Sverker Hård

Parallel fluorescence detection of single biomolecules in microarrays by a diffractive-optical-designed 2 x 2 fan-out element

We have developed a multifocal diffractive-optical fluorescence correlation spectroscopy system for parallel excitation and detection of single tetramethylrhodamine biomolecules in microarrays. Multifocal excitation was made possible through the use of a 2 x 2 fan-out diffractive-optical element with uniform intensity in all foci. Characterization of the 2 x 2 fan-out diffractive-optical element shows formation of almost perfect Gaussian foci of submicrometer lateral diameter, as analyzed by thermal motion of tetramethylrhodamine dye molecules in solution. Results of parallel excitation and detection in a high-density microarray of circular wells show single-biomolecule sensitivity in all four foci simultaneously.

Adaptive beam steering implemented in a ferroelectric liquid-crystal spatial-light-modulator free-space, fiber-optic switch

Active alignment of a 1 x 8 free-space optical switch was studied experimentally. Optical signals, carried on single-mode fibers, were switched by a ferroelectric liquid-crystal-on-silicon spatial light modulator. Continuous measurement of the in-coupled power to the fibers provided feedback for the switch control. The switch automatically located and locked to the output fibers. An advantage with adaptive switches of a similar kind is relaxed geometrical tolerances in the switch assembly. Further, such switches can adapt to possible geometrical changes and light wavelength drift during operation.

Proximity-compensated blazed transmission grating manufacture with direct-writing, electron-beam lithography

Proximity-compensated, as well as uncompensated, blazed transmission gratings with periods of 4, 8, and 16 µm were manufactured with direct-writing, electron-beam lithography in positive resist. The compensated gratings performed better than the uncompensated ones. For the 4-µm compensated grating the measured diffraction efficiency was 67%. It was 35% for the uncompensated grating. The compensation was made by repeated convolutions in the spatial domain with the electron-beam point spread function. We determined this function by retrieving the phase from the measured diffraction pattern of the uncompensated gratings.

Elasticity and viscosity measurements of monomolecular propyl stearate films at air-water interfaces using laser light scattering techniques

Abstract Measurements of propyl stearate monolayers were made using a new laser light scattering apparatus. Thermal capillary waves in the frequency range 7–16 kHz were studied. For the first time the film elasticity and viscosity have been determined from light scattering measurements. The determined elasticity differs at most by a factor of 4 from the elasticity obtained from the equilibrium π-A-isotherm. The viscosity values are of the order of 1 · 10−7 kg/sec and increase with increasing film density.

Single photomask, multilevel kinoforms in quartz and photoresist: manufacture and evaluation

Kinoforms manufactured in photoresist by photolithographic techniques using a single, ten-level, grey scale photomask, exposed in a specially designed laser exposure system, are described. Kinoforms designed for uniform as well as for partial Gaussian beam illumination are discussed. The highest measured diffraction efficiency was 55%. Photoresist kinoforms were transferred into quartz substrates by reactive ion etching. The highest measured diffraction efficiency for the resulting all-quartz kinoforms was 53%.

Replication of continuous-relief diffractive optical elements by conventional compact disc injection-molding techniques

Continuous-relief diffractive optical elements have been replicated by use of conventional compact disc injection-molding techniques. Two continuous-relief microstructures, a blazed grating and a fan-out element, were chosen to evaluate the replication process. Original elements were fabricated by direct-write electron-beam lithography. Optical measurements and atomic force microscopy were used for investigating the replication fidelity.

Diffractive microlenses replicated in fused silica for excimer laser-beam homogenizing

A diffractive beam homogenizer, based on an array of square, off-axis, continuous-relief diffractive microlenses, for use with an excimer laser has been studied. We originally fabricated the homogenizer by direct-write electron-beam lithography, from which we made replicas in UV-grade fused silica by hot embossing and reactive ion etching. Atomic force microscopy measurements of original and replicated elements showed the accuracy of the replication fidelity. One of the replicated homogenizers was evaluated together with a KrF excimer laser. The homogenized beam had a flat-top profile with 31% of the beam energy contained within an area where the beam intensity was above a threshold level of 90% of the maximum intensity.

Fabrication and simulation of diffractive optical elements with superimposed antireflection subwavelength gratings

With the aim of reducing surface reflections and increasing the diffraction efficiency we investigated the superposition of subwavelength phase gratings onto blazed phase gratings. With direct-write electron-beam lithography bare blazed gratings and blazed gratings carrying subwavelength gratings were fabricated and their optical performances compared. For TE polarization the subwavelength-carrying gratings showed a maximum diffraction efficiency of 90.6%, whereas the corresponding maximum value for the bare grating was 86.3%. The experiment was simulated with rigorous diffraction theory.

Study of an ultrafast analog-to-digital conversion scheme based on diffractive optics

A potentially ultrafast optical analog-to-digital (A/D) converter scheme is proposed and was partly studied experimentally. In the A/D converter scheme the input signal controls the wavelength of a diode laser, whose output beam is incident on a grating. The beam from the grating hits a diffractive optical element in an array. The wavelength determines which element is illuminated. Each element fans out a unique spot-pattern bit code to be read out in parallel by individual detectors. In the experiment all patterns but one from 64 array elements were read out correctly.

Multilevel phase holograms manufactured by electron-beam lithography.

Ten-level transmission phase holograms (kinoforms) manufactured in one resist layer by electron-beam lithography are reported for the first time to our knowledge. The measured hologram diffraction efficiencies were 70% for the two resist materials used. This corresponds to 82% of the maximum theoretical value for these holograms and is, to our knowledge, the highest reported to date.