Surface Relief Patterns Research Articles

X-ray Gabor holography

Soft x-ray microscopy offers an approach to transmission imaging of wet, micron-thick biological objects at a resolution superior to that of optical microscopes and with less specimen preparation/manipulation than electron microscopes. Gabor holography has unique characteristics which make it particularly well suited for certain investigations: it requires no prefocussing, it is compatible with flash x-ray sources, and it is able to use the whole footprint of multimode sources. Our method serves to refine this technique in anticipation of the development of suitable flash sources (such as x-ray lasers) and to develop cryo capabilities with which to reduce specimen damage. Our primary emphasis has been on biological imaging so we use x-rays in the water window (between the Oxygen-K and Carbon-K absorption edges) with which we record holograms in vacuum or in air.The hologram is recorded on a high resolution recording medium; our work employs the photoresist poly(methylmethacrylate) (PMMA). Following resist “development” (solvent etching), a surface relief pattern is produced which an atomic force microscope is aptly suited to image.

Manufacture of blazed zone plates in germanium for use in the 10 micrometer spectral region

Blazed zone plates have been manufactured in germanium. A suitable surface relief pattern was first generated by recording in photoresist the circular fringes transmitted by a Fabry-Pérot interferometer. By scanning the fringe pattern and recording a series of exposures, we were able to generate a triangular groove profile. This was then transferred to the germanium substrate by ion-beam etching. By this means, diffraction efficiencies in excess of 80% have been achieved at 10μm for zone plates working in transmission and on axis.

Aztec surface-relief volume diffractive structure

Surface-relief diffractive optical elements made interferometrically typically are recorded with the off-axis technique, for which the fringe maxima lie on planes that are predominantly perpendicular to the recording surface and with an intensity variation that is sinusoidal. Such a structure can be readily replicated by mechanical means. Volume diffractive elements, on the other hand, which result from beams propagating in opposite directions, have fringe planes that are predominantly parallel to the surface and, as such, cannot be mechanically replicated. A new type of surface-relief diffractive structure called Aztec is discussed here; it combines features of both off-axis and volume recording geometries, with the result being a phase-quantized, or terraced, surface-relief pattern. The groove profile, instead of being sinusoidal, resembles a stepped pyramid. This structure has been replicated by metal mastering and molding into plastic in the same manner as conventional embossed surface-relief elements, but the diffraction characteristics are typical of volume phase reflective structures. Light of a given wavelength is resonantly diffracted from steps that are a half-wavelength apart and with a bandwidth that is inversely proportional to the number of steps. Color control has been achieved by overcoating the step structure with a clear dielectric that shifts the resonant wavelength to a new value, depending on the index of refraction of the dielectric. Information content is less for the single-layered, but stepped, Aztec structure than for the usual multilayered volume diffractive element. Deep Aztec stepped gratings have also been fabricated by optical lithography, using multiple-mask techniques.

Deformable Surface Spatial Light Modulator

A spatial light modulator (SLM) based on a deformable gel surface is presented. It has remarkable optical properties and its construction and operation are comparatively simple. It can be optically addressed through a photoconductor layer. The surface relief pattern is read out by total reflection and a schlieren optical system. The device provides good wavefront quality (X/10 over the whole aperture of 30 x 50 mm2) and has a spatial resolution of 10 line pairs/mm. Contrast ratios for modulation up to 40:1 were measured. The input sensitivity is typically 0.3 mW/cm2. The rise and decay times are both approximately 20 ms. Besides its primary application as a light valve in large screen TV projection, it can be used in optical information processing systems, e.g., as an incoherent-to-coherent transducer. Combined with a CRT, the SLM can be addressed electronically.

Polypyrrole for use in information storage

It is shown that conducting polypyrrole can be used for information storage if the information is stored in the form of a surface relief pattern. The preparation of the film with the relief pattern as well as the expected storage time of the information are also briefly discussed.

Holographic local-oscillator beam multiplexing for array heterodyne detection

Linear holographic gratings have been developed that can be used for amplitude and phase matching of local oscillator (LO) and signal wave fronts in heterodyne detection with infrared imaging arrays. With these holographic gratings the system’s signal-to-noise ratio and resolution can be maximized, and the LO power dissipation on the focal plane can be minimized. A holographic surface relief pattern multiplexes the LO beam when a single LO laser beam illuminates it. Each beam of this multiplexed set then has the same amplitude shape as and is collinear with each element of the signal wave front illuminating the array.

Submicrometer-Linewidth Laser Doping

ABSTRACTDopant patterns of 250-nm linewidth have been written in silicon by localized heating with a cw laser beam, and then transferred into positive and negative surface-relief patterns by preferential etching. The tightly focused beam both generates free dopant atoms and simultaneously promotes solidstate diffusion into the substrate. Because of the nonlinear dependence of diffusion rates on temperature, the linewidths of the patterns are substantially narrower than those of both the temperature and the laser-beam profiles on tile surface. In addition, an enhancement is observed in diffusion rates under the strong thermal gradients associated with highly localized heating.

Microfabrication and evaluation of diffractive optical filters prepared by reactive sputter etching

Single or linearly superimposed square-wave surface-relief patterns in a transparent plate yield optical transmission characteristics similar to those of interference filters. Reactive sputter etching of fused quartz in CHF3 using Shipley 1350 H photoresist as an etch mask offers a well-controlled method to produce these complex structures. Gratings with periodicities of 1–2 μm and depths of up to 3 μm are fabricated with dimensional tolerances of ±0.02 μm using laser interferometric techniques. Superposition is obtained by successive masking and etching operations. The optical transmission characteristics of these diffractive filters are analyzed and compared with rigorous diffraction theory.

The Ruticon family of erasable image recording devices

Ruticons are solid-state cyclic image recording devices. They have a layered structure consisting of a conductive transparent substrate, a thin photoconductive layer a thin deformable elastomer layer, and a deformable electrode such as a conductive liquid, a conductive gas, or a thin flexible metal layer. When an electric field is placed between the conductive substrate and the deformable electrode the elastomer will deform into a surface relief pattern corresponding to the light-intensity distribution of an image focused on the photoconductor. Light modulated by the deformation of the elastomer surface can in turn be converted to an intensity distribution similar to the original image by means of simple optics. Ruticons are expected to find initial applications in image intensification, holographic recording, and optical buffer storage.