Incoherent terahertz (THz) sources can be compact, stable, reliable and cheaper alternative to coherent emitters for compact THz systems. Low power of incoherent THz emitters can be compensated by benefit from extremely high sensitivity of THz micro-detectors. Incoherent THz torch device based on Ga(As,Bi)/AlGaAs parabolic quantum well (PQW) is modeled, fabricated and experimentally investigated paying special attention to the THz spectral range and optical properties. The structures for optical characterization were grown using MBE technique on GaAs substrates. The experimental study was carried out to measure the absorption by intersubband transition of electrons in PQW using vacuum Fourier transform spectroscopy, conventional farinfrared Fourier transform spectroscopy and THz time-domain spectroscopy. Transmittance spectra dependence on temperature and photo-excitation of undoped structures for THz torch device is studied exploring impact of the PQW on THz spectra.
In this work, a comparative research of biologically active organic molecules in its natural environment using the terahertz (THz) time domain spectroscopy (TDS) and Fourier transform spectroscopy (FTS) systems is carried out. Absorption coefficient and refractive index of <i>Nicotiana tabacum L.</i> leaves containing nicotine, <i>Cannabis sativa L</i>. leaves containing tetrahydrocannabinol, and<i> Humulu lupulus L</i>. leaves containing α-acids, active organic molecules that obtain in natural environment, were measured in broad frequency range from 0.1 to 13 THz at room temperature. In the spectra of absorption coefficient the features were found to be unique for <i>N. tabacum</i>, <i>C. sativa</i> and <i>H. lupulus</i>. Moreover, those features can be exploited for identification of <i>C. sativa</i> sex and <i>N. tabacum </i>origin. The refractive index can be also used to characterize different species.
We report on the effect of transient selfheating on the spectral modulation of electroluminescence (EL) in high-power
light-emitting diodes (LEDs). In AlGaInP LEDs, which emit due to the band-to-band recombination of free carriers, the
oscillation of junction temperature was found to result in that the modulation depth has a drop around the peak photon
energy, an increased magnitude at lower energies, and a linear increase with photon energy at higher energies. These
properties of the EL modulation spectrum can be explained by a model that takes into account the thermal modulation of
band gap energy and carrier distribution function. In InGaN LEDs, almost no thermal effect on EL modulation was
found around the peak photon energy and at lower energies, whereas at higher energies, the modulation depth also
increases with photon energy. Such a spectrum of EL modulation depth can be understood in terms of localized carrier
effect at peak photon energy and lower energies and of free carrier heating at higher energies. The frequency dependence
of modulation depth at particular photon energies was shown to sensitively replicate the thermal response function of the