4,970 research outputs found
Pump-probe measurements in asymmetric stepped quantum wells using FELIX
No full textThree beam pump-probe measurements in asymmetric stepped quantum wells were conducted using the FELIX free electron laser. We have measured electron intersubband lifetimes of 1.8 ps and 2.5 ps in two GaAs/AlxGa1-xAs stepped quantum well samples. The two samples differ in the total number of quantum wells (80 and 50 periods), donor doping concentrations at the barrier (2 x 1017 cm-3 and 2 x 1018 cm-3) and barrier height (x=0.45 and x=0.35). Experiments were conducted on both samples at temperatures ranging from 4K to room temperature using a liquid Helium cooled cryostat. At saturation pump intensities, however, we observed an absorptive signal of sub-nanosecond lifetime following a normal positive transmissive signal of the order of picosecond lifetime. This slow decay absorptive signal is relatively stronger in intensity than the positive transmissive signal. The absorptive signal is believed to be caused by the absorption from the free electrons pumped from the ground subband to the continuum conduction band in the barrier layers associated with incoherent two-photon process. A three-level electron transition model was built to simulate the two-photon absorption process, which agrees well with the experimental data. The strong intensity dependent feature of the slow decay signal is also consistent with our model
HemosIL D-dimer HS assay in the diagnosis of deep vein thrombosis and pulmonary embolism. Results of a multicenter management study.
No full textWavelength tunable 10-GHz 3-ps pulse source using a dispersion decreasing fiber-based nonlinear optical loop mirror
No full textWe experimentally demonstrate the use of a dispersion decreasing fiber (DDF)-based nonlinear optical loop mirror (NOLM) for the generation of wavelength tunable soliton-like pulses at a repetition rate of 10 GHz. We compress ~12 ps Gaussian pulses from an electro-absorption modulator (EAM) (followed by 125 m of DCF for preliminary linear dispersion compensation) into 3 ps pedestal-free pulses using both high-order soliton compression and nonlinear switching effects within an 8.5 km DDF-based loop mirror. The output pulses from the DDF-based NOLM show considerable pedestal reduction compared to those obtained by directly compressing the EAM seed pulses via a single passage through the DDF. Wavelength tuning of the compressed pulses over a ~15 nm bandwidth (from 1541 to 1556 nm) is demonstrated without a significant increase in pulse duration or degradation in pulse quality
Intersubband lifetimes and free carrier effects in optically pumped far infrared quantum wells laser structures
No full textElectron intersubband lifetimes of 1.8 ps and 2.5 ps were measured in GaAs/AlGaAs asymmetric stepped quantum well samples by using a pump–probe three-beam technique at 4 K to room temperature. At high pump intensities, an absorptive signal of sub-nanosecond lifetime was detected following a normal positive transmissive signal of picosecond lifetime. This absorptive signal is believed to be caused by the absorption from the free electrons pumped from the ground subband to the continuum conduction band in the barrier layers associated with incoherent multi-photon process. The intersubband lifetimes and free carrier effects play an important role in optically pumped multiple-quantum-well far infrared lasers. A three-level electron transition model is built to simulate the process, which agrees very well with the experimental data
Player agency in interactive narrative: audience, actor & author
No full textThe question motivating this review paper is, how can
computer-based interactive narrative be used as a constructivist learn-
ing activity? The paper proposes that player agency can be used to
link interactive narrative to learner agency in constructivist theory,
and to classify approaches to interactive narrative. The traditional
question driving research in interactive narrative is, ‘how can an in-
teractive narrative deal with a high degree of player agency, while
maintaining a coherent and well-formed narrative?’ This question
derives from an Aristotelian approach to interactive narrative that,
as the question shows, is inherently antagonistic to player agency.
Within this approach, player agency must be restricted and manip-
ulated to maintain the narrative. Two alternative approaches based
on Brecht’s Epic Theatre and Boal’s Theatre of the Oppressed are
reviewed. If a Boalian approach to interactive narrative is taken the
conflict between narrative and player agency dissolves. The question
that emerges from this approach is quite different from the traditional
question above, and presents a more useful approach to applying in-
teractive narrative as a constructivist learning activity
Passively mode-locked diode-pumped surface-emitting semiconductor laser
No full textA surface-emitting semiconductor laser has been passively mode locked in an external cavity incorporating a semiconductor saturable absorber mirror. The gain medium consists of a stack of 12 InGaAs-GaAs strained quantum wells, grown above a Bragg mirror structure, and pumped optically by a high-brightness diode laser. The mode-locked laser emits pulses of 22 ps full-width at half maximum duration at 1030 nm, with a repetition rate variable around 4.4 GHz
“Escape to Impersonality”: Personas in H.G. Wells’ Experiment in Autobiography
No full textThis article reads H.G. Wells’ Experiment in Autobiography (1934) through the lens of Persona Studies to situate life writing in the context of (post) human rights, biopolitics, and surveillance capitalism. Carl Jung’s concept of persona pervades Wells’ writing and life. Persona, for Wells, is the path towards the “impersonality” that is essential to humanity’s evolution. Wells recognized that personas are plural, inconsistent, and evolving performances whose fictional unity, if enacted deliberately without self-delusion, can serve real ends—such as the prolific creative and intellectual work that earned him four nominations for the Nobel Prize in Literature. Further, Wells presents life writing as a human right: the right to tell our own stories, access our own records, represent the personas which we elect, and enjoy the freedom to evolve from one persona to the next. A persona’s double movement, poised between the personal and the impersonal, the individual and the world, the biological and the historical, represents both the form and content of Wells’ Experiment in Autobiography. If Wells gives us reason to hope amidst a global pandemic, the specter of World War III, the proliferation of nuclear arms, and climate catastrophe, it is that these existential threats help us answer the question, “What will come after man?” To consider the answer is not to give up on humankind. On the contrary, to imagine non/post human lifeforms is essential in defining human rights and securing a human future
Multi phonon emission in InAs quantum wells studied with a free electron laser and high pulsed magnetic fields
No full textThe short pulsed, tunable output from the Dutch free electron laser FELIX. coupled with a 45 T pulsed magnet has been used to measure the non-radiative decay rates between Landau levels in n-type InAs/GaSb quantum wells. The decay rate is 2 ps(-1) when the cyclotron resonance energy, E-CR = E-LO = 30 meV, and only slightly less, 0.8 ps(-1) when E-CR = 2E(LO) when the principal relaxation pathway is the emission of multiple longitudinal optical (LO) phonons, (C) 2001 Elsevier Science B.V. All rights reserved
Determination of the intersubband lifetime in Si/SiGe quantum wells
No full textA direct pump and probe lifetime determination in the ps regime has been made in quantum wells of Si/Si1-xGex. We have used an rf linac-pumped free-electron laser to determine the relaxation time associated with intersubband absorption in Si/SiGe quantum wells with a subband separation smaller than the optical phonon energy. This measurement yields a lifetime of T1=30 ps.© 1995 American Institute of Physics.</p
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