Integrating Sphere Radiometers
Ideal for measuring laser diodes and other divergent light sources
An integrating sphere radiometer provides a simple solution to measuring the output power of divergent as well as collimated lasers sources, for example high power laser diode bars and arrays or fibre-coupled diodes. The beam size, divergence and power from such lasers can be difficult (if not impossible) to capture with a regular laser power meter. Using an integrating sphere combined with a fast-response photodetector simplifies the measurement of "difficult to measure" lasers and greatly reduces alignment sensitivity compared with regular optical power meters.
A correctly designed integrating sphere will provide accurate and highly repeatable measurements of laser power regardless of the beam size, divergence, polarisation, beam pointing and any dynamic beam displacement. The inherent optical attenuation exhibited by an integrating sphere also reduces the flux reaching the photodetector, allowing the use of fast response photodiode type detectors with high power lasers. Without a sphere, high power lasers have to be measured with thermal detectors which respond much more slowly to changes in the laser power level.
The LPMS Laser Power Measurement System
Labsphere's LPMS series integrating sphere laser power meters are suitable for measuring CW laser powers from 15µW to 200 Watts in the range from 300-1800nm, with a 0.1µW sensitivity. The special integrating sphere design employed is insensitive to changes in laser beam pointing or divergence for angles up to +/- 40° from normal. To put it another way, with a Labsphere LPMS radiometer, you get power measurements you can trust regardless of the laser beam diameter, divergence and static or dynamic beam pointing direction. Conversely, general purpose integrating spheres can suffer from a degree of dependence upon these factors.
To learn more about the design of the LPM laser power measurement integrating spheres - and what sets them apart from regular integrating spheres - click here to go to our LPM Sphere Technical Briefing.
LPM Integrating Spheres
The LPM integrating spheres employed in the LPMS radiometers are available in 2, 4 and 6-inch diameters. All feature a 1-inch input port and two, ½ inch detector ports. The larger the sphere, the higher the attenuation and the greater the power that can be measured. The spheres are coated as standard with Labsphere’s Spectraflect white reflectance coating, but for higher performance, Spectralon spheres are available that provide for increased measurement sensitivity and greater environmental stability.
Normally, the photodetector is mounted at one port on the LPM sphere and the second port is closed off using the supplied port plug. Alternatively, you can mount a optional fibre optic adaptor to the second port that can then attach to a CCD spectrometer for combined spectral and power measurements. The sphere is supplied with a spacer / filter holder for the detector port (this accepts ½ inch diameter filters). The LPM sphere has a ¼-20 tapped mounting hole and is supplied complete with a stand and base assembly
Choose from three photodetectors for your LPMS radiometer. The SDA-050-U is an unfiltered silicon detector for power measurements in the range from 300-1100nm. For the infrared region, choose between the GDA-050-U germanium sensor for the range 800-1800nm, or for greater sensitivity in the 900-1700nm band, the IDA-050-U InGaAs detector.
The SC-6000 is a benchtop radiometer that is calibrated by Labsphere to provide a readout of the photodetector current and to display the power from the laser under test directly in Watts. The SC-6000 is a versatile, programmable meter that has a dynamic range of 8 decades and an ethernet port (TC / IP) to connect to a host computer.
The LPM sphere and photodetector combination are calibrated by Labsphere for spectral radiant flux responsivity every 25nm in the 300-1100nm band (silicon detector), 800-1800nm (Ge detector) or 900-1700nm (InGaAs detector). The calibrations are performed using reference standards that are NIST traceable. The calibration responsivity for each meter is pre-programmed into the memory of the SC-6000 radiometer readout.
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