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- Migal, E. A., et al.
(författare)
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Role of deposited energy density and impact ionization in the processes of femtosecond laser-matter interaction in solids: scaling from visible to mid-IR
- 2019
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Ingår i: Nonlinear Optics and Applications XI. Proceedings Vol. 11026. SPIE OPTICS + OPTOELECTRONICS, 1-4 April 2019. - : SPIE. - 9781510627192
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Konferensbidrag (refereegranskat)abstract
- The deposited energy density (DED) serves as a key parameter in the process of the femtosecond laser pulse energy delivery into the bulk of transparent dielectrics. The laser-induced micromodification can be created if the value of DED exceeds a certain threshold, which is specific for each material and does not depend on the laser wavelength. In this contribution, we present a comprehensive study of the DED evolution with the driving pulse energy and wavelength under femtosecond microstructuring of transparent dielectrics. To precisely determine the laser impact area we applied for the first time a real-time diagnostic of microplasma based on third harmonic generation. This technique gives submicron spatial resolution and is extremely sensitive to the free electron density (about 10(-5) of the critical electron density). We found out that the threshold DED equals to approximately 2.5 kJ/cm(3) for fused silica and roughly corresponds to excess of glass transition temperature. The highest DED is achieved for the shortest wavelength (620 nm) and equals to 16 kJ/cm(3).
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| 3. |
- Oskolkov, Nikolay, et al.
(författare)
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Nematic Ordering of Polymers in Confined Geometry Applied to DNA Packaging in Viral Capsids.
- 2011
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:3, s. 422-432
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Tidskriftsartikel (refereegranskat)abstract
- A density functional theory of the spatial distribution and biaxial nematic order of polymers of arbitrary length and rigidity inside a spherical cavity is proposed. The local order of different chain segments is considered as an alignment to a spatially varying director field of cylindrical symmetry. The steric interactions are taken into account in the second virial approximation. Polymer density and orientational order distributions inside the spherically cavity are the principal results. It was found that short and flexible polymers were located at the center of the sphere and were orientationaly disordered. Upon increasing polymer length and/or polymer rigidity, the location of the polymer was continuously shifted toward the surface of the spherical cavity and the polymer segments became gradually more aligned. Parameters have been selected to model the behavior of genomes in spherical viral capsids.
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- Potemkin, F. V., et al.
(författare)
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Influence of wave-front curvature on supercontinuum energy during filamentation of femtosecond laser pulses in water
- 2018
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 97:3
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that using spatially divergent incident femtosecond 1240-nm laser pulses in water leads to an efficient supercontinuum generation in filaments. Optimal conditions were found when the focal plane is placed 100-400 mu m before the water surface. Under sufficiently weak focusing conditions [numerical aperture (NA) < 0.2] and low-energy laser pulses, the supercontinuum energy generated in divergent beams is higher than the supercontinuum energy generated in convergent beams. Analysis by means of the unidirectional pulse propagation equation shows a dramatic difference between filamentation scenarios of divergent and convergent beams, that explains corresponding features of the supercontinuum generation. Under strong focusing conditions (NA >= 0.2) and high-energy laser pulses, the supercontinuum generation is suppressed for convergent beams in contrast to divergent beams that nevertheless are shown experimentally to allow supercontinuum generation. The presented technique of the supercontinuum generation in divergent beams in water is highly demanded in a development of femtosecond optical parametric amplifiers.
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