RL Associates is developing a small tactical, 5-channel multispectral imager (MSI) for mounting on unmanned aerial systems (UAS). It is based on the volume holographic beamsplitter discussed on the Lidar components page. The MSI includes a single zoom lens system, four high resolution, visible cameras, one mid-wave infrared camera, and 1 multiplexed volume holographic beamsplitter. The effective aperture is 4-6 times larger than currently available systems, resulting in its ability to be used in lower light levels. The single zoom lens allows for the same image to be seen in all cameras while keeping the same zoom ratio. The IR camera, allows for use in extremely low light levels where visible detection is not possible. The entire imager will be approximately 5lbs and 125 in3, making it one of the lightest, smallest and most efficient multispectral imagers available.

This MSI will include 4 mission specific, switchable/selectable wavelengths and 1 mid-wave IR wavelength holographic beamsplitter. For example, searching the ocean for underwater objects
requires wavelengths in the blue-green, where searching the jungle would require wavelengths from green to yellow, and

scanning the desert would require more in
the yellow to red wavelengths. Ideally, the multiplexed volume holographic beamsplitter could be switched remotely for continuous operations over a variety of targets.

Volume Holographic Optical Elements (VHOE)
Numerous state of the art detection systems rely on the ability to discriminate weak optical signals in the presence of significant unwanted background noise such as solar radiation. RL Associates has developed a new type of spectral filter composed of volume Holographic optical elements (VHOE). A volume holographic diffraction grating is formed by writing an interference pattern into a thick material using two beams of light, known as an object beam and a reference beam. Once the grating is formed, if it is illuminated with either one of the write beams at the correct wavelength, the second beam will be reproduced. Gratings can be written to return the diffracted beam on either the same side as the illumination (reflection grating) or the opposite side (transmission grating). The diffraction angle in both configurations is determined by the construction beams. These gratings function as spectral bandpass optical filters because only the range of wavelengths that match the specific written condition are diffracted while all other wavelengths are transmitted with no diffraction. The diffracted signal, which is narrowband in wavelength, is then re-imaged onto a second focal plane. In this way, ambient noise around the desired spectral band can be removed to improve the signal-to-noise ratio of return signals or cleanly separate spectral channels.

Narrowband, Wide-Field-of-View Lidar Receiver Suitable for Day/Night Operation
RL Associates is developing a new type of Lidar receiver using a large aperture telescope for collection of returns from a wide field of view and a two element volume holographic filter at the focal plane of the telescope for spectral filtering and beam shaping to the detector.

The two element volume holographic filter will be comprised of a spherical-planar volume hologram array which accepts light from the wide angular field at the focus of the telescope and collimates this light for acceptance by the second VHOE which will be have an extremely narrow spectral bandpass of 1 Å or less.

Multispectral Beam Splitter
Volume holograms present an advantageous alternative to traditional beam splitters in multispectral systems. A set of volume holograms, used as a beam splitter for a multispectral camera system, replaces a series of beam splitters and filters for each camera with a single, smaller, lighter-weight, optical element.

12 channel beamsplitting element demonstrated

RL Associates has demonstrated a fully-functional 12-channel beamsplitter using a multiplexed a 2x2 array of multiplexed volume holographic gratings. This beamsplitter will replace a series of lenses and filters for each channel with a single optical element that can perform both beam-shaping and spectral filtering. Furthermore, the beamplitter offers a 7x improvement in signal levels at each camera compared to the commonly used interference filters. This beamsplitter would allow for equal performance in much lower-light level environments.

Broadband Infrared Detector Array for Combined Laser Designator / Range Finder
Using current technology, the operator of a targeting system cannot see what he is targeting. He gets coordinates for the target and hopes the laser guide for the weapon is aligned properly and there is no deviation due atmospheric conditions or instabilities in laser pointing. RL Associates is developing a laser designator/range finder that actually shows a 3-D image of the target with the target designation spot on it so that it is always clear what target is being designated.

SEE WHAT YOU ARE TARGETING

Target designation spot visible on 3-D image of target
The LD/RF uses an infrared laser to designate the target. The amplified, range-gated, hi-resolution camera detects the target designator spot, and automatically adjusts the firing solution for increased accuracy. This system allows for approximately 3X the operating range, leading to greater survivability for the aircraft. It increases the automation of the system allowing for manpower reductions and a decrease in time lost to calibration of the system. The camera is very small and light, weighing only 3oz only with a diameter of 3.5”. This laser/camera system offers greater range, increased accuracy and the assurance of seeing what is being targeted without a significant enlargement of the footprint and weight of the current system.