The spectroscopic properties of crystalline silicon wafers are investigated experimentally as a function of the temperature. To this goal, samples of phosphorus-doped silicon are characterized using Terahertz Time-Domain Spectroscopy (THz-TDS) in reflection. Four different samples span resistivities from ∼0.04 − 50Ω cm, for temperatures ranging from room temperature to 200 C. The measurements confirm that the widely used Drude's theory is adequate also to model the dispersion of silicon at higher temperatures. When comparing the corresponding scattering times obtained here using THz TDS pulses with the scattering time derived from the well accepted DC based empirical model of the mobility, differences emerge depending on the doping level. The scattering times predicted and measured are on the same order of magnitude and the anticipated reduction of the scattering time with increasing temperature has also been confirmed by the high frequency measurements. The absorptivity of the samples is also estimated accurately as a function of the frequency up to 1 THz.

We report on high power THz emission from LT-GaAs photoconductive emitters, excited with a frequency-doubled, high power ultrafast Yb laser emitting 100 fs pulses at 515 nm (green) at a high repetition rate of 91 MHz. The device presented in this work incorporates a dedicated connected array. First, we describe the general methodology for designing such impedance matched photoconductive connected array devices, then we describe how this methodology was applied for the design of a 361-element photoconductive connected array specifically optimized for the high optical power (20 W) at 515 nm laser wavelength and 91 MHz repetition rate. The combination of these optimized devices and high power laser at very high repetition rate allow us to demonstrate a high THz power of 10.1 mW during the on-cycle of a chopper with 50% duty cycle.

The mm and sub-mm wave propagation and absorption in n-type c-Si are investigated as a function of temperature by time-domain reflectivity measurements. The temperature range spans from 300 K to 475 K and the complex electric resistivity, extracted from the reflectivity spectra, shows the same free electrons mobility degradation with temperature as observed with previous dc conductivity measurements. The Drude theory of free charge carriers, based on the conduction electron concentration and effective scattering time, well fit the experimental data from 200 GHz to 1 THz. The dependence of the scattering time with respect to the doping concentration and sample temperature is consistent with the empirical unified model for the electron dc mobility, which is widely used in c-Si passive components and device simulations.

Transition metal-doped InGaAs material has proven to be extremely efficient when used as photoconductor in photoconductive antennas excited with a 1550 nm wavelength laser. In this contribution, we apply a time-domain modeling procedure to predict the radiated power by InGaAs:Fe strip-line antennas. The simulations are verified with measurements, showing an excellent match between them. Additionally, we model the reconstructed current when such a strip-line antenna is coupled with a receiver through a Quasi-Optical (QO) link.

We report the highest THz power ever achieved from photoconductive antennas. This result is obtained by employing a photoconductive connected array. Such arrays have previously shown to radiate efficiently when excited by a 780 nm laser source, but their scalability is constrained by the limited optical power available at this wavelength. In this work, we design a 361-element photoconductive connected array specifically optimized for 20 W of 515 nm green laser excitation, and demonstrate a record-high THz power of ~10 mW using this new device.

THz time-domain reflection spectroscopy experiments of crystalline Si samples of different doping and heated to temperatures up to 475 K have been performed to measure their electric permittivity, absorptivity and resistivity dispersion spectra. Free charge carrier volume concentration and scattering time have also been extracted from the measurements, as a function of temperature, to best fit the Drude model to the complex resistivity spectra. The dependence of these microscopic parameters to the temperature resembles the curves from the unified model for the carriers mobility, based on past dc measurements. The high-frequency data acquired with these measurements constitute the fundamental information and parameters, necessary for the characterization of crystalline Si thermal radiation emission.

Photo-conductive antennas (PCAs) are the workhorse of time-domain THz sensing and imaging. In this work, we employ a rigorous Norton equivalent circuit model to identify and estimate the substrate-related parasitic effects, that might limit the THz emission, to better design future PCAs.

Photoconductive antennas (PCAs) are used for imaging and sensing applications because of their ability to radiate short pulses with large bandwidths in the THz regime. The characterization of PCAs has previously been done using a time-domain Norton equivalent circuit. Thanks to a recent contribution, the size of the excited photoconductive area of PCAs that results in an impedance match with the antenna can be determined analytically using only the available optical power and the material parameters of the photoconductor. Through the impedance matching, the radiated THz power is maximized. These insights are used for the dimensioning of a wide-band photoconductive connected array to be used in the low THz band, excited by a high power laser (∼1W).