PROVIDENCE, R.I., March 18 -- Spectra Science Corp. has added Rhonda Landers as Chief Financial Officer and Scott Tillotson as Vice President of Marketing and Business Development. Prior to joining SSC, Landers held management positions at medical and financial firms. Tillotson held marketing positions for GTECH, Lasertron, IBM, and AT&T. Spectra Science is a developer of optical materials and systems.