Showing papers on "Spatial light modulator published in 2010"

A line scanned light-sheet microscope with phase shaped self-reconstructing beams

Abstract: We recently demonstrated that Microscopy with Self-Reconstructing Beams (MISERB) increases both image quality and penetration depth of illumination beams in strongly scattering media. Based on the concept of line scanned light-sheet microscopy, we present an add-on module to a standard inverted microscope using a scanned beam that is shaped in phase and amplitude by a spatial light modulator. We explain technical details of the setup as well as of the holograms for the creation, positioning and scaling of static light-sheets, Gaussian beams and Bessel beams. The comparison of images from identical sample areas illuminated by different beams allows a precise assessment of the interconnection between beam shape and image quality. The superior propagation ability of Bessel beams through inhomogeneous media is demonstrated by measurements on various scattering media.

Spatial light modulator with masking-comparators

Abstract: Described is a device comprising a spatial light modulator comprising a plurality of comparators for computing a respective drive for each pixel of a plurality of pixels.

Multi-focus two-photon polymerization technique based on individually controlled phase modulation.

Abstract: Multi-focus two-photon polymerization with a spatial light modulator is demonstrated. The spatial light modulator generates multi-focus spots via phase modulation technique controlled by a computer generated hologram (CGH) pattern. Each focus spot can be individually addressed in position and laser intensity. The multi-focus two-photon polymerization technique allows the fabrication of complex 2-D and 3-D structures both symmetric and asymmetric. Smooth sine curved polymerized lines with amplitude of 5 microm and a period of 200 microm were obtained by fast switching of the CGH patterns.

Application of cooled spatial light modulator for high power nanosecond laser micromachining

Abstract: The application of a commercially available spatial light modulator (SLM) to control the spatial intensity distribution of a nanosecond pulsed laser for micromachining is described for the first time. Heat sinking is introduced to increase the average power handling capabilities of the SLM beyond recommended limits by the manufacturer. Complex intensity patterns are generated, using the Inverse Fourier Transform Algorithm, and example laser machining is demonstrated. The SLM enables both complex beam shaping and also beam steering.

Phase retrieval by means of a spatial light modulator in the Fourier domain of an imaging system

Abstract: We present an experimental configuration for phase retrieval from a set of intensity measurements. The key component is a spatial light modulator located in the Fourier domain of an imaging system. It performs a linear filter operation that is associated to the process of propagation in the image plane. In contrast to the state of the art, no mechanical adjustment is required during the recording process, thus reducing the measurement time considerably. The method is experimentally demonstrated by investigating a wave field scattered by a diffuser, and the results are verified by comparing them to those obtained from standard interferometry.

Autostereoscopic display apparatus

Abstract: An autostereoscopic display apparatus includes a spatial light modulator in which alignment features such as bump features provide radially symmetric alignment of the molecules of the liquid crystal. A parallax element is arranged over the spatial light modulator to direct light from the pixels into different viewing windows. The apertures of the pixels are shaped such that, for each individual row of pixels, a notional line parallel to the geometric axes of the parallax elements has a total length of intersection with the pixels of the row, weighted for the intensity of light modulated by the alignment features, which is the same for all positions of the notional line. This improves angular intensity uniformity. The pixels may each include plural apertures, wherein the alignment features of the apertures of each individual pixel are offset from one another in a direction perpendicular to said geometric axes. This improves angular contrast uniformity.

Reconfigurable Optically Induced Quasicrystallographic Three-Dimensional Complex Nonlinear Photonic Lattice Structures

Abstract: 2010 WILEY-VCH Verlag Gm Quasicrystals (QCs) are materials that possess a long-range order with defined diffraction patterns, but lack the characteristic translational periodicity of crystals. From the discovery of the non-crystallographic icosahedral quasiperiodic symmetry found in Al6Mn in 1984, [2] the distinct properties of quasicrystallographic structures attracted a great deal of interest in different realms of science in recent years. Another field of technological interest in the recent past is that of photonic crystals (PCs), the structured materials with a translational periodic modulation of the refractive index. Merging these two fields, a new class of material structures called photonic quasicrystals (PQCs) has drawn the attention of researchers stemming from a cumulative effect from both fields. This is mainly due to the fact that the higher rotational symmetry of QCs leads to more isotropic and complete photonic bandgaps (PBGs) even in materials with a low refractive index contrast. However, as in the case of PCs, the fabrication of 3D PQCs is much more involved in comparison to 2D PQCs and remains a real challenge today. Moreover, many of the conventional methods become technically either unsuitable or extremely complicated for the fabrication of 3D PQCs. Therefore, the fabrication and optimization of higher rotational symmetry 3D PQCs demand an approach that is flexible as well as reconfigurable. The purpose of the present Communication is dual fold. On the one hand, we demonstrate for the first time the generation of well-defined reconfigurable 3D quasi-crystallographic photorefractive nonlinear photonic structures with various rotational symmetries, which are experimentally realized in an externally biased cerium doped strontium barium niobate (SBN:Ce) photorefractive material as the nonlinear optical material of choice. These complex structures are envisaged to form a reconfigurable platform to investigate advanced nonlinear light–matter interaction in higher spatial dimensions with various rotational symmetries. On the other hand, we present a generalized versatile experimental approach for the fabrication of complex 3D axial PQCs with higher order rotational symmetry and variants of complex 3D structures similar to those having icosahedral symmetry, using a real-time reconfigurable holographic technique. It involves a programmable spatial light modulator (SLM)-assisted single step optical induction approach based on computer-engineered optical phase patterns. It is also important to note that the versatility of the experimental approach, we present, is not limited to photorefractive materials alone. It can be easily well adapted to various photosensitive materials as per the application requirement in the diverse fields of material science. Among various photosensitive materials, reconfigurable nonlinear photonic lattices can be easily generated by means of a so-called optical induction technique at very low power levels ( micro watts) in a photorefractive material, exploiting the wavelength sensitivity of these materials. The process of refractive index modulation, which leads to photonic lattice formation in such a medium is caused by a two-step process out of the incident light intensity distribution. Under the influence of an externally applied electric field, the incident light intensity distribution causes a charge carrier redistribution that results in a macroscopic space charge field in the photorefractive material. This, in turn, leads to a space-dependent refractive index modulation via the electro-optic effect thereby representing a nonlinear optical effect of third order that creates the refractive index modulation out of the incident intensity distribution. Apart from the possibility of permanent fixing of the generated structures in a photorefractive crystal, the recorded structure is reconfigurable: it can also be erased by the flush of white light so that new patterns could be again recorded in these materials. Therefore, photorefractive materials are ideal materials for reconfigurable PQC generation either to optimize the required photonic structure on the one hand or to be used as a reconfigurable platform to investigate novel nonlinear wave dynamics. From the optical properties point of view, the photonic lattices formed in SBN:Ce show both polarization as well as orientation anisotropy. In order to obtain refractive index modulated structures that mimic the intensity pattern, o-polarized writing beams are used causing a low modulation due to the appropriate electro-optic coefficient addressed. For the case of using e-polarized writing beams, as the relevant electrooptic coefficient is much higher, a strongly nonlinear refractive index modulation can be obtained for the fabricated lattices. Moreover, as maximum refractive index modulation is induced in the direction parallel to the crystal c axis, there exists also orientation anisotropy in SBN:Ce.

High-throughput FCS using an LCOS spatial light modulator and an 8 × 1 SPAD array

Abstract: We present a novel approach to high-throughput Fluorescence Correlation Spectroscopy (FCS) which enables us to obtain one order of magnitude improvement in acquisition time. Our approach utilizes a liquid crystal on silicon spatial light modulator to generate dynamically adjustable focal spots, and uses an eight-pixel monolithic single-photon avalanche photodiode array. We demonstrate the capabilities of this system by showing FCS of Rhodamine 6G under various viscosities, and by showing that, with proper calibration of each detection channel, one order of magnitude improvement in acquisition speed is obtained. More generally, our approach will allow higher throughput single-molecule studies to be performed.

An SLM-based Shack-Hartmann wavefront sensor for aberration correction in optical tweezers

Abstract: Holographic optical tweezers allow the creation of multiple optical traps in 3D configurations through the use of dynamic diffractive optical elements called spatial light modulators (SLMs). We show that, in addition to controlling traps, the SLM in a holographic tweezers system can be both the principal element of a wavefront sensor and the corrective element in a closed-loop adaptive optics system. This means that aberrations in such systems can be estimated and corrected without altering the experimental setup. Aberrations are estimated using the Shack–Hartmann method, where an array of spots is projected into the sample plane and the distortion of this array is used to recover the aberration. The system can recover aberrations of up to ten wavelengths peak–peak, and is sensitive to aberrations much smaller than a wavelength. The spot pattern could also be analysed by eye, as a tool for aligning the system.

High-precision laser beam shaping using a binary-amplitude spatial light modulator

Abstract: We have achieved high-precision laser beam shaping by using a binary-amplitude spatial light modulator, a digital micromirror device (DMD), followed by an imaging telescope that contains a pinhole low-pass filter (LPF). An error diffusion algorithm was used to design the initial DMD pixel pattern based on the measured input beam profile. This pattern was iteratively refined by simulating the optically low-pass filtered DMD image and changing DMD pixels to lift valleys and suppress peaks. We noted the gap between the experimental result of 1.4% root-mean-square (RMS) error and the simulated result for the same DMD pattern of 0.3% RMS error. Therefore, we deemed it necessary to introduce iterative refinement based on actual measurements of the output image to further improve the uniformity of the beam. Using this method, we have demonstrated the ability to shape raw, non-spatially filtered laser beams (quasi-Gaussian beams) into beams with precisely controlled profiles that have an unprecedented level of RMS error with respect to the target profile. We have shown that our iterative refinement process is able to improve the light intensity uniformity to around 1% RMS error in a raw camera image for both 633 and 1064 nm laser beams. The use of a digital LPF on the camera image is justified in that it matches the performance of the pinhole filter in the experimental setup. The digital low-pass filtered results reveal that the actual optical beam profiles have RMS error down to 0.23%. Our approach has also demonstrated the ability to produce a range of target profiles as long as they have similar spatial-frequency content (i.e., a slowly varying beam profile). Circular and square cross-section flat-top beams and beams with a linear intensity variation within a circular and square cross section were produced with similarly low RMS errors. The measured errors were about twice the ultimate limit of 0.1% RMS error based on the number of binary DMD pixels that participate in the beam-formation process.

Structured illumination enhances resolution and contrast in thick tissue fluorescence imaging

Abstract: We introduce a noncontact imaging method utilizing multifrequency structured illumination for improving lateral and axial resolution and contrast of fluorescent molecular probes in thick, multiple-scattering tissue phantoms. The method can be implemented rapidly using a spatial light modulator and a simple image demodulation scheme similar to structured light microscopy in the diffraction regime. However, imaging is performed in the multiple-scattering regime utilizing spatially modulated scalar photon density waves. We demonstrate that by increasing the structured light spatial frequency, fluorescence from deeper structures is suppressed and signals from more superficial objects enhanced. By measuring the spatial frequency dependence of fluorescence, background can be reduced by localizing the signal to a buried fluorescent object. Overall, signal-to-background ratio (SBR) and resolution improvements are dependent on spatial frequency and object depth/dimension with as much as sevenfold improvement in SBR and 33% improvement in resolution for approximately 1-mm objects buried 3 mm below the surface in tissue-like media with fluorescent background.

Experimental detection of optical vortices with a Shack-Hartmann wavefront sensor

Abstract: Laboratory experiments are carried out to detect optical vortices in conditions typical of those experienced when a laser beam is propagated through the atmosphere. A Spatial Light Modulator (SLM) is used to mimic atmospheric turbulence and a Shack-Hartmann wavefront sensor is utilised to measure the slopes of the wavefront surface. A matched filter algorithm determines the positions of the Shack-Hartmann spot centroids more robustly than a centroiding algorithm. The slope discrepancy is then obtained by taking the slopes measured by the wavefront sensor away from the slopes calculated from a least squares reconstruction of the phase. The slope discrepancy field is used as an input to the branch point potential method to find if a vortex is present, and if so to give its position and sign. The use of the slope discrepancy technique greatly improves the detection rate of the branch point potential method. This work shows the first time the branch point potential method has been used to detect optical vortices in an experimental setup.

Azimuthally and radially polarized light with a nematic SLM

Abstract: We demonstrate a technique for generating azimuthally and radially polarized beams using a nematic liquid crystal spatial light modulator and a π phase step. The technique is similar in concept to prior techniques that interfere TEM01 and TEM10 laser modes, but the presented technique removes the requirement of interferometric stability. We calculate an overlap integral of >0.96 with >70% efficiency from an input Gaussian mode. The technique can easily switch between beams with azimuthal and radial polarization.

Depth of field multiplexing in microscopy

Abstract: We demonstrate "depth of field multiplexing" by a high resolution spatial light modulator (SLM) in a Fourier plane in the imaging path of a standard microscope This approach provides simultaneous imaging of different focal planes in a sample with only a single camera exposure The phase mask on the SLM corresponds to a set of superposed multi-focal off-axis Fresnel lenses, which sharply image different focal planes of the object to non-overlapping adjacent sections of the camera chip Depth of field multiplexing allows to record motion in a three dimensional sample volume in real-time, which is exemplarily demonstrated for cytoplasmic streaming in plant cells and rapidly swimming protozoa

Quantitative phase microscopy using defocusing by means of a spatial light modulator

Abstract: A new method for recovery the quantitative phase information of microscopic samples is presented. It is based on a spatial light modulator (SLM) and digital image processing as key elements to extract the sample’s phase distribution. By displaying a set of lenses with different focal power, the SLM produces a set of defocused images of the input sample at the CCD plane. Such recorded images are then numerically processed to retrieve phase information. This iterative process is based on the wave propagation equation and leads on a complex amplitude image containing information of both amplitude and phase distributions of the input sample diffracted wave front. The proposed configuration is a non-interferometric architecture (conventional transmission imaging mode) where no moving elements are included. Experimental results perfectly correlate with the results obtained by conventional digital holographic microscopy (DHM).

Fabrication of three-dimensional 1 x 4 splitter waveguides inside a glass substrate with spatially phase modulated laser beam.

Abstract: Multiple light spots can be generated by modulating the spatial phase distribution of laser beam with a spatial light modulator (SLM). In this paper, we demonstrate the fabrication of three-dimensional 1 × 4 splitter waveguides inside a glass by focusing multiple light spots of femtosecond (fs) laser pulses, which can be controlled by switching spatial phase distributions on an SLM. In the conventional fs laser writing technique, a highly precise positioning of a substrate is essential for fabricating a branched waveguide in a splitter. Using the technique proposed in this paper, a continuously branched waveguide can be produced easily by translating a glass substrate only one time; therefore this technique can eliminate the need for a high precision in positioning of a substrate and save a fabrication time.

Application of dynamic diffractive optics for enhanced femtosecond laser based cell transfection

Abstract: We demonstrate the advantages of a dynamic diffractive optical element, namely a spatial light modulator (SLM) for the controlled and enhanced optoinjection and phototransfection of mammalian cells with a femtosecond light source. The SLM provides full control over the lateral and axial positioning of the beam with sub-micron precision. Fast beam translation enables time-sequenced irradiation, which is shown to enhance the optoinjection efficiency and alleviate the problem of exact beam positioning on the cell membrane. We show that irradiation in three axial positions doubles the number of viably optoinjected cells when compared with a single dose. The presented system also enables untargeted raster scan irradiation which provides a higher throughput transfection of adherent cells at the rate of 1 cell per second. Additionally, fluorescent imaging is used to demonstrate cell selective two-step gene therapy. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure of optical singularities in coaxial superpositions of Laguerre–Gaussian modes

Abstract: We investigate optical singularities in coaxial superpositions of two Laguerre–Gaussian (LG) modes with a common beam waist from the viewpoints of a general formulation of phase structure, experimental generation of various superposition beams, and evaluation of the generated beams’ fidelity. By applying a holographic phase-amplitude modulation scheme using a phase-modulation-type spatial light modulator, output fidelity beyond 0.960 was observed under several typical conditions. Additionally, an elliptic-type folded singularity, which provides a different class of phase structures from familiar helical singularities, was predicted and observed in a superposition involving two LG modes of both radially and azimuthally higher orders.

Optical imaging writer system

Abstract: System and method for applying mask data patterns to substrate in a lithography manufacturing process are disclosed. In one embodiment, the method includes providing a parallel imaging writer system which has a plurality of spatial light modulator (SLM) imaging units arranged in one or more parallel arrays, receiving a mask data pattern to be written to a substrate, processing the mask data pattern to form a plurality of partitioned mask data patterns corresponding to different areas of the substrate, identifying one or more objects in an area of the substrate to be imaged by corresponding SLMs, and controlling the plurality of SLMs to write the plurality of partitioned mask data patterns in parallel by performing multiple exposures to image the one or more objects in the area of the substrate.

A high-resolution, adaptive beam-shaping system for high-power lasers

Abstract: A high-resolution, high-precision beam-shaping system for high-power-laser systems is demonstrated. A liquid-crystal-on-silicon spatial light modulator is run in closed-loop to shape laser-beam amplitude and wavefront. An unprecedented degree of convergence is demonstrated, and important practical issues are discussed. Wavefront shaping for the applications in OMEGA EP laser is demonstrated, and other interesting examples are presented.

Adaptive optics for direct laser writing with plasma emission aberration sensing

Abstract: Aberrations affect the focal spot quality in direct laser write applications when focusing through a refractive index mismatch. Closed loop adaptive optics can correct these aberrations if a suitable feedback signal can be found. Focusing an ultrafast laser beam into transparent dielectric material can lead to plasma formation in the focal region. We report using the supercontinuum emitted by such a plasma to measure the optical aberrations, the subsequent aberration correction using a spatial light modulator and the fabrication of nanostructures using the corrected optical system.

Quantitative SLM-based differential interference contrast imaging

Abstract: We describe the implementation of quantitative Differential Interference Contrast (DIC) Microscopy using a spatial light modulator (SLM) as a flexible Fourier filter in the optical path. The experimental arrangement allows for the all-electronic acquisition of multiple phase shifted DIC-images at video rates which are analyzed to yield the optical path length variation of the sample. The resolution of the technique is analyzed by retrieving the phase profiles of polystyrene spheres in immersion oil, and the method is then applied for quantitative imaging of biological samples. By reprogramming the diffractive structure displayed at the SLM it is possible to record the whole set of phase shifted DIC images simultaneously in different areas of the same camera chip. This allows for quantitative snap-shot imaging of a sample, which has applications for the investigation of dynamic processes.

Optical reconstruction of digital holograms recorded at 10.6 μm: route for 3D imaging at long infrared wavelengths

Abstract: We demonstrate the optical reconstruction in the visible range (0.532μm) of digital holograms recorded at long IR wavelengths (10.6μm) by means of a spatial light modulator. By using an integrated recording-reconstruction system, it is, in fact, feasible to achieve direct imaging of holograms acquired outside the visible range, i.e., in the IR spectrum. By choosing a Fourier recording configuration, the reconstructed image, obtained at about a 20 times shorter wavelength than the acquisition image, exhibits minor aberrations, which do not significantly affect the optical reconstruction. The high NA achievable at a long IR wavelength allows us to image large objects at reasonable distances.

Realization of curved Bessel beams: propagation around obstructions

Abstract: We present an experimental realization of spiraling and snaking zero-order Bessel beams; light modes designed to deviate from straight-line propagation. We show that these modes can be generated with a tunable lateral deviation, amplitude and axial periodicity using a dynamic adaptive optical element, namely a spatial light modulator. We demonstrate that such beams can elude obstructions placed on the optical axis. We discuss their applications for micromanipulation and within lab-on-a-chip systems.

On resolution and viewing of holographic image generated by 3D holographic display

Abstract: In the paper Wigner Distribution (WD) representation analysis of holographic display is presented. The display reconstructs holographic image by means of Spatial Light Modulator. Two major aspects are covered: imaging and viewing. Optically reconstructed images are characterized by low and spatially variant resolution. Utilizing WD representation we present a simple formula for resolution as a function of both coordinates: transverse and longitudinal. The analysis of an aliasing effect allows for meaningful extension of the field of view. All theoretical results are proven experimentally. The WD representation of angularly and spatially limited holographic image is extended to cover its visual perception as well. Angular resolution and field of view are theoretically examined. Both monocular and binocular perception are studied and illustrated experimentally.

Generation and nonlinear self-trapping of optical propelling beams

Abstract: We generate optical beams with rotating intensity blades by employing the moire technique. We show that the number of the blades and the speed and direction of rotation can be controlled at ease with a spatial light modulator, while no mechanical movement or phase-sensitive interference is involved. By applying a noninstantaneous self-focusing nonlinearity, we demonstrate both theoretically and experimentally self-trapping of such optical propelling beams.

Stretching single DNA molecules to demonstrate high-force capabilities of holographic optical tweezers

Abstract: The well calibrated force-extension behaviour of single double-stranded DNA molecules was used as a standard to investigate the performance of phase-only holographic optical tweezers at high forces. Specifically, the characteristic overstretch transition at 65 pN was found to appear where expected, demonstrating (1) that holographic optical trap calibration using thermal fluctuation methods is valid to high forces; (2) that the holographic optical traps are harmonic out to >250 nm of 2.1 μm particle displacement; and (3) that temporal modulations in traps induced by the spatial light modulator (SLM) do not affect the ability of optical traps to hold and steer particles against high forces. These studies demonstrate a new high-force capability for holographic optical traps achievable by SLM technologies. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Turbidity suppression by optical phase conjugation using a spatial light modulator

Abstract: A detector of light transmitted through a turbid medium, comprising: one or more Digital Optical Phase Conjugation (DOPC) devices, wherein the DOPC devices include (1) a sensor for detecting input light that has been transmitted through the turbid medium and inputted on the sensor; and (2) a spatial light modulator (SLM) for outputting, in response to the input light detected by the sensor, output light that is an optical phase conjugate of the input light.

Laser-Based Head-Tracked 3D Display Research

Abstract: The construction and operation of two laser-based glasses-free 3D (autostereoscopic) displays that have been carried out within the European Union-funded projects MUTED and HELIUM3D is described in this paper. Both use a multi-user head tracker to direct regions viewer's referred to as exit pupils to viewer's eyes. MUTED employs a direct-view LCD whose backlight comprises novel steering optics and in HELIUM3D image information is supplied by a horizontally-scanned fast light valve whose output is controlled by a spatial light modulator (SLM). The principle of operation, construction and results obtained are described.