An apparatus and a method for measuring surface topography of a work-piece are described. The apparatus comprises a light emitting assembly configured to emit an emitted beam of light, the emitted beam being emitted at a plurality of wavelengths and modulated at modulating frequency, the emitted beam being directed onto a surface of a work-piece. A detector is configured to receive a reflected beam of light that includes at least a portion of the emitted beam as reflected from the surface of the work-piece. The detector is further configured to generate a signal indicative of a position of the reflected beam on the detector. A signal processing unit is configured to remove noise from the signal thus generated based on the modulating frequency to obtain a processed signal. A control unit is configured to determine topography of the surface based on the processed signal.