Model N-STP Operation Manual
Normalized Output Power vs. Frequency
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Curve 1
Curve 2
Figure 1-8. Normalized Output Power vs. Frequency normalized to have the
same peak power.
Curve 1: New tube; Curve 2: Tube near end-of-life.
Curve 2 depicts the doppler profile that exists at the end of the operating life if the laser tube
excitation parameter (total single pass gain/total losses) falls to 80% of its original value. This
gain decrease may be from gas cleanup or increased absorption loss changes of the cavity
mirrors. The peak output power available (at center-line) drops to nearly half its original
value.
If one normalizes both curves in Figure 1-8, it can be noted that this extreme degradation
does not appreciably affect the shape of the doppler curve. Thus, if one were to know the
peak value of output power (at center-line), a reasonably accurate calibration of output
frequency could be attained by using a power meter a calibration curve similar to Figure 1-7.
8.0. Frequency Calibration
As explained in Section 7.0, the Model N-STP-910, N-STP-912, single frequency laser system
may be tuned over a wide range of frequencies from center-line. Using calibration curves,
such as those shown in Figure 1-7, the output frequency can be calibrated to typically better
than
10% accuracy of a given frequency on the "Blue" side of the doppler output profile
for the 632.991 nm transition in
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Ne.
Figure 1-7 was constructed from measurements of a typical model N-STP-910 system
producing peak center-line power of about 1.3 mW and a typical model N-STP-912 system
producing peak center-line power of about 1.8 mW. As shown in Figure 1-8, the shape of
these curves will not deviate substantially over the useful life of the laser.
A laser power meter may be used for calibration by noting the peak center-line power during
the warm-up period while in the "Peak" detection mode. The desired frequency can then be
adjusted by looking up on the ordinate of Figure 1-7, the appropriate percentage of peak
center-line power for the desired frequency. By multiplying this percentage by the peak level
noted on the power meter, the output power may be adjusted for the desired frequency.
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