Page 147 - Chalcogenide Glasses for Infrared Optics

124 Cha pte r F i v e

modulation transfer function (MTF) of the lens using collimated mono-
chromatic light. The focal length of the lens is confirmed, and the quality
of imaging in terms of line pairs per millimeter is resolved on and off
axis and is calculated and tabulated. In the early years of AMI, the Night
Vision Laboratory at Ft. Belvoir (NVL) required AMI to run an image
spoiling test on each Amtir 1 blank before shipping. NVL provided the
funds for AMI to purchase from Lou Fantozzi of Diversified Optics, a
computer-controlled MTF instrument. In the test, the instrument mea-
sured the MTF of a high-performance three-element infrared lens
designed by Fantozzi and fabricated at Diversified Optics. A carefully
polished Amtir 1 blank was then placed in the optical path, and the MTF
of the lens was remeasured. The relative MTF score at 10 line pairs per
millimeter had to be 94 percent or better for the blank to pass. AMI used
the instrument for this test several years until the test was deemed costly
and unnecessary because the pass rate was 99 percent. Eventually the
instrument was no longer functional and was not replaced by AMI.
In 2000, AMI began molding chalcogenide glass lenses in a joint pro-
gram with Lockheed Martin in Orlando, Florida. The molds used were of
very high quality, and as the work progressed, it became important to
have a method to verify the accuracy of the molding process. AMI pur-
chased a ZYGO interferometer instrument, shown in Fig. 5.6 mounted on
a stabilized optical table. Not visible in the photograph on the right-hand
side of the table is a WYKO interferometer used to evaluate the optical
homogeneity of each Amtir 5 plate produced by AMI to be used in the
Lockheed Martin JSF Fighter. Figure 5.7 shows a ZYGO evaluation sheet

FIGURE 5.6 Photo of the AMI ZYGO interferometer.