Geometric-phase-based phase-knife mask for stellar nulling and coronagraphy.

Exoplanets can be detected very close to stars using single-mode cross-aperture nulling interferometry, a photonic technique that relies on the inability of an anti-symmetric stellar point-spread function to couple to the symmetric mode of a single-mode fiber. We prepared an asymmetric field distribution from a laboratory point source using a flat geometric-phase-based pupil-plane phase-knife mask comprised of a planar liquid crystal polymer layer with orthogonal optical axes on opposite sides of a linear pupil bisector. Our mask yielded an on-axis laboratory point-source rejection (i.

Detectability of unresolved particles in off-axis digital holographic microscopy.

Off-axis digital holographic microscopy (DHM) provides both amplitude and phase images, and so it may be used for label-free 3D tracking of micro- and nano-sized particles of different compositions, including biological cells, strongly absorbing particles, and strongly scattering particles. Contrast is provided by differences in either the real or imaginary parts of the refractive index (phase contrast and absorption) and/or by scattering. While numerous studies have focused on phase contrast and improving resolution in DHM, particularly axial resolution, absent have been studies quantifying the limits of detection for unresolved particles.

Improving image resolution on point-like sources in a type 1 light-field camera.

A ray-trace simulation of a type 1 light-field imager is used to show that resolutions significantly better than the lenslet scale can be deterministically reached in reconstructed images of isolated point-like sources. This is enabled by computationally projecting the system pupil onto the lenslet-array plane to better estimate the lenslet-plane-crossing locations through which the rays from a point source have passed on their way to the detector array. Improving light-field type 1 image resolution from the lenslet scale to the pixel scale can significantly enhance signal-to-noise ratios on faint point-like sources such as fluorescent microbes, making the technique of interest in, e.

Using the Gouy phase anomaly to localize and track bacteria in digital holographic microscopy 4D images.

Described over 100 years ago, the Gouy phase anomaly refers to the additional phase shift that is accumulated as a wave passes through focus. It is potentially useful in analyzing any type of phase-sensitive imaging; in light microscopy, digital holographic microscopy (DHM) provides phase information in the encoded hologram. One limitation of DHM is the weak contrast generated by many biological cells, especially unpigmented bacteria.

Enhancing final image contrast in off-axis digital holography using residual fringes.

We show that background fringe-pattern subtraction is a useful technique for removing static noise from off-axis holographic reconstructions and can enhance image contrast in volumetric reconstructions by an order of magnitude in the case for instruments with relatively stable fringes. We demonstrate the fundamental principle of this technique and introduce some practical considerations that must be made when implementing this scheme, such as quantifying fringe stability. This work also shows an experimental verification of the background fringe subtraction scheme using various biological samples.

Ground-based measurements of the 1.3 to 0.3 millimeter spectrum of Jupiter and Saturn, and their detailed calibration.

One of the legacies of the now retired Caltech Submillimeter Observatory (CSO) is presented in this paper. We measured for the first time the emission of the giant planets Jupiter and Saturn across the 0.3 to 1.

Compact, lensless digital holographic microscope for remote microbiology.

In situ investigation of microbial life in extreme environments can be carried out with microscopes capable of imaging 3-dimensional volumes and tracking particle motion. Here we present a lensless digital holographic microscope approach that provides roughly 1.5 micron resolution in a compact, robust package suitable for remote deployment.

High-Contrast Imaging of Intermediate-Mass Giants with Long-Term Radial Velocity Trends.

A radial velocity (RV) survey for intermediate-mass giants has been operated for over a decade at Okayama Astrophysical Observatory (OAO). The OAO survey has revealed that some giants show long-term linear RV accelerations (RV trends), indicating the presence of outer companions. Direct imaging observations can help clarify what objects generate these RV trends.

Near-infrared imaging polarimetry of LkCa 15: A possible warped inner disk.

We present high-contrast -band polarized intensity images of the transitional disk around the young solar-like star LkCa 15. By utilizing Subaru/HiCIAO for polarimetric differential imaging, the angular resolution and the inner working angle reach 007 and = 0″.1, respectively.

A Submersible, Off-Axis Holographic Microscope for Detection of Microbial Motility and Morphology in Aqueous and Icy Environments.

Sea ice is an analog environment for several of astrobiology's near-term targets: Mars, Europa, Enceladus, and perhaps other Jovian or Saturnian moons. Microorganisms, both eukaryotic and prokaryotic, remain active within brine channels inside the ice, making it unnecessary to penetrate through to liquid water below in order to detect life. We have developed a submersible digital holographic microscope (DHM) that is capable of resolving individual bacterial cells, and demonstrated its utility for immediately imaging samples taken directly from sea ice at several locations near Nuuk, Greenland.

Robust, compact implementation of an off-axis digital holographic microscope.

Recent advances in digital technologies, such as high-speed computers and large-format digital imagers, have led to a burgeoning interest in the science and engineering of digital holographic microscopy (DHM). Here we report on a novel off-axis DHM, based on a twin-beam optical design, which avoids the limitations of prior systems, and provides many advantages, including compactness, intrinsic stability, robustness against misalignment, ease of use, and cost. These advantages are traded for a physically constrained sample volume, as well as a fixed fringe spacing.

A Mach-Zender digital holographic microscope with sub-micrometer resolution for imaging and tracking of marine micro-organisms.

Digital holographic microscopy is an ideal tool for investigation of microbial motility. However, most designs do not exhibit sufficient spatial resolution for imaging bacteria. In this study we present an off-axis Mach-Zehnder design of a holographic microscope with spatial resolution of better than 800 nm and the ability to resolve bacterial samples at varying densities over a 380 μm × 380 μm × 600 μm three-dimensional field of view.

Improving vector vortex waveplates for high-contrast coronagraphy.

Vector vortex waveplates (VVWs) open the door to new techniques in stellar coronagraphy and optical communications, but the performance of currently available liquid-crystal-polymer-based VVWs tends to be limited by defects in the axial region of the vortex pattern. As described here, several steps allow for a reduction in the size of such axial defects, including the use of photoalignment materials with high photosensitivity and reversible response, and a reduction in exposure energy. Moreover, redistributing the writing beam's intensity from the axial region to its periphery (using a VVW) allows the production of large area VVWs with a small defect area.

Speckle-phase measurement in a tandem-vortex coronagraph.

A tandem-vortex coronagraph can in theory enable high-contrast imaging behind a classical on-axis telescope. Here we point out that a tandem-vortex coronagraph configuration can also directly enable the measurement of the phases of focal-plane speckles, thereby allowing for their suppression in the resultant high-contrast image.

Improved high-contrast imaging with on-axis telescopes using a multistage vortex coronagraph.

The vortex coronagraph is one of the most promising coronagraphs for high-contrast imaging because of its simplicity, small inner working angle, high throughput, and clear off-axis discovery space. However, as with most coronagraphs, centrally obscured on-axis telescopes degrade contrast. Based on the remarkable ability of vortex coronagraphs to move light between the interior and exterior of pupils, we propose a method based on multiple vortices, that without sacrificing throughput, reduces the residual light leakage to (a/A)(n), with n ≥ 4, and a and A being the radii of the central obscuration and primary mirror, respectively.

Experimental evaluation of achromatic phase shifters for mid-infrared starlight suppression.

Phase shifters are a key component of nulling interferometry, one of the potential routes to enabling the measurement of faint exoplanet spectra. Here, three different achromatic phase shifters are evaluated experimentally in the mid-infrared, where such nulling interferometers may someday operate. The methods evaluated include the use of dispersive glasses, a through-focus field inversion, and field reversals on reflection from antisymmetric flat-mirror periscopes.

Deep nulling of laser light with a single-mode-fiber beam combiner.

The detection of faint companions to bright stars requires the development of very-high-contrast-ratio detection techniques such as nulling interferometry. Here we present, to our knowledge, the first experimental test of a novel beam-combination method, which is based on coupling the light at the center of a dual-aperture interference pattern into a single-mode fiber. Using such a "fiber nuller" approach, a visible He-Ne laser has been stably nulled to as low as 1.

Symmetric nulling coronagraph based on a rotational shearing interferometer.

We describe a fully symmetric nulling coronagraph for single-aperture telescopes that is based on a rotational shearing interferometer (RSI) and that is intended for the imaging of faint companions to nearby bright stars. In the proposed layout, all asymmetries inherent in previous single-aperture RSI-based nulling coronagraphs have been eliminated, and the bright and dark outputs are both accessible. As a resulty deep, broadband, dual-polarization rejection of on-axis starlight should be possible with this system.