The high-resolution absorption spectroscopy branch on the VUV beamline DESIRS at SOLEIL.

A VUV absorption spectroscopy facility designed for ultra-high spectral resolution is in operation as a dedicated branch on the DESIRS beamline at Synchrotron SOLEIL. This branch includes a unique VUV Fourier transform spectrometer (FTS) and a dedicated versatile gas sample chamber. The FTS instrument can cover a large UV-VUV spectral range from 4 to 30 eV, with an ultimate line width of 0.08 cm(-1) on a large spectral window, ΔE/E = 7%, over which all spectral features can be acquired in a multiplex way. The performance can be considered to be a middle ground between broadband moderate-resolution spectrometers based on gratings and ultra-high-spectral-resolution VUV tunable-laser-based techniques over very narrow spectral windows. The various available gaseous-sample-handling setups, which function over a wide range of pressures and temperatures, and the acquisition methodology are described. A selection of experimental results illustrates the performance and limitations of the FTS-based facility.

VUV Fourier-transform absorption study of the Lyman and Werner bands in D2.

An extensive survey of the D(2) absorption spectrum has been performed with the high-resolution VUV Fourier-transform spectrometer employing synchrotron radiation. The frequency range of 90,000-119,000 cm(-1) covers the full depth of the potential wells of the B (1)Σ(u)(+), B' (1)Σ(u)(+), and C (1)Π(u) electronic states up to the D(1s) + D(2l) dissociation limit. Improved level energies of rovibrational levels have been determined up to respectively v = 51, v = 13, and v = 20. Highest resolution is achieved by probing absorption in a molecular gas jet with slit geometry, as well as in a liquid helium cooled static gas cell, resulting in line widths of ≈0.35 cm(-1). Extended calibration methods are employed to extract line positions of D(2) lines at absolute accuracies of 0.03 cm(-1). The D (1)Π(u) and B'' (1)Σ(u)(+) electronic states correlate with the D(1s) + D(3l]) dissociation limit, but support a few vibrational levels below the second dissociation limit, respectively, v = 0-3 and v = 0-1, and are also included in the presented study. The complete set of resulting level energies is the most comprehensive and accurate data set for D(2). The observations are compared with previous studies, both experimental and theoretical.

Probing multilayer stack reflectors by low coherence interferometry in extreme ultraviolet.

We use low coherence interferometry to investigate the depth structure of a complex multilayer stack reflector. The probing instrument is an interferometer based on a Fresnel's bi-mirror illuminated by relatively wide-band synchrotron undulator light near 13.5 nm. Simulations clearly confirm that our test object generates two back propagated signals that behave as if reflected on two effective planes. First results in this spectral range may open the way to a new physical approach to extreme ultraviolet sample characterization in the form of line-scan optical coherence tomography.

Wave-front correction methods for extreme-ultraviolet multilayer reflectors.

In this theoretical study we show that by removing or depositing additional multilayer (ML) periods of a thin-film interference coating, distortions in the reflected wave front induced by surface figure errors can be corrected. At lambda = 13.4 nm in the extreme-ultraviolet region the removal or deposition of a single period of the standard two-component molybdenum-silicon (Mo/Si) ML interference coating induces an effective phase change of magnitude 0.043pi with respect to an identical optical thickness in vacuum. The magnitude of this wave-front shift can be enhanced with multicomponent MLs optimized for phase change on reflection. We briefly discuss the contributions of the shift in the effective reflection surface of the ML on the phase change. We also predict the feasibility of novel phase-shifting mask for subwavelength imaging applications.

Aberration generation by contact lenses with aspheric and asymmetric surfaces.

PURPOSE: We explored the potential of aberration correction in the human eye by using a new generation of soft contact lenses with aspheric and asymmetric surfaces. METHODS: Soft contact lens samples were designed with one asymmetrical surface (front) and one spherical (back) to produce predetermined amounts of desired pure defocus, astigmatism, trefoil, coma, and spherical aberration. Contact lens wavefront aberrations were measured ex vivo using a Fizeau-Tolanski interferometer and compared with the in vivo wavefronts obtained by subtracting the aberrations of the eye with and without the contact lenses. These second set of measurements were obtained using a Shack-Hartmann sensor. RESULTS: We found that an aberration-free contact lens sample induced in the eye a small amount of residual aberration. We obtained a good match between the ex vivo and in vivo wavefront measurements for most of the samples of the contact lenses. CONCLUSIONS: The aberrations generated by soft contact lenses on the eye were predictable. Rotations and translations of the contact lenses with respect to correct position on the eye were, however, the main limitation for precise correction of the ocular aberrations.