What are the atmospheric absorption windows in the terahertz frequency range?
Atmospheric Propagation at Terahertz Frequencies
Atmospheric absorption is the fundamental limitation for terrestrial terahertz systems. Unlike microwave frequencies below 100 GHz where atmospheric loss is generally manageable, the terahertz range is dominated by strong rotational absorption lines of water vapor that carve the spectrum into discrete transmission windows.
Frequently Asked Questions
Can I use terahertz for outdoor wireless communication?
Below 350 GHz, short-range outdoor links of 100-500 meters are feasible with high-gain antennas. The 200-310 GHz band has been demonstrated for 100+ Gbps point-to-point links over distances of 100-800 meters. Above 500 GHz, atmospheric absorption limits outdoor use to very short ranges or requires operation at high altitude in dry conditions.
Why are terahertz observatories at high altitude?
Water vapor is concentrated in the lower 2-3 km of the atmosphere. At altitudes above 4,000-5,000 meters (like Mauna Kea at 4,200 m or the Atacama Desert at 5,000 m), the precipitable water vapor drops to 0.5-1 mm, reducing terahertz attenuation by 10-100x compared to sea level. ALMA, the premier terahertz telescope array, sits at 5,050 m elevation.
Does rain affect terahertz propagation?
Yes, rain significantly increases attenuation at terahertz frequencies. Rain attenuation at 300 GHz is approximately 5-10 dB/km for moderate rain (10 mm/hr), adding to the already high atmospheric attenuation. Fog and humidity also increase absorption. Practical terahertz links must include rain fade margins or be deployed in controlled environments.