36
Chapter 4.
Operation with Thermopile Absorber Sensors
Warning:
Before using the sensor for power or energy
measurement, check that your laser power, energy
and energy density do not exceed the sensor ratings.
See Table 5. and Table 6.
in Chapter 10.
If the sensor is a water-cooled type, ensure that the
cooling water is flowing at an adequate rate; see table
below. Also, note that the reflectance from the absorber
could be as much as 10% and with CO2 lasers, the
reflected beam can be quite specular, so it is advisable to
provide a beam stop for the reflected beam with the
highest power lasers.
Sensor
Type
Liters
per
Minute At Full
Power
Min
Pressure
Bar
US Gallons
per Minute
10K-W
9
2
2.5
5000W
4.5
0.8
1.2
1500W
2.5
0.5
0.7
1000W
1.8
0.5
0.5
Table 1
.
Minimum Flow Rates For Water-Cooled Sensors
4.1 Thermopile Absorber Sensors
When a radiant heat source, such as a laser, is directed
at the absorber sensor aperture, a temperature gradient
is created across the thermopile of the enclosed detector
disc. This generates a voltage proportional to the incident
power.
The display unit amplifies this signal and indicates the
power level received by the sensor. At the same time,
signal processing software causes the display unit to
respond faster than the thermal rise time of the detector
disc, thus reducing the response time of the Vega.
