Defense Intelligence Reference Document High-Frequency Gravitational Wave Communications

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received signal, S, is (1.48xl0 14)/(7xl06)2 = 3 wm· 2, more than adequate for an
effective communication system.
With this configuration, the width of the needle-like, narrow HFGW beam at the receive
end is (2.3x10- 4 ) x (7x10 6 ) = 1.6 km, and multiple HFGW carrier frequencies can be
used, so the signal is very difficult to intercept, and is therefore useful as a low-
probability-of-intercept (LPI) signal, even with widespread adoption of the technology.
From Equation (2) the amplitude A of the HFGW at 7,000 km with the HFGW frequency
(twice the IR frequency of VGW = l.2x10 14 s· 1) given by: A= 1.2sx10·18 (S/VGW )'1' =
l.SxlQ-32 (in dimensionless units or m/m), which would be detectable by the currently
designed Li-Baker HFGW detector. Since the exact frequency and phase of the HFGW
signal is known (unlike the stochastic relic HFGWs, for which the Li-Baker detector was
designed), a much more sensitive, optimized HFGW detector will likely be developed.
As shown in Figure 8, from Grishchuk (2008), there will be negligible relic HFGW noise
at the IR HFGW generator's frequency of l.2xl0 14 s- 1 and no other cosmic sources at
these frequencies are currently hypothesized. Prior to the proof-of-concept test, one
can assume a noise figure at the Li-Baker detector of 10-s wm- 2 .
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1 ◊-12
u , n = 1.0
_gw .
1 0-20 10·10 10·" 10°
Frequency v, Hz
Figure 8. Predicted Relic GW Energy Density as a Function of Frequency
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