Task one. Get ready to translate first three passages and to give a summary of the text. Super-accurate atomic clock sets time travel record

27 April 2012 by Jacob Aron

Setting the time on a clock is easy – unless it's one of the most accurate in the world. Now a light signal sent between two German cities has set a new record for the transmission of an atomic clock's tick. The feat, involving an optical fibre more than 900 kilometres long, could pave the way for a global network of synchronised, ultra-accurate clocks capable of testing fundamental physics.

Atomic clocks use precisely tuned electromagnetic waves to track the incredibly regular vibrations of atoms. Older atomic clocks tracked atoms that vibrate at microwave frequencies, while the latest generation use even faster optical frequencies. But while microwave clocks can be synchronised using satellite transmissions, these signals are too noisy for the more precise optical clocks.

Instead, Katharina Predehl of the Max Planck Institute of Quantum Optics in Garching, Germany, and colleagues sent laser signals from an optical clock at Germany's national metrology institute (PTB) in Braunschweig through 920 km of optical fibre to their receiver at the Max Planck Institute, about 600 kilometres away.

The uncertainty in the frequency of the signal that arrived was just 4 x 10 ^-19 seconds, around 1000 times more accurate than signals transmitted by satellite methods. This means it should be possible to synchronise two distant optical clocks.

The distance is enough to beat the team's previous record – an optical fibre 146km long, stretching over a distance of 70 km.

Predehl suggests creating a network of optical clocks spread across the world. "That's the dream," she says, adding that talks are now underway for a European clock network.

Such a network is unlikely to impact everyday timekeeping, but accurate clocks are essential for measuring potential changes in fundamental physical constants or testing general relativity. Though Einstein's theory of gravity is the accepted one, it might break down if measured with greater accuracy.

TASK TWO. Discuss the given abstract.

Lightning directed by laser beams. The idea of using a powerful laser to create a low-resistance path through the atmosphere - a virtual lightning rod - gained momentum in the 1990s. Lasers were developed that could generate terawatts (trillions of watts) of power for femtoseconds (millionths of billionths of a second). These created pulses so intense that they ripped electrons from air molecules, forming channels of ionised air along the beam path. These paths focused the laser light in high intensity zones called filaments, which kept the air ionised long after the laser passed through, but failed to trigger or direct lightning.

In 2008, a group led by André Mysyrowicz of the applied optics laboratory at ENSTA ParisTech in France took a trailer-sized laser to New Mexico for field experiments with clouds. The group found that its laser filaments increased electrical activity in storm clouds, but did not trigger lightning. group is planning more field experiments with the laser. Kasparian thinks success will require a more powerful laser, and the development of pulses shaped precisely for guiding lightning through the air.