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Photomixing with dual-mode and multi-mode lasers in the sub-terahertz frequency region is presented with a description on the principle and efficiency of photomixing on low-temperature-grown-GaAs photoconductive antennae for generation of continuous-wave terahertz (THz) radiation. The difference frequency stabilization by the common-mode-rejection effect in the dual-mode lasers is discussed with several reported experimental results. It is also shown that generation and detection of broadband sub-THz radiation is possible by photomixing with multi-mode semiconductor lasers on the emitter and detector photoconductive antennae (multi-mode-laser-diode-based terahertz time-domain spectroscopy, MLD-TDS). The MLD-TDS system can be a low-cost and broadband spectrometer in the sub-THz frequency region, which is useful for measurement of complex refractive indices and carrier densities of semiconductor wafers.

Tumor necrosis factor-alpha (TNF-alpha) is thought to be important in the development of pulmonary fibrosis. However, surfactant protein-C/TNF-alpha transgenic mice do not spontaneously develop pulmonary fibrosis but instead develop alveolar enlargement and loss of elastic recoil. We hypothesized that overexpression of TNF-alpha in the lung requires an additional insult to produce fibrosis. In this study we evaluated whether TNF-alpha overexpression altered the development of pulmonary fibrosis due to bleomycin or transforming growth factor-beta (TGF-beta). Either 0.2 U bleomycin or saline was administered into left lung of TNF-alpha transgenic mice and their transgene-negative littermates. To overexpress TGF-beta, an adenovirus vector containing either active TGF-beta (AdTGF-beta) or LacZ was administered at a dose of 3 x 108 plaque-forming units per mouse. Fibrosis was assessed histologically and by measurement of hydroxyproline. TNF-alpha transgenic mice tolerated bleomycin or AdTGF-beta, whereas the transgene-negative littermates demonstrated severe pulmonary fibrosis after either agent. An increase in prostaglandin E2 and downregulation of TNF receptor I expression were observed in the TNF-alpha transgenic mice. In addition, recombinant human TNF-alpha attenuated bleomycin-induced pulmonary fibrosis. TNF-alpha has a complex role in the development of pulmonary fibrosis. Endogenous TNF-alpha may be important in the development of fibrosis as indicated in other reports, but overexpression of TNF-alpha or exogenous TNF-alpha limits pulmonary fibrosis in mice.

Optical properties of doped silicon wafers have been measured by means of terahertz time domain reflection spectroscopy. A method is proposed to obtain the relative phase by reflection accurately. By using this method, the relative phase is obtained within an error of less than 10 mrad at 1 THz. The experimentally obtained complex conductivity of relatively high-doped silicon (ϭ0.136 ⍀ cm) in the terahertz region agrees with the simple Drude model.

A subterahertz (sub-THz) spectroscopic system using a multimode laser diode and photoconductive antennas (PA) has been proposed. It employs a random fluctuation of the light intensity to produce the subterahertz radiation from the emitter PA and also to trigger the detector PA. The signal is obtained as the cross correlation between the sub-THz radiation amplitude and laser light intensity. The decrease in the amplitude and phase delay of the radiation due to transmission from a sample can be calculated from the signal in a broad spectral region of sub-THz. This system is applied to the measurement of the complex refractive indices of Si wafers. The obtained dispersion of the refractive indices is well explained by the Drude model.

A system for measuring transmittance of electromagnetic waves in the sub-THz region is proposed. The electromagnetic radiation is generated by the excitation of a photoconductive antenna with a commercially available multimode laser diode. The spectral coverage of the radiation is increased by defocusing the light spot on the photoconductive antenna. Transmitted radiation is detected by a hot-electron bolometer through a Martin–Puplett-type interferometer. Transmittance is measured for n-type Si wafers with various doping levels. The carrier densities calculated from the transmittance agree well with those obtained from the dc conductivity measurement.

It is believed that the two-dimensional massless N = 2 Wess-Zumino model becomes the N = 2 superconformal field theory (SCFT) in the infrared (IR) limit. We examine this theoretical conjecture of the Landau-Ginzburg (LG) description of the N = 2 SCFT by numerical simulations on the basis of a supersymmetric-invariant momentum-cutoff regularization. We study a single supermultiplet with cubic and quartic superpotentials. From two-point correlation functions in the IR region, we measure the scaling dimension and the central charge, which are consistent with the conjectured LG description of the A 2 and A 3 minimal models, respectively. Our result supports the theoretical conjecture and, at the same time, indicates a possible computational method of correlation functions in the N = 2 SCFT from the LG description.

Articles you may be interested inUltrafast time-domain spectroscopy based on high-speed asynchronous optical sampling Rev. Sci. Instrum. 78, 035107 (2007);Free-carrier Faraday ellipticity and Faraday rotation are measured for a moderately doped n-type silicon wafer with the resistivity of 1.1 ⍀ cm under magnetic fields of ±3 T using the terahertz time-domain spectroscopy. From the experimental data, we obtain the time evolution of the electric-field vector of the terahertz radiation pulses. When the magnetic field is applied to the sample, the transmitted radiation has an elliptic polarization with its major axis rotated from the polarization direction of the incident radiation ͑Faraday effect͒. The Faraday ellipticity and Faraday rotation angle are obtained for the directly transmitted pulse ͑first terahertz pulse͒ and the pulse reflected twice at the sample surfaces ͑second terahertz pulse͒ separately. They are compared with the calculations using the Drude model. A slight deviation is observed between the experimental and calculated Faraday ellipticities and Faraday rotation angles probably due to the energy dependence of the carrier scattering time.