||Quantum noise disadvantage is overcome by
antenna gain advantage.
||Planckian starlight noise reduced by very
small optical detection bandwidth of heterodyne receiver and diffraction limited telescope
||High Doppler shifts not important when we
don't know the "magic frequencies", and if we can tune over all frequencies.
||High Doppler chirps (drifts) at the
transmitter may be compensated by the aliens. Local Doppler chirps at the receiver may be
compensated by de-chirping the local oscillator laser.
||Laser linewidths can be obtained which are
less than 1 kHz. Bandwidths of optical transmissions likely to be much greater than 1 kHz.
||Beamwidth not limited for spaced-based
optical telescopes or ground-based adaptive optical telescopes. Aliens would not find it
too difficult to aim a beam with a beamwidth 0.01 arcsecond, to fall at a specified point
within a nearby star system. At ranges of hundreds of light years and greater, the beam
only has to be aimed at where the star will be in the round-trip time, to strike all the
planets in the star system.
||Other that the CO2 laser
frequency, we don't presently know what are the "magic frequencies" in the
optical spectrum. However, this just makes the search more difficult - not impossible.
||There are many families of lasers available to cover
the range of frequencies of interest. If we can narrow down the specific "magic
frequencies" we can save considerable effort in having to develop special lasers, and
substantially reduce the search time.
||Directed alien transmissions in the optical regime are
expected to be strong and sufficiently wideband to be unaffected by interstellar spectral
broadening. Hence the number of frequencies or bins to search may not be much greater than
in the 1 GHz to 10 GHz microwave regime.