No abstract

Surface-Enhanced Raman spectroscopy (SERS) has been increasingly utilized as an analytical technique with significant chemical and biological applications [1][2][3][4][5][6][7]. However, production of a robust, homogeneous and large-area SERS substrate with the same ultra high sensitivity and reproducibility still remain an important issue. Here, we describe a large-area ultrahighuniformity tapered silver nanopillar array made by laser interference lithography on the entire surface of a 6-inch wafer. Also presented is the rigorous optical characterization method of the tapered nanopillar substrate to accurately quantify the Raman enhancement factor, uniformity and repeatability. An average homogeneous enhancement factor of close to 10 8 was obtained for benzenethiol adsorbed on a silver coated nanopillar substrate.

No abstract

Experimental measurements of the absolute energy yields and conversion efficiencies of high-order harmonic radiation in the spectral range of 31 to 17 nm are presented. We examine energy yields as a function of a number of parameters including drive laser wavelength, target atom, focal geometry, and peak laser intensity, and we have generated individual harmonics with energies as high as 60 nJ at wavelengths as short as 20 nrn. Under optimum conditions, we find that conversion efficiencies of as high as 10 into each harmonic are possible.PACS number(s): 42.65. Ky, 32.80.Rm The generation of high-order harmonic radiation by an intense laser pulse is now a well documented phenomenon [1,2] and is one of the principal new sources of bright XUV radiation being developed for a variety of applications that rely on the interaction of short-wavelength radiation with matter. To date, wavelengths as short as 7 nm have been generated by harmonic generation [3,4]. When compared to other XUV sources such as synchrotrons, FELs (freeelectron lasers), and x-ray lasers, harmonic generation exhibits many advantages such as short pulse duration (40 fs -100 ps), high peak brightness, and tunability. Harmonic generation has been extensively studied by a number of groups using drive lasers with a range of wavelengths and pulse widths [3 -8] and much work has been done to understand the short-wavelength limit and related scaling formulas.In spite of these early studies, the work of characterizing and optimizing high-order harmonic generation as a general purpose XUV source is incomplete. A number of groups have examined the angular divergence and spatial coherence of the harmonics [9 -11]. Previous experiments have also characterized the linewidths of the harmonics [12,13]. The utilization of high-order harmonics in applications has been recently demonstrated by Balcou et aI. , who have used photon energies in excess of 100 eV in photoionization spectroscopy [14].Though there have been preliminary studies [7], a complete measurement of the photon yields achievable with high-order harmonics has not yet been undertaken. In this Rapid Communication we report on measurementsof the absolute energy yields and conversion efficiencies of harmonics generated in the 31 -17-nm wavelength range under a variety of conditions. These experiments were performed using a Nd:glass laser that produced 650-fs pulses at 1052.7 nm with energies up to 8 J, and pulses of its second harmonic at 526 nm with energies up to 4 J [15].The laser was focused into the plume of a pulsed, supersonic nozzle, gas jet. This jet produces localized atomic densities from 10 to 2 X 10 atoms/cm and exhibits a linear density dependence with gas jet backing pressure, verified by backward stimulated Raman scattering measurements [16]. The interaction length through the gas jet is 0.8 mm. Our measurements were conducted with an atom density of 2X10' atoms/cm~30%. The harmonic radiation is sampled by an astigmatic compensated, grazing incidence, XUV spectrometer. A calibrated alum...

We investigate tunable plasmon resonant cavity arrays in paired parallel nanowire waveguides. Resonances are observed when the waveguide length is an odd multiple of quarter plasmon wavelengths, consistent with boundary conditions of node and antinode at the ends. Two nanowire waveguides satisfy the dispersion relation of a planar metal−dielectric−metal waveguide of equivalent width equal to the square field average weighted gap. Confinement factors over 103 are possible due to plasmon focusing in the interwire space.