THORLABS PM320E, Руководство по эксплуатации

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© 2016 Thorlabs GmbH 18
PM320E
3.3 Thermal Power Sensor Operation
Thermal sensors of the Thorlabs S3xxC series can be connected to both CH1 and CH2 Sub-D
jacks in the rear panel. The sensor will be recognized immediately after plugging in. With a
power meter sensor plugged-in at the rear panel, the related photo-diode input in the front
panel is disabled.
Attention
Refer to the sensor data sheet and pay attention to the optical damage threshold! Exceeding
these values will permanently destroy the sensor!
Thermal sensors absorb the incident laser power, whereby the developing heat gets turned into
a small voltage caused by heat flow through thermocouple elements between absorbing area
and sensor heat sink. The Thorlabs S3xxC series thermal sensors contain black broadband
coatings or hard coatings as absorber and show a nearly flat response from the UV to the mid-
IR. The sensors have stored a wavelength dependent response curve, that is used to adjust the
power reading to the specific operating wavelength.
The output voltage of a thermal sensor is linear to the incident laser power, as long the thermal
system is properly zeroed. The main use of thermal sensors are high power applications from
100mW and up.
3.3.1 Zeroing
Thermopile sensors need to be zeroed when thermal differences appear between the active
area (thermal disk) and the sensor heat sink with no light incident to the active area or when the
heat sink gets hot under light exposure. An indicator that the sensor needs to be zeroed is
when with a switched off laser either a strong 0.000W reading (negative thermal voltage) or a
reading much greater than zero is displayed.
To perform the zero adjustment press the <CH1 Setup> button, navigate to the ‘Zero Voltage’
menu and press the Control knob or the <Enter> soft key. A new zero value will appear in the
menu.
The zero value will be negative when the heat sink is hotter than the active area and positive,
when the active area is hotter than the heat sink. When both heat sink and active area are at
room temperature a zero voltage of some µV is normal.
3.3.2 Wavelength Correction
To adjust the operating wavelength proceed as described in section Wavelength Correction .
3.3.3 Readout Acceleration
Thermal sensors show a fairly slow response. When laser power hits the active area, it takes
up to some 5 to 10 seconds until the system has settled and the power reading shows the right
value.
This settling time can be shortened to approximately 1 second using a special circuitry that
'predicts' the final power value. As a downside, in this ‘High Speed’ mode the resulting power
reading is more noisy.
To select the response behavior, enter the <CH1 Setup> and navigate to the ‘Mode’ menu.
Toggle between ‘Low Noise’, where the acceleration circuit is switched off, and ‘High Speed’
with enabled acceleration circuit.