Scientists at the Vienna University of Technology have discovered a way to compress ultrashort laser pulses while increasing the peak power to half a terawatt – a value often produced by nuclear reactors. This new result can be applied in multiple applications and was published in the journal Nature Communications.
The breakthrough was achieved by sending high-energy infrared pulses through a solid crystal medium, compressing the pulses in both time and space. In doing this the energy of the pulse stays roughly the same, but it can now be deposited over a shorter timescale, increasing the peak power to half a terawatt. This power corresponds to the output of certain nuclear reactors, but unlike power plants, which produce the power steadily, the compressed laser pulse only lasts 30 femtoseconds.
‘It is very hard to combine these three properties – long infrared wavelength, short duration and high energy,' said Valentina Shumakova, lead author of the publication. ‘But this combination is exactly what we need for many interesting strong-field applications.’
The team used an yttrium aluminium garnet (YAG) crystal with a width of only a few millimetres to achieve the results. By sending the laser pulse through the crystal, its duration decreased from 94 to 30 femtoseconds. The energy stayed almost the same, but the power increased by a factor of three to almost half a terawatt. ‘As the pulse is very short, its extremely high power opens the door to many exciting experiments and maybe even to new technologies in laser science,' stated Audrius Pugzlys, a co-author of the publication.
The researchers passed the infrared light through the YAG crystal in order to increase the rate of transmission through space. ‘The material causes some components of the laser pulse to move faster than others. If this effect is cleverly used, the laser pulse is compressed, it becomes shorter just by travelling through the material,' said Skirmantas Alisauskas another co-author of the publication.
‘This is a well-known phenomenon in laser science,' said Pugzlys. ‘But until now, people used to believe that self-compression in solid media at extremely high intensities is impossible.’
This technique, although now possible, is not always applicable. ‘If a pulsed laser beam of very high intensities is sent through a material, the beams tends to collapse chaotically into many separate filaments,' continued Pugzlys. ‘It is like a bolt of lightning that spontaneously breaks up into various branches.’ Each of these branches only carries a small part of the energy of the original beam, therefore the resulting beam cannot be used for advanced strong-field laser applications.
The research group, in collaboration with researchers from Moscow State University, were able to identify the conditions that lead to self-compression and an extremely high peak power without causing the beam to collapse into filaments. ‘As it turns out, we are dealing with two different length scales,’ said Shumakova. ‘The length scale of the unwanted filamentation is longer than the length on which self-compression occurs. Therefore, it is possible to find a parameter regime in which the pulse is compressed but filamentation does not yet set in.’ Using this, the collaboration was able to achieve a power 10,000 times higher than the filamentation threshold in the laser pulse without experiencing collapse.