Nanometer-resolution distance and surface structure measurement bv incoherent laser-feedback

Abstract

We provide a simple analysis to explain how the wavelength of a diode laser is shifted by the strong, incoherent optical feedback. Our preliminary experiments indicate that, in addition to wavelength changes, the laser diode's driving current is also extremely sensitive to the feedback. Thus, by detecting the bias current variations we could obtain similar nm ranging resolution without the complexity of a spectrometer. The technique can be made more compatible with integrated optics and existing technologies facilitating its applications in more difficult physical environments that may exist in industry or a medical'setting. Experimental results are provided that show 3-D surface structure imaging obtained by implementing this incoherent confocal laser-feedback technique in a scanning microscope.