Search results for " laser"
showing 10 items of 1455 documents
Inelastische Lichtstreuung von Cellulosenitratlösungen
1974
Es wird ein Homodyngerat zur Messung der inelastischen Lichtstreuung beschrieben, das mit einem Argon-Ionenlaser ausgerustet ist und mit einem Autokorrelator arbeitet. Das Gerat wird benutzt, um das Verhalten der Fadenmolekule von Cellulosenitrat in verdunnter Losung zu untersuchen. Mit dieser Technik wird es moglich, sogar fur unabgebaute native Cellulose die Diffusionskoeffizienten der Translation D zu bestimmen, die ein sehr niedriges D (<10−7 cm2 s−1) aufweisen und bisher nur naherungsweise bekannt waren, da die konventionellen Mestechniken der optischen Beobachtung eines Konzentrationsausgleiches dann recht ungenau werden. A homodyne light beat spectrometer equipped with an argon ion l…
Ultrafast Twisting of the Indoline Donor Unit Utilized in Solar Cell Dyes: Experimental and Theoretical Studies
2015
Previous time-resolved measurements on D149, the most-studied dye of the indoline family, had shown a fast time-component of 20–40 ps that had tentatively been attributed to structural relaxation. Using femtosecond transient absorption, we have investigated the isolated indoline donor unit (i.e., without acceptor group) and found an ultrafast decay characterized by two lifetimes of 3.5 and 23 ps. Density functional theory calculations show π-bonding and π*-antibonding character of the central ethylene group for the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO), respectively. The LUMO is localized on the flexible vinyl-diphenyl region of the donor unit and a twist…
Triple-resonance autoionization of uranium optimized for diode laser excitation
2007
Abstract The photoionization of uranium via three-step excitation has been optimized for isotope selective trace analysis. A search found 13 new J = 6, 7, and 8 odd-parity states in the 36,850–37,200 cm− 1 region that allow blue–red–red three-photon excitation at wavelengths favorable for commercial diode laser systems. From each of these 13 states, near-threshold autoionization spectra were recorded at a resolution of 3 × 10− 4 cm− 1. Some 30 even-parity autoionizing levels with J = 5 to 9 have also been observed and characterized. Comparison of the spectra allows J assignment for the new intermediate levels as well as selection of an optimized path for trace analysis. We show that, for a …
Dynamics of ground and excited state chlorophylla molecules in pyridine solution probed by femtosecond transient absorption spectroscopy
1999
Abstract Femtosecond pump–probe spectroscopy was used to investigate the ground and excited state dynamics of chlorophyll a (Chl a ) in pyridine following excitation by a 100 fs optical pulse. The transient absorption spectrum and kinetics reveal spectral evolution on two ultrafast time scales: ∼100 fs and ∼3 ps. We attribute these dynamics to ground-state transient hole-burning and solvation dynamics. Transient absorption anisotropy at early times (∼500 fs) was measured for Chl a in pyridine and shows a pronounced wavelength dependence, where anisotropy varies between 0 and 0.5. Strong contribution from excited state absorption is the origin of the variation.
Resonant Ionization Laser Ion Source for Radioactive Ion Beams
2009
A resonant ionization laser ion source based on all‐solid‐state, tunable Ti:Sapphire lasers is being developed for the production of pure radioactive ion beams. It consists of a hot‐cavity ion source and three pulsed Ti:Sapphire lasers operating at a 10 kHz pulse repetition rate. Spectroscopic studies are being conducted to develop ionization schemes that lead to ionizing an excited atom through an auto‐ionization or a Rydberg state for numerous elements of interest. Three‐photon resonant ionization of 12 elements has been recently demonstrated. The overall efficiency of the laser ion source measured for some of these elements ranges from 1 to 40%. The results indicate that Ti:Sapphire lase…
Demonstration of an efficient pumping scheme for a 7.36-nm Ni-like samarium soft x-ray laser
2010
The demonstration of a 7.36 nm Ni-like Sm soft x-ray laser pumped by 36 J of a Nd:glass chirped pulse amplification laser is presented. Double-pulse single-beam non-normal incidence pumping was applied for the efficient soft x-ray laser generation. Here the applied technique included a new single optic focusing geometry for large beam diameters, a single-pass grating compressor traveling-wave tuning capability and an optimized high energy laser double-pulse. This scheme has the potential for even shorter wavelength soft x-ray laser pumping.
Ytterbium-doped fibers for high-power fiber lasers
2021
Ytterbium (Yb) doped optical fibers are widely used in high-power applications and ultrafast lasing since they show adequate power-handling capability and provide desirable beam quality. Yb-doped fibers with large core area can support high power but often act as a multimode fiber and compromise the output beam quality. Hence, it is important to attain a proper balance between the power-handling capability and the beam quality. Yb-doped fibers as a gain medium in pulsed fiber laser systems are prone to nonlinear optical effects due to the presence of high peak power in the ultrashort pulses. Nonlinearity such as self phase modulation (SPM) affects the width and the shape of the pulse, both …
Pigment−Pigment and Pigment−Protein Interactions in Recombinant Water-Soluble Chlorophyll Proteins (WSCP) from Cauliflower
2007
Plants contain water-soluble chlorophyll-binding proteins (WSCPs) that function neither as antennas nor as components of light-induced electron transfer of photosynthesis but are likely constituents of regulatory protective pathways in particular under stress conditions. This study presents results on the spectroscopic properties of recombinant WSCP from cauliflower reconstituted with chlorophyll b (Chl b) alone or with mixtures of Chl a and Chl b. Two types of experiments were performed: (a) measurements of stationary absorption spectra at 77 and 298 K and CD spectra at 298 K and (b) monitoring of laser flash-induced transient absorption changes with a resolution of 200 fs in the time doma…
Characterisation of Chlorophyll a and Chlorophyll b Monomers in Various Solvent Environments with Ultrafast Spectroscopy
1998
In photosynthesis the energy from the sun is captured by light harvesting chlorophyll pigments and converted to stable chemical energy, by the photochemical reaction center. Photosynthetic energy transfer in the antenna systems of green plants has previously been studied by ultrafast time resolved spectroscopy. The characteristics of the chlorophyll pigments itself is important to study in order to understand the dynamics on a femtosecond timescale. One way to study the energy transfer is to use transient absorption spectroscopy and follow the increase or decrease in the transient absorption signal with time (1). Another way to study the energy transfer is to monitor the change in dichroism…
Light-harvesting chlorophyll protein (LHCII) drives electron transfer in semiconductor nanocrystals
2017
Type-II quantum dots (QDs) are capable of light-driven charge separation between their core and the shell structures; however, their light absorption is limited in the longer-wavelength range. Biological light-harvesting complex II (LHCII) efficiently absorbs in the blue and red spectral domains. Therefore, hybrid complexes of these two structures may be promising candidates for photovoltaic applications. Previous measurements had shown that LHCII bound to QD can transfer its excitation energy to the latter, as indicated by the fluorescence emissions of LHCII and QD being quenched and sensitized, respectively. In the presence of methyl viologen (MV), both fluorescence emissions are quenched…