1/2016

No gravitational waves exactly, but the speed of light nonetheless

The discovery of gravitational waves was one of the major science news of this century, measured with the super-precise LIGO measurement equipment in the US. An interferometer operating with the same principle is also used for measurements in the student laboratory for TUT’s Department of Physics.

Professor Martti Kauranen

 

Optics and photonics is a field that makes contributions everywhere, says Professor Kauranen.

 

Professor Martti Kauranen presents the Michelson interferometer in the Department of Physics student laboratory at TUT. The device on the table is less than a meter in length. Once plugged in, a red laser beam branches off into two separate beams and forms a circular shape on a white background when reflected by mirrors.

“This is a very basic model, the cost of these components is only a few hundred euros. Our students use this device to learn how to determine the refraction index of air and glass. In other words, to measure the speed of light in various media,” Kauranen explains.

Similar interferometers have been used around the world since the late 1800s. The TUT student laboratory has been equipped with one for a long time. Kauranen recalls making similar tests during his study years.

“These are among the very basic measurements in physics studies.”

Incredible precision

The LIGO interferometer used for gravitational wave measurement in the United States is basically a billion-dollar state-of-the-art version of the same device.

In the student model, the length of the fork, i.e., the distance travelled by the laser beam, is ten centimetres each way. With LIGO, the laser beam travels four kilometres back and forth in a long vacuum tube.

“LIGO is the most precise measurement device ever built. Its precision is incredible really: within the travel of four kilometres, they are measuring distances in the scale of thousandths of the size of a proton. To achieve such a precision level, the laser beams must travel in a vacuum and the device must also be protected from other types of perturbations, Kauranen relates.

There are two LIGO devices in the United States, 3,000 kilometres apart, in the states of Louisiana and Washington. There is also one in Italy and one is being planned in India.

“Measurements this precise are highly sensitive to external perturbations. If several measurement devices detect the same phenomenon, however, it is possible to minimize the uncertainty related to the results and induced by the environment. Having several measurement devices also enables a more accurate analysis of the entrance direction of gravitational waves.”

Contributions everywhere

The detection of gravitational waves also aroused a lot of interest at the Department of Physics.

“We received an advance notice of the discovery and we gathered in a meeting room to watch live broadcast from the announcement event. This is certainly a Nobel-worthy discovery for someone,” Kauranen speculates.

Optics and photonics have recently hoarded several Nobel prizes – and no wonder. Their applications include space exploration and medicine, to name but a few, and also cover several everyday applications, such as led lights.

“This is a field that makes contributions everywhere,” Kauranen concludes.

Text and photo: Sanna Schildt

 
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