Department of Physicshttp://hdl.handle.net/1957/138312014-10-22T15:34:50Z2014-10-22T15:34:50ZA versatile femtosecond stimulated Raman spectroscopy setup with tunable pulses in the visible to near infraredZhu, LiangdongLiu, WeiminFang, Chonghttp://hdl.handle.net/1957/528332014-10-09T17:40:21Z2014-07-28T00:00:00ZA versatile femtosecond stimulated Raman spectroscopy setup with tunable pulses in the visible to near infrared
Zhu, Liangdong; Liu, Weimin; Fang, Chong
We demonstrate a versatile and efficient setup to perform femtosecond stimulated Raman
spectroscopy (FSRS). Technical innovations are implemented to achieve the wavelength tunability
for both the picosecond narrowband Raman pump pulse and femtosecond broadband Raman probe
pulse. Using a simplified one-grating scheme in a home-built second harmonic bandwidth compressor
followed by a two-stage noncollinear optical parametric amplifier, we tune the Raman pump
pulse from ca. 480 to 750 nm. To generate the suitable Raman probe pulse in tandem, we rely on our
recently demonstrated broadband up-converted multicolor array technique that readily provides tunable
broadband laser sidebands across the visible to near-infrared range. This unique setup has
unparalleled flexibility for conducting FSRS. We measure the ground-state Raman spectra of a
cyclohexane standard using tunable pump-probe pairs at various wavelengths across the visible
region. The best spectral resolution is ~12 cm⁻¹. By tuning the pump wavelength closer to the electronic
absorption band of a photoacid pyranine in water, we observe the pre-resonantly enhanced
Raman signal. The stimulated Raman gain of the 1627 cm⁻¹ mode is increased by over 15 times.
This is the publisher’s final pdf. The published article is copyrighted by the American Institute of Physics Publishing and can be found at: http://scitation.aip.org/content/aip/journal/apl.
2014-07-28T00:00:00ZEnhanced charge photogeneration promoted by crystallinity in small-molecule donor-acceptor bulk heterojunctionsPaudel, KeshabJohnson, BrianThieme, MattsonHaley, Michael M.Payne, Marcia M.Anthony, John E.Ostroverkhova, Oksanahttp://hdl.handle.net/1957/528262014-10-09T16:28:05Z2014-07-28T00:00:00ZEnhanced charge photogeneration promoted by crystallinity in small-molecule donor-acceptor bulk heterojunctions
Paudel, Keshab; Johnson, Brian; Thieme, Mattson; Haley, Michael M.; Payne, Marcia M.; Anthony, John E.; Ostroverkhova, Oksana
We examined sub-nanosecond time-scale charge carrier dynamics in crystalline films of a functionalized
anthradithiophene (ADT) donor (D) with three different acceptor (A) molecules. A four-fold
enhancement in ultrafast charge carrier separation efficiency was observed in D/A blends with a fullerene
acceptor added at 7–10 wt. % concentrations, whereas a gradual decrease in peak photocurrent amplitude
with acceptor concentration was observed with functionalized pentacene and indenofluorene acceptors.
The results were directly correlated with the ADT-tri(ethylsilyl)ethynyl-F donor crystallinity. In the best-performing
blends, the presence of crystalline acceptor domains was also established.
This is the publisher’s final pdf. The published article is copyrighted by the American Institute of Physics Publishing and can be found at: http://scitation.aip.org/content/aip/journal/apl.
2014-07-28T00:00:00ZLandauer, Kubo, and microcanonical approaches to quantum transport and noise: A comparison and implications for cold-atom dynamicsChien, Chih-ChunDi Ventra, MassimilianoZwolak, Michaelhttp://hdl.handle.net/1957/528022014-10-08T21:52:13Z2014-08-18T00:00:00ZLandauer, Kubo, and microcanonical approaches to quantum transport and noise: A comparison and implications for cold-atom dynamics
Chien, Chih-Chun; Di Ventra, Massimiliano; Zwolak, Michael
We compare the Landauer, Kubo, and microcanonical [J. Phys.: Condens. Matter 16, 8025 (2005)] approaches
to quantum transport for the average current, the entanglement entropy, and the semiclassical full-counting
statistics (FCS). Our focus is on the applicability of these approaches to isolated quantum systems such as
ultracold atoms in engineered optical potentials. For two lattices connected by a junction, we find that the current
and particle number fluctuations from the microcanonical approach compare well with the values predicted by
the Landauer formalism and FCS assuming a binomial distribution. However, we demonstrate that well-defined
reservoirs (i.e., particles in Fermi-Dirac distributions) are not present for a substantial duration of the quasi-steady
state. Thus, on the one hand, the Landauer assumption of reservoirs and/or inelastic effects is not necessary for
establishing a quasi-steady state. Maintaining such a state indefinitely requires an infinite system, and in this limit
well-defined Fermi-Dirac distributions can occur. On the other hand, as we show, the existence of a finite speed
of particle propagation preserves the quasi-steady state irrespective of the existence of well-defined reservoirs.
This indicates that global observables in finite systems may be substantially different from those predicted by
an uncritical application of the Landauer formalism, with its underlying thermodynamic limit. Therefore, the
microcanonical formalism which is designed for closed, finite-size quantum systems seems more suitable for
studying particle dynamics in ultracold atoms. Our results highlight both the connection and differences with
more traditional approaches to calculating transport properties in condensed matter systems, and will help guide
the way to their simulations in cold-atom systems.
This is the publisher’s final pdf. The published article is copyrighted by the American Physical Society and can be found at: http://journals.aps.org/pra/.
2014-08-18T00:00:00ZName the experiment! Interpreting thermodynamic derivatives as thought experimentsRoundy, DavidKustusch, Mary BridgetManogue, Corinnehttp://hdl.handle.net/1957/499152014-06-30T23:53:07Z2014-01-01T00:00:00ZName the experiment! Interpreting thermodynamic derivatives as thought experiments
Roundy, David; Kustusch, Mary Bridget; Manogue, Corinne
We introduce a series of activities to help students understand the partial derivatives that arise in thermodynamics. Students construct thought experiments that would allow them to measure given partial derivatives. These activities are constructed with a number of learning goals in mind, beginning with helping students to learn to think of thermodynamic quantities in terms of how one can measure or change them. A second learning goal is for students to understand the importance of the quantities held fixed in either a partial derivative or an experiment. Students additionally are given an experimental perspective—particularly when this activity is combined with real laboratory experiments—on the meaning of either fixing or changing entropy. In this paper, we introduce the activities and explain their learning goals. We also include examples of student work from classroom video and follow-up interviews.
This is an author's peer-reviewed final manuscript, as accepted by the publisher. The article is published by the American Association of Physics Teachers and can be found at: http://scitation.aip.org/content/aapt/journal/ajp.
2014-01-01T00:00:00Z