If we want to check soon the EQE with a different beam size, we may want just to add (for a kind of quick check) an additional lens in the path without changing what we already have.
> My interpretation of this is that we get ~2% increase in the peak EQE for p-pol by doing the extra bounce. Is that correct? If so, its a pretty good result.
Your interpretation for the current result is collect. However, there are still several errors which aren't took into consideration, such as the error of the resistances and so on. Thus, for saying that the EQE is increased by about 2%, we must obtain more accurate data or analyse the results more preciselly.
> I wonder if you can do some more angles to see if there are any features in the angular dependence.
We plan to do a finer angular scan with the more accurate setup.
> It would also be interesting to modify the beam size to see if there is any change in the EQE. What is the estimated beam size now in the x & y directions? Does the reflected beam overlap the first beam? It would be good if the 2nd reflection from the PD can be steered to not go back into the fiber.
Actually, it is not easy to change the beam size immediatelly because the lenses and the PD are fixed. However, we plan to change the beam size for observing the BRDF. Thus in that time we will measure the EQE changing the beam size.
The estimated beam size of the first incident light on the PD is 215 um in the x direction and 210 um in the y direction, and the size of the second reflected light on the PD is 436 um in the x direction and 422 um in the y direction.
The second reflected light is aligned not to overlap the first incident light. However, so far, the distance of the two beams cannot not be measured because the second light is so weak that we cannot see.
> Is there a diagram with the reflector in place?
This is the diagram with the reflector.
> Is it possible to use the camera to take an image of the reflection from the PD? I wonder if its Gaussian or messy.
It's possible. We will measure the beam profile of the reflection light from the PD for confirming if the PD can be regarded to be well-polished and flat.
> What about repeating this experiment with the 1.5 micron laser now? Or maybe a HeNe where the IQE is lower?
For now, we don't have the plan to change the wavelength. Before the wavelength is changed, we would like to do the whole measurement includidng the noise estimation such as the back scattering noise. Once we establish the whole experimental method, we will change the wavelength and the PD.