17 research outputs found
Scalable microstructured semiconductor THz pulse sources
In recent years several microstructured lithium niobate THz pulse source were suggested for high-energy applications. Two types of those, the reflective and the transmissive
nonlinear slab are adopted here for semiconductors. These new sources are scalable both in THz energy and size. Furthermore, they can outperform the already demonstrated contact grating source in diffraction and THz generation efficiency. Compared to the lithium niobate sources,
they are more feasible, thanks to the easier manufacturing and the longer pump wavelength.
They can produce intense, nearly single-cycle THz pulses at higher frequencies. With 20 mJ pumping at 1.8 μm wavelength, 45 μJ THz energy, and 17 MV/cm focused peak electric field can be expected at 3 THz phase matching frequency from the transmissive nonlinear echelon slab setup consisting of a 4 mm thick structured plan-parallel gallium phosphide crystal
Investigation of terahertz pulse generation in semiconductors pumped at long infrared wavelengths
We present designs of semiconductor contact grating high energy terahertz pulse sources pumped by femtosecond pulses in the 1 to 5 µm wavelength range. Nearly wavelength-independent diffraction efficiencies as high as 69% and 75% in the ±1st diffraction orders in the transverse electric field polarization state were predicted in GaAs and GaP, respectively, based on a rectangular grating. Numerical simulations—including, for the first time, to our knowledge, the effects of both a nonlinear refractive index and free carrier absorption—were performed to investigate the possible advantage of using longer pumping wavelengths to suppress the two- to seven-photon absorption. Conversion efficiency larger than 1.0% is predicted for both crystals. We also recognized that the nonlinear refractive index and the wavelength-dependent optical parametric amplifier efficiency can significantly reduce the overall terahertz generation efficiency; thus, optimum pump wavelengths exist for the highest conversion efficiency, which are 2 and 3µm for GaP and GaAs, respectively
Programmable generation of terahertz bursts in chirped-pulse laser amplification
Amplified bursts of laser pulses are sought for various machining,
deposition, spectroscopic and strong-field applications. Standard frequency-
and time-domain techniques for pulse division become inadequate when intraburst
repetition rates reach the terahertz (THz) range as a consequence of
inaccessible spectral resolution, requirement for interferometric stability,
and collapse of the chirped pulse amplification (CPA) concept due to the loss
of usable bandwidth needed for safe temporal stretching. Avoiding the burst
amplification challenge and resorting to a lossy post-division of an isolated
laser pulse after CPA leaves the limitations of frequency- and time-domain
techniques unsolved. In this letter, we demonstrate an approach that
successfully combines amplitude and phase shaping of THz bursts, formed using
the Vernier effect, with active stabilization of spectral modes and efficient
energy extraction from a CPA regenerative amplifier. As proof of concept, the
amplified bursts of femtosecond near-infrared pulses are down-converted into
tunable THz-frequency pulses via optical rectification.Comment: 7 pages, 5 Figure