StarBright User Manual
31
5
Thermopile Sensors
For a list of the available Thermopile Sensor models that can be used with StarBright, see
Warning:
Before using the Thermopile sensor for power or energy measurement, check that your
laser power, energy, and energy density do not exceed the sensor ratings. See
If the sensor is a water-cooled type, ensure that the cooling water is flowing at an adequate rate
(see
). 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.
Table
5-1 Minimum Flow Rates for Water-Cooled Sensors
Sensor Type
Liters per Minute at Full Power
Min Pressure Bar
US Gallons per Minute
30K-W
25
2
7
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
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 StarBright. Energy of a single
pulse is measured on the StarBright by digitally integrating the pulse power over time.
Most Thermopile sensors have somewhat different absorption at different wavelengths. To
compensate for this, each sensor has been calibrated by the laser at several wavelengths. When
you choose the correct laser wavelength, the correction factor for that wavelength is
automatically introduced. Note that the laser wavelength selected is displayed in the upper left
section of the display.
Thermopile sensors with the LP1 absorber have large variation of absorption at different
wavelengths. Therefore a continuous spectral curve is stored in the sensor, enabling the user to
choose the desired wavelength from the range specified in the specification sheet and the
correction factor for that wavelength is automatically introduced.
The StarBright can be set to various settings while operating. In addition, the StarBright
automatically saves the settings for the next power up. This way the StarBright will be in the
desired configuration when turned on the next time.
On power up, the StarBright meter checks its own memory as well as the sensor’s to decide on the
measurement configuration. For example, if in the last session, the sensor was used to measure
power in the Bargraph screen in autoranging with a YAG laser and averaging for 10 seconds, this