Simultaneous electronic and the magnetic excitation of a ferromagnet by intense THz pulses

The speed of magnetization reversal is a key feature in magnetic data storage. Magnetic fields from intense THz pulses have been recently shown to induce small magnetization dynamics in Cobalt thin film on the sub-picosecond time scale. Here, we show that at higher field intensities, the THz electric field starts playing a role, strongly changing the dielectric properties of the cobalt thin film. Both the electronic and magnetic responses are found to occur simultaneously, with the electric field response persistent on a time scale orders of magnitude longer than the THz stimulu

High energy terahertz pulses from organic crystals: DAST and DSTMS pumped at Ti:sapphire wavelength

High energy terahertz pulses are produced by optical rectification (OR) in organic crystals DAST and DSTMS by a Ti:sapphire amplifier system centered at 0.8 microns. The simple scheme provides broadband spectra between 1 and 5 THz, when pumped by collimated 60 fs near-infrared pump pulse and it is scalable in energy. Fluence-dependent conversion efficiency and damage threshold are reported as well as optimized OR at visible wavelength.Comment: 8 pages, 6 figure

Femtosecond resolution timing jitter correction on a TW scale Ti:sapphire laser system for FEL pump-probe experiments

Intense ultrashort pulse lasers are used for fs resolution pumpprobe experiments more and more at large scale facilities, such as free electron lasers (FEL). Measurement of the arrival time of the laser pulses and stabilization to the machine or other sub-systems on the target, is crucial for high time-resolution measurements. In this work we report on a single shot, spectrally resolved, non-collinear cross-correlator with sub-fs resolution. With a feedback applied we keep the output of the TW class Ti:sapphire amplifier chain in time with the seed oscillator to ~3 fs RMS level for several hours. This is well below the typical pulse duration used at FELs and supports fs resolution pump-probe experiments. Short term jitter and long term timing drift measurements are presented. Applicability to other wavelengths and integration into the timing infrastructure of the FEL are also covered to show the full potential of the device

Micromachining of hardened Portland cement pastes using femtosecond laser pulses

Femtosecond laser pulses (30fs in length) of various energies were utilised for production of single and multiple overlapping ablation sites on flat polished surfaces of hardened Portland cement pastes. In order to assess the sizes of the ablation sites and possible subsurface laser-induced damage, the ablation sites were investigated using environmental scanning electron microscopy (ESEM) - both from normal top-down view and in cross-sections. Furthermore, approximately 10-µm wide notches were produced using femtosecond pulses on cylindrical microspecimens (150µm in diameter) of hardened Portland cement pastes. In addition to electron microscopy observations, several microspecimens were investigated using synchrotron-based X-ray computed microtomography (SRμCT). The results suggest that production of "damage-free” samples for micromechanical testing of hardened Portland cements pastes is possibl

Generation of broadband THz pulses in organic crystal OH1 at room temperature and 10 K

We studied the effects of cryogenic cooling of a 2-[3-(4-hydroxystyryl)-5, 5-dimethylcyclohex-2-enylidene] malononitrile (OH1) crystal on the generation of broadband THz pulses via collinear optical rectification of 1350 nm femtosecond laser pulses. Cooling of the OH1 crystal from room temperature to 10 K leads to a ~10% increase of the pump-to-THz energy conversion efficiency and a shift of the THz pulse spectra to a higher frequency range. Both effects are due the temperature variation of THz absorption and the refractive index of the OH1 crystal. This conclusion has been verified by temperature dependent measurements of the linear absorption in the THz frequency region

Air nonlinear dynamics initiated by ultra-intense lambda-cubic THz pulses

Air turns into a nonlinear medium for electromagnetic waves under exceptionally strong fields. However up to present, its minuscule nonlinear response has limited the exploration to the optical frequency regime owing to the availability of intense near-infrared lasers. Here, we report on the observation of large-amplitude nonlinearity in air induced by an extremely intense light bullet at Terahertz frequencies (0.1-10 THz) provoking strong air birefringence. The observed nonlinearity manifests itself as third order susceptibility. The presented nonlinear observations break the barrier for the entire exciting THz-induced nonlinear phenomena in air ranging from THz-induced self-focusing and self-phase modulation to THz solitons and filamentation