Nanoneedle probes magnetic field of light
A team of AMOLF scientists, together with LioniX BV, has developed a sensor that can make the magnetic field of light visible. The magnetic field itself is very difficult to detect because it has almost no interaction with matter. The sensor that has now been developed first converts the magnetic field into an electrical oscillation, which in turn generates light which can subsequently be measured with a photodiode. This breakthrough is of great importance for the research into new nanostructures with which so called invisibility cloaks can be made. Placing the cloak, that is invisible itself, over an object makes the object invisible as well. Research into this revolves around the manipulation of the optical magnetic field. Carefully mapping out these fields is therefore crucial. The research results will soon be published in the renowned journal Science and is available online from October 1st on 'ScienceExpress'.
The magnetic field often serves as an example to explain forces and fields. In a popular experiment a bar-magnet is placed on a table and a compass is moved around the table. Depending on where the compass is with regard to the magnet, the compass needle points into a certain direction. This way, we can visualize the magnetic field in each place. This experiment is easy and instructive, because the force of the permanent magnet is so strong. This image changes completely when we look at magnetic fields oscillating at high frequencies.
Light is an electromagnetic wave, in which an electrical field and a magnetic field vibrate at an immensely high frequency (approximately 300 billion per second). At this high frequency we only notice the electrical field; the magnetic field has a completely negligible interaction with natural materials. When we see light we ‘see’ the electrical field; we are blind to the magnetic field. When there is no interaction between matter and magnetic fields with such high frequencies, it seems impossible to study the magnetic field of light.
The sensor that the AMOLF team developed together with LioniX BV, is based on the principle that the German physicist Heinrich Hertz first demonstrated more than 120 years ago. When a metal ring is placed in a variable magnetic field, a variable current will travel through the metal ring. As a side note, an everyday transformer is based on this same principle of magnetic induction. By putting a small slit of interruption in the ring, causing the current to not completely revolve around the ring, Hertz was able to observe the presence of the variable magnetic field in radio waves as tiny sparks that jumped over the slit. The sensor that has been developed in Amsterdam works in exactly the same way, but because the wavelength of light is so much smaller than that of radiowaves, the sensor is also much smaller (1000 times thinner than a human hair). The AMOLF researchers now have a compass needle that can be used to study the magnetic field of light with a resolution that is better than that of the wavelength of the light.
Reference
Probing the magnetic field of light at Optical Frequencies, M. Burresi, D. van Oosten, T. Kampfrath, H. Schoenmaker, R. Heideman, A. Leinse en L. Kuipers.
http://www.sciencemag.org/cgi/content/abstract/1177096
Information
For more information, please contact:
Prof.dr. Kobus Kuipers, telefoon (020) 754 71 94.
Melissa van der Sande, telefoon (020) 754 72 34.