Tutorial; Definitions And Explanations; Power Meter Specifications - THORLABS PM100USB Operation Manual

PM100USB

9.3 Tutorial

Content

Definitions and explanations

tions and application to sensor families.
Calculations : Here common formulas are given - power, energy and densities can be calcu-
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lated based on different given parameters.
9.3.1 Definitions and Explanations
In this section the key parameters of Thorlabs Power Meters and Sensors are commented.

9.3.1.1 Power Meter Specifications

· Measurement Ranges
It is important to keep in mind that the optical power and energy measurement is based on a
current measurement (photodiode sensors) or on a voltage measurement (thermal and pyro-
electric sensors). That is why the measurement ranges are stated sensor dependent: For
photodiode sensors, they are stated as the current ranges; For thermal and energy sensors,
they are stated as voltage ranges.
· Display Resolution
Note
The resolution is the minimum detectable change of power (energy), it is not the minimum
measurable power (energy)!
As the power meter measures a current or a voltage, the display resolution can be stated
only in A or V. In the specifications the resolution is stated for the most sensitive measure-
ment range. The optical power resolution depends on the actual sensors responsivity.
Current input (photodiode sensors): The resolution is specified as:
Therefore, the PM100USB has a resolution of 1 pA at the lowest measurement range (50
nA). The responsivity of a photo diode sensor is wavelength dependent and thus the power
resolution is wavelength dependent as well.
Example: A S120C sensor has a responsivity of 7.35 × 10
A/W at 455 nm. In the lowest measurement range, the displayed power resolution d at 930
nm is:
and at 455 nm
In contrast to above resolution values, the minimum measurable optical power for S120C is
50 nW. This should clarify the difference between resolution and minimum power.
Voltage input (thermopile sensors): The resolution is specified as
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: This section gives an overview on specifications, their defini-
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1 pA / responsivity value [A/W]
1 µV / responsivity value [V/W]
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A/W at 930 nm, and 5.05 × 10
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