Achromatic Image Research Articles

Chromatically modeling the parsec-scale dusty structure in the center of NGC 1068

Context. The Very Large Telescope Interferometer (VLTI) has been providing breakthrough images of the dust in the central parsecs of active galactic nuclei (AGNs), which is thought to be a key component of the AGN unification scheme and AGN host galaxy interaction. In single infrared bands, these images can enjoin multiple interpretations, some of which could challenge the unification scheme. This is the case for the archetypal type 2 AGN of NGC 1068, whereby the degeneracy is reduced by multi-band temperature maps that are hindered by an ambiguity in the alignment between different single-band images. Aims. We aim to solve this problem by creating a chromatic model capable of simultaneously explaining the VLTI GRAVITY+MATISSE 2 μm–13 μm observations of AGNs hosted by NGC 1068. Methods. We employed a simple disk and wind geometry populated by spherical black-body emitters and dust obscuration to create a versatile multi-wavelength modelling method for chromatic IR interferometric data of dusty objects. Results. This simple geometry is capable of reproducing the spectro-interferometric data of NGC 1068 from the K through N bands. It explains the complex single band images with obscuration and inclination effects, and it solves the alignment problem between bands. We find that the resulting model disk and wind geometry is consistent with previous studies of comparable and larger scales. For example, compared to molecular gas emission, our model wind position angle (PA) of 2322° is close to the mas-scale outflowing CO(6–5) PA of ∼33° seen with ALMA. The equivalent 90° offset model disk PA is also consistent with the CO(6–5) disk axis of 112° as well as the mas-scale disk axis from CO(2–1), CO(3–2), and HCO+(4–3) of 115 ± 5°. Furthermore, the resulting model images visually resemble the multiple achromatic image reconstructions of the same data when evaluated at the same wavelengths. We conclude that the IR emitting structure surrounding the AGN within NGC 1068 can indeed be explained by the clumpy disk+wind iteration of the AGN unification scheme. Within the scheme, we find that it is best explained as a type 2 AGN and the obscuring dust chemistry can be explained by a mix of olivine silicates and 16 ± 1% amorphous carbon.

Gaussian curvature and stigmatic imaging relations for the design of an unobscured reflective relay

We derive the relationship between Coddington's equations and the Gaussian curvature for a stigmatic reflective imaging system. This relationship allows parameterizing off-axis conic optical systems using traditional first-order optics by considering the effective curvature at the center of the off-axis sections. Specifically, we demonstrate parameterizing the system requirements of a 2× achromatic image relay for a terawatt laser system. This system required both collimation (far-field) and pupil imaging (near-field) simultaneously. Long working distances and specific spatial constraints limited the available layout options for the imaging components. By parameterizing these system requirements and packaging constraints, the final specifications could be quickly iterated, while allowing for flexibility in the layout of the system during a multi-year conceptual period.

Programmable Multiwavelength Achromatic Focusing and Imaging Through Scattering Media

Optical imaging and focusing through complex samples is a challenge with important applications in many fields. The critical problem is that turbid media such as biological tissue and multimode optical fibers randomly scatter and diffuse light, preventing the formation of diffraction-limited focus and image. We demonstrate with numerical simulations that a multiple scattering can be controlled via a serial optical transmission matrix and a parallel optical transmission matrix in order to obtain an achromatic focus and image at an arbitrary position. Simulation results of three-dimensional achromatic focusing and imaging based on this approach are agreed with the theoretical analysis. A scattering diffuser can be used as functional optical elements for focusing and imaging, moreover it can be manipulated and designed for multifunctional optical elements beyond traditional design. Our method will pave a way for using scattering media as unique optical achromatic elements for various applications, as well as for guiding the light and tailoring the light field.

Implementation of ultraviolet Thomson scattering on SG-III laser facility.

An ultraviolet Thomson-scattering system has been designed and implemented on the Shenguang-III laser facility, a 48-beam, 3ω (351 nm), 180 kJ-level laser driver for high energy density physics and inertial confinement fusion researches. The 4ω (263.3 nm) probe beam of the Thomson-scattering system is injected from the north pole (top) of the target chamber, with an assistant beam-pointing monitor to achieve high pointing accuracy. The Thomson-scattered light is collected by a double-Cassegrain optical transmission system, which provides an achromatic image over a wide wavelength range of 200-800 nm. A novel on-line alignment method is developed and applied to the diagnostic system, ensuring a volumetric positioning accuracy of ∼30 μm for the scattering volume. An online calibration is also conducted to provide the wavelength benchmark and the spectral resolution of the system. This Thomson-scattering system has been tested in a complicated experimental environment with gas-filled hohlraums, and a high-quality ion feature of the scattered light has been obtained.

Chromatic and achromatic monocular deprivation produce separable changes of eye dominance in adults.

Temporarily depriving one eye of its input, in whole or in part, results in a transient shift in eye dominance in human adults, with the patched eye becoming stronger and the unpatched eye weaker. However, little is known about the role of colour contrast in these behavioural changes. Here, we first show that the changes in eye dominance and contrast sensitivity induced by monocular eye patching affect colour and achromatic contrast sensitivity equally. We next use dichoptic movies, customized and filtered to stimulate the two eyes differentially. We show that a strong imbalance in achromatic contrast between the eyes, with no colour content, also produces similar, unselective shifts in eye dominance for both colour and achromatic contrast sensitivity. Interestingly, if this achromatic imbalance is paired with similar colour contrast in both eyes, the shift in eye dominance is selective, affecting achromatic but not chromatic contrast sensitivity and revealing a dissociation in eye dominance for colour and achromatic image content. On the other hand, a strong imbalance in chromatic contrast between the eyes, with no achromatic content, produces small, unselective changes in eye dominance, but if paired with similar achromatic contrast in both eyes, no changes occur. We conclude that perceptual changes in eye dominance are strongly driven by interocular imbalances in achromatic contrast, with colour contrast having a significant counter balancing effect. In the short term, eyes can have different dominances for achromatic and chromatic contrast, suggesting separate pathways at the site of these neuroplastic changes.

Hololujah; A One Kilometre Art Hologram

This paper will outline the production of the white light transmission achromatic image art hologram titled Hololujah displaying forward projecting real imagery of text and measuring 100,000 × 3.5 cm. Materials and methods: The paper will cover the use of Slavich VRP-M film 33.3 × 1.05 metres that was exposed and processed as thirty-three and a third 100 × 105 cm frames. These thirty-three and a third frames were subsequently cut into one thousand 100 × 3.5 cm strips with their ends cold laminated together to form the kilometre length hologram. This paper will expand on the use of a Coherent Compass 315M, 532 nm, 150 mW DPSS laser diode in a lensless setup, using a single beam through diffuse glass, no isolation systems and a two minute exposure time with the film lying flat on the floor. Lastly, this paper will illustrate how the hologram was produced in a 220 × 200 × 300 cm confined area of a suburban bedroom. Theme: This artwork is a comment on the social networking site Twitter.

Spatiochromatic statistics of natural scenes: first- and second-order information and their correlational structure

Spatial filters that mimic receptive fields of visual cortex neurons provide an efficient representation of achromatic image structure, but the extension of this idea to chromatic information is at an early stage. Relatively few studies have looked at the statistical relationships between the modeled responses to natural scenes of the luminance (LUM), red-green (RG), and blue-yellow (BY) postreceptoral channels of the primate visual system. Here we consider the correlations among these channel responses in terms of pixel, first-order, and second-order information. First-order linear filtering was implemented by convolving the cosine-windowed images with oriented Gabor functions, whose gains were scaled to give equal amplitude response across spatial frequency to random fractal images. Second-order filtering was implemented via a filter-rectify-filter cascade, with Gabor functions for both first- and second-stage filters. Both signed and unsigned filter responses were obtained across a range of filter parameters (spatial frequency, 2-64 cycles/image; orientation, 0-135 degrees). The filter responses to the LUM channel images were larger than those for either RG or BY channel images. Cross correlations between the first-order channel responses and between the first- and second-order channel responses were measured. Results showed that the unsigned correlations between first-order channel responses were higher than expected on the basis of previous studies and that first-order channel responses were highly correlated with LUM, but not with RG or BY, second-order responses. These findings imply that course-scale color information correlates well with course-scale changes of fine-scale texture.

Improved Performance of a Single-Polarizer DTN-LCD with a Retardation Film

We numerically analyzed the relationship between the electro-optical properties and the on-voltage of a TFT-LCD in a single-polarizer reflective double-layered TN-LCD (DTN-LCD) with a retardation film in order to confirm the possibility of reducing power consumption. Our results demonstrate that the LCD exhibits an achromatic image of high luminous reflectance of about 50% and very high contrast ratio, even if the on-voltage is reduced to 2 V. The power consumption can thus be decreased to about 1/6 that of the presently used reflective 5 V TFT-LCD in the on-state.

Image-plane disk-type multiplex hologram.

We demonstrate, both theoretically and experimentally, that a disk-type multiplex hologram can be fabricated as an image-plane hologram that is suitable for white-light line-source reconstruction. By adopting the method of direct object-image relationship, we build the theory based on the imaging property of lenses and on coordinate transformation. Numerical simulation shows the characteristics of this type of hologram. Experimental results reveal that the picket-fence effect that is encountered in the traditional multiplex hologram for images viewed at various distances has been eliminated. Using a reconstruction white-light line source of sufficient length, we observed an achromatic three-dimensional image.

Ultrabroadband collection and illumination optics for Raman and photoluminescence spectroscopy in the 200–700 nm wave band

The design and construction of an optical instrument is described to enable accurate and reliable resonance Raman scattering and photoluminescence measurements to be acquired in the 200–700 nm (1.77–6.2 eV) wave band, with minimum user intervention between changes of the excitation wavelength. An f/6 line or point focus is formed at the sample. f/2 achromatic catadioptric optics image the scattered light to the entrance slit of an f/7.5 spectrometer. An ultraviolet sensitive charge coupled device camera enables imaging and alignment of samples within the excitation laser region, providing an imaging resolution of better than 13 μm (results presented elsewhere suggest a resolution limit of 7 μm). The use of an aperture plate allows pseudo-confocal operation, leading to considerable improvement in depth discrimination when interrogating extended volume scatterers. This mode of operation furthermore eliminates stray light derived from the Rayleigh line, thereby enabling line focus spectra to be obtained to very low wave numbers. The optics present a unique method of interrogating a sample with an extended lateral and well-defined axial interaction region with a high collection efficiency (optical throughput of >41%), simultaneously offering broadband achromatic spectral response in collection from 200 to 700 nm.

Indexing chromatic and achromatic patterns for content-based colour image retrieval

In this paper, we present a method to represent achromatic and chromatic image signals independently for content-based image indexing and retrieval for image database applications. Starting from an opponent colour representation, human colour vision theories and modern digital signal processing technologies are applied to develop a compact and computationally efficient visual appearance model for coloured image patterns. We use the model to compute the statistics of achromatic and chromatic spatial patterns of colour images for indexing and content-based retrieval. Two types of colour images databases, one colour texture database and another photography colour image database are used to evaluate the performance of the developed method in content-based image indexing and retrieval. Experimental results are presented to show that the new method is superior or competitive to state-of-the-art content-based image indexing and retrieval techniques.

Image-plane cylindrical holographic stereogram

A two-step holographic process is introduced to fabricate a cylindrical multiplex hologram as an image-plane hologram. By adoption of the achromatic angle in the process the hologram is capable of generating an achromatic image. The most important factors, the location as well as the width of the viewing slits, that affect the quality of the observed image are analyzed and discussed. The change of aspect ratio for the observed image as a function of the viewing distance is theoretically and numerically analyzed. This method can not only eliminate the annoying picket-fence effect but can also increase the vertical viewing range for the observer. Computer simulations as well as experimental results are provided.

White-light implementation of the Wigner-distribution function with an achromatic processor

A temporally incoherent optical processor that combines diffractive and refractive components is proposed for performing two different operations simultaneously: an achromatic image along an axis and an achromatic one-dimensional Fourier transformation along the orthogonal axis. These properties are properly employed to achieve the achromatic white-light display of the Wigner-distribution function associated with a one-dimensional real signal, with high redundancy and variable scale.

126 COLOR HOLOGRAPHIC STEREOGRAM

Using the rainbow holographic technique, a color or an achromatic image can be obtained from the superposition of various rainbow holograms on a single plate. Since the color of the reconstructed image depends on the observation angle, the desired image is obtained at a specific viewing position. Using Kogelnik's theory an analysis of the image's color variation under different recording and reconstruction conditions is performed. The analysis helps to find adequate recording parameters to improve the luminance of the final reconstructed image.

Some fundamental limitations of achromatic holographic systems

Fundamental limitations on achromatic holographic systems are examined by using Gaussian-bracket expressions for the first order and chromatic properties of a general holographic system. It is shown that there is one and only one holographic triplet that is corrected for both primary-color errors and secondary axial color. Secondary color is shown to be fundamentally uncorrectible in a holographic triplet. Also, a rigorous proof is given that any achromatic image of a real object that is formed by an all-holographic imaging system must be virtual, regardless of the number of holographic elements in the system.

Neutron microscope.

We report successful operation of a neutron microscope using ultracold neutrons at the high-flux reactor at Grenoble. A sharp, achromatic image of an object slit was obtained at a magnification of 50. The measured resolution of 0.1 mm was limited mainly by the available beam intensity, not by aberrations.

Achromatic and sharp real imaging of a point by a single aspheric lens

By a single lens (two refracting surfaces, one dispersive medium) an achromatic real point image can be obtained. We show how such a lens brings a large aperture bundle of axial-parallel rays to the same sharp focus for two wavelengths, that is, for two refractive-index values. The normal of one of the two refracting surfaces is, in general, discontinuous at the axis. The numerical aperture which is practically attainable can be enhanced by off-axis steps in the refracting surfaces. The design principles for such lenses, computational formulas, and examples of results are given. Limitations and further possibilities are discussed.

Application of weigert effect to the pseudocoloration of a black and white signal

We propose here a method to transform the grey levels of a black and white transparency into different colours. The transparency to be processed, illuminated by a beam of linearly polarized white light, is twice recorded on a photograph silver-chloride emulsion. The direction of the light vector is rotated through π/2 between the exposures. The resulting plate is characterized by a spatially varying anisotropy. The main point is that the wavelength λ B and λ D, respectively corresponding to the cancellation of birefringence and dichroism, are function of the irradiance of the signal and of the successive exposure times. The plate is then illuminated in white light and observed between two polarizers P and A. It reconstructs an achromatic image of T when the respective axes of P and A are mutually perpendicular. A rotation of A from its setting crossed with P generate a colour distribution on the plate.

On the colours of the striæ in mica, and the radiation from laminar diffracting boundaries

The phenomenon which forms the subject of this paper was briefly described in a preliminary communication in ‘Nature,' made jointly by Prof. C. V. Raman and the author of this paper, accompanied by a short but suggestive note by Lord Rayleigh. It is observed when a clear sheet of transparent mica is placed in front of a good achromatic lens, and examined by the well-known Foucault “knife-edge” test, otherwise referred to also as the Topler “Schlieren” method. The arrangement is shown in fig. 1. White light from a slit, S (illuminated by a half-watt incandescent lamp of 100 C.P.), is incident upon the lens, L, which forms an achromatic image of the slit at some distance from the lens. A knife-edge, K, is put in the focal plane, and so placed that the light coming to a focus in the ordinary way is completely cut off. The telescope, T, with its objective just behind the plane of the knife-edge, is pointed towards the lens, and is focussed on the surface of the mica (M. M.) placed immediately in front of the lens.