The First Operation of Two Color Mode in Infrared Free Electron Laser

The Fritz Haber Institute of the Max Planck Institute in Berlin has achieved a technological milestone. The infrared free electron laser operates in dual color mode for the first time. This globally unique technology makes it possible to conduct experiments on synchronous dual color laser pulses, opening up new possibilities for research.

There are over a dozen free electron lasers worldwide, with significant differences in size, wavelength range, and cost. However, they all generate strong short radiation pulses. In the past few decades, free electron lasers have become an important radiation source and have been widely applied in basic research and applied science.

FHI researchers have now collaborated with American partners to develop a method that can simultaneously generate two different colored infrared pulses. This innovation is particularly important for studying the temporal processes of solids and molecules.

In FEL, the electron beam is first accelerated by an electron accelerator to a very high kinetic energy, reaching a speed close to the speed of light. Then, the fast electrons pass through a undulator, where they are forced into a path similar to a turbulent vortex by a strong magnetic field with periodic changes in polarity.

The oscillation of electrons leads to the emission of electromagnetic radiation, and its wavelength can be changed by adjusting the electron energy and/or magnetic field strength. For this reason, FEL can be used to generate laser like radiation in almost all parts of the electromagnetic spectrum, ranging from long terahertz to short X-ray wavelengths.

Since 2012, FEL has been operating at FHI, generating strong pulsed radiation in the mid infrared range, with wavelengths continuously adjustable in the range of 2.8 to 50 micrometers. In recent years, scientists and engineers at FHI have been dedicated to dual color expansion, installing a second FEL branch to generate far-infrared radiation with wavelengths between 5 and 170 microns.

The FIR-FEL branch includes a new hybrid magnet wave generator, which was specifically built at FHI. In addition, a 500 MHz kick chamber is installed behind the electron linear accelerator for lateral electron deflection. The kicking chamber can change the direction of high-energy electron beams at a speed of 1 billion times per second.

In June 2023, the FHI team demonstrated the first "laser" of the new FIR-FEL, guiding all electron beams from LINAC to FIR-FEL. In December 2023, they demonstrated the dual color operation for the first time. In this mode, the strong oscillating electric field formed in the kicking chamber causes every two electron beams to deflect to the left and every other electron beam to deflect to the right.

In this way, the high repetition rate electron beam from LINAC is divided into two beams, with each beam having half the repetition rate; One is guided to the old MIR-FEL, and the other is guided to the new FIR-FEL. In each FEL, changing the magnetic field intensity of the oscillator can continuously tune the wavelength up to four times.

For about a decade, FHI-FEL has enabled FHI's research team to conduct experiments on nonlinear solid-state spectroscopy and surface science from the spectra of clusters, nanoparticles, and biomolecules in the gas phase. To date, there have been approximately 100 peer-reviewed publications.

The new dual color mode is not available in any other IR FEL facility worldwide, and it will enable new experiments such as MIR/MIR and MIR/FIR pump probe experiments. This is expected to open up new opportunities for experimental research in different fields such as physical chemistry, materials science, catalytic research, and biomolecular research, thereby contributing to the development of new materials and drugs.

Source: Laser Net