the ion gets amplified. At a certain intensity, the threshold, a transition from thermal irregular motion to harmonic oscillations is observed, just like in an optical laser. But the analogy carries even further: The harmonic oscillation is initiated by a spontaneously emitted phonon and sustained by stimulated generation of phonons. Like in its optical counterpart, the oscillation of the ion is stabilized by amplification saturation. As is shown in the figure below, this behavior has in fact been observed and compared with theory by taking a series of time averaged pictures of the single oscillating ion. "An important step in the realization of this kind of phonon laser was the insight that blue-detuned laser light does not merely heat an ion as it is widely believed, but instead, by appropriate choice of frequency and intensity, can stimulate coherent amplification of its motion", Dr. Maximilian Herrmann of the Laser Spectroscopy Division explains.
Current research is directed towards controlling the phonon laser using tools and techniques that can be adapted from the laser world. One example is a technique called injection locking whereby a weak, external control field is used to phase-synchronize the phonon laser with an external reference. This method was used to generate a time resolved image of the coherent motion of the ion as it oscillates.
When implemented in a solid, a phonon laser could enable applications such as high-resolution tomography. This task has yet been hampered by the large number of atoms in bulk solids. Therefore people are interested in one- or two-dimensional structures. "Our single-ion zero-dimensional system anticipates the endpoint of this development", Herrmann says. "It is ideally suited to investigate the transition to a one-dimensional system by adding further ions in a controlled way." Besides these fundamental aspects the scientists also consider to use the oscillating ion as a probe for extremely weak external forces, but "that's all still up in the air", Herrmann concedes. [Maximilian Herrmann/Olivia Meyer-Streng]Original publication:
Dr. Olivia Meyer-Streng | Max-Planck-Institut
Researchers discover link between magnetic field strength and temperature
21.08.2018 | American Institute of Physics
Smallest transistor worldwide switches current with a single atom in solid electrolyte
17.08.2018 | Karlsruher Institut für Technologie (KIT)
There are currently great hopes for solid-state batteries. They contain no liquid parts that could leak or catch fire. For this reason, they do not require cooling and are considered to be much safer, more reliable, and longer lasting than traditional lithium-ion batteries. Jülich scientists have now introduced a new concept that allows currents up to ten times greater during charging and discharging than previously described in the literature. The improvement was achieved by a “clever” choice of materials with a focus on consistently good compatibility. All components were made from phosphate compounds, which are well matched both chemically and mechanically.
The low current is considered one of the biggest hurdles in the development of solid-state batteries. It is the reason why the batteries take a relatively long...
New design tool automatically creates nanostructure 3D-print templates for user-given colors
Scientists present work at prestigious SIGGRAPH conference
Most of the objects we see are colored by pigments, but using pigments has disadvantages: such colors can fade, industrial pigments are often toxic, and...
Scientists at the University of California, Los Angeles present new research on a curious cosmic phenomenon known as "whistlers" -- very low frequency packets...
Scientists develop first tool to use machine learning methods to compute flow around interactively designable 3D objects. Tool will be presented at this year’s prestigious SIGGRAPH conference.
When engineers or designers want to test the aerodynamic properties of the newly designed shape of a car, airplane, or other object, they would normally model...
Researchers from TU Graz and their industry partners have unveiled a world first: the prototype of a robot-controlled, high-speed combined charging system (CCS) for electric vehicles that enables series charging of cars in various parking positions.
Global demand for electric vehicles is forecast to rise sharply: by 2025, the number of new vehicle registrations is expected to reach 25 million per year....
17.08.2018 | Event News
08.08.2018 | Event News
27.07.2018 | Event News
21.08.2018 | Power and Electrical Engineering
21.08.2018 | Life Sciences
21.08.2018 | Medical Engineering