to create a surface relief hologram binary optic by exposing an emulsion to create a volume hologram or by manufacturing a micro fresnel lens mfl a suitable objective lens 22 is custom manufactured by companies such as teledyne brown engineering using techniques such as ion milling or reactive ion etching a positioner 25 establishes a coarse location in range of the scanned depth of field by mechanically positioning objective lens 22 the focused light reflected from target 6 is collimated since it is reflected from a point the reflected light is returned through objective lens 22 and reflected by beamsplitter 15 along an optical axis 21 the light is then focused onto a pinhole 27 by a lens 26 the light passing through pinhole 27 is incident on a detector 5 lens 26 has negligible chromatic dispersion lenses 9 22 and 26 preferably are approximately the same size pinhole 27 passes only the reflected light from the central maximum of the diffraction pattern of objective lens 22 the light that passes through pinhole 27 exhibits a high degree of wavelength dispersion this wavelength dispersion is a function of the distance from objective lens 22 of the particular point on the target from which the light is being reflected detector 5 is preferably a high gain avalanche photodiode apd or a silicon pin diode in a current integrating mode detector 5 outputs a signal 28 which consists of a pulse whose temporal centroid corresponds to the distance between objective lens 22 and the point on target 6 the temporal width of this pulse is approximately proportional to the depth of focus of objective lens 22 an example of the calculation to determine the height of the peak of a pulse includes 1 compute an amplitude that is 70.