and is ideal for placing the eoscs 38 a 38 b 38 c to get optimal etalon performance the mirrors m 2 40 m 3 12 a m 4 12 b m 5 12 c are 2 axis mirrors are adjusted to select the desired eosc 38 a 38 b 38 c and implement perfect alignment with the etalon chip note that each eosc 38 a 38 b 38 c can be positioned at the desired locations in the sensing zone such as a power plant or aircraft engine an embodiment for the eosc 38 a 38 b 38 c is single crystal silicon carbide that acts as a natural etalon light reflected from the chosen etalon chip traces the path back via the mirrors and sl 1 36 to reflect via bs 1 24 towards spherical lens sl 2 42 with focal length f 2 the distance from sl 2 42 to the eosc 38 a 38 b 38 c plane is ideally f 2 the returning light 48 via sl 2 42 then passes via the beamforming mirror tm 44 to strike a freespace coupled photodetector pd 1 46 tm 44 is a beam spoiling correction mirror such as a deformable mirror that corrects wavefront distortions and keeps the returning beam aligned on pd 1 46 to produce the optimal sensing signal based on opl changes in the frontend etalon chip 38 a 38 b 38 c because the eoscs 38 a 38 b 38 c can be mounted on various platforms.