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This Defense Intelligence Reference Document was prepared by the Defense Intelligence Agency under its Advanced Aerospace Weapon System Applications (AAWSA) program, is dated 6 April 2010 and is part of a series of advanced technology reports produced in FY 2009. It reviews proposed laboratory generators and detectors of high-frequency gravitational waves for communications. It favors an infrared-excited molecules transmitter and the Li-Baker detector, estimating about 1.9 million bits per second over 7,000 km through the Earth. It also discusses timing standards and interplanetary navigation uses.
“Masse”14 pages
UNCLASSIFIED/ ,SFIHl 8FFHil.tzk Wili &HkY Coherent Versus Stochastic SOL The question under consideration in this paper is whether or not the Li-Baker detector, Figure 14, is quantum-limited when detecting relic HFGW. In other words, does the standard quantum limit (SQL) interfere with the sensitivity of the Li-Baker detector design? The answer will be negative if the SQL is less than 10-32 m/m. Grishchuk ( 1977, 2007) has calculated the SQL for GW detectors in general, which for a coherent GW is hdet = (l/Q)(l>w/E)V2 (5) and for a stochastic GW is: (6) where hdet is the metric (strain) detection limit in m/m, (rJ is the frequency of sensed gravitational waves (typically around 10 GHz in the Li-Baker detector), Eis the effective energy contained within the detector cavity summed over the detection averaging time, and Q is the quality factor or selectivity of the signal over noise. The SQL depends on the values of these parameters. For the remainder of this paper, we will consider the SQL of only the stochastic signal detection case. In the following subsections the best possible value of the SQL using current technology will be estimated to determine the fundamental limitations of the Li-Baker detector as now envisioned. Impact of Contained Energy Levels on SQL First attempt to estimate a realistic best case for the energy contained within the detection process, E. Typically it is expected that for a refrigerated microwave resonant cavity the best possible electrical quality factor will be around 2rrx10 5 . Assuming a "best efforts" value of 1000 W for the power of the Gaussian beam in a laboratory installation, the effective total RF energy stored in the microwave resonant cavity of the Li-Baker detector, summed over the system averaging time, is estimated to be given by (Grishchuk, 2007): ERF = (10 3 W) x (1000s) x (2rrxl0 5/2rr) = 10 11] (7) over a typical 1000 s averaging time. Both the Li-Baker detector and a detector using the Gertsenshtein effect use a large static magnetic field 8. For the present suggested outline design for the Li-Baker detector, the nominal value of 8 = 3 T, so that the magnetic energy density is given by The interaction volume in a practical laboratory-based detector is likely to be a maximum of around 1 m 3 . So, the effective total stored energy from the Gaussian 18 UNCLASSIFIED/ /r;OA. oi;i;1@IAI! l!l!II! 9HL I ( 8)
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Report, from the dia collection. The PDF is mirrored here; the original link is under it. 57 pages are in the text index: search them above, or from the library's search.