Periodically intensity-modulated pulses by optical parametric amplification for multicycle tunable terahertz pulse generation

The superposition of signal and idler pulses in dual- chirped optical parametric amplification is proposed for the efficient generation of intensity-modulated pulses with periodic modulation. Both the duration and the modulation period are easily and independently adjustable. Numerical simulations for a three-stage optical parametric amplifier system predicted an efficiency as high as ~50% for about 40 mJ of output pulse energy at a wavelength of 2 μm. Sources of such intensity-modulated pulses near 1.6 μm or 2 μm wavelength, pumped by Ti:sapphire or Yb-doped lasers, can be ideally suited for intense multicycle THz pulse generation with tunable frequency and bandwidth by optical rectification for example in organic, semiconductor, or lithium niobate materials

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

Prospects of Semiconductor Terahertz Pulse Sources

Extremely high pump-to-terahertz (THz) conversion efficiencies up to 0.7% were demonstrated in recent experiments with ZnTe THz pulse sources. Such high efficiencies could be achieved by pumping at an infrared wavelength sufficiently long to suppress both two- and three-photon absorption and the associated free-carrier absorption at THz frequencies. Here, high-field high-energy THz pulse generation by optical rectification in semiconductor nonlinear materials is investigated by numerical simulations. Basic design aspects of infrared-pumped semiconductor THz sources are discussed. Optimal pumping and phase-matching conditions are given. Multicycle THz pulse generation for particle acceleration is discussed

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