Laser-driven plasma sources as transfer standards for spectral irradiance

This work presents the adaptation and characterization of laser-induced plasma light sources as transfer standard light sources for radiometry and photometry after phaseout of incandescent lamps. These commercially available sources generate a point-like xenon plasma using a continuous-wave laser, producing broadband emission from the ultraviolet (UV) to the near-infrared (NIR). While it has been shown that these sources can be efficiently coupled to monochromator setups for applications that require spectral tuning, this study focuses on their utilization as broadband sources for spectral irradiance calibration using off-the-shelf optics for collimating and homogenizing the plasma spot emissions. Collimated, uniform irradiance distributions were produced using lenses for collimation and either diffusers or microlens arrays for homogenization. With the help of the microlens array, a uniform irradiance field was achieved at the measurement plane, with deviations of the measurement results under 0.1% for spectroradiometer entrance optics with a diameter between 10 mm and 30 mm. However, adding homogenization optics reduces spectral irradiance, particularly in the visible (VIS) and near NIR, compared to incandescent lamp standards. Temporal stability of about 0.5% was shown over repeated operation periods of several hours to days across the VIS to NIR spectral ranges. A different setup with a diffuser and a custom-built temperature-stabilized monitor detector produces similar temporal stability after correction. Strong xenon peaks and ozone absorption features remaining in the output must also be accounted for during irradiance calibrations. The trade-offs between spectral irradiance levels and spatial uniformity of the beam produced with different beam-shaping approaches are evaluated.