ULTRAFAST LASERS FEATURE
explained that the spectrum of ultrashort pulses broadens because of non-linear interactions, which need to be avoided. ‘You need to apply some special techniques in optical parametric amplifiers to narrow the generation spectra. We use spectral filtration by diffraction gratings or synchronously pumped optical parametric oscillators in this case,’ he said. While femtosecond lasers do offer high
temporal resolution, their spectra are usually too broad for probing molecules, according to Kuprionis, which is why Ekspla is selling more and more tuneable picosecond lasers that are synchronised with femtosecond lasers for this purpose. ‘This allows scientists to achieve more accurate and precise results,’ he commented. Out of the various emerging
advancements in laser design that have occurred, for Ekspla, according to Kuprionis, the most significant is the development of OPCPA (optical parametrical chirped pulse amplification) technology. ‘For us it’s a very important area because our picosecond lasers are very suitable to pump OPCPAs,’ he said. ‘With our partners Light Conversion and National Energetic, we develop ultra- high intensity ultrafast OPCPAs.’ With these partners Ekspla is producing
OPCPAs for the European Extreme Light Infrastructure (ELI) project, which aims to develop and offer the world’s most intense laser systems and make them available to the international scientific community. Ekspla has already produced a five terawatt, 1kHz OPCPA-based laser system worth €4 million with Light Conversion for the project. Now it is developing an additional terawatt laser system with 6fs pulse duration with Light Conversion, and an additional 10-petawatt laser system with National Energetics.
Toptica’s ultrafast lasers are based on fibre technology ‘There are completely new types of
applications for these sources,’ commented Kuprionis. ‘These are extreme light applications like fusion energy experiments, compact high gradient electron and proton accelerators. Also with these sources it’s possible to generate ultrafast x-rays for structural studies of solids and molecules and to create extreme states of matter.’ These extreme sources can also be used for generating pulses only attoseconds in duration, a completely new area of physics that is just at its beginning.
Lasers of the future While ultrafast lasers are currently around the size of two shoeboxes – one containing the laser, the other the supply electronics – Paasch-Colberg of Toptica Photonics believes that they will be shrunk down even further in the coming years. ‘I think the future will lead to size
reductions without lowering the performance or changing the important laser parameters (wavelength, pulse duration etc),’ he said. ‘Micro optics will be a key technology for reducing the size of lasers, as well as photonic integrated circuits. Shrinking the components down to a smaller chip while maintaining the same level of power and other specifications will be a big true challenge. I think for biophotonics applications [however], this will be the future.’ Kuprionis of Ekspla believes that
hybrid laser technology is set to have a positive impact on ultrafast lasers, a laser format already used in micromachining applications and for OPCPA pumping. ‘This involves using a fibre-based seeder, which gives you a lot of opportunities to choose the pulse wavelength, duration and shape needed. But the limitation of fibre lasers is the intensity of the pulse, so for the final stage we use a diode-pumped free space amplifier,’ he explained. ‘So part of the hybrid laser is fibre, part of it is solid state.’ These hybrid lasers can be made to be very compact, economical, and with very good output parameters, according to Kuprionis. Chui of Spectra-Physics expressed that
Ekpla’s sum frequency generation microscope provides the ability to investigate spatial and chemical variations across the surface as a function of time
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ultrafast lasers could progress in two particular directions in the future. ‘One is achieving even more capability for research applications – imaging deeper, having higher peak power and longer wavelengths. The other is more towards clinical applications in the long term, finding the right parameter set for the end application and then optimising the solution for that.’ While the tools that Spectra-Physics currently produces are very capable and flexible for research applications, for clinical applications, according to Chui, a more compact, single-purpose solution is needed. EO
December 2017/January 2018 Electro Optics 47
Ekspla
Toptica Photonics
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