Gentle terahertz light
Switzerland: In the limelight
No longer groping in the dark
The intensive PSI terahertz laser was specially developed for future applications on the SwissFEL. The free-electron laser SwissFEL is currently being built at the PSI and will be put into operation from the end of 2016. It will produce X-ray light pulses with the properties of laser light. That terahertz light can now be visualised with CCD sensors will provide various benefits, as the terahertz lasers will be used in combination with the SwissFEL's X-ray light. For example, to research new materials for magnetic data storage, a terahertz laser pulse will trigger a change in the magnetisation of a sample of the examined material. A few femtoseconds later, the sample will be X-rayed with the SwissFEL's X-ray laser pulse. Thus, researchers can find out what has happened within the sample during these femtoseconds.
The researchers are particularly interested in the fact that CCD sensors can now visualise terahertz light in its experimental environment. «This allows us to record the terahertz beam's exact spatial location during the experiment», Hauri emphasises. Furthermore, the CCD sensor's refresh rate is high enough to keep up with the speed at which experiments take place on the SwissFEL. The SwissFEL fires 100 X-ray light pulses per second and with each of these, a separate experiment is conducted. After the researchers have now demonstrated that the visualisation of terahertz light with CCD sensors works in principle, their goal is to further develop this idea. «It is of course possible to tailor CCD sensors for specific research applications», says Carlo Vicario, who has carried out the experiment with Mostafa Shalaby. But the researchers also see great potential for applications outside of research. «CCD sensors are inexpensive and robust. But for widespread application, there would also have to be marketable terahertz lasers of sufficient intensity. But since CCD sensors not only perform better but also cost less than one-tenth of a bolometer, they will surely quickly gain a foothold in the rapidly growing discipline of Terahertz science», Hauri is convinced.