Defense Intelligence Reference Document Metamaterials For Aerospace Applications

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amplitudes ( A(k,) and A(k1 ) ). Therefore, a new concept has to be developed, and the
multi-detector technique is such a concept.
The concept requires two detectors and two coherent laser beams. The two beams are
formed using a beam-splitter and a variable delay line imparting a phase shift to the
two beams (see the actual experimental photograph in Figure 13 where the beam-
splitter BS and the Delay Line are shown). We have theoretically demonstrated that the
intensity dependences of the two detector intensities 11{t.f/) and / 2 (/fl) as a function of
the phase delay !JI provides enough information to recover both A(kt) and A(k2).
Unequal grating p~ase interference: rJh. 21~' crd!!rs
Figure 12. (Left): Schematic for 2-Beams/2-Detectors Interferometric Measurement. (Right):
Numerical Simulation: intensity on the two detectors as a function of the phase delay between beams A and B
produced by the interference between the zeroth and first diffractive orders of the bottom dlffractive gratlng
(numerical simulation). The second detector provides the necessary second data point which is necessary for
separating the contributions of different diffractive orders.
Two sets of experiments demonstrating the feasibility of the concept are conducted.
None of these experiments constitutes imaging per se. However, without demonstrating
the two key milestones described below, proper imaging experiments cannot be
attempted.
The first milestone involves demonstrating that IPM indeed supports propagating (non-
evanescent) sub-diffraction waves. Figure 11 shows the experimental schematic (left
panel) and experimental results. The bottom grating "imprints" its Fourier components
(zeroth, first, second, third, and so forth) onto the incident laser pulse thereby
generating electromagnetic waves that are launched into the SiC-based IPM. The zeroth
harmonic is inside the radiation zone (that is, it is not sub-diffraction), while the first,
second, and so forth sub-diffraction. These EM waves scatter off the top grating having
a slightly different period and are released into the far field. Because the direction in
which waves are released depend on the Fourier harmonic's number, we can
experimentally separate and measure them. Clearly, the relative magnitudes of these
diffractive orders dramatically vary as a function of the laser wavelength. For example,
the zeroth diffraction order clearly dominates in the B.1 Ofrequency range.
However, in the t.· 1 > 0,€11 < Ofrequency range the first diffractive order becomes larger
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