Reflectometry apparatus includes a radiation source, adapted to irradiate
a sample with radiation over a range of angles relative to a surface of the sample,
and a detector assembly, positioned to receive the radiation reflected from the
sample over the range of angles and to generate a signal responsive thereto. A
shutter is adjustably positionable to intercept the radiation, the shutter having
a blocking position, in which it blocks the radiation in a lower portion of the
range of angles, thereby allowing the reflected radiation to reach the array substantially
only in a higher portion of the range, and a clear position, in which the radiation
in the lower portion of the range reaches the array substantially without blockage.
