4,590 research outputs found
Onboard utilization of ground control points for image correction. Volume 1: Executive summary
Operation of a navigation system, centered around image correction, was simulated and the system performance was analyzed. Onboard utilization of ground control points for image correction is summarized. Simulation results, and recommendations for future mission requirements are presented
Swept source optical coherence tomography Gabor fusion splicing technique for microscopy of thick samples using a deformable mirror
We present a swept source optical coherence tomography (OCT) system at 1060 nm equipped with a wavefront sensor at 830 nm and a deformable mirror in a closed-loop adaptive optics (AO) system. Due to the AO correction, the confocal profile of the interface optics becomes narrower than the OCT axial range, restricting the part of the B-scan (cross section) with good contrast. By actuating on the deformable mirror, the depth of the focus is changed and the system is used to demonstrate Gabor filtering in order to produce B-scan OCT images with enhanced sensitivity throughout the axial range from a Drosophila larvae. The focus adjustment is achieved by manipulating the curvature of the deformable mirror between two user-defined limits. Particularities of controlling the focus for Gabor filtering using the deformable mirror are presented. © 2015 Society of Photo-Optical Instrumentation Engineers
Development of a light-sheet fluorescence microscope employing an ALPAO deformable mirror to achieve video-rate remote refocusing and volumetric imaging.
There are numerous situations in microscopy where it is desirable to remotely refocus a microscope employing a high numerical aperture (NA) objective lens. This thesis describes the characterisation,
development and implementation of an Alpao membrane deformable mirror-based system to achieve this goal for a light-sheet fluorescence microscope (LSFM).
The Alpao deformable mirror (DM) DM97-15 used is this work has 97 actuators and was sufficiently
fast to perform refocus sweeps at 25 Hz and faster. However, a known issue with using Alpao
deformable mirrors in open-loop mode is that they exhibit viscoelastic creep and temperature-
dependent variations in the mirror response. The effect of visco-elastic creep was reduced by
ensuring that the mirror profile was on average constant on timescales shorter than the characteristic time of the visco-elastic creep. The thermal effect was managed by ensuring that the electrical power delivered to the actuators was constant prior to optimisation and use. This was achieved by ensuring that the frequency and amplitude of oscillation of the mirror was constant prior to optimisation, so that it reached a thermal steady state, was approximately constant during optimisation and constant during use.
The image-based optimisation procedure employed used an estimate of the Strehl ratio of the optical system calculated from an image of an array of 1 ÎĽm diameter holes. The optimisation procedure
included optimising the amount of high-NA defocus and the Zernike modes from Noll indices 4 to 24. The system was tested at 26.3 refocus sweeps per second over a refocus range of -50 to 50 ÎĽm with a 40x/0.85 air objective and a 40x/0.80 water immersion objective. The air objective enabled a mean Strehl metric of more than 0.6 over a lateral field of view of 200x200 microns and for a refocus range of 45 microns. The water objective achieved a mean Strehl metric of more than 0.6 over a lateral field of view of 200x200 microns over a larger refocus range of 77 microns.
The DM-based refocusing system was then incorporated into a LSFM setup. The spatial resolution of the system was characterised using fluorescent beads imaged volumetrically at 26.3 volumes per second. The performance of the system was also demonstrated for imaging fluorescence pollen grain samples.Open Acces
A day-night high resolution infrared radiometer employing two-stage radiant cooling Quarterly report, 1 Apr. - 1 Jul. 1967
Test evaluation of radiant cooler for day-night high resolution infrared radiometer, and electronic design of breadboard radiomete
A compact, large-aperture tunable lens with adaptive spherical correction
In this paper, we present the proof of concept of a very fast adaptive glass
membrane lens with a large aperture/diameter ratio, spherical aberration
correction and integrated actuation. The membrane is directly deformed using
two piezo actuators that can tune the focal length and the conical parameter.
This operating principle allows for a usable aperture of the whole membrane
diameter. Together with the efficient actuation mechanism, the aperture is
around 2/3 of the total system diameter - at a thickness of less than 2mm. The
response time is a few milliseconds at 12mm aperture, which is fast compared to
similar systems.Comment: Presented at the IEEE 2014 International Symposium on Optomechatronic
Technologies (ISOT 2014), 4 pages PD
Comparison of nematic liquid-crystal and DMD based spatial light modulation in complex photonics
Digital micro-mirror devices (DMDs) have recently emerged as practical spatial
light modulators (SLMs) for applications in photonics, primarily due to their modulation rates,
which exceed by several orders of magnitude those of the already well-established nematic liquid
crystal (LC)-based SLMs. This, however, comes at the expense of limited modulation depth and
diffraction efficiency. Here we compare the beam-shaping fidelity of both technologies when
applied to light control in complex environments, including an aberrated optical system, a highly
scattering layer and a multimode optical fibre. We show that, despite their binary amplitude-only
modulation, DMDs are capable of higher beam-shaping fidelity compared to LC-SLMs in all
considered regime
Spaceborne synthetic-aperture imaging radars: Applications, techniques, and technology
In the last four years, the first two Earth-orbiting, space-borne, synthetic-aperture imaging radars (SAR) were successfully developed and operated. This was a major achievement in the development of spaceborne radar sensors and ground processors. The data acquired with these sensors extended the capability of Earth resources and ocean-surface observation into a new region of the electromagnetic spectrum. This paper is a review of the different aspects of spaceborne imaging radars. It includes a review of: 1) the unique characteristics of space-borne SAR systems; 2) the state of the art in spaceborne SAR hardware and SAR optical and digital processors; 3) the different data-handling techniques; and 4) the different applications of spaceborne SAR data
Comparison of nematic liquid-crystal and DMD based spatial light modulation in complex photonics
Digital micro-mirror devices (DMDs) have recently emerged as practical spatial light modulators (SLMs) for applications in photonics, primarily due to their modulation rates, which exceed by several orders of magnitude those of the already well-established nematic liquid crystal (LC)-based SLMs. This, however, comes at the expense of limited modulation depth and diffraction efficiency. Here we compare the beam-shaping fidelity of both technologies when applied to light control in complex environments, including an aberrated optical system, a highly scattering layer and a multimode optical fibre. We show that, despite their binary amplitude-only modulation, DMDs are capable of higher beam-shaping fidelity compared to LC-SLMs in all considered regimes
- …