16 research outputs found
Transmittance of a tunable filter at terahertz frequencies
A metallic photonic crystal filter has been demonstrated at terahertz frequencies, with the passband tunable over the range of 365â386 GHz. Tuning is achieved by a relative lateral shift of two metallic photonic crystal plates. Each plate is comprised of two orthogonal layers of gratings and integral mounting lugs. The plates are micromachined from silicon wafers then coated in gold to provide metallic electromagnetic behavior. An insertion loss of 3â7 dB and Q in the range of 20â30 was achieved. A shift of 140 ”m gave a tuning range of 21 GHz, tuning sensitivity of 150 GHz/mm, and a fractional tuning range of 6%
Optimization of photomixers and antennas for continuous-wave terahertz emission
We have studied terahertz emission from interdigitated
finger photomixers coupled to planar antenna structures.
Using both pulsed and continuous-wave excitation, polarization
measurements reveal that the antenna design dominates the properties
of the radiated output at frequencies below 0.6 THz, while
the efficiency at higher frequencies is additionally dependent on
the design of the photomixer fingers. We have produced terahertz
maps of the device, characterizing the photomixer by measuring
the generated power as a function of the excitation position. Together,
these measurements have allowed us to understand better
the distinct roles of the photomixer and antenna in emission at
different fre
Aerobic and anaerobic energy expenditure during rest and activity in montane Bufo b. boreas and Rana pipiens
The relations of standard and active aerobic and anaerobic metabolism and heart rate to body temperature ( T b ) were measured in montane groups of Bufo b. boreas and Rana pipiens maintained under field conditions. These amphibians experience daily variation of T b over 30°C and 23°C, respectively (Carey, 1978). Standard and active aerobic and anaerobic metabolism, heart rate, aerobic and anaerobic scope are markedly temperature-dependent with no broad plateaus of thermal independence. Heart rate increments provide little augmentation of oxygen transport during activity; increased extraction of oxygen from the blood probably contributes importantly to oxygen supply during activity. Development of extensive aerobic capacities in Bufo may be related to aggressive behavior of males during breeding. Standard metabolic rates of both species are more thermally dependent than comparable values for lowland relatives. Thermal sensitivity of physiological functions may have distinct advantages over thermally compensated rates in the short growing season and daily thermal fluctuations of the montane environment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47726/1/442_2004_Article_BF00348070.pd
Spectroscopic investigations of type II GaAS/AlGaAs superlattices at elevated pressures
SIGLEAvailable from British Library Document Supply Centre- DSC:D182951 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Interwell intersubband electroluminescence from Si/SiGe quantum cascade emitters
The quantum cascade laser provides one potential method for the efficient generation of light from indirect materials such as silicon. While to date electroluminescence results from THz Si/SiGe quantum cascade emitters have shown higher output powers than equivalent IIIâV emitters, the absence of population inversion within these structures has undermined their potential use for the creation of a laser. Electroluminescence results from Si/SiGe quantum cascade emitters are presented demonstrating intersubband emission from heavy to light holes interwell (diagonal) transitions between 1.2 THz (250 ÎŒm) and 1.9 THz (156 ÎŒm). Theoretical modeling of the transitions suggests the existence of population inversion within the system
Towards a Si/SiGe quantum cascade laser for terahertz applications
While electroluminescence has been demonstrated at terahertz frequencies from Si/SiGe quantum cascade emitters, to date no laser has been achieved due to poor vertical confinement of the optical mode. A method of increasing the vertical confinement of the optical mode for a Si/SiGe quantum cascade laser is demonstrated using silicon-on-silicide technology. Such technology is used with epitaxial growth to demonstrate a strain-symmetrised 600 period Si/SiGe quantum cascade interwell emission and the polarisation is used to demonstrate the optical confinement. Electroluminescence is demonstrated at âŒ3 THz (âŒ100 ÎŒm) from an interwell quantum cascade emitter structure. Calculated model overlap and waveguide losses for ridge waveguides are comparable to values from GaAs quantum cascade lasers demonstrated at terahertz frequencies. The effects of high doping levels in Si/SiGe quantum cascade structures is also investigated with impurity emission demonstrated rather than intersubband emission for the highest doping levels used in the cascade active regions
In search of a Si/SiGe THz quantum cascade laser
While electroluminescence has been demonstrated at terahertz frequencies from Si/SiGe quantum cascade emitters, to date no laser has been achieved due to poor vertical confinement of the optical mode. A method of increasing the vertical confinement of the optical mode for a Si/SiGe quantum cascade laser is demonstrated using silicon-on-silicide technology. Such technology is used with epitaxial growth to demonstrate a strain-symmetrised 600 period Si/SiGe quantum cascade interwell emission and the polarisation is used to demonstrate the optical confinement. Electroluminescence is demonstrated at /spl sim/3 THz (/spl sim/100 /spl mu/m) from an interwell quantum cascade emitter structure. Calculated model overlap and waveguide losses for ridge waveguides are comparable to values from GaAs quantum cascade lasers demonstrated at terahertz frequencies