100,079 research outputs found
A Step-by-step Guide to the Realisation of Advanced Optical Tweezers
Since the pioneering work of Arthur Ashkin, optical tweezers have become an
indispensable tool for contactless manipulation of micro- and nanoparticles.
Nowadays optical tweezers are employed in a myriad of applications
demonstrating the importance of these tools. While the basic principle of
optical tweezers is the use of a strongly focused laser beam to trap and
manipulate particles, ever more complex experimental set-ups are required in
order to perform novel and challenging experiments. With this article, we
provide a detailed step- by-step guide for the construction of advanced optical
manipulation systems. First, we explain how to build a single-beam optical
tweezers on a home-made microscope and how to calibrate it. Improving on this
design, we realize a holographic optical tweezers, which can manipulate
independently multiple particles and generate more sophisticated wavefronts
such as Laguerre-Gaussian beams. Finally, we explain how to implement a speckle
optical tweezers, which permit one to employ random speckle light fields for
deterministic optical manipulation.Comment: 29 pages, 7 figure
A Grism Design Review and the as-built performance of the silicon grisms for JWST-NIRCAM
Grisms are dispersive transmission optics that find their most frequent use
in instruments that combine imaging and spectroscopy. This application is
particularly popular in the infrared where imagers frequently have a cold pupil
in their optical path that is a suitable location for a dispersive element. In
particular, several recent and planned space experiments make use of grisms in
slit-less spectrographs capable of multi-object spectroscopy. We present an
astronomer-oriented general purpose introduction to grisms and their use in
current and future astronomical instruments. We present a simple, step-by-step
procedure for adding a grism spectroscopy capability to an existing imager
design. This procedure serves as an introduction to a discussion of the device
performance requirements for grisms, focusing in particular on the problems of
lithographically patterned silicon devices, the most effective grism technology
for the 1.1-8 micron range. We begin by summarizing the manufacturing process
of monolithic silicon gratings. We follow this with a report in detail on the
as-built performance of parts constructed for a significant new space
application, the NIRCam instrument on JWST and compare these measurements to
the requirements.Comment: Accepted for publication in PAS
Recommended from our members
An Integrated Approach to Seismic Event Location: 1. Evaluating How Method of Location Affects the Volume of Groups of Hypocenters
When seismic events occur in spatially compact clusters, the volume and geometric characteristics of these clusters often provides information about the relative effectiveness of different location methods, or about physical processes occurring within the hypocentral region. This report defines and explains how to determine the convex polyhedron of minimum volume (CPMV) surrounding a set of points. We evaluate both single-event and joint hypocenter determination (JHD) relocations for three rather different clusters of seismic events: 1) nuclear explosions from Mururoa relocated using P and PKP phases reported by the ISC, 2) intermediate depth earthquakes near Bucaramanga, Colombia, relocated using P and PKP phases reported by the ISC, and 3) shallow earthquakes near Vanuatu (formerly, the New Hebrides), relocated using P and S phases from a local station network. This analysis demonstrates that different location methods markedly affect the volume of the CPMV, however, volumes for JHD relations are �not always smaller than volumes for single-event relocations.Phillips Laboratory, Directorate of Geophysics, Air Force Material Command, Hanscom Air Force Base, MassachusettsInstitute for Geophysic
Horn-like space-coiling metamaterials toward simultaneous phase and amplitude modulation
Acoustic metasurfaces represent a family of planar wavefront-shaping devices garnering increasing attention due to their capacity for novel acoustic wave manipulation. By precisely tailoring the geometry of these engineered surfaces, the effective refractive index may be modulated and, consequently, acoustic phase delays tuned. Despite the successful demonstration of phase engineering using metasurfaces, amplitude modulation remains overlooked. Herein, we present a class of metasurfaces featuring a horn-like space-coiling structure, enabling acoustic control with simultaneous phase and amplitude modulation. The functionality of this class of metasurfaces, featuring a gradient in channel spacing, has been investigated theoretically and numerically and an equivalent model simplifying the structural behavior is presented. A metasurface featuring this geometry has been designed and its functionality in modifying acoustic radiation patterns experimentally validated. This class of acoustic metasurface provides an efficient design methodology enabling complete acoustic wave manipulation, which may find utility in applications including biomedical imaging, acoustic communication, and non-destructive testing.We thank Boston University Materials Innovation Grant and Dean's Catalyst Award. We also thank the Boston University Photonics Center for technical support. (Boston University Materials Innovation Grant; Dean's Catalyst Award
Eliminating stray radiation inside large area imaging arrays
With increasing array size, it is increasingly important to control stray
radiation inside the detector chips themselves. We demonstrate this effect with
focal plane arrays of absorber coupled Lumped Element microwave Kinetic
Inductance Detectors (LEKIDs) and lens-antenna coupled distributed quarter
wavelength Microwave Kinetic Inductance Detectors (MKIDs). In these arrays the
response from a point source at the pixel position is at a similar level to the
stray response integrated over the entire chip area. For the antenna coupled
arrays, we show that this effect can be suppressed by incorporating an on-chip
stray light absorber. A similar method should be possible with the LEKID array,
especially when they are lens coupled.Comment: arXiv admin note: substantial text overlap with arXiv:1707.0214
Planar Airy beam light-sheet for two-photon microscopy
We demonstrate the first planar Airy light-sheet microscope. Fluorescence
light-sheet microscopy has become the method of choice to study large
biological samples with cellular or sub-cellular resolution. The
propagation-invariant Airy beam enables a ten-fold increase in field-of-view
with single-photon excitation; however, the characteristic asymmetry of the
light-sheet limits its potential for multi-photon excitation. Here we show how
a planar light-sheet can be formed from the curved propagation-invariant Airy
beam. The resulting symmetric light sheet excites two-photon fluorescence
uniformly across an extended field-of-view without the need for deconvolution.
We demonstrate the method for rapid two-photon imaging of large volumes of
neuronal tissue.Comment: 7 pages, 4 figure
Confocal Laser Induced Fluorescence with Comparable Spatial Localization to the Conventional Method
We present measurements of ion velocity distributions obtained by laser induced fluorescence (LIF) using a single viewport in an argon plasma. A patent pending design, which we refer to as the confocal fluorescence telescope, combines large objective lenses with a large central obscuration and a spatial filter to achieve high spatial localization along the laser injection direction. Models of the injection and collection optics of the two assemblies are used to provide a theoretical estimate of the spatial localization of the confocal arrangement, which is taken to be the full width at half maximum of the spatial optical response. The new design achieves approximately 1.4 mm localization at a focal length of 148.7 mm, improving on previously published designs by an order of magnitude and approaching the localization achieved by the conventional method. The confocal method, however, does so without requiring a pair of separated, perpendicular optical paths. The confocal technique therefore eases the two window access requirement of the conventional method, extending the application of LIF to experiments where conventional LIF measurements have been impossible or difficult, or where multiple viewports are scarce
- …