Radiometers for Laser Radiation
Laser Power Meters, Radiometers, Dosimeters and Data Loggers for Irradiance, Laser Power, Laser Energy and Pulse Shape in the 400 nm - 1800 nm Wavelength Range.
For the measurement of laser radiation different measurands are of interest. The most important is usually the total radiant power (see our application about laser power measurement). For this measurement either directly photodiode detectors, thermopiles/pyroelectric detectors or integrating spheres are used. Especially integrating sphere detectors are the ideal choice if the laser beams are divergent or in general of larger size. In any case a modern intuitive optometer (current amplifier with display) is needed in order to store calibration data of different laser wavelength or even different detectors. Please see our range of Optometers, Amplifiers and Display Meters for Laser Power.
Pyroelectric detectors are generally used to measure the energy of pulsed lasers with high-powers up into the kW range. However, these are less suitable for the low peak power and short pulse lengths of semiconductor lasers. Therefore, photodiodes are usually used.
For precise radiant power measurements a high sampling of the laser pulse is needed. Since these pulses are very often in the ns range a standard sampling of a transimpedance amplifier is not sufficient. A smart techniques to solve this challenge is to stretch the pulse by a multiple of the expected pulse length. This is called the pulse stretching method (P-21 Touch Screen Laser Power Meter or P-9710 Classic Laser Power Meter). The resulting ‘stretched pulse’ becomes flatter, but remains constant in its area, so constant in its radiant power. The stretched pulse can be sampled with an higher amount of sampling points.
Conversion of short pulses into stretched pulses with the same energy (area). A1: original signal input, A2: signal output transimpedance amplifier, Area A1 = area A2
The pulse waveform of the stretched pulse can be recorded in a time-resolved manner using a data logger with sufficiently high sampling rate. The pulse energy is thereby calculated from the pulse waveform. See our application page about laser power and waveform measurements.
We offer a range of Optometers suited for measuring the pulse energy of laser diodes using the pulse stretching method. Models P-21 and P-9710 have signal amplifiers with time constants which are designed ideally to the analog-to-digital converter with sufficient sampling time. Due to their high readout rate, electronic measurement uncertainty of less than ± 1% is possible with careful adjustment of electronic offsets.
These days additionally the pulse shape is of high interest due to very short pulses e.g. used in LiDAR applications. Laser diodes used for LiDAR distance measuring devices have furthermore very often a diverging elliptical beam profile with typical peak powers of up to 100 W or even in the kW range. They are operated in a short pulse width, low pulse frequency mode with low average power. The short pulses are of advantage in terms of the temporal resolution of the LiDAR system. For quality assurance, the peak power and the pulse waveform are of primary interest. These two optical parameters cannot be measured with a single detector if lowest measurement uncertainties are needed. Therefore, pulse energy and pulse waveform must each be measured separately, see e.g. our compact and well thought out ISD-1.6-SP-Vxx series and its larger size versions ISD-5P-SP and ISD-10P-SP.
The pulse waveform is measured using fast, small-area photodiodes terminated with a low-impedance shunt resistor. The temporal voltage curve across the resistor is measured and recorded with a digital oscilloscope. Rise times of less than a nanosecond are possible. The responsivity of this type of detector is very low because of the low-resistance circuitry.
Beside the design of the measurement system as well a traceable calibration with low calibration uncertainty is essential. We at Gigahertz-Optik offer ISO 17025 calibrations and testing according to DAkkS. Please see our ISO 17025 laboratory for traceable laser power meter calibrations.
Please see also our application examples in the laser power measurements section. In the product list below we present a selection of measurement solutions. Since we are experts in customized solutions in laser power measurements, the following customizations are of course possible:
- adapt the laser radiation range (laser power range) to your needs
- adapt the sphere diameter, sphere port size, etc. fitting to your device under test (DUT)
- find the perfect suited calibration strategy, e.g. ISO 17025
- finding the perfect suited optometer/display unit/transimpedance amplifier