132 research outputs found
Sub-10 fs pulses tunable from 480 to 980 nm from a NOPA pumped by a Yb:KGW source
We describe two noncollinear optical parametric amplifier (NOPA) systems
pumped by either the second (515 nm) or the third (343 nm) harmonic of an
Yb:KGW amplifier, respectively. Pulse durations as short as 6.8 fs are readily
obtained by compression with commercially available chirped mirrors. The
availability of both second and third harmonic for NOPA pumping allows for
gap-free tuning from 520 to 980 nm. The use of an intermediate NOPA to generate
seed light at 780 nm extends the tuning range of the third-harmonic pumped NOPA
towards 450 nm
Vibrationally coherent crossing and coupling of electronic states during internal conversion in beta-carotene
Coupling of nuclear and electronic degrees of freedom mediates energy flow in
molecules after optical excitation. The associated coherent dynamics in
polyatomic systems, however, remain experimentally unexplored. Here, we
combined transient absorption spectroscopy with electronic population control
to reveal nuclear wavepacket dynamics during the S2-S1 internal conversion in
beta-carotene. We show that passage through a conical intersection is
vibrationally coherent and thereby provides direct feedback on the role of
different vibrational coordinates in the breakdown of the Born-Oppenheimer
approximation
Direct detection of single molecules by optical absorption
The advent of single molecule optics has had a profound impact in fields
ranging from biophysics to material science, photophysics, and quantum optics.
However, all existing room-temperature single molecule methods have been based
on fluorescence detection of highly efficient emitters. Here we demonstrate
that standard, modulation-free measurements known from conventional absorption
spectrometers can indeed detect single molecules. We report on quantitative
measurements of the absorption cross section of single molecules under ambient
condition even in their dark state, for example during photoblinking or strong
quenching. Our work extends single-molecule microscopy and spectroscopy to a
huge class of materials that absorb light but do not fluoresce efficiently.Comment: 15 pages, 4 figure
Direct observation of the coherent nuclear response after the absorption of a photon
How molecules convert light energy to perform a specific transformation is a
fundamental question in photophysics. Ultrafast spectroscopy reveals the
kinetics associated with electronic energy flow, but little is known about how
absorbed photon energy drives nuclear or electronic motion. Here, we used
ultrabroadband transient absorption spectroscopy to monitor coherent
vibrational energy flow after photoexcitation of the retinal chromophore. In
the proton pump bacteriorhodopsin we observed coherent activation of hydrogen
wagging and backbone torsional modes that were replaced by unreactive
coordinates in the solution environment, concomitant with a deactivation of the
reactive relaxation pathway
Sensing force and charge at the nanoscale with a single-molecule tether
Measuring the electrophoretic mobility of molecules is a powerful
experimental approach for investigating biomolecular processes. A frequent
challenge in the context of single-particle measurements is throughput,
limiting the obtainable statistics. Here, we present a molecular force sensor
and charge detector based on parallelised imaging and tracking of tethered
double-stranded DNA functionalised with charged nanoparticles interacting with
an externally applied electric field. Tracking the position of the tethered
particle with simultaneous nanometre precision and microsecond temporal
resolution allows us to detect and quantify electrophoretic forces down to the
sub-piconewton scale. Furthermore, we demonstrate that this approach is capable
of detecting changes to the particle charge state, as induced by the addition
of charged biomolecules or changes to pH. Our approach provides an alternative
route to studying structural and charge dynamics at the single-molecule level.Comment: 23 pages, 7 figure
Wide-Field Detected Fourier Transform CARS Microscopy.
We present a wide-field imaging implementation of Fourier transform coherent anti-Stokes Raman scattering (wide-field detected FT-CARS) microscopy capable of acquiring high-contrast label-free but chemically specific images over the full vibrational 'fingerprint' region, suitable for a large field of view. Rapid resonant mechanical scanning of the illumination beam coupled with highly sensitive, camera-based detection of the CARS signal allows for fast and direct hyperspectral wide-field image acquisition, while minimizing sample damage. Intrinsic to FT-CARS microscopy, the ability to control the range of time-delays between pump and probe pulses allows for fine tuning of spectral resolution, bandwidth and imaging speed while maintaining full duty cycle. We outline the basic principles of wide-field detected FT-CARS microscopy and demonstrate how it can be used as a sensitive optical probe for chemically specific Raman imaging
Myosin II filament dynamics in actin networks revealed with interferometric scattering microscopy
The plasma membrane and the underlying cytoskeletal cortex constitute active platforms for a variety of cellular processes. Recent work has shown that the remodeling acto-myosin network modifies local membrane organization, but the molecular details are only partly understood due to difficulties with experimentally accessing the relevant time and length scales. Here, we use interferometric scattering (iSCAT) microscopy to investigate a minimal acto-myosin network linked to a supported lipid bilayer membrane. Using the magnitude of the interferometric contrast, which is proportional to molecular mass, and fast acquisition rates, we detect, and image individual membrane attached actin filaments diffusing within the acto-myosin network and follow individual myosin II filament dynamics. We quantify myosin II filament dwell times and processivity as functions of ATP concentration, providing experimental evidence for the predicted ensemble behavior of myosin head domains. Our results show how decreasing ATP concentrations lead to both increasing dwell times of individual myosin II filaments and a global change from a remodeling to a contractile state of the acto-myosin network
Electric-Double-Layer-Modulation Microscopy
The electric double layer (EDL) formed around charged nanostructures at the
liquid-solid interface determines their electrochemical activity and influences
their electrical and optical polarizability. We experimentally demonstrate that
restructuring of the EDL at the nanoscale can be detected by dark-field
scattering microscopy. Temporal and spatial characterization of the scattering
signal demonstrates that the potentiodynamic optical contrast is proportional
to the accumulated charge of polarisable ions at the interface and its time
derivative represents the nanoscale ionic current. The material-specificity of
the EDL formation is used in our work as a label-free contrast mechanism to
image nanostructures and perform spatially-resolved cyclic voltametry on ion
current density of a few attoamperes, corresponding to the exchange of only a
few hundred ions.Comment: 6 pages, 4 figrue
Peranan Kepemimpinan Camat Dalam Menumbuhkan Kedisiplinan Pegawai Di Kantor Kecamatan Jebres Kota Surakarta
Absract: The objectives of this research are to investigate: (1) how Chief of Jebres Sub-district Office, Surakarta city plays his leadership role in growing the discipline behavior of its employees; (2) what constraints are encountered by Chief of Jebres Sub-district Office, Surakarta city in internalizing the discipline of its employees; and (3) what solutions are taken by Chief of Jebres Sub-district Office to deal with the prevailing constraints to the materialization of the discipline behavior of its employees. This research used the qualitative embedded single case study method. The results of the research are as follows: 1) Chief of Jebres Sub-district Office, Surakarta city plays his leadership role through the discipline behavior internalizations such as: (a) giving exemplification through discipline attitude; (b) giving motivation to the employees; (c) attempting to fulfill their needs and prosperity; and (d) implementing the discipline upholding consistently. 2) The constraints occurring in nurturing the discipline of the employees of Jebres Sub-district Office are as follows: (a) internal constraints: some employees bear the characters and personalities which are apathetic to advices, and some are lack of responsibilities in executing their duties and work and (b) external constraints: the external constraints occurring in internalizing the discipline of the employees of Jebres Sub-district Office are mainly related to the work environment. 3) The prevailing constraints occurring in internalizing the discipline of the employees are as follows: (a) upholding the prevailing laws and regulations and nurturing the employees; and (b) maintaining the communication and good relations among the employees
- …