THORLABS PM100D User Manual

5.9 Fiber Based Measurements
5.9 Fiber Based Measurements
Laser light emits from an optical fiber in a conical shape, with an angle twice the
acceptance angle of the fiber. The acceptance angle is calculated by the numerical
aperture of the fiber and is defined as the inverse sine of the numerical aperture.
Fore typical single mode fibers the total angle of the emitted light is between 15° and
25°, for an angled connector (APC) the cone shifts by approximately 4° from the fiber
axis.
This expansion of the beam has to be considered to avoid overfilling the detector and
getting wrong results. On the other hand for measurements with high power fiber
lasers a certain gap between fiber tip and detector surface has to be kept to
decrease the power density.
Thorlabs offers fiber adapters with the most common connectors that are verified with
the S12xC series optical sensors and with most thermal sensors.
For large divergence angles or fiber measurements that are critical to back-
reflections it is recommended to use an integrating sphere based sensor from the
S14xC series.
Another good choice for fiber based measurements are the new ‘Fiber-Heads’ of the
S15xC series. They plug directly to the meter and go without a disturbing cable
between sensor and console.
5.10 Energy Measurement with Pyroelectric Sensors
The application depending best suitable pyroelectric energy sensor must be chosen
with respect to the following parameters:
- Energy to Measure
The maximum load allowed is determined from the absorption layer (too high
load causes mechanical damages on the layer); and also by the sensor ma-
terial, that must remain in a certain temperature level. It is important to pay
attention to the maximum power density during a pulse, the maximum energy
density and the average power.
The detection limit on the low side is given by the resolution and the minimum
settable trigger level of the display unit, as well as the noise level. To minimize
the noise level and ground loops it is advisable to mount the detectors isolated
with the supplied isolation adapters.
- Beam Diameter
The active area of the detector should be chosen that it has a slightly larger
cross section than the beam diameter. It is not a must that the beam should
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THORLABS PM100D Specifications

General

Data Logging	Yes
Storage Temperature Range	-20 °C to 70 °C
Power Accuracy	±0.5% of reading
Interface	USB
Power Supply	USB or AC Adapter
Display Update Rate	10 Hz
Detector Type	Photodiode or Thermopile (Sensor Dependent)