Multiwavelength Astronomy

Photo of IR Science Docent

Infrared Science, Judy Pipher

Building Detectors

When I was working with Martin and we were preparing for the rocket launches, there were no infrared array detectors that would allow one to take pictures. An array of detectors is a contiguous set of pixels arranged across the surface. It allows a picture to be taken with one pointing, like a camera. There were only single-pixel infrared detectors, and what you had to do was scan the telescope over the target source, building up an image one pixel at a time. Another graduate student and I were building detectors for various infrared wavelengths. During this time Martin went on leave to Czechoslovakia for a year. Martin’s post-doc, later a faculty member, Jim Houck, became responsible for our work and the responsibility for running Martin’s lab weighed pretty heavily on him.

At one stage we needed a particular type of detector. Some of the things I had to do to get this one detector working involved some pretty dangerous procedures, both with the development of the detector and the wavelength-selecting filters that went with it, which I also had to make. The bonding of wire leads to the detectors had to be done in a highly flammable hydrogen atmosphere, and the filters I built included poisonous powder embedded in a polyethylene matrix. In both cases, heat had to be applied. Jim kept telling me: “You can’t do this and you can’t do that,” because he was worried about my safety. I would sneak in on the weekends when Jim wasn’t there to work on the detector and filter. Of course, I took reasonable precautions in doing this. One day he came into the lab and asked, “Damn it, Pipher, when are you going to work on this detector?” I responded, “I’m testing it now.” He was completely stunned. He was just very concerned about my safety.

Those first rocket experiments using the single-pixel detectors we made were very successful. I was working primarily in the far infrared at that point— wavelengths of 100 microns, 160 microns, and 300 microns, far beyond the infrared sensitivity of the human eye. Perhaps the most stunning results were from a scan of the plane of our galaxy which showed the center of the galaxy, and giant molecular clouds associated with ionized hydrogen regions, both strong infrared sources by virtue of dust grains that were heated and glowing in them. The dust grains also absorb visual wavelength light, so infrared light allows us to see sources embedded in dusty clouds that we couldn't see otherwise. This made infrared astronomy exciting.

When Jim Houck turned sixty, I was asked to review some of the earlier experiments at a symposium in his honor. I took some of our earlier measurements and compared them against the present-day measurements, which of course are much more sophisticated, but we did very well in those early days. That’s the best anyone can say. We did well with these limited technologies.

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This material is based upon work supported by NASA under Grant Nos. NNX09AD33G and NNX10AE80G issued through the SMD ROSES 2009 Program.

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