Obtained the generation and measurement of an isolated X-ray attosecond pulse
JPA/DICYT The Research Group in Extreme Optics of the University of Salamanca works with scientists of Universities of Colorado in Boulder and Delaware in the United States, and Tsing Hua in Taiwan, with the objective of studying the generation of X-rays by laser. The renowned scientific magazine Proceedings of the National Academy of Sciences of the United States of America (PNAS) has just published a new work of this team of scientists whose novelty is that they have been able to generate and measure an isolated X-ray attosecond pulse. This advance has consequences in the development of nanotechnology because it supposes a step ahead in the control of extremely fast processes which involve high levels of energy.
“Nowadays, the development of technology is based on the control of smaller processes which already exist in nature, for example, the ones which occur in scales smaller than the thousandth of a millimeter have opened the way to nanotechnology”, explains to DiCYT Luis Plaja, scientist of the University of Salamanca, and Carlos Hernández García, researcher of the same institution, who, at present, has a post-doctoral contract with JILA (Join Institute for Laboratory Astrophysics) of University of Colorado thanks to the European scholarship Marie Curie. In conclusion, according to experts, knowing nature in its nanotechnological or even smaller scale is one of the keys for the development of XXI century technology.
Curiously, in nature “the smallest phenomena are also the ones which happen faster”. Thus, the processes in nanotechnology and in smaller scales are used to be extremely fast and its control consists in not only elaborating manufacture techniques to this scale, but also in dominating them in time.
The conventional electronics is extremely slow to measure and interact with nature in nanoscopic scale, and only light offers a sufficiently fast tool. “Nowadays, with the development of intense lasers, we have controlled visible and infrared light, which offers us the possibility of observing and modifying extra fast processes like chemical reactions or molecule dynamics, all of them between a hundred and a thousand times faster than the fastest electronics”, the experts guarantee.
Nevertheless, there is a lot to do to develop the same skills for the ultraviolet light or the X-rays, which could be used to observe and master processes until one million times faster than the extra fast electronics. According to scientists, the control of the ultraviolet light or the X-rays will open doors to the universe of atomic processes, that is, the ones which happen inside the atoms. They are time scales that can be measured in trillionth of seconds, attoseconds, and which name this knowledge challenge that the scientists have called Attoscience.
Laser to accelerate particles
The dramatic development of intense extra fast laser technology during the last 20 years made it possible that, in 2001, the first laser pulses with about some hundreds of attoseconds were measured. It was the birth of Attoscience. In this process, a laser with great power is used to fragment gas atoms in a controlled way, so that the extracted electrons are carried by the intense field again towards the rest of the atoms (the ions) at the same time in which they are accelerated.
“This way, each atom becomes a tiny collider particle, a one millionth of millimeter nanoaccelerator, of which, as a result of the collision, photons of high energy surface, from empty ultraviolet until X-rays”, Carlos Hernández and Luis Plaja relate. Though, what makes these nanocolliders really exceptional is not their size, but the fact that they all work in a synchronized way. The perfect metaphor is a great orchestra following the baton of high power laser swings. “The emitted radiation is formed by organized electromagnetic field swings, what is called a coherent radiation, which, in addition, is emitted in the form of attosecond pulses”, they add.
An isolated pulse and of great energy
Since the early beginning of Attoscience, huge scientific efforts have been made in order to improve the radiation sources of attosecond pulses in two directions. In the first place, the generation of a single isolated pulse with duration of about a few attoseconds, since they are used to be produced in the form of bursts of which it is difficult to extract only one. The production of a single pulse seems to be very complicated, since it requires an extremely fine control of generation processes.
In the second place, they have tried to increase the energy of the attosecond pulses in order to obtain X-ray pulses. The X-rays allow the climb of visible light applications to physical systems with dimensions one thousand times smaller, with which the scientists hope to multiply the storage capacity, measurement precision and other variables which have already been considered revolutionary with visible light. In addition to other X-ray properties, like their penetration in opaque materials for visible light, they offer new perspectives for the last property’s conventional applications.
For all of these reasons, the work which is being published at PNAS is a meaningful advance considering what was published two years ago in the magazine Science, in which the same groups of the University of Colorado and the University of Salamanca, among others, have demonstrated the generation of coherent X-rays by laser. In this way, the same route is also capable of generating isolated attosecond pulses, combining the two most wanted properties in attosecond pulses: being isolated and having high energy.
A theoretical and experimental work
In this research, the Research Group in Extreme Optics of the University of Salamanca has contributed with the theoretical simulations which reproduce and explain the underlying physics to this experiment. The scientists have used simulation codes of generation and propagation of attosecond pulses which they have developed in the last years, and they have extended them to the limit to reproduce the extreme conditions present in this experiment. In order to do it, they have had to use the supercomputer Janus of University of Colorado, which makes its calculations in parallel with more than a thousand processors at the same time. “This kind of calculations would take, at least, half a year in a single computer, while in this supercomputer, it takes about four hours”, Luis Plaja and Carlos Hernández García comment.
In their opinion, this work demonstrates, once again, the importance of the synergy between an experimental and a theoretical group. “The theoretical calculations not only help validate the experimental results, but also are, frequently, the only way to know details about the attosecond pulses obtained in the lab, which are beyond the possibilities of measurement instruments available”, they emphasize. With these calculations, they also have the easiness to change parameters and geometries and explore "virtual" experiments that show up to what point the efforts in the lab should go.
Generation of bright isolated attosecond soft X-ray pulses driven by multicycle midinfrared lasers. Ming-Chang Chen, Christopher Mancuso, Carlos Hernández-García, Franklin Dollar, Ben Galloway, Dimitar Popmintchev, Pei-Chi Huang, Barry Walker, Luis Plaja, Agnieszka A. Jaroń-Becker, Andreas Becker, Margaret M. Murnane, Henry C. Kapteyn, and Tenio Popmintchev. PNAS, 2014. DOI: 10.1073/pnas.1407421111