Example Configuration: Radiant Power and Energy Measurement of Laser Rangefinders
The measurement of laser power is not always possible with off-the-shelf instruments due to the design and specifications of the laser. For such cases, the ability to configure systems from modular components is a good approach.
In the following example, a laser power meter was required to measure the intensity of a combined laser rangefinder and laser pointer system. For the laser rangefinder the energy of single pulses and pulse sequences (at 1550nm) need to be measured and for the laser pointer the average power is specified (at 830nm). The maximum beam diameter is 45 mm. The system must be traceable to a National Metrology Institute in order to obtain the certificate of conformity for Class 1 according to EN 60825-1 classification.
Picture: Schematic representation of the measuring device
A convenient solution was configured from Gigahertz-Optik’s portfolio of optical radiation measurement modules. A 300mm diameter integrating sphere with 50mm entrance port was used due to the large beam diameter to be measured. To cover the required spectral range, the sphere was configured with both a Si photodiode and an InGaAs photodiode. An internal baffle prevented any direct irradiation of the photodiodes from the incident beam as well as indirect irradiation by the first reflection from the back face of the sphere. The large sphere diameter and the design of the two detectors with diffuse windows ensure the best possible level of optical integration. A dual-channel Optometer was used to measure the average laser power or the laser energy of either a single pulse or pulse train. The laser energy was measured according to the pulse-stretching method.
The integrating sphere was configured with components from the UM-Series of modular integrating spheres from Gigahertz-Optik GmbH. The two photodiode detector heads were standard Gigahertz-Optik GmbH devices from the PD-11 Series connected to the two-channel P-2000 Optometer. The calibration of the spectral sensitivity from 400 nm to 1800 nm takes place in the calibration laboratory for optical radiation measurements of Gigahertz-Optik GmbH. The calibration laboratory was also responsable for the conformity test of the measurement device by the use of pulse frequency and pulse width modulated lasers.