# Index of Refraction Measurement Uncertainty

Tags:
1. Jul 22, 2015

### C. C.

Hello All,
I am having some issues with calculating the measurement uncertainty when there is a mismatch in the index of refraction between a fluid and an interface. If am using an unobtrusive measurement technique such as Laser Doppler Velocimetry, how would I be able to quantify the uncertainty associated with a slight mismatch in the index of refraction, such as glass and water. From LDV, I can get a velocity measurement, but how would I be able to quantify the uncertainty in the velocity measurement given that there is some difference in the two mediums. Given that I know the two refractive indexes of the mediums and the thickness of the material, how can I calculate the uncertainty?

If anyone has any references to this subject or hints, I would greatly appreciate it.

Thanks!

2. Jul 22, 2015

### Andy Resnick

I'm a little confused- LDV measures the doppler shift of scattered light; because the window/fluid interface does not move, it's not clear why you think it would introduce uncertainty.

3. Jul 23, 2015

### C. C.

Hi Andy,
The uncertainty is brought about from the mismatched IOR and the curvature of my model. Because both of these issues, my measuring volume is slightly altered and affects my near wall measurements. If you need some further information, I can go into more detail.

Thanks for your time.

4. Jul 23, 2015

### Staff: Mentor

How does the measured velocity depend on the indexes of refraction?

In general, if you have some $f(a,b,c)$ and if a, b, and c have some uncertainties then you can calculate the uncertainty in f. But you have to know that function.