Indian scientists solve a century old light puzzle

    Image source Thehindu

    Indian scientists once again proved their worth in the field of science. Indian scientists have proved to the world that they are rich in technology with the success of Mars Orbiter Mission. Two Indian scientists have cracked the light puzzle that remained unsolved since centuries.

    This started early 20th century since the scientists Max Abraham and Hermann Minkowski came up with contradicting equations that both seemed to be supported by contradicting experimental data, the controversy has extended without a solution as equipment failed to be sensitive enough to detect the light induced tiny deformations at the interface between water and air. Does the momentum of light increase or decrease when it passes through a material/medium? This question, which formed the crux of a debate between these two German physicists.

    Using an experimental set-up researchers from the Indian Institute of Science Education and Research (IISER), Mohali. Dr. Kamal Singh of IISER Mohali and his PhD student Gopal Verma used an indigenous experimental set-up to calculate the bulge in the water particle due to the collision of photon beam. Both of them have achieved a breakthrough that shows that Minkowski was right and proved that the light gains momentum as it enters another medium.

    The simple setup involved a shining laser on a water drop to study the chain of events. The Helium-Neon laser was incident at the Total Internal Reflection (TIR) it’s a critical angle where all the light is reflected like a mirror. The probe laser produces high-contrast Newton’s ring, the concentric circles of light and dark on the water drop. The modulation of these fringes allowed the scientists to observe bulges on surface of heights lesser than 5 nanometer precision. On conducting the experiment at different angles that are close to Total Internal reflection the water surface was found to be bent upwards due to the pressure exerted by the photon beam and spread to 100 times beyond the area of the pumped laser. The analysis shows that the light particles actually gained momentum.

    Kamal P. Singh, an IISER scientist who co-authored the paper with his colleague Gopal Verma says that their experiment validates the century old Minkowski theory near Total Internal reflection. This is very sensitive technique and has wide applications .It can be used to precisely measure properties of light non-invasively. Apart from solving a century-old problem light puzzle, the equipment designed can aide in developing better biosensors, lab-on-chip devices, easily reconfigurable lenses and molecular imaging tools.

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