Gravity-wave detection

This paper reports a sensitive optical interferometric technique dual frequency modulation (DFM) for measuring and stabilizing a laser frequency by comparison, in a single step, to a radio frequency (rf) standard. Conversely, a low-noise rf source can be stabilized by a laser frequency reference. A prototype has demonstrated a resolution of 2 parts in 10 , but devices currently under development should have a resolution of 10 and an absolute accuracy of 10" . The method may be competitive with the optical frequency synthesis chain in accuracy and its simplicity suggests its convenient use in metrology, high-precision optical spectroscopy, and gravity wave detection. 

A more far-reaching phenomenon is the possibility of generating radiation in "squeezed" states [4.19]. Such radiation exhibits reduced noise below the quantum limit and could have important applications for optical communication and precision interferometric measurements of small displacements, e.g. in gravity-wave detection experiments. A considerable degree of "squeezing" has recently been experimentally demonstrated [4.20, 21]. Various aspects of modern quantum optics have been discussed in [4. 22-25]. 

Lombardini PP, Fiscella B, Trivero P, Cappa C, Garrett WD (1989) Modulation of the spectra of short gravity waves by sea surface films slick detection and characterization with a microwave probe. J Atmos Oceanic Technol 6 882-890... 

Helioseismic waves are detected by measuring the Doppler shift of lines in the solar spectrum due to vertical motion of the Sun s surface along the line of sight. With appropriate data-reduction techniques, the frequencies for global oscillations can be determined to an accuracy of 5 ppm. This extreme accuracy requires long-term, continuous observations that are best done by spacecraft such as the joint ESA/NASA SOHO spacecraft, which observes the Sun from the Lagrangian point where the Earth gravity balances that of the Sun. 

Because only waves, say, in the range A = 4-30A can be detected, the gravity contribution is often negligible, except when y is very small. For normal liquids the root-mean-square value of the surface elevations is in the order of 0.5 nm. 

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