| CPC G01N 21/956 (2013.01) [G01N 2021/95676 (2013.01)] | 13 Claims |

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1. A system, comprising:
a radiation source configured to generate coherent radiation;
a grating structure optically coupled to the radiation source and configured to:
receive the coherent radiation from the radiation source,
generate a focused coherent radiation beam based on the coherent radiation,
transmit the focused coherent radiation beam toward a region of a surface of a substrate, wherein the grating structure comprises a grating with variable line spacing and is coupled to the radiation source via a waveguide, and
receive photons scattered from the region in response to an illumination of the region by the focused coherent radiation beam; and
a photodetector optically coupled to the grating structure and configured to:
measure the photons received by the grating structure, and
generate an electronic signal based on the measured photons.
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