1. A method for producing a proof-mass assembly, comprising:forming a proof mass with a curved flapper hingedly supported at a straight end by a bifilar flexure that extends radially inwardly from a support ring, wherein one side of the bifilar flexure comprises a pair of adjacent flexure arms spaced apart by a window;
scanning a femtosecond laser on the flexure arms over a plurality of passes to gradually thin bifilar flexure regions on a first side of the flexure arms;
feathering with the femtosecond laser in areas where the flexure arms connect to the curved flapper or reed and producing a gradual transition from a thick to a thin section; and
periodically reducing femtosecond laser output to minimize damage from laser scanning and maximize bifilar flexure strength until the bifilar flexure arms reach a predetermined thickness to form the proof-mass assembly.