High speed optical modulation of THz radiation is of interest for information processing and communications applications. In this paper infrared femtosecond pulses are used to generate free carriers that reduce the THz transmission of silicon based waveguides over a broad spectral range. Up to 96 6 70 modulation is observed from 0.5 to 7 THz in an optical fiber with a 210 mu m diameter gold-doped silicon core. The observed carrier recombination time of 2.0 +/- 0.2 ns makes this material suitable for high speed all-optical signal processing. These results show both enhanced modulation depth and reduced carrier lifetime when compared to the performance of a high resistivity float zone silicon rectangular guide with comparable cross sectional area.

Silicon waveguide structures are a viable alternative for the transmission of signals over a wide range of frequencies, and new fabrication methods are key to increased applications. In this work, THz transparency of silicon-core, silica clad fibers, refined using a traveling solvent method, is demonstrated. The approximate to 200 mu m core of these fibers is shown to have good transmission from 4.8-9 mu m and 1-7 THz. Fibers were drawn on a conventional optical fiber tower using the scalable molten core technique and CO2 laser annealed, resulting in large-grain crystalline cores with broadband transmission. The spectral properties are comparable to those of rectangular guides of similar cross-sectional area cut from high resistivity float zone silicon wafers.

The waveguiding properties of high-resistivity float zone silicon slab waveguides are characterized over the spectral range from 0.5 to 7.5 THz. Waveguide modes and dispersion are observed for lengths of 1.2 cm and silicon thicknesses from 40 to 300 mu m. The influence of core thickness and cladding glass attenuation is characterized, and modeled transmitted pulse shapes compare well to the measured signals. Fused silica cladding allows propagation in the 40 mu m thick wafer, demonstrating the feasibility of developing flexible semiconductor core fibers for THz transmission.

There is an ongoing development of THz sources for high-field applications, especially with the view of potential for THz-driven particle accelerators. For such sources nonlinear materials with high optical damage threshold and low loss are required. KTiOPO4, (KTP) is a well-established material for nonlinear optical applications in the visible and near-IR region thanks to its large transparency, high nonlinear coefficient and damage threshold. Its reasonably low absorption [1, 2] and strong coupling to phonon-polariton degree of freedom [1]. This shows promise for efficient IR to THz conversionprocess. Indeed,Wu et al.[2] recently demonstrated its superiority to LiNbO3and LiTaO3in a back to back experiment. In view of this, it is important to determinethe spectrum of complex refractive index over larger spectral range and with higher accuracy than has been do so far. KTP is an orthorhombic crystal belonging to mm2 point group with a rather complex vibrational mode structure containing 192 degrees of freedom. Earlier spectroscopic studies of KTP have either lacked the possibility of directly extracting the complex refractive index [3] or been limited by absorption of the transmitted signal due to the strong resonances of KTP, limiting the spectral extenttoabout 2.5 THz [4]. In this work we utilize reflection THz time-domain spectroscopy (TTDS) to determine the spectrum of the refractive index, n, and the absorption coefficient, , between 0.5 THz and up to 7 THz for two eigenpolarizations on the (001) plane.

Terahertz (THz) radiation has been of increasing interest in the last decades, for security, manufacturing, quality control, medical and security imaging applications. The field requires more efficient and affordable sources and nonlinear upconversion schemes point in this direction. KTiOPO, (KTP) is a well-established material for nonlinear optical applications in the visible and near-IR region thanks to its large transparency, high nonlinear coefficient and damage threshold. Its reasonably low absorption [1, 2] and strong polariton resonances [1] show promise for efficient IR to THz upconversion and Wu et al. [2] recently demonstrated its superiority to LiNbO₃ and LiTaO₃ in a back to back experiment. However, the complex refractive index needs to be measured before further power scaling is realistic.

Terahertz (THz) radiation has been of increasing interest in the last decades, for security, manufacturing, quality control, medical and security imaging applications. The field requires more efficient and affordable sources and nonlinear upconversion schemes point in this direction. KTiOPO, (KTP) is a well-established material for nonlinear optical applications in the visible and near-IR region thanks to its large transparency, high nonlinear coefficient and damage threshold. Its reasonably low absorption [1, 2] and strong polariton resonances [1] show promise for efficient IR to THz upconversion and Wu et al. [2] recently demonstrated its superiority to LiNbO3 and LiTaO3 in a back to back experiment. However, the complex refractive index needs to be measured before further power scaling is realistic.

We report on THz time-domain spectroscopy measurements of flux grown KTiOPO₄ in the frequency range 0.6–7.0 THz (20 to 240 cm⁻¹). Our results compare well with earlier Raman and far-infrared measurements. We theorize that the differences between the optical phonon mode resonances reported in the literature are due to what growth parameters and melt compositions are used to grow the crystals. We also report on a new feature at 1.4 THz (47 cm⁻¹).

Fe-doped ZnS films of high optical quality were fabricated using vacuum vapor deposition. Preferential crystalline orientation and phase purity of the host ZnS films were increased by the addition of small amounts of Fe, and the spectral shape of the 2-4 μm absorption peak is maintained up to the highest concentration tested (9 at.%). However, Raman shifts of the Fe:ZnS films indicate the inclusion of disordered material at high Fe concentrations, and below-gap optical Kerr effect measurements show an increase in χ(3) correlated with this data. Nonlinear optical properties of the films were also measured using the Z-scan method at 532 nm, and saturable absorption of the Fe-based intraband levels at 2.94 μm was confirmed.