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We report a systematic study of free-space terahertz (THz) emission from photoconductive antennas (PCAs) nanodecorated with gold nanoparticles (Au-NPs) deposited by using the pulsed laser deposition (PLD) technique. H-shaped dipole micro-structured PCAs fabricated on semi-insulating GaAs substrates were decorated under various PLD conditions. Thus, by increasing the number of laser ablation pulses (NLP) of the Au target, both the average size of Au-NPs and the surface loading of PCAs increase. Compared with non-decorated PCAs, those decorated with Au-NPs exhibit significant enhancement in the radiated THz pulse amplitude. A maximum enhancement of ∼2.3 was achieved at NLP = 1250. Under this optimal NLP condition, not only is the average Au-NP size (of ∼15 nm) favorable for light absorption via localized surface plasmons, but also the inter-distance between NPs, the light reflectance, and facilitated transport of photocarriers, all combine to yield a stronger THz field emission. For higher NLP (≥2000), NPs coalesce and tend to form continuous film NPs, which not only significantly limits the light scattering toward the GaAs underlying substrate, but also electrically shorts the PCA. Finally, the Au-NP decoration of GaAs PCAs was also found to improve their overall thermal conductivity, making them much more thermally stable than their non-decorated counterparts. [ABSTRACT FROM AUTHOR]

In this work, we study THz generation and detection using cadmium telluride (CdTe) crystals pumped by amplified (1.025 μm wavelength) and oscillator (1.045 μm wavelength) ytterbium (Yb) lasers. For each laser, we compare the performances of the CdTe THz emitter and detector to those of GaP crystals. Under optimum conditions, we demonstrate that the former shows 3 and 5 times better performances compared with the latter for detection and generation, respectively. When pumped by an amplified Yb laser, we find that the CdTe crystal is more efficient than the GaP crystal for emission at optical fluences lower than 250 μJ/cm2. Although CdTe has some limitations in comparison with GaP, such as high THz absorption above 1 THz and the appearance of two-photon absorption at relatively low optical intensity, our findings demonstrate the potential of this crystal to be used as the emitter and detector in combination with the Yb laser. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate intense extreme-ultraviolet optical vortices generated using laser-ablation plume as the nonlinear medium. We used two types of plumes that are known to generate intense high-order harmonics for driving lasers with Gaussian beam profiles, but through different mechanisms, namely, carbon (diatomic carbon molecules) and tin (resonance with the autoionizing state). We find that the harmonic fluxes for diatomic carbon molecules are similar for Gaussian and vortex driving fields. However, for harmonics from the autoionizing state of tin (∼26.3 eV), the enhancement factor of the resonant harmonic intensity decreases by ∼50% when using the vortex driving field. The intense extreme-ultraviolet optical vortices demonstrated in this study will be useful for many applications including a material characterization technique known as optical angular momentum dichroism as well as the spectroscopy of spin-forbidden electronic transitions. [ABSTRACT FROM AUTHOR]