Intense THz Pulses with large ponderomotive potential generated from large aperture photoconductive antennas

Abstract

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.

Laser‐Driven Strong‐Field Terahertz Sources

“…[12,102] Along these lines, ZnSe [102] and, in particular, 6H-SiC [103] were recently shown to be promising materials. To mitigate these issues, semiconductors with large electronic bandgap, high thermal conductivity, and high carrier mobility should be used.…”

“…[12,102] Along these lines, ZnSe [102] and, in particular, 6H-SiC [103] were recently shown to be promising materials. [102] Using this strategy and a ZnSe interdigitated 12.2 cm 2 largearea photoconductive antenna with a phase mask and 2.5 mJ, 400 nm laser pulses, THz pulses with an energy of 8.3 µJ and peak electric field of 331 kV cm −1 in the focus were demonstrated. [102,104] To prevent destructive superposition of THz waves from regions with opposite bias, every other gap is either blocked by a shadow mask [104] or its emission is phase-shifted by 180° using a phase mask.…”

“…[12,[100][101][102] As schematically shown in Figure 18a, in these devices, an external bias voltage breaks the in-plane inversion symmetry and accelerates the optically generated carriers. [12,[100][101][102] As schematically shown in Figure 18a, in these devices, an external bias voltage breaks the in-plane inversion symmetry and accelerates the optically generated carriers.…”

“…To mitigate these issues, semiconductors with large electronic bandgap, high thermal conductivity, and high carrier mobility should be used. [102,104] To prevent destructive superposition of THz waves from regions with opposite bias, every other gap is either blocked by a shadow mask [104] or its emission is phase-shifted by 180° using a phase mask. In addition, to reduce the bias voltage while maintaining a bias field on the order of 10 kV cm −1 over a length of ≈1 cm, multiple electrode pairs with smaller cathode-anode distance rather than one pair are used (see Figure 18b).…”

“…In addition, to reduce the bias voltage while maintaining a bias field on the order of 10 kV cm −1 over a length of ≈1 cm, multiple electrode pairs with smaller cathode-anode distance rather than one pair are used (see Figure 18b). [102] Figure 18c displays an example waveform from a ZnSe emitter with shadow mask, while Figure 18d shows that the spectrum covers the range from < 0.05 to 1 THz. [102] Using this strategy and a ZnSe interdigitated 12.2 cm 2 largearea photoconductive antenna with a phase mask and 2.5 mJ, 400 nm laser pulses, THz pulses with an energy of 8.3 µJ and peak electric field of 331 kV cm −1 in the focus were demonstrated.…”