MIL-DTL-62422D(AT)
4.5.3.2.1 Results. Transmission at each wavelength and angle shall be determined by:
Radiance with the filter in the optical train
T =
Radiance without filter in optical train
4.5.3.2.2 Optical density. The optical density shall be defined as:
O.D. = log (1/T)
4.5.3.3 Optical density scan. Two filters per chamber load shall be tested for compliance
with row A of table I (see 3.5.1). One filter shall be chosen from the upper (or inner) area of the
coating zone and one filter shall be chosen from the bottom (or outer) area of the coating zone.
Optical density shall be measured in 0.5 degree increments (or less) with light incidence angles
from 0±1.5 degrees to 80±1.5 degrees. The optical density scan shall be performed at the center
of the filters. The energy incident on the filters shall be "P" polarized with a minimum 100:1
ratio of "P" to "S". The incident light shall have a collimated beam diameter of 4.8±1.7 mm
(1/e2) and a full angle beam divergence less than or equal to 1 millirad (1/e2). Filters shall be
measured using a ruby laser setup as in 4.5.3.1.1. The system shall be calibrated over the optical
density range of 3 through 5. The optical density shall be measured for at least one pulse per
angle.
4.5.3.3.1 Inflection point. Optical density for each angle shall be measured in
accordance with 4.5.3.3. The contractor shall determine the optical density verses angle of
incidence from 0 to 80 degrees. For any region of a valley where the optical density decreases
by more than 0.7 and increases by more than 0.7 in 2 degrees or less and the minimum optical
density is less than 4.4, the contractor shall locate the inflection point (angle) and the minimum
optical density within that region by remeasuring the optical density within that region in
0.1 degree increments or less.
4.5.3.4 Melt verification. The contractor shall verify substrate performance to rows B
and C of table I (see 3.2.1 and 3.5.1).
4.5.3.5 Laser optical density measurements. Unless otherwise specified (see 6.2), all
readings shall be determined as an average of at least 100 pulses. The contractor may reduce the
minimum number of pulses averaged from 100 to 10 if it is shown that all 10 single pulse optical
density readings are within ±5 percent of the 10 pulse average optical density reading.
4.5.4 Ruby coating characterization. The spectral transmission from 680 nm to 880 nm
shall be measured in 1 nm increments for a minimum of one sample per lot to verify compliance
to 3.5.1.1. The system shall be calibrated for optical density of 2 using a NIST calibrated neutral
density filter(s).
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