910-m propagation of THz ps pulses through the Atmosphere.

We measured the atmospheric propagation of ps THz pulses with a 0.4-THz bandwidth through a 910-m distance; the pulse delay corresponded to 255 pulses down the pulse train of the mode-locked ring laser excitation pulses. The complexity of the atmosphere requires the use of the complete theory of Essen and Froome to compare the measured time shifts due to both the dry atmosphere and water vapor with theoretical calculations. A new procedure involving the measurement of phase in the frequency domain is introduced and achieves comparable results for the calculated time shifts, compared to the previous direct measurements of time shifts. When the THz pulses were sequentially measured for a distance of 186 and 910 m at the same weather condition, the time variation due to atmospheric turbulence between the two pulses of the 910 m measurement was up to 4 times larger than that between the two pulses of the 186 m measurement. THz long path WVD studies are necessary to evaluate proposed applications in the atmosphere, such as communications and monitoring pollutants and dangerous gases.