Nonlinear THz applications
Terahertz–driven magnetization dynamics in ferromagnetic film
The time-resolved investigations were performed by measurement of the magneto optical Kerr rotation induced on a 50 fs Ti:Sapphire optical probe. The results are presented in the figure below. The evolution shows a magnetization (red curve) which is phase-locked to the THz magnetic field (blue dotted). Unexpectedly, the magnetization evolution linked to the Terahertz magnetic laser field is well described by the semi-empirical Landau-Lifschitz-Gilbert (LLG) equation (black plot). The observed direct steering of magnetization on an ultrafast timescale is expected to play a significant role in the future ultrafast data storage by purely optical means.
Intense Terahertz transients offer moreover intriguing opportunities in other cutting edge experiment such as ultrashort pulse diagnostics or to enhance the soft x-ray photon fluence by high harmonic generation in noble gas.
- C. Ruchert, C. Vicario and C.P. Hauri, Phys. Rev. Lett. 110, 123902 (2013)
- C. Vicario, C. Ruchert, F. Ardana-Lamas, P.M. Derlet, B. Tudu, J.Luning and C.P. Hauri, Nature Photonics 7, 720 (2013)
HHG applicationsA table-top soft x-ray laser based on high-harmonic generation is an ideal tool for investigating matter on the sub-femtosecond timescale.
We are aiming to overcome limitations of present HHG sources in (a) photon energy and (b) photon flux by using mid-infrared laser technology and exploring phase matching schemes. These parameters are crucial for our three main applications.
- Investigation of ultrafast magnetization dynamics at the M absorption edge
- Attosecond physics in the water window spectral region (285eV-420 eV)
- Free Electron Laser seeding in the soft x-ray region (<10 nm)
Ultrafast magnetization dynamics
Seeding of a free electron laser (FEL)FELs are capable provide intense, femtosecond x-ray pulses down to 0.1 nm wavelength. The x-ray radiation is produced by a relativistic electron bunch travelling through undulator sections. The underlying principle to produce intense x-ray pulses is self-amplified stimulated emission (SASE), which leads to microbunching of the electron beam and to narrowband emission of x-rays.
SASE FELs suffer from a poor temporal coherence since the lasing process starts from noise. In principle, the temporal coherence can be improved by superposing an external temporal coherent seed beam to the electron beam. The challenge is that the noise floor increases at shorter FEL wavelengths and it gets difficult to overcome the power level by an external coherent seed. A promising candidate for a coherent seed beam is radiation from high-order harmonic generation (HHG). Our group is actively pushing the development of high-power HHG sources towards wavelengths as short as 1 nm (~1 keV photon energy). The goal is to realize a soft x-ray source strong enough to seed the future soft x-ray branch of SwissFEL, which lase between 1-7 nm. To reach this objective we study advanced phase-matching schemes, explore novel HHG schemes and combine those with cutting edge laser technology.