New technique to program the propagation of ultrashort laser pulses

Currently there are commercial laser devices that emit light in the form of pulses with extremely short duration. These emissions are known as ultrashort laser pulses. The duration of these light pulses is on the order of several femtoseconds. A femtosecond is one billionth of a second. To put it in context, a femtosecond is to a second what a second is to about 32 million years.

Ultra-short laser pulses also have another characteristic that makes them unique: they can reach extraordinary power (on the order of petawatts, equivalent to a thousand trillion watts) when focused. Matter exposed to light of such extraordinary power reacts in an unusual way, being able to generate extreme physical phenomena of great interest.

These two very peculiar attributes of this type of laser pulses, ultra-short duration and extraordinary powers, constitute them as a fundamental tool in science and technology. For example, these laser pulses have been used to investigate extremely fast physical and chemical phenomena such as molecular vibration and rotation, or chemical reactions. They have also been used for microfabrication of devices, as a seed to synthesize light pulses with much shorter durations (on the order of attoseconds, one thousandth of a femtosecond), and have even been applied to create X-ray radiation sources, neutrons and protons.

The current and future development of scientific and technological applications based on ultrashort laser pulses requires simultaneous control of the spatial and temporal behavior of the pulse in order to completely govern its propagation. However, this is a complex problem for which there has so far been no sufficiently satisfactory solution. The techniques available to control the pulse induce undesired effects that even frustrate their characteristic ultra-short duration, temporarily dilating them.

Researchers from the Interdisciplinary Group of Computational Optics, from the Department of Optics of the Complutense University of Madrid (UCM), have addressed this problem and have devised an innovative technique and a device that allow the propagation of ultra-short laser pulses to be controlled in a versatile and programmable way at along any spatial trajectory required by the considered application.

The new technique allows the propagation of ultra-short laser pulses to be programmed. (Image: UCM)

Enar Franco, Óscar Martínez-Matos and José A. Rodrigo show, for the first time, that it is possible to simultaneously control the spatial and temporal behavior of the laser pulse without altering its characteristic ultra-short duration. In this way, it is possible to govern both the three-dimensional trajectory that the laser pulse will follow when it propagates, as well as the speed and acceleration of its luminous intensity peak. As a result, a “light projectile” propagates along the desired trajectory with a pre-programmed speed and acceleration. Furthermore, this technique allows to independently control the properties of the pulse along the propagation path, such as its intensity and phase. Phase is another fundamental characteristic of light and its control is key in the generation of light vortices capable of moving particles or encoding information in telecommunication systems. The study authors also demonstrate how to generate structured ultrashort laser vortices, on demand, for any shape defined by any curved path.

This scientific breakthrough is an unprecedented achievement. It is the first tool that allows the propagation of ultra-short laser pulses to be controlled in a versatile and programmable way along any trajectory, as well as their intensity and phase, both in space and in time. The creators of the technique believe that the new possibilities offered by it can drive the development of a new generation of optical manipulation tools, facilitating the performance of advanced experiments that are essential to progress in the study of the physics of the interaction between light and matter. This engineering of ultra-short laser pulses can facilitate the development of laser technology applications in different sectors, from ultra-fast imaging to ultra-precise medical treatment of tissues by laser.

The experiments for this research were carried out in the laboratories of the Computational Optics Interdisciplinary Group and in the Center for Ultrafast Lasers (CLUR), both at the Complutense University of Madrid.

Enar Franco and his colleagues present the technical details of their advance in the academic journal Optica, under the title “Curve-shaped ultrashort laser pulses with programmable spatiotemporal behavior”. (Source: UCM)