Page 121 - Chalcogenide Glasses for Infrared Optics

98 Cha pte r F o u r

Calculated IR Transmission for Amtir 4
Absorption
Wavelength Refractive Coefficient Thickness
−1
(µm) IR Index (cm ) (cm) Reflectivity Transmission
Fiber Results
1.00 2.7788 0.04 2.6 0.221588 0.568757
1.50 2.6995 0.005 2.6 0.211036 0.642296
2.00 2.6778 0.003 2.6 0.208115 0.649923
2.5 2.6686 0.003 2.6 0.206873 0.651618
3.00 2.6637 0.002 2.6 0.20621 0.654372
4.00 2.6588 0.002 2.6 0.205547 0.655281
5.00 2.6561 0.002 2.6 0.205181 0.655783
6.00 2.6541 0.001 2.6 0.20491 0.658012
7.00 2.6524 0.001 2.6 0.204679 0.658329
8.00 2.6508 0.001 2.6 0.204462 0.658628
9.00 2.6491 0.009 2.6 0.204231 0.644245
10.00 2.6472 0.012 2.6 0.203973 0.639178
11.00 2.6452 0.014 2.6 0.203702 0.635961
12.00 2.643 0.024 2.6 0.203403 0.618777
13.00 2.6407 0.35 2.6 0.20309 0.257349
14.00 2.638 0.47 2.6 0.202723 0.187959

TABLE 4.2 AMI Program to Calculate Transmission of Amtir 4 as a Function of
Thickness and Wavelength

incorporating absorption coefficient results calculated from the plate
scan. Table 4.2 illustrates this procedure when applied to Amtir 4.
Specifications for wavelengths less than 2 µm (NIR) require the use
of a different kind of an instrument. In this case, the AMI Beckman
UV 5240 spectrophotometer covers the wavelength range of 0.5 to
2.5 µm. AMI uses a reflection attachment specifically designed for the
instrument to evaluate antireflection coating results. The attachment
mounts inside the sample area that may be closed when it is neces-
sary to keep light out of the instrument. In double-beam operation,
the instrument is an electronic null instrument not designed for high-
index solid materials. Care must be exercised in taking measure-
ments, and the results must be carefully evaluated. The fundamental
absorption edge, where the glasses begin to transmit, cannot be mea-
sured using either of the FTIR instruments. The Beckman instrument
must be used. As an example, a plot of the transmission edge for an
8-in-diameter Amtir 4 glass plate is shown in Fig. 4.7. Notice the plate
is 2.6 cm thick.