Tuesday, August 04, 2015

Looking at the universe using Germanium based photodetectors

I would like to sound out readers of this post about some speculative ideas. The assumption is that advanced civilizations might have discovered that the abundance of elements such as Germanium in stellar atmospheres is pretty close to zero. They could have also discovered that one could build Germanium based photon detectors and Ge based lasers. This opens up the possibility of interstellar signalling using photons produced by Ge based Lasers. An alternative method of sending a strong signal would involve sending spacecraft made of Germanium to fall into the atmosphere of a nearby star in a controlled time sequence. Each spacecraft falling into the stellar atmosphere ought to produce several megawatts of radiation from Germanium heated to very high temperatures. 

The weak element in the communication chain would be the Germanium based photo-detectors put together by another civilization, presumably scanning for these signals at some far away location; their spectral selectivity would not be adequate to reject extraneous light. While they will optimally detect photons with the right energies, they will also detect photons with other energies. The question that arises is if there is a way to design detectors that will be highly selective to radiation produced by excited Ge atoms only. A way to do this might be to use silicon doped only with Ge and operating at a voltage where Ge originated photons would create a cascade, while other photons will not. If we can create such a detector, we can get amazing signal-to-noise ratios for the whole system. Ideally, we would need an array of detectors so that we can scan an area of the sky using parallel detection elements.

I would like to add a couple of more thoughts. The universe creates little light at the wavelengths we have talked about except perhaps in some supernovae. Secondly, red shift may not be insurmountable problem, because we hope to look for signals arising within a few hundred light years from the earth. The red shift involved may be small enough to be handled in some way.  
Please do share your thoughts. I do moderate comments to avoid advertisements and such, but shall be happy to publish comments even if they say why this method of interstellar signalling will not work.
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Srinivasan Ramani said...

Let me also comment on the possible use of communication in "heavy element wavelengths" within the solar system. The relative darkness of the sky in these wavelengths would give a significant advantage to such communication.

Srinivasan Ramani said...

Obviously, stimulated emission of photons in a laser is a process very sensitive to the frequency of the incoming light. This means that a laser with a controlled amount of pumping can act as an amplifier for light at very specific frequencies and serve as a detector. The main problem I notice is that making a detector array using such lasers is not that easy; but there are other methods of imaging a small region of the sky using a single detector, for instance using a rotating prism with the detector. All this could mean that a performing a search for interstellar signals over the heavy element spectral lines is practical. Such a search may well be one of our major hopes for finding intelligent life elsewhere in the universe.