Terehertz Absorption Studies

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What happens when terahertz waves travel through the atmosphere?

 

The plots below show how terahertz waves with particular frequencies are heavily absorbed by water vapor.  As the water vapor density (think relative humidity) rises, more absorption occurs.  Absorption is measured as power attenuation in decibels per kilometer.  Notice the first major absorption line is at about 0.18 THz (180 GHz).  Much stronger lines occur at frequencies like 0.55 THz or 0.75 THz.  At these frequencies, the terahertz waves are completely absorbed after just a short distance of propagation.

 

 

There are also frequencies at which terahertz waves are absorbed relatively weakly. The gray vertical bars show "bands" wherein terahertz waves are absorbed much less. These bands indicate where terahertz wireless communication can occur without too much loss.