MB 700 Anthropology for Christian Mission

Textbook: Cultural Anthropology: An Applied Perspective, fifth edition by Gary Ferraro Readings: Anthropology and Christian Mission: A Reader, Darrell Whiteman (ed.)Customs and Cultures by Eugene Nidahttps://place.asburyseminary.edu/syllabi/2521/thumbnail.jp

High-field magnetotransport in a two-dimensional electron gas in quantizing magnetic fields and intense terahertz laser fields

We present a combined experimental and theoretical study of interactions between two-dimensional electron gases (2DEGs) and terahertz (THz) free-electron lasers in the presence of quantizing magnetic fields. It is found both experimentally and theoretically that when an intense THz field and a quantizing magnetic field are applied simultaneously to a GaAs-based 2DEG in the Faraday geometry, a strong cyclotron resonance (CR) effect on top of the magnetophonon resonances can be observed by transport measurements at relatively high temperatures. With increasing radiation intensity and/or decreasing temperature, the peaks of the CR are broadened and split due to magnetophoton-phonon scatterin

Intersubband lifetimes in InAs/GaSb superlattices using saturated absorption spectroscopy

We investigate intersubband relaxation rates above the optical phonon energy in a InAs/GaSb superlattice using saturation spectroscopy. A high-intensity free-electron laser tuned to the intersubband transition energy is used to saturate the absorption process revealing picosecond relaxation rates. The effects of the parallel magnetic field and laser energy on the relaxation processes are explored. (C) 1998 Elsevier Science B.V. All rights reserved

Two-dimensional magnetopolaron coupling to both homopolar and longitudinal optic phonons in the layer compound InSe

The authors have studied cyclotron resonance of the two-dimensional electron gas (2DEG) found in the layered semiconductor InSe at magnetic fields up to 30 T. The results show the first direct observation of resonant polaron coupling to a homopolar optic phonon, coupling via a deformation potential. They have also observed a large increase in the cyclotron effective mass as the LO phonon energy is approached, indicating the strongest polaron effects yet seen in any 2D system ( alpha approximately=0.3)

Landau level lifetimes in an InAs/AlSb quantum well determined by a picosecond far-infrared pump-probe technique

We present measurements of Landau level lifetimes in a doped quantum well structure of InAs/AlSb using a combination of pump-probe and saturation spectroscopy measurements. The cyclotron resonance was studied using far-infrared radiation from a free-electron laser has yielded the energy relaxation lifetime as a function of applied magnetic field, in the range h omega(c) = 14.5 to 18.5 meV. An energy of 15 meV corresponds to the magnetophonon resonance Delta l h omega(c) = h omega(LO) with Delta l=2. The lifetime at this energy is at or below the resolution limit of the pump-probe measurement: which is 10 ps. The results both at T = 4 K and 80 K, show that the Landau level lifetime, tau is 50 +/- 5 ps off resonance. The so-called \u27\u27LO phonon bottleneck\u27\u27 is evidently important in quenching the relaxation away from resonance

Excitation mechanism of Er in Si studied with a free-electron laser

We investigate the influence of infrared illumination using a free-electron laser on the photoluminescence of erbium-implanted silicon material. In addition to the earlier reported quenching of the Er-related photoluminescence due to dissociation of the intermediate excitation stage, two more features of the energy transfer mechanism are revealed. In the wavelength dependence of the quenching effect a local extreme is detected for a beam energy of approximately 100 meV. A possible origin of this effect is discussed. Further, the current experiment revealed the presence of non-radiative recombination centers which could transfer their energy to Er ions under the influence of the infrared beam. The centers were found to be characterized by extremely slow generation and decay kinetics. (C) 1999 Elsevier Science B.V. All rights reserved

Terahertz Response of Zero-Dimensional States in Resonant-Tunneling Diodes

The photoresponse of zero-dimensional states in double barrier resonant tunneling diodes has been observed using high intensity THz radiation (photon frequencies ranging from 4 to 10 THz) from a free-electron laser. The double barrier resonant tunneling diodes have silicon donors in the quantum well which act as individual localized tunneling channels. The high frequency response of these diodes shows additional features due to the presence of these extra channels. The temperature dependence allows us to identify the contribution of the zero-dimensional states. The absence of wavelength dependence in the observed photoresponse indicates that photoassisted tunneling does not occur under these measurement conditions. (C) 1995 American Institute of Physics

Direct observation of the LO phonon bottleneck in wide GaAs/AlxGa1-xAs quantum wells

We report the direct observation of a bottleneck in electron cooling in wide GaAs quantum wells. Intersubband lifetimes tau and their dependence on intensity, lattice temperature T-L, and well width have been measured using a ps excite-probe technique in wells with subband separation less than the longitudinal optical (LO) phonon energy. Above an electron temperature of about T-e=35 K the lifetime depends on T-e and is determined by LO-phonon emission. Below this bottleneck temperature acoustic phonons dominate the plasma cooling. An energy balance model of these interactions, with no adjustable parameters, gives good agreement with our results. At electron temperatures below 35 K we determine tau=500 and 200 ps for samples of subband energy 19.5 and 26.6 meV, respectively