Modern sensing systems often are required to pick out a very specific wavelength in a sea of other light (such as in daylight), making precise optical filtering a vital part of many sensing systems. Michigan Aerospace Corporation (MAC) plans to design, build and test an agile, frequency-tunable Fabry-Perot interferometer (etalon) for use as an optical filter of background light as part of a Differential Absorption LIDAR (DIAL) system. MAC's extensive history with designing and building rugged etalons for NASA and other customers will be key to this effort. Phase I will involve the design of this specific etalon and the testing of a faster method for precisely tuning it. Phase II will then involve the construction and test of the etalon.