A recently devised new method for numerical Abel inversion is compared with four other commonly used methods. One of them, the convolution method, is employed in computer tomography for reconstructing asymmetrical objects. It is investigated whether this method can be adapted for the case of radial symmetry.As a first approach the comparison is performed by computer simulation. Special attention is given to the propagation of errors according to their origin. The result is a recipe for minimizing errors and for choosing the optimal method for reconstruction.The second step is a comparison of experimentally obtained radial profiles with functions resulting from Abel inversion of measured side-on data. Thus it is shown that the concept developed by computer simulation can be applied in practice.
A styrene copolymer of 4-vinylbenzyl thiocyanate (PST-co-VBT) was employed as recording
material for optical interference patterns with periods Λ < 1 μm. Using lower intensity laser
irradiation (4 mJ cm-2, λ = 266 nm), refractive index gratings were produced in PST-co-VBT by an UV-induced photoisomerization SCN → NCS. Subsequent modification of the
patterns with gaseous amines yielded surface relief gratings via the formation of derivatives
of thiourea. Laser irradiation with higher pulse energies (7 mJ cm-2, λ = 266 nm) directly
produced surface relief gratings via laser ablation (modulation depth 30 nm). Also these
gratings were reactive toward amine reagents and allowed a selective functionalization of
the grooves of the relief (“reactive gratings”). Under selected conditions, a doubling of the
grating frequency was achieved by postexposure modification with gaseous amines. Optically
inscribed gratings in PST-co-VBT were employed as optical resonators for distributed
feedback (DFB) lasing. With a laser dye (DCM) dissolved in PST-co-VBT, optically pumped
DFB laser action was observed after inscribing index and relief gratings. The pumping
threshold for lasing I
th was 250 nJ cm-2 at λ = 532 nm.
Laser ignition has been discussed widely as a potentially superior ignition source for technical appliances such as internal combustion engines. Ignition strongly affects overall combustion, and its early stages in particular have strong implications on subsequent pollutant formation, flame quenching, and extinction. Our research here is devoted to the experimental investigation of the early stages of laser-induced ignition of CH4/air mixtures up to high pressures. Tests were performed in a 0.9-l combustion cell with initial pressures of up to 25 bar with stoichiometric to fuel-lean mixtures using a 5-ns 50-mJ 1064-nm Nd:YAG laser. Laserinduced fluorescence (LIF) was used to obtain two dimensionally resolved images of the OH radical distribution after the ignition event. These images were used to produce an animation of laser ignition and early flame kernel development. Schlieren photography was used to investigate the laserinduced shock wave, hot core gas, and developing flame ball. We extend existing knowledge to high-pressure regimes relevant for internal combustion engines.
A time-dependent, zero-dimensional collisional-radiative model has been developed to study capillary discharge plasmas in view of possibilities for obtaining population inversion leading to laser action in the extreme ultraviolet and soft x-ray spectral region, by amplifying the Balmer-α (Hα) line of different hydrogenlike ions with nuclear charges from Z=3 to Z=6. The model is described in detail, and results for the case of a carbon plasma are presented. Limitations of the model are discussed and comparison is made between our calculations and recent experimental results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.