We report the generation of free space terahertz (THz) pulses with energy up to 8.3 ± 0.2 µJ from an encapsulated interdigitated ZnSe Large Aperture Photo-Conductive Antenna (LAPCA). An aperture of 12.2 cm² is illuminated using a 400 nm pump laser with multi-mJ energies at 10 Hz repetition rate. The calculated THz peak electric field is 331 ± 4 kV/cm with a spectrum characterized by a median frequency of 0.28 THz. Given its relatively low frequency, this THz field will accelerate charged particles efficiently having very large ponderomotive energy of 15 ± 1 eV for electrons in vacuum. The scaling of the emission is studied with respect to the dimensions of the antenna, and it is observed that the capacitance of the LAPCA leads to a severe decrease in and distortion of the biasing voltage pulse, fundamentally limiting the maximum applied bias field and consequently the maximum energy of the radiated THz pulses. In order to demonstrate the advantages of this source in the strong field regime, an open-aperture Z-scan experiment was performed on n-doped InGaAs, which showed significant absorption bleaching.

We have developed an averaging picosecond x-ray streak camera using a dc-biased photoconductive switch as a generator of a high-voltage ramp. The streak camera is operated at a sweep speed of up to 8 ps/mm, shot-to-shot jitter is less than Ϯ1 ps. The streak camera has been used to measure the time history of broadband x-ray emission from an ultrashort pulse laser-produced plasma. Accumulation of the streaked x-ray signals significantly improved the signal-to-noise ratio of the data obtained.

We study the generation of free-space terahertz (THz) pulses at low THz frequencies using 6H-SiC and 4H-SiC photoconductive antennas. We investigate the dependence of the THz electric field radiated from the biased SiC emitters on the applied bias field and on the incident optical fluence. In this work, bias fields as high as 32 kV/cm, and optical fluences up to 2.5 mJ/cm 2 (for the 400 nm laser), and 7.5 mJ/cm 2 (for the 800 nm laser) were used. THz generation with back-and front-side illumination of the antennas is also examined. It is found that the SiC antenna, when illuminated from the backside, generates higher THz electric fields. The performance of 6H-SiC and ZnSe photoconductive antennas are compared. We show that, taking advantage of the superior thermal properties of SiC compare with ZnSe, the THz output power generated with the 6H-SiC photoconductive antenna under optimum conditions is 2.3 times larger that with a ZnSe photoconductive antenna. V C 2014 AIP Publishing LLC. [http://dx.

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