High-quality Optics Research Articles

Fabrication of silicon kinoform lenses for hard x-ray focusing by electron beam lithography and deep reactive ion etching

The focusing of subnanometer wavelength x rays is limited by the ability to fabricate high-quality optics. In general, the resolution is of the order of the smallest feature of the optic, so nanometer spot sizes are extremely difficult to achieve with lenses made by traditional fabrication methods. In addition, gains in resolution for a given lithography limit are often made at a sacrifice of focusing efficiency. Kinoform lenses offer a compromise position of high resolution and efficiency. The object of this work is to describe the fabrication of kinoform lenses and to show how their unique properties could provide a path toward nanometer scale focusing. Fabrication is made easier by using higher order focusing and larger features. By combining 100keV electron beam lithography and deep reactive ion etching, the authors have fabricated cylindrical kinoform lenses in silicon. These lenses can be used in a crossed pair to produce a two-dimensional focus, but to maintain a large aperture and high resolution this requires etch depths of up to 100μm. Such large etch depths require careful consideration of lens design—feature sizes and densities can be changed with some latitude in the kinoform lens pattern without affecting the lens performance. Multiple lenses are fabricated in serial stacks to increase the resolution and provide a path forward to nanometer resolution.

TEM/local excision: Indications, techniques, outcomes, and the future

Transanal endoscopic microsurgery (TEM) has emerged as a safe method for excising virtually any rectal adenoma and carefully selected cancers. Extended applications include treatment of extra- and supra-sphincteric fistulae, rectovaginal fistulae, anastomotic strictures, and sinus tracts. The procedure utilizes an air-tight system, long shafted instruments, high-quality magnifying optics, and constant carbon dioxide insufflation, all of which facilitate a precise excision and closure with clear margins. Complications are few, most patients can be treated as an outpatient.

Technical Report: Recent Major Improvements to the ALS Sector 5 Macromolecular Crystallography Beamlines

Although the Advanced Light Source (ALS) was initially conceived primarily as a low-energy (1.9-GeV) third-generation source of vacuum ultraviolet (VUV) and soft X-ray radiation, it was realized very early in the development of the facility that a multipole wiggler source coupled with high-quality (brightness-preserving) optics would result in a beamline whose performance across the optimal energy range (5–15 keV) for macromolecular crystallography (MX) would be comparable to, or even exceed, that of many existing crystallography beamlines at higher-energy facilities. Hence, starting in 1996, a suite of three beamlines, branching off a single wiggler source, was constructed, which together formed the ALS Macromolecular Crystallography Facility [1]. From the outset, this facility was designed to cater equally to the needs of both academic and industrial users, with a heavy emphasis placed on the development and introduction of high-throughput crystallographic tools, techniques, and facilities, including large-area CCD detectors, robotic sample-handling and automounting facilities [2], a service crystallography program, and a tightly integrated, centralized, and highly automated beamline control environment for users.

Effect of wavefront error on 10^−7 contrast measurements

Received October 11, 2005; accepted November 10, 2005; posted December 2, 2005 (Doc. ID 65234) We have measured a contrast of 6.5 x 10(-8) from 10 to 25 lambda/D in visible light on the Extreme Adaptive Optics testbed, using a shaped pupil for diffraction suppression. The testbed was designed with a minimal number of high-quality optics to ensure low wavefront error and uses a phase-shifting diffraction interferometer for metrology. This level of contrast is within the regime needed for imaging young Jupiter-like planets, a primary application of high-contrast imaging. We have concluded that wavefront error, not pupil quality, is the limiting error source for improved contrast in our system.

Millimeter wave reimaging optics for the 100 m Green Bank telescope

Large bolometer arrays capable of operating at millimeter wavelengths are being built for astronomical use. For optimal sensitivity, high-quality optics with wide fields of view are needed. We report on the design of reimaging optics for use on the 100-m Green Bank telescope with a 64-element bolometer array.

A mems electromagnetic optical scanner for a commercial confocal laser scanning microscope

A MEMS electromagnetic optical scanner for horizontal scanning of a commercial confocal laser scanning microscope has been developed. The purpose is to replace the currently used commercially available scanner with our new MEMS scanner in an existing microscope product, and therefore, the scanner specifications have to be compatible with those of the current one. Electromagnetic actuation is selected because of the millimeter-sized mirror, and a single crystal silicon hinge is used for realizing high-speed scanning with sufficient scan angle. In order to maintain mirror flatness for high quality optics requirement, the whole wafer thickness (300 μm) is used as the mirror, resulting in a large moment of inertia, and this has been taken into consideration in the actuator design. Although few MEMS actuators have been commercialized to date, it has successfully satisfied all the specifications including not only the fundamentals such as resonant frequency and scan angle but also those for the commercial product such as scanning stability and reliability. It has been commercialized as a part of our product, Olympus OLS1100 (remodeled as OLS1200 in August 2002).

Stitching Interferometry: A Flexible Solution for Surface Metrology

The fabrication of large high-quality optics continues to be a challenge, in part because of the difficulty of measuring extensive surface areas. One alternative is to measure many subapertures of the surface and “stitch” the results together to synthesize a full aperture map.

Limitations of the Shack–Hartmann sensor for testing optical aspherics

Aspheric lenses and surfaces are increasingly used in modern high-quality optics. Therefore, new measuring methods for an accurate quantification of these aspheres are also necessary. The current approach to quantify aspheres is to apply null systems such as computer-generated holograms as a part of a null lens in a interferometer. An alternative to this method is the Shack–Hartmann wavefront sensor. The dynamic range of this sensor can be adjusted by the optical parameters of the applied microlens array. Hence, large wavefront aberrations can be measured directly without a null lens. However, there are basic limitations in the dynamic range of a Shack–Hartmann sensor (SHS) depending on the curvature of the incident wavefront. In this paper, an analytical expression to determine the strongest wavefront curvature which can be measured with a defined microlens array of an SHS is derived. It allows to calculate the microlens parameters required to measure the wavefront of a test lens. Particularly, the influence of rotational symmetric aspherical wavefront shapes to the dynamic range of an SHS has been studied. A comparison between interferometry and the SHS has been accomplished. Numerical solutions using scalar diffraction theory illustrate the analytical predictions.

Magnetic whispering-gallery mirror for atoms

Videotape with a sinusoidal magnetization of $31 \ensuremath{\mu}\mathrm{m}$ wavelength is used to reflect Cs atoms with unit reflectivity in a 75 m/s atomic beam. The atoms serve as a probe, allowing us to measure the magnetic field at the surface. A technique is presented for mounting the videotape so that its surface can be curved to a specific shape or made flexible. We show that such a reflector provides high-quality grazing-incidence atom optics and we demonstrate deflections as large as $23\ifmmode^\circ\else\textdegree\fi{}$ in a whispering-gallery geometry.

Nuclear emulsion readout techniques developed for the CHORUS experiment

The CHORUS experiment is pursuing the study of the production and decay of short lived particles from neutrino interactions in a nuclear emulsion target. The extraction of the full information from the emulsion sheets has been possible only thanks to the development of fully automatic microscopes. The technique of automatic scanning, pioneered in Nagoya, involves precision mechanics, high quality optics and a readout scheme allowing for fast decisions. From the R&D efforts within the various institutes of the CHORUS collaboration, the complementary approaches adopted by the Nagoya and CERN/NIKHEF groups are described here. Both are based on the principle that all information from the emulsion sheets should be extracted at the highest possible rate, limited only by the camera readout and the mechanical stability of the microscope stage.

High-resolution X-ray fluorescence microtomography of homogeneous samples

First experimental results of fluorescence microtomography with 6 /spl mu/m resolution obtained at ESRF, Grenoble, France, are described. The setup comprises high-quality optics (monochromator, mirror, focusing lenses) coupled to the high-energy/brilliance/coherence of the ID 22 undulator beamline. The tomographic setup allows precise measurements in the "pencil-beam" geometry. The image reconstruction is based on a modification of the algebraic reconstruction method but includes simplifications of the model. The quality and precision of the two-dimensional reconstructed elemental images of a phantom sample are encouraging. The method will be further refined and applied for the analysis of more complex inhomogeneous samples.

49.4: Ergonomic Wearable Personal Display

AbstractThe inherently small size and efficiency of a liquid crystal on silicon (LCOS) microdisplay magnified by compact, high quality optics has enabled the design of an ergonomic and even fashionable wearable display. This binocular, virtual display system provides a high resolution SVGA, full‐color image of excellent clarity and vivid saturation in comparison to TFT based displays.

Preparation of CaF2 precursors for laser grade crystal growth

The expansion of commercial excimer lasers has increased the need of high-quality optics manufactured from CaF2. The key technical parameters, affecting the long-term quality of CaF2 excimer laser optics, are controlled by the purity of the raw material. The new purifying techniques provide 99.99% purity of the starting (material which rises up to 99.999% into the grown crystals. However, the techniques are rather expensive which leads to a significant rise in the price of the final crystal product. The present paper describes an alternative highly effective and relatively low-cost technique providing a precise control over a set of preparatory and purifying procedures and crystal growth. Using an original apparatus for electro-chemical grinding of the thermo-broken starting material, the grained product, uncontaminated by unintentional impurities, may be highly purified by two complementary methods to produce precursors used for UV-and laser-grade CaF2 crystal growth.

On image quality of microlens arrays in diurnal superposition eyes

High-resolution compound eyes of the superposition type have been found in some diurnal insects, suggesting high-quality optics. Here we study whether a superposition eye could potentially achieve a higher resolution than that of a single, diffraction-limited facet, like in modern optical instruments made of a number of facets. We have developed a schematic diffractional model of the particularly acute superposition eye of the diurnal lepidopteran agaristid moth Phalaenoides Tristifica, and estimated the amount of aberrations required to fit the experimental data. Our results show that if the ommatidia were perfect (aberration-free) and perfectly aligned towards a common centre O, the resolution of the superposition image would be about 10 times higher than that provided by a single facet, and this in spite of the large phase lags between the pencils of light stemming from neighbouring ommatidia, due to the spherical geometry of the eye. In the insect species taken as a model system here, however, retinal sampling is too coarse to take full advantage of the high spatial frequency content of the superposition image. We show that the experimental data can be fitted if aberrations such as misalignment are introduced. A corollary of these results is that a superposition compound eye which was better constructed and avoided misalignment would provide its host with a better resolution than its `apposition eye counterpart'. This might explain why some diurnal compound eyes such as that of the fast-flying lepidopteran Macroglossum can afford sampling the focal image with a number of rhabdom exceeding the number of ommatidia (Warrant et al 1998 J. Exp. Biol. at press).

Photolithography at 193 nm

Photolithography at 193 nm is a natural continuation of the progression from 436 to 365 to 248 nm in lithography, dictated by the requirement for continually higher resolution. It is anticipated that 193-nm lithography will enable 0.25-μm patterning in volume production with conventional masks, and 0.18-μm resolution with phase-shifting masks. The main issues related to lithography at this new wavelength are being addressed. It has been shown that highly transparent optical materials are available at 193 nm. Also, they are damaged by the laser radiation at a slow enough rate that high-quality projection optics are expected to perform within specifications for ten years of full-time operation. Consequently, a 193-nm step-and-scan system is being constructed, and it has been designed to attain 0.25-μm resolution over a 22 by 35 mm field. A range of 193-nm photoresist schemes has been demonstrated. They include semitransparent single-layer resists, positive-tone surface imaging (silylation), and negative-tone bilayers using ultrathin silicon-based polymers. In most instances we have demonstrated sub-0.25-μm resolution, high photosensitivity, good exposure–defocus latitude, and very low levels of etch residue. In sum, the first successful steps towards a fully engineered 193-nm photolithography have been taken, and no major obstacles are anticipated.

Simulating the scratch standards for optical surfaces: theory

I show how to simulate the scattering generated by a scratch on the surface of high-quality optics and their elements. This is accomplished by first describing how the present cosmetic scratch standards tend to be used in the optics industry. Second, I derive from first principles, using the scalar model for electromagnetic radiation, the first-order scattering coefficients for the far-field radiation due to a particular scratch pattern. There are approximations made to get these coefficients. The results allow construction of a set of secondary scratch standards. These are a pattern of rectangular grooves that can be made precisely reproducible during the manufacturing phase. Appropriate selection from this set can provide the same range of scattering power and character as is present in the current scratch standards, which are not easily reproducible. Because the method for construction of these new secondary standards is nonrandom, to guarantee the reproducible construction between these standards it is necessary to restrict the observation range 5– 10° from the direct beam.

Simplified vibrating-reed technique for the measurement of the temperature dependence of Young’s modulus of small samples

A simplified vibrating-reed technique for the measurement of the temperature dependence of Young’s modulus of small thin samples is described. The vibration of the reed is detected optically rather than with a capacitively coupled electrode as has been used by previous investigators. The optical coupling greatly simplifies the sample stage and electronic circuitry. It is made possible by the use of a microminiature Joule–Thomson-effect refrigerator which mounts directly onto the X–Y stage of a metallurgical microscope. Because of the refrigerator’s small size and lack of mechanical vibrations, the high-quality room temperature optics of the microscope can be used to detect the small amplitude vibration of the reed over a wide temperature range. We observe the Curie and Neel points of the magnetic phase transitions of terbium at Tc =221 K and TN =233 K, respectively. In addition, we measure Young’s modulus at 280 K to be 5.90×1011 dyn/cm2.

Fabricating Infrared Optics

The tolerances on optical components used in multicomponent infrared systems handling large power levels may be comparable to or even more severe than those commonly used in high quality optics for the visible spectral region. In addition, the optician may be asked to polish unconventional materials in such a way as to obtain minimum surface absorption and high laser damage resistance as well as good optical figure. Minimum microroughness and scratch density are also often required both for components used in infrared lasers and for more conventional applications where scattered light is the primary concern. Fortunately, techniques are being developed which satisfy these often conflicting requirements to a large degree.

Optical Correlation of Fresnel Images

A real-time optical correlator is described that uses an ultrasonic light modulator (ULM) in conjunction with an amplitude mask or replica of the signal to achieve linear, phase-coherent detection, without need for high quality optics. When the mask is placed in a Fresnel image plane of the ULM, optimum correlation and collinear heterodyning are achieved. Correlator response has been calculated and measured as a function of mask-ULM separation for a pulse modulated cw signal and a square wave modulated fm waveform. For essentially band-limited signals, the output is a pair of symmetrically time-shifted, matched filter responses, possessing negligible quadratic phase distortion.