When the laser was invented in 1960, people were wondering what is going to be the use of it. Today we know that lasers are used almost everywhere. Since laser’s invention, researchers have endeavored to create more and more intense laser pulses that goes together with creating shorter and shorter pulses.
The duration of laser pulses has, over the years, been reduced from ms (10-3 s) to fs (10-15 s) and eventually to sub-fs entering the attosecond (10-18 s) temporal scale. As the characteristic times of motion increase with the size of the moving object, short pulses allow the study of ultrafast dynamics occurring in the microworld. Indeed for the investigation of phenomena with ps or fs duration, like molecular or atomic processes in gases, liquids and solids, only laser based techniques can be used, as electronics are not fast enough. Femtochemistry made it possible using fs lasers to “see” how atoms move in a molecule during a chemical reaction. Attosecond pulses can now be used, as the fastest ever “camera”, for capturing ultrafast electron dynamics, like the evolution of atomic coherences or charge migration in large molecules, as well as electron-electron correlation times.
THigh intensity lasers are used in relativistic and ultra-relativistic interactions with matter. Such interactions lead to very compact particle accelerators and novel radiation sources. Electrons have been accelerated to 7.8 GeV over an acceleration length of 20 cm. Lasers produce 100 MeV scale protons from laser-film interactions. Table top coherent XUV and soft x-ray sources are based on laser-gas and laser-surface interactions, in a process known as high order harmonic generation, while 100 keV scale betatron radiation is co-emitted in laser electron acceleration sources. Recently, non-linear Compton scattering between an electron and several hundred laser photons has been demonstrated, inaugurating laser induced QED phenomena.
In addition to curiosity driven physics, compact and user-friendly, high-power, ultra-short pulse laser systems are used in many industrial, medical and other practical applications. Because of the minimal thermal energy deposition by a fs laser when interacting with materials, it causes negligible collateral damage beyond the targeted interaction volume, providing high precision and controllable material processing. High-aspect-ratio holes that are required for stents can be drilled with fs lasers. fs lasers are in clinical use in refractive surgical procedures or in changing the properties of matter like converting electrical insulators to conductors, acting as ultrafast optical switches.
The journey towards high peak power, short pulse lasers seemed, by the mid-1980s, as having reached the end of the road. For short pulses it was no longer possible to increase their intensity without destroying the amplifying material. At that time the new technique, known as chirped pulse amplification, CPA, came to overcome the bottleneck. A short laser pulse is stretched it in time, amplified and squeezed back generating high peak power ultrashort pulses. The CPA-technique has revolutionized laser science and applications. It is used in all high-intensity lasers and a gateway to new research areas and applications in physics, chemistry, medicine and industry.
This year’s Onassis Lectures are dedicated to the science and applications of extreme light. The lead speaker is Gerard Mourou, co-inventor (with his at that time PhD student Donna Strickland) of CPA. The individual presentations will cover a wide range of topics related to current and future applications of high peak power, ultra-short pulse lasers.