Quartz glass Used to Compress Space Laser Beams
Meta description: Russian scientists have developed a method of focusing laser beams through quartz glass. Read on to find out more.
Laser pulse filamentation is a process where a laser beam focuses into a high-intensity beam, or filament, of pulses that may be just tenths of a centimetre in width.
Once generated, these beams can be controlled so that they occur at distances of many kilometres from their source. The laser beams are also highly sensitive and are used in remote sensing, such as the search for atmospheric pollutants and trace elements. This is a field that scientists call non-linear optics.
Ordinary light propagates through any medium in a straight line until that medium changes. This occurs at the boundaries of solids, liquids and gases as well as during the change in density of any single medium. Light beams are reflected, refracted or diffracted as the medium changes. In physics, this is called linear optics.
However, a strong beam of light such as a laser beam behaves in a different way. Rather than reflecting, refracting and dispersing, it gathers into pulses of narrow strands called filaments. These are called non-linear effects and can be affected by conditions in the prevailing atmosphere, the intensity of the beam and numerous other factors.
The generation of such non-linear effects requires an electrical power input in the gigawatt range. It needs 20 gigawatts to produce a laser pulse of 2.2 millijoules energy that is compressed into about 100 femtoseconds. One femtosecond is equivalent to one millionth of one billionth – a quadrillionth – of one second. Once such a beam is focused within a diameter of about three millimetres, it has a light intensity that is about ten times that of the light emitted close to the surface of the Sun.
Scientists from the Lebedev Institute in Moscow discovered a method of focusing a laser beam into a filament by using a spherical mirror and passing the beam through a quartz glass plate. The beam is later directed between a pair of ring electrodes at 300 volts. This starts a process where the laser ionizes surrounding air, creates current between the electrodes and creates plasma clusters of light that form the filament.
By changing the thickness and position of the quartz glass, the scientists discovered that they could alter the length of the plasma channel and the point at which it arises.
The ability to concentrate laser beams into ultra-fine filaments of choice opens up more applications, ranging from medical applications to diamond etching.
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