Image Analysis with the DMD in Convergent Path

Digital micromirror devices (DMDs) are micro-electro- mechanical systems, originally developed to display images in projector systems. A DMD in the focal plane of an imaging system can be used as a reprogrammable slit mask of a multi-object spectrometer (MOS) by tilting some of the mirrors towards the spectrometer and tilting the rest of the mirrors away, thereby rejecting the unwanted light (due to the background and foreground objects). A DMD-based MOS can generate new, arbitrary slit patterns in seconds, which significantly reduces the overhead time during astronomical observations. Critically, DMD-based slit masks are extremely lightweight, compact and mechanically robust, which makes them attractive for use in space-based telescopes. As part of a larger effort to investigate the use of DMDs in space telescopes (sponsored by a NASA Strategic Astrophysics Technologies grant), we characterized the optical performance of Texas Instruments DMDs to determine their suitability for use in multi-object spectrometers. The performance of a DMD-based MOS is significantly affected by its optical throughput (reflectance), contrast ratio (the ability of the DMD to reject unwanted light) and scattering properties (which could lead to crosstalk and reduced signal-to-noise ratio in the spectrometer). We measured and quantified the throughput and contrast ratio of a Texas Instruments DMD in several configurations (which emulate the operation of a typical DMD-based MOS) and investigated the scattering properties of the individual DMD mirrors. In this work we present the results of our analysis, describe the performance of a typical DMD- based MOS and discuss the practical limitations of these instruments (such as maximum density of sources and expected signal-to- noise ratio).

OPTRA is developing a next generation digital micromirror device (DMD) based two-band infrared scene projector (IRSP) with infinite bit depth independent of frame rate and an order of magnitude improvement in contrast over the state of the art. Traditionally, DMD-based IRSPs have offered larger format, superior uniformity, and pixel operability relative to resistive and diode arrays. However, they have been limited in contrast and also by the inherent bit depth/frame rate tradeoff imposed by pulse width modulation (PWM). OPTRA’s high dynamic range IRSP (HIDRA SP) has broken this dependency with a dynamic structured illumination solution. The HIDRA SP uses a source-conditioning DMD to impose the structured illumination on two projector DMDs—one for each spectral band. The source-conditioning DMD is operated in binary mode, and the relay optics that form the structured illumination act as a low-pass spatial filter. The structured illumination is, therefore, spatially grayscaled and more importantly is analog with no PWM. In addition, the structured illumination concentrates energy where bright objects will be projected and extinguishes energy in dark regions; the result is a significant improvement in contrast. The projector DMDs are operated with 8-bit PWM; however, the total projected image is analog with no bit depth/frame rate dependency. We describe our progress toward the development, building, and testing of a prototype HIDRA SP.

Diagnostics are crucial to the operation of all particle accelerator facilities. They provide a means of optimising beam parameters and monitoring beam quality for users. However, for the next generation of accelerators, operating in extreme parameter spaces, most current beam diagnostics will fail; either through material failure or lack of resolution. This thesis presents three new diagnostic concepts to address this imminent diagnostic need. These novel diagnostics are supported by a simulation-based algorithm, successfully benchmarked throughout this work. All work has been conducted by the Author unless otherwise stated and referenced. The first technique measures sub-micron transverse beam profiles using optical transition radiation (OTR). Simulations were used to design a new imaging system, which was then installed at KEK (Japan). OTR images were then collected for a range of beam sizes. Comparisons were then made with simulations to successfully achieve sub-micron beam size measurements. Validation of these results was found in the agreement across different imaging systems for fixed beam parameters, providing a self-consistency check for the algorithm in lieu of alternate corroboration. The next diagnostic is a bunch length monitor for ∼<100 fs particle bunches; based on imaging the spatial distribution of coherent transition radiation (CTR) in the THz regime. Simulations demonstrated a relationship between image width and intensity, with bunch length. A THz imaging system was then installed at MAX IV (Sweden). CTR images were taken for a range of compressions. Maximum compression was successfully identified by monitoring relative changes in the properties of the images. Bunch lengths were then acquired from these images through comparison with simulations. Finally, the optical performance of a Digital Micro-mirror Device (DMD) was assessed. Image resolution produced by a DMD was quantified by measuring the Point Spread Function (PSF) of an imaging system, which was capable of remotely replacing a DMD with a planar mirror. The PSFs were measured using the sub-micron focus of a laser. Results show no measurable alteration to a PSF with the introduction of a DMD. This provides a foundation for the development of future diagnostics centred around this device. This thesis provides several validated proof-of-principle experimental results and supporting simulations. Future work has been identified for each topic, only possible following the results presented here, which will provide an array of novel next generation diagnostics.

The digital micromirror device DMD is widely used in visible light projection, special-purpose spatial light modulation, and infrared scene simulation, due to its high resolution, uniformity and energy concentration. In some applications that require high frame rate scene image display, it is necessary to ensure that the DMD displays high gray level images at a high frame rate. However, the display frame rate of the pulse width modulation (PWM) method is limited by the minimum time required for DMD loading data, unable to achieve high frame rate display. Although the DMD binary display mode can meet the requirements of high frame rate display, it cannot meet the requirements of high gray level. The paper proposes an image display method that uses light source and DMD to synchronize modulation. Decompose the high-order gray image into bit planes according to the gray threshold, and the DMD displays each bit plane in binary mode under the trigger of an sync pulse. The intensity of the illumination laser source is modulated by an acousto-optic modulator to match the bit plane and the radiated laser power. This method makes use of the function of high frame rate display in DMD binary mode cooperate with light intensity modulation of illumination laser source, and realizes high frame rate and high dynamic range image display. With this method, the maximum frame rate of 8-bit gray level image with 1920 ×1080 resolution can reach 2KHz. The experimental system has realized 200Hz frame rate display of 8-bit gray level image with 1920 ×1080 resolution.

We have developed a new coronagraph using digital micromirror device (DMD) to observe faint emissions close to a bright objects in our solar system such as water plumes on Europa and Enceladus, plasma emissions in giant planet’s magnetospheres, escaping plasma and neutrals from Venus and Mars, and so on. The focal plane DMD mask enables us to occult planet’s disks and their moons even when their angular dimeter and geometry vary with time. The coronagraph composed of a DMD as an occulting mask on a telescope focal plane, a pupil stop, a narrow-band filter, and others. The DMD located at the focal plane produces color dispersion of entrance aperture on a pupil plane for an extended lightsource. Thus, we designed a proper shape of pupil mask to reduce remaining from the occulted light-source considering wavelength and bandwidth of observations. The coronagraph was installed on a Cassegrain focus of the Tohoku 60-cm telescope at Haleakala observatory in Hawaii. We have been using the coronagraph for observing sulfur ion emissions [SII] 671.6 and 673.1 nm from Io plasma torus since 2018. The DMD occultation reduces light from Jupiter disk and Galilean moons by 2.6×10-3. The system throughput is 56 % of a previous conventional coronagraph. In observation of Io plasma torus, north-south position of [SII] brightness peak shifted by 0.07 jovian radii toward the magnetic equator during three days. Increase of flesh pickup ion possibly makes higher anisotropy or higher ion perpendicular temperature causing the observed magnetic-equatorward shift of the plasma torus.

High-speed 3D optical microscopy is an indispensable requirement in studying rapid processes like signaling in neuronal networks, flagellar motion, or complex motion of living and highly dynamic subcellular components. However, the 3D imaging capability often compromises either the acquisition speed or the complexity of the imaging system. Multi-plane imaging offers a parallelized acquisition of several focal planes at the same time, which tremendously enhances the temporal resolution. Nonetheless, most of the current multi-plane approaches are complex and require several optical elements to create multiple beams with different optical path lengths, limiting their broad application. To address these problems, in this thesis, employing a multi-plane prism, we introduce three novel techniques that each improve the concept of rapid 3D optical microscopy in a different direction: First, we accomplish a multi-plane detection for a phase-contrast microscope resulting in a 3D, label-free, and non-complex imaging system with a ~ 4ms of temporal resolution. We applied this system in real-time studying isolated bare axonemes of Chlamydomonas beating in the vicinity of a surface. This enabled us to observe their non-zero torsional motion where the torsion sign slowly changes from negative at the basal end toward positive at the distal end of flagella. Second, straightforwardly, we combine an experimental spectral unmixing setup with the multi-plane detection and obtain an instant 3- color 3D microscope with a minimal axial color aberration of 140 nm in a ~ 2.5 μm axial range. The performance of such a microscope is verified in volumetric imaging of three different subcellular components in fixed COS-7 cells. Third, a single-color multi-plane fluorescence microscope has been employed as a rapid 3D particle tracking velocimetry method in microscale to study single particles tracing the so-called Marangoni flow. Using that, besides the velocity fields of single particles, we achieve a localization precision of ~ 60 nm in the lateral and ~ 300 nm in the axial direction over a 120 120 13 m3 field of view. Altogether, using these three techniques, we extend the temporal resolution, throughput, and applicability of 3D optical microscopy. In another project, we implemented image scanning microscopy simultaneously in two colors on a conventional wide-field microscope by applying an LED light source and a digital micro-mirror device. This permits us to realize an inexpensive, speckle noise-free, and easy-to-implement super-resolution add-on for a conventional epi-fluorescence microscope.

The <i>Infrared Multi-Object Spectrometer (IRMOS)</i> is a principle investigator-class instrument for the Kitt Peak National Observatory 2.1 m and Mayall 3.8 m telescopes. <i>IRMOS</i> is a near-IR (0.8-2.5 micron) spectrometer with low- to mid-resolving power (R = &#955;/&#916;&#955; = 300-3000). On the 3.8 m telescope, <i>IRMOS</i> produces simultaneous spectra of ~100 objects in its 2.8 x 2.0 arcmin field of view using a commercial micro electro-mechanical systems (MEMS) digital micro-mirror device (DMD) from Texas Instruments. The multi-mirror array DMD operates as a real-time programmable slit mask. The all-reflective optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the DMD field stop, and the spectrograph images the DMD onto a large-format detector. The instrument operates at ~90 K, cooled by a single electro-mechanical cryocooler. The bench and all components are made from aluminum 6061. There are three cryogenic mechanisms. We describe laboratory integration and test of <i>IRMOS</i> before shipment to Kitt Peak National Observatory. We give an overview of the optical alignment technique and integration of optical, mechanical, electrical and cryogenic subsystems. We compare optical test results to model predictions of point spread function size. We discuss some lessons learned and conclude with a prediction for performance on the telescope.

In this paper, we introduce the notion of a programmable imaging system. Such an imaging system provides a human user or a vision system significant control over the radiometric and geometric characteristics of the system. This flexibility is achieved using a programmable array of micro-mirrors. The orientations of the mirrors of the array can be controlled with high precision over space and time. This enables the system to select and modulate rays from the scene's light field based on the needs of the application at hand. We have implemented a programmable imaging system that uses a digital micro-mirror device (DMD), which is used in digital light processing. Although the mirrors of this device can only be positioned in one of two states, we show that our system can be used to implement a wide variety of imaging functions, including, high dynamic range imaging, feature detection, and object recognition. We also describe how a micro-mirror array that allows full control over the orientations of its mirrors can be used to instantly change the field of view and resolution characteristics of the imaging system. We conclude with a discussion on the implications of programmable imaging for computer vision.

In this paper, we report on a type of SU-8 microstructure with vertical sidewalls used for polydimethydiloxane (PDMS) microchannels. Multi-layer lithography using focal plane changing approach is proposed to expose the SU-8 photoresist based on a digital micromirror device (DMD) maskless lithography system. We used a light-emitting diode source with a wavelength of 405 nm. The thickness of the SU-8 is divided into multi-layers according to the depth of focus. Each layer corresponds to a depth of focus, and then, a virtual mask is designed for the layer. Finally, each layer is exposed to changes in the focal plane. The results indicate that the actual profile of the SU-8 mold shows good agreement with the design profile without any T-profiles. Additionally, there is better linewidth in the proposed method compared with multi-exposure by a single fixed focal plane. The PDMS microchannels result also demonstrate the stability of the SU-8 mold.

The continuous development of laser systems toward more compact and efficient devices constitutes an increasing threat to electro-optical imaging sensors, such as complementary metal–oxide–semiconductors (CMOS) and charge-coupled devices. These types of electronic sensors are used in day-to-day life but also in military or civil security applications. In camera systems dedicated to specific tasks, micro-optoelectromechanical systems, such as a digital micromirror device (DMD), are part of the optical setup. In such systems, the DMD can be located at an intermediate focal plane of the optics and it is also susceptible to laser damage. The goal of our work is to enhance the knowledge of damaging effects on such devices exposed to laser light. The experimental setup for the investigation of laser-induced damage is described in detail. As laser sources, both pulsed lasers and continuous-wave (CW)-lasers are used. The laser-induced damage threshold is determined by the single-shot method by increasing the pulse energy from pulse to pulse or in the case of CW-lasers, by increasing the laser power. Furthermore, we investigate the morphology of laser-induced damage patterns and the dependence of the number of destructive device elements on the laser pulse energy or laser power. In addition to the destruction of single pixels, we observe aftereffects, such as persistent dead columns or rows of pixels in the sensor image.

Optical path length, temperature, and wavelength effects simulation on ozone gas absorption cross sections towards green communications

The generation and coding of multi-cycle terahertz (THz) pulses offer interesting possibilities, such as frequency comb spectroscopy or ultra-fast packet communication. In contrast to the radio frequency domain, which has largely exploited packet communication, this research area is almost unexplored at THz frequencies. Indeed, because of the lack of fast modulation and detection methods at THz frequencies, current developments often rely on hybrid techniques mixing photonics and ultrafast electronics. Here, we present a method for the generation and modulation of a coded THz pulse train. Our scheme is based on the combination of a spintronic THz emitter (STE) with an echelon mirror and a digital micromirror device. This highly scalable configuration is capable of modulating a hundred or more THz pulses in parallel with sub-picosecond accuracy. Strikingly, the temporal resolution of our modulation scheme depends on geometric optics and not on a high-speed electronic device. Furthermore, our scheme confirms the ability of STEs to generate quasi-continuous THz pulses and offers a new photonic solution on dynamic THz pulse train control.

There are many different modes of microscopy, and all of these modes deliver light in a controlled fashion to the object to be examined and collect as much of the light containing the desired information about the object as possible. The system being presented replaces the simple irises of a conventional microscope with digital micromirror devices (DMDs, made by Texas Instruments) to produce a digital microscope. The DMDs are placed in the optical path at positions corresponding to the field and aperture diaphragms of a conventional microscope. This allows for more precise and flexible control over the spatial location, amount, and angles of the illumination light, and the light to be collected. This digital microscope will improve existing modes of microscopy, specifically in quantitative microscopy. Using the intensity modulation feature of the DMDs, the system can correct for inhomogeneous illumination sources to achieve uniform distributions. In various configurations, one can perform brightfield, darkfield, confocal and fluorescence microscopy. In addition, new microscopy modes will be possible, such as reconstruction microscopy. Utilizing the fast switching times of the mirrors (under 20 microseconds), one can switch between modes efficiently.

In this paper a novel method for determining refractive indices of a multi-layered samples using low coherence interferometry (LCI), developed at the National Physical Laboratory, UK, is introduced. Conventional Optical Coherence Tomography (OCT) utilises a lateral scanning optical probe beam to construct a depth resolved image of the sample under investigation. All interfaces are detected in optical path length, resulting in an image depending on the refractive index of all prior layers. This inherent ambiguity in optical and geometric path length reduces OCT images to purely qualitative ones. We have demonstrated that by optically probing the sample at multiple angles we can determine bulk refractive index of layers throughout plane parallel samples. This method improves upon current approaches of extracting refractive index parameters from multi-layered samples as no prior geometrical information is required of the sample and the phase index for each layer is obtained as opposed to the group index. Consequently the refractive index result for each layer is independent of the refractive index of surrounding layers. This technique also improves on conventional measurements, as it is less susceptible to error due to surface defects. This technique is easily implemented, and can easily be modified to obtain in situ measurements. Investigating a silica test piece and comparing the refractive index obtained by that of standard critical angle refractometry has validated the robustness of the technique.

We demonstrate an electrowetting-based liquid optical phase shifter. The phase shifter consists of two immiscible liquid layers with different refractive indices. Sandwiched between the two liquids is a rigid membrane that moves freely along the optical axis and supported by a compliant surround. When applied with a pressure, the thicknesses of both liquid layers change, which induces a difference in optical path, resulting in a phase shift. A miniaturized electrowetting-based actuator is used to produce hydraulic pressure. A multi-layered SU8 bonded structure was fabricated. A phase shift of 171° was observed when the device was incorporated in a Mach-Zehnder interferometer and driven with 100 V.