The advantages of the optical approach to SETI over microwave SETI have been well described by Dr. Stuart Kingsley at the Columbus Optical SETI Observatory, as well as others. Near-infrared (IR) laser communications enable broadband data to be transmitted across thousands of light years with high effective signal-to-noise ratio and with less interstellar dispersion and scintillation effects to contaminate the signal. Laser frequencies are approximately five orders of magnitude higher than microwave frequencies, and accordingly percentage modulation bandwidths at visible wavelengths are five orders of magnitude more modest than at microwave wavelengths. Furthermore, near-IR wavelengths are less attenuated by galactic dust than visible ones, making the near-IR spectral region an excellent choice for SETI. The ability of near-IR imaging to penetrate galactic dust has been demonstrated by the astronomical community.
Star Forming Region G45.45+0.06, Gemini North Image, June 1999 Left/Top: Image at "J", 1250 nm, Right/Bottom: Image at "K", 2200 nm. Color composite infrared image using adaptive optics on the Gemini North telescope (Mauna Kea on the Big Island of Hawaii). Dust obscures this star forming region at optical wavelengths but is visible at longer infrared wavelengths. (Resolution = 0.12 arcseconds FWHM) Photo Credit: Gemini Observatory, US National Science Foundation, and University of Hawaii Institute for Astronomy
A basic near-IR SETI system with high gain can be easily assembled at relatively low cost. An article from tauthors at the Department of Physics at the University of Chicago in 1989 (Phillip Gleckman, Joseph O'Gallagher, and Roland Winston, "Concentration of sunlight to solar-surface levels using non-imaging optics", Nature, 339, 18 May 1989, pp. 198-200) described the use of nonimaging optics to achieve concentration of light to extremely high irradiance levels (theoretically in excess of the irradiance of the solar surface). The same technique can be used to build a functional "light bucket" for SETI.
A few substitutions can be made in the basic Winston design to customize it for SETI:
Near-IR Telescope System Components
One meter visible/near-IR Fresnel lens
Aluminum compound parabolic concentrator
Interference filters (tilting), and Fabry-Perot interferometer
CCD visible camera (for star lock)
x-y-z translation stage / tracking and detector dithering
LN2 Dewar and detectors (PbS [1100-3000 nm], InSb [1000-5500 nm], and InGaAs [800-2200 nm])
Focus with oscilloscope and optical chopper
Preamplifier with 26 dB gain and 50 MHz bandwidth (max. data rate approximately 3 Gb per minute)
A/D 5 MHz average sampling rate
The detectors and Dewar (especially for long wavelength detectors) mount on a 3-axis translation stage for star tracking. In the photograph the light baffles, mirror and concentrator have been removed to reveal the detector and stage.
This photo, made during construction and testing of lower telescope module, shows the chopper and preamplifier under test. The front door, baffles, and dewar stage have not been installed.
The assembled modules of the instrument are two meters tall and fit in az-el mount. Assembly and testing begin a few hours before data collection is scheduled to start. Data are collected in the time domain, and are being analyzed using auto- and cross-correlation techniques, cluster analysis, and Fourier transform methods. To see more on these methods, follow this link.
Background Presentation on Construction and Testing of the Near-IR Telescope
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