498 research outputs found
Absorption-reduced waveguide structure for efficient terahertz generation
An absorption-reduced planar waveguide structure is proposed for increasing the efficiency of
terahertz (THz) pulse generation by optical rectification of femtosecond laser pulses with tiltedpulse-
front in highly nonlinear materials with large absorption coefficient. The structure functions
as waveguide both for the optical pump and the generated THz radiation. Most of the THz power
propagates inside the cladding with low THz absorption, thereby reducing losses and leading to the
enhancement of the THz generation efficiency by up to more than one order of magnitude, as
compared with a bulk medium. Such a source can be suitable for highly efficient THz pulse generation
pumped by low-energy (nJ-lJ) pulses at high (MHz) repetition rates delivered by compact
fiber lasers
Nonlinear distortion of intense THz beams
Near- and far-field beam profiles were measured for THz pulses generated in LiNbO3 by optical rectification of 200 fs pulses with a tilted pulse front. The variation of the THz beam size and a dramatically increasing divergence angle with increasing pump fluence were observed in the
(horizontal) plane of the pulse front tilt. No significant variation was observed in the vertical direction.
The reason for the observed nonlinear beam distortion is the shortening of the effective interaction length for THz generation caused by the combined effect of pump spectral broadening and angular dispersion in the tilted pulse front geometry. Our results indicate that nonlinear THz beam distortion effects have to be taken into account when designing intense THz sources and related experiments
Intense tera-hertz laser driven proton acceleration in plasmas
We investigate the acceleration of a proton beam driven by intense tera-hertz (THz) laser field from a near critical density hydrogen plasma. Two-dimension-in-space and three-dimension-in-velocity particle-in-cell simulation results show that a relatively long wavelength and an intense THz laser can be employed for proton acceleration to high energies from near critical density plasmas. We adopt here the electromagnetic field in a long wavelength (0.33 THz) regime in contrast to the optical and/or near infrared wavelength regime, which offers distinct advantages due to their long wavelength (k ¼ 350 lm), such as the k2 scaling of the electron ponderomotive energy. Simulation study delineates the evolution of THz laser field in a near critical plasma reflecting the enhancement in the electric field of laser, which can be of high relevance for staged or post ion acceleration
- …