ABSTRACT
This paper describes a filled-aperture coherent beam combining (CBC) system based on locking of optical coherence via single-detector electronic-frequency tagging (LOCSET). The sensing and control architecture is implemented using a field-programmable gate array and high-bandwidth electro-optic phase modulators. The all-fiber optical configuration consists of a narrow linewidth 1560 nm seed laser separated into three channels, each containing 7 W erbium-doped fiber amplifiers. The system was demonstrated experimentally, achieving a total stabilized output power of 20 W, a combination efficiency greater than 95%, and an output RMS phase stability of λ/493. As this architecture employs an entirely digital sensing and control scheme based on LOCSET, it presents a highly scalable and cost-effective solution for CBC that is wavelength agnostic and can support an arbitrarily large number of channels.
ABSTRACT
The far-field spatial distributions of higher order electro-magnetic mode supercontinua were resolved spectrally and recorded. The supercontinua were created by precise control and direction of input pump energy offset axially from the photonic crystal fiber core. By processing the measured spectra, the spatial mode shape at each wavelength was determined. Discrete spectral features are associated with symmetrical spatial patterns arising from the host fiber geometry and suggest the electromagnetic mode pairing between the longer wavelength solitons and associated visible dispersive waves. Clear differences between supercontinua generated in fundamental and higher order electromagnetic modes exist. These data should inform theoretical studies as the solitons and the dispersive wave generated by fission may be matched by spatial orientation of the electromagnetic mode that both occupy.
ABSTRACT
This paper describes the development and preliminary testing of a competitive surface-enhanced Raman scattering (SERS) immunoassay for calcitriol, the 1,25-dihydroxy metabolite (1,25-(OH)(2)-D(3)) of vitamin D(3). Deficiencies in 1,25-(OH)(2)-D have been linked to renal disease, while elevations are linked to hypercalcemia. Thus, there has been a sharp increase in the clinical demand for measurements of this metabolite. The work herein extends the many attributes of SERS-based sandwich immunoassays that have been exploited extensively in the detection of large biolytes (e.g., DNA, proteins, viruses, and microorganisms) into a competitive immunoassay for the low level determination of a small biolyte, 1,25-(OH)(2)-D(3) (M(w) = 416 g mol(-1)). The assay uses surface modified gold nanoparticles as SERS labels, and has a dynamic range of 10-200 pg mL(-1) and a limit of detection of 8.4 ± 1.8 pg mL(-1). These analytical performance metrics match those of tests for 1,25-(OH)(2)-D(3) that rely on radio- or enzyme-labels, while using a much smaller sample volume and eliminating the disposal of radioactive wastes. Moreover, the SERS-based data from pooled-patient sera show strong agreement with that from radioimmunoassays. The merits and potential utility of this new assay are briefly discussed.