How do I measure with an ISP-R?
Measurements with an ISP-R require an external light source, which is routed with a fiber to an input port at 8° to the sample port. These spheres are compatible with all UV, visible, and NIR light sources between 200 and 2500 nm. The read port is at 90°, with baffling to isolate it from the sample port. The gloss trap versions of the ISP-R spheres come with two plugs. One is coated in PTFE for including the specular component, and the other is a black light trap to exclude specular reflection.
ISP-R integrating spheres come in 30 to 80 mm diameter, with sample ports from 6 to 8 mm (and even up to 20 mm on a custom basis). Smaller spheres give the strongest signal, but larger spheres with smaller port fractions mix the light better due to the higher number of reflections. It’s best to figure out what sample port size is needed first, then pick a sphere diameter based on whether you need more mixing (larger sphere) or more signal (smaller sphere).
No matter which sphere is used, an L2 or L4 lens will probably be needed in the spectrometer configuration to get enough signal, and possibly a 50 μm slit. The increased sensitivity needed for integrating sphere measurements often results in a lower resolution spectrometer, so if sub-nanometer resolution is needed, a reflection probe may be a better choice.
Each sphere has a maximum illumination fiber size specified for input light. This helps match the illumination spot size to the sample port opening diameter accurately, reducing stray light inside the sphere.
This leads to another point. When coupling a light source to an ISP-R sphere, it is important to adjust the focus of the collimating lens used to deliver light to the sphere until the illumination spot size is small enough that it slightly under-fills the sample port. This can be checked visually with a piece of white paper over the sample port opening. Adjusting the collimating lens and using the proper diameter fiber is extremely important, otherwise stray light will be created when the light source reflects off the sphere around the edge of the sample port.