The International Space Station (ISS) is an unparalleled laboratory for studying colloidal suspensions in microgravity. The first colloidal experiments on the ISS involved passive observation of suspended particles, and current experiments are now capable of observation under controlled environmental conditions; for example, under heating or under externally applied magnetic or electric fields. Here, we describe the design of a holographic optical tweezers (HOT) module for the ISS, with the goal of giving ISS researchers the ability to actively control 3D arrangements of particles, allowing them to initialize and perform repeatable experiments. We discuss the design’s modifications to the basic HOT module hardware to allow for operation in a high-vibration, microgravity environment. We also discuss the module’s planned particle tracking and routing capabilities, which will enable the module to remotely perform pre-programmed colloidal and biological experiments. The HOT module’s capabilities can be expanded or upgraded through software alone, providing a unique platform for optical trapping researchers to test new tweezing beam configurations and routines in microgravity.
This paper describes the development of a new instrument for calibrating satellite imaging sensors - the Polarization
Hyperspectral Image Projector (PHIP). The PHIP instrument is capable of producing realistic standards-based satellite
imagery, simultaneously projecting spectral, spatial and polarization scenes. The feasibility study outlined here
demonstrates that liquid crystal devices are capable of producing arbitrary polarization states. Boulder Nonlinear
Systems is currently developing a complete spectral/spatial/polarization instrument to be delivered to NASA in 2013.
Over the last few years, Boulder Nonlinear Systems (BNS) and North Carolina State University (NCSU) have developed
a new beam steering technique that uses a stack of thin liquid crystal polarization gratings (LCPGs) to efficiently and
non-mechanically steer a beam over a large field-of-regard (FOR) in discrete steps. This technology has been
successfully transferred to BNS through an exclusive license agreement, and a facility has been completed to enable
commercial production of these devices. This paper describes the capabilities enabled by both the LCPGs and the
successful transfer of this technology.
Liquid Crystal on Silicon micro-displays are the enabling components on a variety of commercial consumer products
including high-definition projection televisions, office projectors, camera view-finders, head-mounted displays and picoprojectors.
The use and potential application of LCOS technology in calibrated scene projectors is just beginning to be
explored. Calibrated LCOS displays and projectors have been built and demonstrated not only in the visible regime, but
also in the SWIR, MWIR and LWIR. However, LCOS devices are not only capable of modulating the intensity of a
broadband illumination source, but can also manipulate the polarization and/or phase of a laser source. This opens the
possibility of both calibrated polarization displays and holographic projection displays.
A phase shifting differential interference contrast (DIC) microscope, which provides quantitative phase information and
is capable of imaging at video rates, has been constructed. Using a combination of phase shifting and bi-directional
shear, the microscope captures a series of eight images which are then integrated in Fourier space. In the resultant image
the intensity profile linearly maps to the phase differential across the object. The necessary operations are performed by
various liquid crystal devices (LCDs) which can operate at high speeds. A set of four liquid crystal prisms shear the
beam in both the x and y directions. A liquid crystal bias cell delays the phase between the e- and o-beams providing
phase-shifted images. The liquid crystal devices are then synchronized with a CCD camera in order to provide real-time
image acquisition. Previous implementation of this microscope utilized Nomarski prisms, a rotation stage and a
manually operated Sénarmont compensator to perform the necessary operations and was only capable of fixed sample
imaging. In the present work, a series of images were taken using both the new LCD prism based microscope and the
previously implemented Sénarmont compensator based system. A comparison between these images shows that the new
system achieves equal and in some cases superior results to that of the old system with the added benefit of real-time imaging.
Boulder Nonlinear Systems (BNS) has demonstrated a MWIR step and stare imaging system for AFRL that eliminates
the need for turrets and multiple cameras to scale the performance of available thermal imagers. The demonstration
system non-mechanically switches between fields-of-regard in a Hex-7 pattern to achieve 0.1 milliradian resolution
within a 17.5x17.5 degree field-of-regard. The sub-millisecond shutter switching time and polarization independence
maximizes the imaging integration time and sensitivity. The system uses a 1024x1024 (19.5 micron square pixels) InSb
camera with a 4.5 to 5 micron passband filter. Larger area detectors could be used to obtain larger fields-of-view, or the
system could be scaled to a larger pattern of shutter arrays. The system was developed to provide a cost-effective
method of providing night-vision and thermal imaging capabilities for persistent, high-resolution surveillance
applications with sufficient resolution to track mounted and un-mounted threats. The demo hardware was engineered to
enable near-term field and flight testing.
A hyperspectral image projector (HIP) is introduced that is built with liquid crystal based spatial light modulators (SLM)
as opposed to micromirror arrays. The use of an SLM as a broadband intensity modulator presents several benefits to this
application. With slight modifications to the SLM design, SLMs can be built for a wide range of spectral regimes,
ranging from the ultraviolet (UV) to the long-wavelength infrared (LWIR). SLMs can have a large pixel pitch,
significantly reducing diffraction in the mid-wavelength infrared (MWIR) and LWIR. Liquid crystal based devices offer
direct analog intensity modulation, thus eliminating flicker from time sequential drive schemes. SLMs allow for an on-axis
configuration, enabling a simple and compact optical layout. The design of the HIP system is broken into two parts
consisting of a spectral and spatial engine. In the spectral engine a diffraction grating is used to disperse a broadband
source into spectral components, where an SLM modulates the relative intensity of the components to dynamically
generate complex spectra. The recombined output is fed to the spatial engine which is used to construct two-dimensional
scenes. The system is used to simulate a broad range of real world environments, and will be delivered to the National
Institute of Standards and Technology as an enabling tool for the development of calibration standards and performance
testing techniques for multispectral and hyperspectral imagers. The focus of this paper is on a visible-band HIP system;
however, related work is presented with regard to SLM use in the MWIR and LWIR.
A Computed Tomography Imaging Spectrometer (CTIS) is an imaging spectrometer which can acquire a multi-spectral
data set in a single snapshot (one focal plane array integration time) with no moving parts. Currently, CTIS instruments
use a specially designed computer generated hologram (CGH) to disperse the light from a given spectral band into a
grid of diffraction orders. The capabilities of the CTIS instrument can be greatly improved by replacing the static CGH
dispersing element with a reconfigurable liquid crystal spatial light modulator. The liquid crystal spatial light modulator
is tuned electronically, enabling the CTIS to remain a non-scanning imaging spectrometer with no moving parts. The
ability to rapidly reconfigure the dispersing element of the CTIS allows the spectral and spatial resolution to change by
varying the number of diffraction orders, diffraction efficiency, etc. In this work, we present the initial results of using
a fully addressable, 2-D liquid crystal spatial light modulator as the dispersing element in a CTIS instrument.
Novel tunable polarization interference filters (PIF) employing active liquid crystal devices are presented, and the principles of operation are described. Filter designs are presented based on a requirement for tunable nulls in the visible and near infrared spectral regions, of high optical density, for protection from intense electromagnetic radiation outside of the spectral range of interest which can saturate an imaging or sensor system. Two types of PIFs are presented with their modeled results and device performances. Analog filters in a generalized Lyot-Ohmann geometry are presented which are capable of tuning an optical null through 260 nm, by employing a single active device per filter stage. Binary filters are also presented which can switch between two complimentary and non-overlapping spectral states. Both types of filter can operate in a “normally on” state with a broadband “white light” throughput.
The detection and measurement of vapour-phase or liquid-phase water is important in many industrial and chemical processes. Water exhibits strong absorption bands compared to other substances in the near infrared (NIR), and for this reason NIR spectroscopy is especially well suited to moisture determination. A lack of suitable sources in the NIR, however, has impeded the application of optical sensors to water detection. We have developed a modulatable IR source for use in a moisture sensor. In the system, the luminescent emission from optically pumped rare earth doped glasses is used. Thulium doped zirconium fluoride glass, which luminesces at 1.83 mm was the material chosen. The spectral overlap with the water absorption band is significant, and the output stability matches that of the pump source, which is typically an internally modulated diode laser emitting at 685nm. The detection system uses a reference beam and a probe beam to monitor changes in absorption due to moisture or water vapour. Results illustrating the effectiveness of the novel IR source in a sensor platform to measure trace amounts of liquid water and water vapor will be presented.