We report on terahertz (THz) emission from tellurium crystal surfaces excited by femtosecond optical pulses. Measurements were performed on three differently cut Te samples and with different wavelength optical excitation pulses. THz pulse amplitude dependences on the azimuthal angle measured at various excitation wavelengths have evidenced that three different mechanisms are responsible for THz generation in tellurium: second order nonlinear optical rectification effect, dominating at lower excitation photon energies, as well as transverse and ordinary photo-Dember effects, which emerge at energies larger than 0.9 eV. The shapes of the azimuthal angle dependences were also explained by theoretical model.

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Performance of the antenna-coupled detectors was measured by the quasi-optical setup in wide frequency range from 0.1 to 1.0 THz. Studied sensors were based on the titanium microbolometers coupled with the double-dipole-or log-periodictype antenna for room temperature THz detection. The THz radiation of the selectively filtered broadband LTG-GaAs photoconductive emitter and the system generating narrow band THz bursts were used for measurements.

A terahertz time-domain spectroscopy (TDS) system based on a femtosecond Yb: KGW laser, photoconductive emitters and detectors made from as-grown and from annealed at moderate temperatures (~400°C) low-temperature-grown GaAs (LTG GaAs) layers was demonstrated. The measured photoconductivity of these layers increased linearly with the optical power, showing that transitions from the defect band to the conduction band are dominant. The largest amplitude THz pulse with a useful signal bandwidth reaching 3 THz and its signal-to-noise ratio exceeding 50 dB was emitted by the device made from the LTG GaAs layer annealed at 420°C temperature. The detector made from this material was by an order of magnitude less sensitive than conventional GaBiAs detectors.

We report on the performance of photoconductive terahertz detectors made from low temperature grown GaAs (LTG GaAs) and Ga0.7In0.3As (LTG GaInAs) in the wavelength range from 620 to 1550 nm. These THz detectors exhibited a significant sub‐bandgap photoconductivity due to the electron transitions from the defect band. A simple model evaluating picosecond photoconductivity was proposed to explain the experimental data. By comparing the modeling results with the experimental data, the defect band position was found to be at 0.77 and at 0.4 eV below the conduction band minimum for LTG GaAs and LTG GaInAs, respectively.