With a new method, the colour of pulsed high-power lasers can be freely adjusted over a comparatively large range. The method improves the application possibilities of such systems in industry and research. Until now, there was no efficient way to freely adjust the wavelength, i.e. the colour, of high-power lasers, as a research team from DESY, the Helmholtz Institute Jena and the GSI Helmholtz Centre for Heavy Ion Research reports in the journal Nature Photonics. The team led by Christoph Heyl has filed a patent for the method.

Lasers have become a key technology in numerous disciplines, from materials processing to semiconductor production and medicine to basic research. It is often necessary to optimally adapt the wavelength of the laser to the respective application. Especially when lasers are used to study materials, the tunability of the wavelength is an almost indispensable requirement.

However, the colour of a laser usually depends on the laser medium used and is thus precisely determined by the laser system design. Lasers are available in numerous colours today, from infrared to ultraviolet wavelengths. But if, for example, a slightly different red is needed than a laser delivers, the wavelength has to be shifted with elaborate procedures. A lot of power is lost in the process, or the laser flash smears out and is no longer as short and sharp as before – or both. In contrast, the new method even improves the temporal profile of ultra-short laser pulses.

“Current laser technology offers no way to satisfactorily shift the wavelengths of ultrashort high-power laser pulses,” explains Heyl. “With our work, we now provide a solution to this problem by successfully transferring a well-known technique from the radio frequency domain to the optical domain.” Using the so-called Serrodyn frequency shift, the team has succeeded in freely tuning the wavelength of an infrared high-power laser between 1000 and 1060 nanometres.

The method employs a fundamental mathematical principle: a suitable change in the so-called time-dependent phase of a signal such as a radio wave or a light pulse leads directly to a change in the wavelength. The temporal change of the phase can be brought about in a so-called multi-pass cell. The frequency shift that can be achieved is about 1000 times greater than the shift which could be reached with previous Serrodyn methods.

“With this innovation, which takes a completely new approach, we overcome a decades-old problem in laser physics and enable numerous new applications,” explains Heyl. “For example, we expect that lasers for microscopy, spectroscopy or gas analysis applications, which are not only used in basic research but also in the medical field, for example, can be built much more cost-effectively in the future. At the same time, the newly created possibility to significantly improve the temporal profile of high-power laser pulses offers ideal conditions for future laser-based accelerators whose performance requires laser pulses with a sharp temporal profile.”

 

Reference:
Ultrafast serrodyne optical frequency translator; Prannay Balla, Henrik Tünnermann, Sarper H. Salman, Mingqi Fan, Skirmantas Alisauskas, Ingmar Hartl, Christoph M. Heyl; Nature Photonics, 2022; DOI: 10.1038/s41566-022-01121-9