Teresa W. Ayers has been appointed to the Fischer Imaging board of directors. She will also serve as the chairman of Fischer's audit committee. . . .   Denis Helm has joined FLIR Systems Inc. as senior vice president for corporate development.   . . .    Zia Laser, developer of Quantum Dot laser technology for data and telecommunications networks, announces the following appointments: Joseph Dixon, chief of operations; Faisal Nabulsi, director of test and package; Tom Tumolillo Jr., director of product management; Lei Zhang, principal engineer; and Charles Bryan, sales engineer.