Hyperspectral Imaging Instruments

Most Hyperspectral imaging instruments
are based on either:

• An LCTF, AOTF, or an interferometer, to "flip" filters: Good for fixed, inert samples or

• A wavelength dispersive device, such as a prism or diffraction grating:
  Fast, simultaneous wavelength acquisition makes this technique great for objects that move, or are otherwise chemically, or physiologically, dynamic.

The Spectral Imaging Animations
The following animation that compares filter flippers with wavelength dispersive hyperspectral imaging systems such as PARISS. After the movie has downloaded you can click to select, or replay, any segment shown in the left side-column.

1. The first animation shows how the PARISS, like all wavelength dispersive systems, captures all wavelengths simultaneously
2. The second animation illustrates how LCTF (Liquid Crystal Tunable Filter) , AOTF (Acousto-Optic Tunable Filter) and interferometers acquires each wavelength sequentially, and
3. Finally a side by side comparison of the two techniques.

For security setting help click here

Wavelength dispersive systems
Wavelength dispersive systems (WDS) use either a prism or a diffraction grating as the wavelength dispersive element. WDS systems sweep across an unlimited field of view (FOV) in what is referred to as a "push-broom" system later on this page you can see how this works in an animation. All wavelengths are acquired simultaneously over the entire spectral range.

The PARISS® Wavelength Dispersive Hyperspectral Imaging System (WDSI)
The PARISS imaging spectrometer uses a unique patented curved prism as the wavelength dispersive element. Unlike a filter-flipper systems PARISS is a wavelength dispersive system that grabs all wavelengths simultaneously - there is no delay between the acquisition of the first and last wavelength in the range.

In fact, PARISS acquires all wavelengths between
365 and 920 nm in a single shot.

The use of a prism ensures that there is absolutely NO second order contamination. (Higher orders do not exist with a prism; which partially explains why prisms produce such very high light throughput). Click here for a comparison between a prism and a diffraction grating. See also the "Imaging Spectrometer - tutorial"

"Filter Flippers" (LCTF/AOTF/Interferometer)
Filter flippers include Liquid Crystal Tunable filters, (LCTF), Acousto Optic Tunable filters (AOTF) and interferometers.

Filter flippers acquire spectra, wavelength by wavelength, sequentially over a period of time. Each pixel of a CCD camera accumulates the spectrum of a target in a rigidly fixed FOV.

Because the FOV is fixed the technique fails when either an object moves or a chemical or biological interaction changes the spectral content. In order to "speed things up" it is not uncommon to take as few wavelength data points as possible.

Interferometers function in an analogous way to LCTF and AOTF devices because they too take wavelength information sequentially. An interferogram is constructed either by scanning a mirror or translating an optic. The net result is that it emulates a filter system that acquires wavelengths sequentially to form a "spectrum" in each pixel of a CCD. (See the animation at the bottom of the page)

Security settings and your ability to play the animations
Your computer may have security settings that will not allow the flash application to run unless you have deliberately enabled it. You may have to keep your finger on the "CTRL" when you click the link or answer "yes" to a message at the top of the content window. If you have a problem getting the animation to run, or you would like to discuss it, call me!

Most if not all versions of Windows XP and Vista already have a Flash player installed. If you have Win 2000 or an older version of XP you can download a free version of Macromedia Flash here. Note you may have to reboot your computer before it takes effect.

Prism assembly is manufactured under a license to US patent 5,127,728 owned by The Aerospace Corporation.
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