Light Duality

That’s one small step for man, one giant leap for mankind.

〜 Neil Armstrong

Recently, scientists at EPFL (École polytechnique fédérale de Lausanne – a research institute/university in Lausanne, Switzerland) have succeeded in capturing the first ever photograph of light as both a particle and wave, simultaneously. As you all know light behaves both as a particle and as a wave but since the days of Einstein, scientists have been trying to directly observe both of these aspects of light at the same time, which we accomplished recently and being able to image and control quantum phenomena at the nano meter scale like this also opens up a new route towards quantum computing. Now that’s what I call “One supercalifragilisticexpialidocious giant, humongous leap for mankind!”.

This picture shows the dual nature of light.

HISTORY OF LIGHT (WAVE-PARTICLE DUALITY)

For centuries, physicist all over the word were having a heated debate regarding the nature of light, and for many years there were two opinion groups among them. Supporters of the first group believed that light was a transverse electromagnetic wave which can travel through vacuum. While members of the other group believed that the electromagnetic radiation had a particle nature. However, quantum mechanics showed that neither of them were right and the answer to this question is much more stranger and complicated than any thinkers could have imagined – it has a dual nature. It had both wave and particle nature. To prove this there were series of experiments conducted where one of them was Young’s double Split experiment (proving the wave nature of light) and Einstein’s Photoelectric Effect.

Yong’s Double Split Experiment – This experiment was used to prove that light exhibits properties that only waves consist, diffraction and constructive and destructive interference.

Einstein’s Photoelectric Effect – The photoelectric effect refers to the emission of electrons (photoelectrons) from the surface of a metal in response to incident light. Imagine light as a stream of particles, increase in intensity of radiation increases number of photons in an electromagnetic wave so higher intensity, more number of photons to be absorbed so by absorbing photons electrons gain energy and are released from a shell of the atom.

The recent experiment is set up like this: A pulse of laser light is fired at a tiny metallic nanowire. The laser adds energy to the charged particles in the nanowire, causing them to vibrate. Light travels along this tiny wire in two possible directions, like cars on a highway. When waves traveling in opposite directions meet each other they form a new wave that looks like it is standing in place. Here, this standing wave becomes the source of light for the experiment, radiating around the nanowire. Then the scientists shoot a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons interacted with the confined light on the nanowire, they either sped up or slowed down. Using the ultrafast microscope to image the position where this change in speed occurred, physicist could now visualize the standing wave, which acts as a fingerprint of the wave-nature of light.