Efficient fiber coupling of down-conversion photon pairs

We develop and apply an effective analytic theory of a non-collinear, broadband type-I parametric down-conversion to study a coupling efficiency of the generated photon pairs into single mode optical fibers. We derive conditions necessary for highly efficient coupling for single and double type-I crystal producing polarization entangled states of light. We compare the obtained approximate analytic expressions with the exact numerical solutions and discuss the results for a case of BBO crystals.Comment: 15 pages, 4 figure

Point-by-point inscription of 250-nm-period structure in bulk fused silica by tightly-focused femtosecond UV pulses: experiment and numerical modeling

By conducting point-by-point inscription in a continuously moving slab of a pure fused silica at the optimal depth (170 μm depth below the surface), we have fabricated a 250-nm-period nanostructure with 30 nJ, 300 fs, 1 kHz pulses from frequency-tripled Ti:sapphire laser. This is the smallest value for the inscribed period yet reported, and has been achieved with radical improvement in the quality of the inscribed nanostructures in comparison with previous reports. The performed numerical modeling confirms the obtained experimental results

Efficient second harmonic generation by para-nitroaniline embedded in electro-spun polymeric nanofibres

Intense well polarized second harmonic light was generated by poly(methyl methacrylate) nanofibres with embedded para-nitroaniline nanocrystals. Subwavelength diameter fibres were electro-spun using a 1.2 weight ratio of chromophore to polymer. Analysis of the generated second harmonic light indicates that the para-nitroaniline molecules, which nominally crystalize in the centrosymmetric space group, were organized into noncentrosymmetric structures leading to a second order susceptibility dominated by a single tensor element. Under the best deposition conditions, the nanofibrers display an effective nonlinear optical susceptibility approximately two orders of magnitude greater than that of potassium dihydrogen phosphate. Generalizing this approach to a broad range of organic molecules with strong individual molecular second order nonlinear responses, but which nominally form centrosymmetric organic crystals, could open a new pathway for the fabrication of efficient sub-micron sized second harmonic light generators.Hugo Goncalves thanks the Portuguese Foundation for Science and Technology (FCT) for the support under grant PD/BD/111873/2015. The equipment used to characterize the second harmonic response of the electro-spun fibres was acquired within the framework of the Portuguese National Program for Scientific Re-equipment, contract REEQ-25/FIS/2005 with funds from POCI 2010 (FEDER) and FCT. The Raman microscope was acquired through the project nSTeP Nanostructured Systems for Tailored Performance, NORTE-07-0124-FEDER-000039, ON. 2. This work was in part developed in the scope of the projects CICECO-Aveiro Institute of Materials (UID/CTM/50011/2013), financed by national funds through the Fundacao para a Ciencia e a Tecnologia/Ministerio da Educacao e Ciencia (FCT/MEC) and co-financed by FEDER under the PT2020 Partnership Agreement. The authors are grateful to A M P Botas (University of Aveiro) for help in acquiring the hyperspectral microscopy data.info:eu-repo/semantics/acceptedVersio