Quantum optics physicists have, for the first time, generated 'white' light pulses which pave the way for unprecedented control of the motion of electrons.
Teams from the Max Planck Institute of Quantum Optics, pictured, and LMU Munich are able to control the pulses' field on a time scale shorter than an optical oscillation. Monitoring the enormous speeds of electrons requires ultra short flashes of light, however, in order to control them, the structure of these light pulses needs to be tamed as well. The researchers have now achieved this type of control over light for the first time. By taking advantage of the fact that light possesses both particle like and wave like properties, the teams sculpted fine features into the waveform of the pulses of white light. They were also able to make their pulses shorter than a complete light oscillation, thereby creating isolated sub optical cycle flashes of light for the first time. According to the researchers, the tools enable the precise control of electron motion and the understanding of atomic processes, permitting more precise timing of electronic processes in molecules and atoms. The motion of electrons occurs on an attosecond time scale, where one attosecond is a billionth of a billionth of a second. On such a short scale only light is able to keep up with the motion. Because of the fast oscillations of its own electromagnetic field, light can act on electrons like a pair of tweezers, influencing motions and interactions. The time it takes light generated by modern laser sources to complete one full oscillation amounts to around 2.6femtoseconds, where one femtosecond is 1000 attoseconds, or one millionth of a billionth of a second. Although light is a promising tool for controlling electron dynamics, its electromagnetic field must be precisely and completely controllable on a time scale which is shorter than one complete oscillation cycle. The researchers claim to have taken a major step towards this goal, managing to sculpt the waveforms of laser pulses with subcycle precision. In order to control light pulses on a subcycle time scale, it is necessary to use white laser light, as it contains wavelengths (light colours) ranging from the near ultraviolet through the visible all the way to the near infrared region of the electromagnetic spectrum. The physicists have created these light pulses and sent them into a newly developed 'light field synthesiser' which superimposes optical waves of different colours and phases to create various field shapes. The apparatus first splits the incident white laser light into red, yellow and blue colour channels. After manipulating the properties of the individual colours, these are recombined to form the synthesised wave form. Using this technology, the scientists were able to generate completely new isolated waveforms and, in doing so, they managed to compose the shortest pulses ever measured in the visible spectral range, lasting only 2.1femtoseconds. These pulses are more intense than those commonly afforded by current femtosecond light sources, because all the energy of the electromagnetic field is confined within a tiny temporal window. It is these electromagnetic forces which are necessary to control electrons in atoms and molecules, as they are similar in strength to the forces encountered in such microscopic systems. According to the team, the new technology paves the way for light based electronics.