UV Laser Power Measurement in UV Laser Confocal Microscopes

UV laser scanning confocal microscopes provide sample illumination from a UV laser via a microscope objective which results in a highly convergent beam. Therefore, in order to measure the total radiated power in the beam a detector with a large acceptance angle is required.

The photodiodes routinely used for radiometric measurements have a two-dimensional sensor surface. At shallow angles a portion of the incident radiation is reflected from the surface thereby reducing the measured radiation power. This can result in a significant measurement error when measuring the highly convergent beam of a confocal microscope.  By appropriately combining the photodiode with a compact integrating sphere this source of error can be minimized. This design of detector offers a large acceptance angle and can also withstand higher laser power levels. Due to the size and shape of an integrating sphere detector it must be possible to rotate the microscope’s sample table to enable positioning of the detector.

Microscope objective with highly convergent beam coupled into integrating sphere.

The compact ISD-5P-SiUV integrating sphere detector combines a 50mm diameter integrating sphere with a UV-enhanced Si photodiode.  Gigahertz-Optik’s Calibration Laboratory for optical radiation quantities provides calibration of spectral radiant power sensitivity (in W) over the 250 to 1100nm spectral range. Therefore, it is suitable for measuring a wide range of UV, visible and NIR lasers.