Campbell Scientific TGA100 Trace Gas Analyzer Manual - Manual (Page 57)

Next, look at the reference detector transmittance as a function of temperature. The transmittance should have a
minimum at the (optimum) laser temperature. It should be higher at temperatures above and below the optimum
temperature. This increased transmittance results from an increased fraction of the laser’s energy at undesired
frequencies (multimode operation). Again, it is usually not necessary to plot the data, but Figure 4-7 shows a typical
example.
50
55
60
65
70
75
80
85
90
95
102.5 103 103.5 104 104.5 105 105.5
Laser Temperature (K)
R
eference
Transm
ittance
(%)
Figure 4-7. Typical Reference Transmittance as a Function of Laser Temperature
Finally, look at the concentration noise as a function of temperature. The concentration noise should also have a
minimum at the optimum laser temperature. Normally the minimum concentration noise occurs at the same laser
temperature as the minimum reference transmittance, and the laser temperature is simply set to this value. This is
illustrated in Fig
. ure 4-8
Figure 4-8. Typical Concentration Noise as a Function of Laser Temperature
0
10
20
30
40
50
60
70
80
90
100
102.5 103 103.5 104 104.5 105 105.5
Laser Temperature (K)
Co
n
cen
trati
o
n
N
o
ise (p
p
b
)
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