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Knowledge on All Scales

Optics are central to a number of fields, including telecommunications, astronomy, the life sciences, or fundamental physics. Following a key meeting in Lille last July between academia and industry, we take a closer look at this branch of physics whose many applications are as diverse as they are unexpected.

A scientific and technical field that deals with physical phenomena and technologies connected with the emission, propagation, manipulation, detection, and use of light.” This official definition of optics conceals a host of applications that the general public can scarcely imagine. But in one field at least–telecommunications–optics has brought about a highly noticeable revolution. “Internet wouldn't be what it is today without the progress that's been made in the field of optical fibers and lasers that carry millions of messages in the form of beams of light,” points out Christian Chardonnet, deputy scientific director at CNRS' Institute of Physics in Paris. “A revolution in which our researchers have played a significant part.”

toroidal mirror

© E. Perrin/INSU/LAM/CNRS Photothèque

A scientist controls the polishing of a toroidal mirror that will equip the Very Large Telescope in Chile.

Optics not only helps transmit data, it also makes it readable, as shown by the laser scanners we use every day. They let us read information stored in increasingly compact form on media like CDs and DVDs. But what will be the next revolution? It will probably deal with the manipulation of photons, which, amazingly, can now be produced and detected individually. This could pave the way for emerging applications like quantum cryptography, which would make data exchanged on the internet impossible to hack. And it could even lead to the holy grail: a quantum computer, with hugely increased computing power.
Whether pointing to the Earth or to the stars, optics is providing high-performance observation tools. Teams at CNRS are developing pulsed lasers called lidars, which are used to study the composition of the Earth's atmosphere. Astronomy is also benefiting from the progress being made in adaptive optics. “Developed by astronomers, this method makes it possible to correct the distortion that starlight undergoes when it passes through the layers of the atmosphere,” Chardonnet explains. “In practice, the surface of the telescope is modified in real time so that it compensates exactly for the distortion, and optimizes the quality of the images. This is the case for the Very Large Telescope in Chile, which our scientists are working on.” This technique has subsequently been introduced in biology for so-called “biophotonics” applications, to eliminate the disturbance caused by biological fluid during tissue observation.
In medicine also, optics has become an essential tool, used in laser eye surgery, endoscopy, or imaging, to mention just a few. “The development of ultra-intense lasers should make it possible to generate laser-accelerated protons for proton therapy, a technique that targets cancer tumors far more effectively than radiotherapy,” adds Chardonnet.
Such ultra-intense lasers are also of great importance to study the quantum vacuum in fundamental physics. In the European ELI project, for example, researchers plan to build a laser that will deliver a pulse of around 200 petawatts1 for a duration of approximately 10-15 seconds.”Yet at these levels of power, there are still many technological obstacles that we need to overcome,” warns Chardonnet.
Far more compact lasers, with a power of a few milliwatts, can be used to cool down atoms which, in turn, stabilize other lasers: The entire set-up constitutes an atomic clock that is 1000 times more accurate than those used in the well-known GPS system. But lasers have many other applications, in telemetry, navigational aids, the control of chemical reactions, and even the cleaning of historical monuments. “Optics is a discipline that spills over into every field, and it's also an area in which France is a front runner, thanks to its optics research clusters2 and to the excellence of CNRS laboratories,” Chardonnet concludes.

Jean-Philippe Braly

Notes :

1. 1 petawatt = 1015 watts.
2. Opticsvalley, Popsud, Alpha, and Route des lasers.

Contacts :

Christian Chardonnet,
INP, Paris.


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