Equation Icon  S (f) = S (f) = 16sin2(pf L)[3 + 2cos(2pf L) + cos(4pf L)]Sproof mass(f) A E y + 8sin2(pf L)[2 + cos(2pf L)]Soyptical path(f ), (77) 2[ 2 proof mass optical path ] ST (f) = 2[1 + 2 cos(2pf L)] 4sin (pf L)S y + Sy (f) . (78)