A scanning apparatus having a stage adapted to hold a specimen to be imaged and to move the specimen in a first direction, and a light source that includes a tunable laser that generates a light beam having an illumination wavelength that varies as a function of an input signal is disclosed. The apparatus includes an imaging system having a scanning assembly that includes a focusing lens that focuses the light beam to a measurement point on the specimen, a first mirror that moves in a second direction relative to the stage such that the focusing lens maintains a fixed distance between the focusing lens and the stage, and a displacement sensor that measures a distance between the scanning assembly at a mapping point on the specimen, and a light detector that measures an intensity of light leaving the measurement point on the specimen.