Warren W. Johnson
Dept. of Phys. and Astron., Louisiana State Univ., Baton Rouge, LA 70803
Gravitational wave detectors, aimed at detecting the momentary gravitational perturbation that might come from the gravitational collapse of a star, share almost every attribute of a very sensitive acoustic detector, except the requirement that they be completely decoupled from any true acoustic source. There are now four multiton cryogenic resonant detectors around the world that have operated with burst amplitude sensitivity in the attometer (10[sup -18]-m) range, including the ALLEGRO detector at LSU. Even at liquid helium temperature, one possible fundamental noise source is the Langevin force, whose spectral density is determined by the mechanical Q of the relevant antenna resonances. Two practical materials, aluminum--magnesium alloy and high-purity niobium, have proven to have Q's greater than 10 million under some conditions. Now that many other noise sources have been eliminated, further improvements in sensitivity will come from further increases in Q.