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E Cojocaru

Publications and source records attributed to E Cojocaru.

8 recordsLinked to original sources
PubMed2006

Dispersion analysis of hollow-core modes in ultralarge-bandwidth all-silica Bragg fibers with nanosupports.

Dispersion of the fundamental confined modes in hollow-core all-silica Bragg fibers with nanosupports is analyzed. The transfer-matrix formalism is applied. Anomalies in the group-velocity dispersion are evidenced at long wavelengths, toward the upper limit of the bandgap. The results confirm that, as in microstructured photonic crystal fibers, this anomalous dispersion is due to prevention of the confined hollow-core modes from crossing the surface modes, the avoided crossings are more apparent in the variation of group velocity with wavelength. The dependence of these avoided crossings on the hollow-core radius and the layer thicknesses is briefly analyzed.

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PubMed2004

Quarter-wave discrete wavelet design of dichroic highly reflecting-transmitting mirrors for ultrafast solid-state lasers.

Thin-film wavelets are further analyzed for the design of dichroic mirrors for ultrafast solid-state lasers that provide both high reflectance on the lasing wavelength range and high transmittance of the pump light. Discrete quarter-wave-thick dielectric thin-film structures of homogeneous refractive indices following a quintic-wavelet envelope are considered. Relations for the reflectance on the lasing wavelength range are given. Adding several index-matching quarter-wave layers to both sides of the discrete wavelet optimizes the transmittance of the pump light. The design is further optimized to get minimum phase distortion on the lasing wavelength range.

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PubMed2003

Analytic expressions for the fourth- and the fifth-order dispersions of crossed prisms pairs.

In case of tunable ultrashort-pulse lasers, besides the prism material, separation, and insertion, one may choose the central wavelength providing a better high-order dispersion compensation. Because of errors that accumulate in numerical iterations, the analytic approach may be preferable for high-order dispersion examination. Analytic expressions for the fourth- and the fifth-order dispersions of crossed prisms pairs, both at arbitrary and Brewster-angle incidences are presented. Examples are given for e-sapphire slabs and for one or two pairs of fused-silica prisms. Results are shown providing compensation of both the second- and the third-order dispersions, by keeping as low as possible the higher-order ones.

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PubMed2002

Omnidirectional reflection from finite periodic and Fibonacci quasi-periodic multilayers of alternating isotropic and birefringent thin films.

Omnidirectional reflection from periodic and Fibonacci quasi-periodic multilayers that are embedded in an isotropic medium is further analyzed. Besides the isotropic structures, birefringent structures are considered that comprise uniaxial layers in the principal-axis system, alternating with isotropic layers so that the refractive index of isotropic layers is equal to the principal extraordinary refractive index of the uniaxial layers. The transfer-matrix method is applied, and the same formalism is used forboth the isotropic and the uniaxial media in the principal-axis system. Simple and original relations are obtained for the invariant of the one-dimensional Fibonacci sequences at oblique incidence. Numerical examples are given comparatively for the isotropic and the birefringent structures in the case of periodic and Fibonacci quasi-periodic sequences at different values of the refractive indices.

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