Clement,   In the context of integrating sphere system, I imagine you want to measure diffuse relectance into hemispherical space.  Your 3 port sphere has no port in front of the entrance port, implying yours is a standard sphere such as one with 0, 90 degrees, north pole ports.  Let us configulate 0 degree as illumination entrance and north pole for measurement.  Then, 90 degree is for sample placement and illumination angle is limited to 45 degree, which is typically ~10 degree in reflectance measurement.   If this is inconvinient, locate sample on an extention tube at the center of sphere and the extention tube is fixed on 90 degree port plate.   This approach needs great care in painting the tube in white so as to be totally invisible in the sphere.  Regards, Shigeo.

Shigeo,

Thank you for your explanations. I will try to make some measurements without placing the sample in the center of the sphere with the help of a white tube. But if I cannot obtain correct results, I will try your solution.

However, based on this tutorial to obtain total transmittance, diffuse reflectance and collimated transmittance measurements http://www.azooptics.com/Article.aspx?ArticleID=769 and on your advices, I am wondering if I have to target the bottom of the sphere (file attached, scheme A) or the sample (file attached, scheme B)?

Yesterday, I tried to make some measurements with a sample of 10% intrapilid solution (to validate my optical bench and because optical properties are available here http://omlc.org/spectra/intralipid/). My solution was placed in a transparent quartz “cuvette” used for spectrophotometer of 10mm thick. My Laser beam was almost totally absorbed in this sample. In the paper of Flock et al., Optical properties of intralipid: A phantom medium for light propagation studies. Lasers in Surgery and Medicine, 1992. 12(5): p. 510-519., they mentioned a sample thickness of 0.83mm. What equipment can I use to obtain a sample thickness as thin as that? Again, thank you for help.

Clément

Edit :

To obtain values of total transmittance, diffuse reflectance and collimated transmittance, I just have to measure power with and without sample placed in the optical bench and then, compute the ratio (power measurement with sample)/(power measurement without sample) for each measurement setup? Am I wrong?

Clement,      

First question:  Scheme B does make sense!   

About your idea:  My opinion is transparent quartz causes specular reflection (regular reflection in your terminology), which might be noise in your measurement. 

Last question:  When you measure power without sample, I do not know what power you measure.    Probably reflected light power from uncovered part of port plate where to locate sample.   You should put reference plate of which diffuse reflectance is known in place of sample.   I recommend you spectralon, or BaSO4, both are sphere wall coating materials.  

Powder BaSO4 can be used to paint extention tube in white, much better than transparent one.    (Available from Edmund?)  

Regards,     Shigeo

Shigeo, thank you again for your answer.

When I mentioned “without sample”, I meant “with the quartz cuvette placed in the optical bench but empty, without the intralipid liquid inside”. Thus, I hoped to avoid specular reflection noise due to interfaces air/quartz/sample/quartz...