Generation of structured coherent extreme ultraviolet beams from an MgO crystal.

Short wavelength high-harmonic sources are undergoing intense development for applications in spectroscopy and microscopy. Despite recent progress in peak and average power, spatial control over coherent extreme ultraviolet (XUV) beams remains a formidable challenge due to the lack of suitable optical elements for beam shaping and control. Here we demonstrate a robust and precise approach that structures XUV high-order harmonics in space as they are emitted from a nanostructured MgO crystal. Our demonstration paves the way for bridging the numerous applications of shaped light beams from the visible to the short wavelengths, with potential uses for applications in microscopy and nanoscale machining.

Detection of leukemia markers using long-range surface plasmon waveguides functionalized with Protein G.

A novel optical biosensor based on long-range surface plasmon-polariton (LRSPP) waveguides is demonstrated for the detection of leukemia markers in patient serum using a functionalization strategy based on Protein G. The sensor consists of thin straight Au waveguides (5 µm × 35 nm × 3.2 mm) embedded in fluoropolymer CYTOP™ with a fluidic channel etched into the top cladding. B-cell leukemia is characterized by a high B-cell count and abnormal distribution of immunoglobulin G kappa (IgGκ) and lambda (IgGλ) light chains in serum. The detection of leukemic abnormalities in serum was performed based on determining IgGκ-to-IgGλ ratios (κ : λ). Three patient sera were tested: high kappa (HKS, κ : λ ~12.7 : 1), high lambda (HLS, λ : κ ~6.9 : 1) and normal (control) sera (NS, κ : λ ~1.7 : 1). Au waveguides were functionalized with Protein G and two complementary immobilization approaches were investigated: a) the reverse approach, where the Protein G surface is functionalized with patient serum and then tested against goat anti-human IgG light chains in buffer, and b) the direct approach, where the Protein G surface is functionalized with goat anti-human IgGs first and then tested against patient serum. The reverse approach was found to be more effective and robust because Protein G-functionalized surface performs as an "immunological filter" by capturing primarily IgGs out of the pool of serum proteins. For the reverse approach, the ratios measured were 3.7 : 1(κ : λ), 9.7 : 1(λ : κ) and 1.9 : 1(κ : λ) for HKS, HLS and NS, respectively, which compare favorably with corresponding protein densitometry measurements. The respective ratios for the direct approach were 2.6 : 1(κ : λ), 2.6 : 1(λ : κ) and 1.7 : 1(κ : λ). The binding strength and cross-reactivity of goat anti-human IgGs light chains were also determined using pure solutions. The LRSPP biosensor along with the innovative "reverse approach" can provide a low-cost and compact solution to B-cell leukemia screening.

Plasmon-polariton modes guided by a metal film of finite width bounded by different dielectrics.

The properties of some purely bound plasmon-polariton modes guided by an asymmetric waveguide structure composed of a thin lossy metal film of finite width supported by a dielectric substrate and covered by a different dielectric superstrate are presented for what is believed to be the first time. The mode spectrum supported by these structures is quite different from the spectrum supported by corresponding asymmetric slab structures or similar finite-width symmetric waveguides. Unlike these limiting cases, the dispersion with film thickness exhibits an unusual oscillatory character that is explained by a "switching" of constituent interface modes. This mode switching is unique to asymmetric finite-width structures. Above a certain cut-off film thickness, the structure can support a long-ranging mode and its attenuation decreases very rapidly with decreasing film thickness, more so than the long-ranging mode in symmetric structures. Also, the cutoff thickness of the long-ranging mode is larger than the cutoff thickness of the long-ranging mode in the corresponding asymmetric slab waveguide, which implies that propagation along finite-width films is more sensitive to the asymmetry in the structure than propagation along a similar slab structure. Both of these results are potentially useful for the transmission and control of optical radiation.

Efficient and accurate numerical analysis of multilayer planar optical waveguides in lossy anisotropic media.

This paper discusses a numerical method for computing the electromagnetic modes supported by multilayer planar optical waveguides constructed from lossy or active media, having in general a diagonal permittivity tensor. The method solves the dispersion equations in the complex plane via the Cauchy integration method. It is applicable to lossless, lossy and active waveguides, and to AntiResonant Reflecting Optical Waveguides (ARROW's). Analytical derivatives for the dispersion equations are derived and presented for what is believed to be the first time, and a new algorithm that significantly reduces the time required to compute the derivatives is given. This has a double impact: improved accuracy and reduced computation time compared to the standard approach. A different integration contour, which is suitable for leaky modes is also presented. Comparisons are made with results found in the literature; excellent agreement is noted for all comparisons made.

Plasmon polariton modes guided by a metal film of finite width.

The properties of purely bound plasmon-polariton modes guided by a symmetric thin metal film of finite width are described for what is believed to be the first time, and a suitable mode nomenclature for identifying them is proposed. The dispersion characteristics of the modes as a function of film thickness are presented. It has been found that long-range plasmon-polariton modes exist in a symmetric film structure and that one of them may be suitable for optical signal transmission.

Experimental observation of plasmon polariton waves supported by a thin metal film of finite width.

What are believed to be the first experimental observations of the existence of long-range plasmon-polariton waves, guided by a thin metal film of finite width, are presented. A waveguide composed of an 8-mum-wide, 20-nm-thick, 3.5-mm-long Au metal film embedded in SiO (2) was successfully excited at a free-space wavelength of 1.55 mum in an end-fire experiment. The theoretical nature of the phenomenon is described, and experimental observations of field confinement provided by this metal waveguide are presented in detail.