Speed camera: Prof. Subal Kar in his lab

How about a camera that can capture events lasting for a millionth of a trillionth of a second? If you think nothing happens that fast, you’re mistaken. Chemical reactions ? atoms of different elements coming together to form all sorts of molecules ? which are the basis of most of the changes taking place around us, occur at that speed. So a machine working as fast is a useful tool for scientists.

Such a machine is being built by an international team of researche-rs at the Lawrence Berkeley National Laboratory (LBNL) of the University of California, Berkeley. Known as Laser-based Ultra-fast X-ray Source (LUX), it will generate extremely bright and ultra-small pulses of x-rays that will probe atomic motions in chemical reactions, or in nuclear fusions that fuel stars like our sun.

Dr Subal Kar, professor, department of radio physics and electronics, Calcutta University, is collaborating with Dr John N. Corlett, head, Centre for Beam Physics, Accelerator and Fusion Research Division at LBNL, to build LUX. Experts from the KEK High-Energy Accelerator, Japan, Joseph Henry Laboratory, Princeton University, and Stanford University, US, are also involved in the project.

It has been a technical challenge. “The smaller the objects you’ve to see, the shorter the wavelength of light you need to focus on it,” explains Kar. “Ordinary light’s wavelength is far too large to make a molecule or an atom visible.” This is why x-rays have been chosen for building LUX. “Their wavelengths are of the order of, or smaller than, the size of atoms,” says Kar.

“At the LBNL, LUX could peer into the domain of atoms and molecules by producing extremely short-lived pulses of x-rays,” says Kar. Such pulses last for a millionth of a trillionth of a second, or an attosecond. Each pulse is 1,80,000 times thinner than a human hair.

For LUX to work, beams of electrons are accelerated very close to the speed of light inside a superconducting linear accelerator (linac). Inside the linac, a specially designed cavity, called RF (radio frequency) cavity, gives a kick to the fast-moving bunch of electrons, increasing their energy manifold.

“While surfing through the linac, the energy of the electrons is further enhanced by a set of microwave amplifiers via the RF cavity,” Kar explains. “The microwave boosts the electrons’ energy by amplifying the signals (like those that transmit data for television or telephone ? with wavelengths ranging from 1 millimetre to 30 centimetres). The laser light comes from a source known as master laser.”

Kar and his colleagues have designed and tested the prototypes of the microwave amplifier and microwave generator at the Radio Physics and Electronics lab of the Calcutta University.

After emerging from the tunnel of the linac, energetic electrons enter undulators, or specially designed vacuum chambers fitted with magnets. There the electrons are exposed to high-frequency, short pulses of laser coming from the master laser as well as the magnetic field generated by the undulators.

This exposure makes the electrons emit ultra-fast and ultra-short pulses of x-rays. These rays reach end stations, which are designed to produce ultra-small (180 times thinner than a human hair) pulses of laser and carry out various biological and physical experiments.

During such experiments, a pulse of laser lasting for a thousandth of a trillionth of a second excites nano-sized particles (two large atoms across) under study, while the x-ray pulse probes the particles, recording events that last for attoseconds.

According to Kar, by 2008, the new machine (about 10 kilometres long) will be ready to catch a glimpse of specific chemical reactions. “It will unveil the secrets of many ultra-fast and ultra-small events, for example, those behind driving sophisticated computers or triggering the flow of brain chemicals between nerve cells, evoking consciousness,” he adds.

LUX may yield a better understanding of photosynthesis, an extremely fast chemical reaction. This may have implications for future energy planning and agriculture, because photosynthesis allows plants subsist and grow. “This machine may even explore the conditions that prevail in a planet like Jupiter without going there,” Kar points out.