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• a very well developed high speed communications diode laser wavelength for fiber optic communications where both fiber attenuation and dispersion can be minimized
• in a very transparent spectral window of Earth's atmosphere, even down to sea level (when the weather is good!) update: that link includes light that reachest the ground by scattering as well as direct. For the direct, un-scattered beam only, @Hobbes' answer shows an example of a NASA calculation - for Pueblo Colorado (a better model for Mt. Palomar than San Francisco) it looks like the loss is about 1.4 dB, meaning about 72% transmission.

• a very well developed high speed communications diode laser wavelength for fiber optic communications where both fiber attenuation and dispersion can be minimized
• in a very transparent spectral window of Earth's atmosphere, even down to sea level (when the weather is good!) update: that link includes light that reachest the ground by scattering as well as direct. For the direct, un-scattered beam only, @Hobbes' answer shows an example of a NASA calculation - for Pueblo Colorado (a better model for Mt. Palomar than San Francisco) it looks like the loss is about 1.5 to 3 dB, meaning about 70 to 50% transmission.

• a very well developed high speed communications diode laser wavelength for fiber optic communications where both fiber attenuation and dispersion can be minimized
• in a very transparent spectral window of Earth's atmosphere, even down to sea level (when the weather is good!)

• a very well developed high speed communications diode laser wavelength for fiber optic communications where both fiber attenuation and dispersion can be minimized
• in a very transparent spectral window of Earth's atmosphere, even down to sea level (when the weather is good!) update: that link includes light that reachest the ground by scattering as well as direct. For the direct, un-scattered beam only, @Hobbes' answer shows an example of a NASA calculation - for Pueblo Colorado (a better model for Mt. Palomar than San Francisco) it looks like the loss is about 1.4 dB, meaning about 72% transmission.

Right now the primary target receiver is not the small optical array at Goldstone, but the 5.1 meter diameter Hale telescope on Mt. Polomar where a special superconducting wire detector will convert those faint laser signals directly to electrical signals without first producing photoelectrons like normal photodetectors do. For more on that, see

Right now the primary target receiver is not the small optical array at Goldstone, but the 5.1 meter diameter Hale telescope on Mt. Palomar where a special superconducting wire detector will convert those faint laser signals directly to electrical signals without first producing photoelectrons like normal photodetectors do. For more on that, see