Fabrication and evaluation of elliptical X-ray mirrors, such as Kirkpatrick-Baez (K-B) mirrors
produced by the profile-coating technique, requires accurate surface figure measurements over a wide range of
spatial frequencies. Microstitching interferometry has proven to fulfill this requirement for length scales from a
few μm up to the full mirror length. At the Advanced Photon Source, a state-of-the-art microroughness
microscope interferometer that incorporates advanced microstitching capability has been used to obtain
measurements of profile-coated elliptical K-B mirrors. The stitched surface height data provide previously
unattainable resolution and reproducibility, which has facilitated the fabrication of ultrasmooth (< 1 nm rms
residual height) profile-coated mirrors, whose hard X-ray focusing performance is expected to approach the
diffraction limit. This paper describes the system capabilities and limitations. Results of measurements obtained
with it will be discussed and compared with those obtained with the Long Trace Profiler.
Continuing improvements in the fabrication of super-smooth spherical and aspheric optical surfaces for applications such as extreme-ultraviolet lithography have given rise to the need to characterize the surface roughness of these optics to the sub-Angstrom level. Phase-shifting interference microscopes are well suited to acquire high-precision, three-dimensional surface structure rapidly, without contact, and over a wide range of spatial frequencies. This paper describes a new phase-shifting interference microscope by ADE Phase Shift, together with exemplary measurements of Angstrom-level surface roughness. The microscope was designed to measure large diameter (up to 500 mm) convex, concave and aspheric optics. To access all areas of the test surface, samples are placed symmetrically at the center of an R-theta stage. The phase-shifting microscope head pivots in the direction of the translation stage travel by ±20 degrees to match the major component of surface slope, while a second tilt control nulls minor tilt in the orthogonal direction. A 1K by 1K high-resolution, digital camera reduces random noise in the system to below 0.15 Angstrom rms for 16 averaged maps of nulled interferograms. When testing non-planar surfaces, the interference fringes cannot be nulled out, and special care has to be taken to minimize phase-dependent errors, commonly known as fringe print-through. A print-through level of less than 0.2 Angstrom rms has been achieved with a careful opto-mechanical system design in combination with an advanced phase algorithm whose filtering action suppresses higher-order harmonics caused by phase-shifter and detector non-linearity, as well as vibrations.
Burn depth determination is a critical factor in the treatment of thermal injury. We have developed a technique, polarization sensitive optical coherence tomography (PS- OCT), to assess burn depth non-invasively. Thermal injury denatures collagen in human skin. PS-OCT is able to measure the resulting reduction in collagen birefringence using depth resolved changes in the polarization of light propagated and reflected from the sample. In a previous study, we used a free space PS-OCT system at 850 nm to image in vivo the skin of rats burned for various amounts of time. Using a high-speed system at 1.3 micrometers has the advantages of greater depth penetration and reduction of motion artifacts due to breathing and small movements of the animal. Stokes vectors were calculated for each point in the scans and the relative birefringence was determined using different incident polarization states. Birefringence was correlated with actual burn depth determined by histological analysis. Our results show a marked difference between normal tissue and even the slightest burn, and a consistent trend for various degrees of burns.
In optical coherence tomography (OCT), mapping the polarization state of the reflected light provides additional information about tissue structure and prevents polarization induced image artifacts. As OCT is increasingly used with subjects in vivo, demands on the imaging system and data acquisition rates increase. We present a fiber- based, rapid scanning, polarization-sensitive OCT system capable of acquiring image data at the rate of 20K pixel/s. To achieve high scan rates, a rapid-scanning optical delay line generates a reference arm group delay while a waveguide-based phase modulator generates a suitable, stable carrier frequency for the detection electronics. Group delays up to 4.5 mm are obtained at frequencies approaching 1 kHz. The group delay and carrier frequency are independently controllable, which has the advantage that either the lateral or the axial scan direction may be chosen as the fast axis. Tomographic images corresponding to the intensity and polarization components of the Stokes vector describing the back scattered light are obtained by analyzing the interference signals from two orthogonally polarized channels in the detection arm for each of four polarization states incident on the sample. Polarization images of human skin taken in vivo are shown.
We used a novel phase-resolved optical Doppler tomographic (ODT) technique, with very high flow velocity sensitivity and high spatial resolution, to image blood flow in port wine stain (PWS) birthmarks in human skin. The variance of blood flow velocity is used to locate the PWS vessels in addition to the regular ODT images. Our device combines an ODT system and laser so that PWS blood flow can be monitored in situ before and after treatment. To our knowledge, this is the first clinical application of ODT to provide a fast semi-quantitative evaluation of the efficacy of PWS laser therapy in situ and in real-time.
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