Spatial Light Modulators and Fourier Optics

[Qiao]

Hi,
I'm working with a Digital Micro-mirror Device type SLM and my goal is to convert my laser from a gaussian to flat-head intensity profile. And then the tricky part is to make the beam oscillate up and down on the camera using just the SLM.

Apparently I was to naive to think that moving my image pattern on the SLM equals movement in the focus plane.

Does anyone have any suggestions or ideas I should try?

 

[Andy Resnick]

Is your SLM correctly placed in a conjugate plane to either the image or the FT plane?

 

[Qiao]

The SLM is placed in the front focus plane of the first lens then there is a second lens afterwards with a shorter focal distance w.r.t. the first lens. Then a camera is placed at the end such that the camera is in both the back focal planes of both lenses.
So to answer the question, it's placed conjugate to the FT plane of the first lens.

 

[Andy Resnick]

Then, in order to translate the beam at the image plane, you need to adjust the phase at the FT plane. AFAIK, DMM devices only modulate the intensity, so if you instead place your device at a plane conjugate to the image, you should be able to do what you need.

 

[Qiao]

Thanks, I'll try that. I've also managed to get oscillation using a cylindric lens, but only in the axis where the beam is unfocused. But the intensity profile is still very ugly with higher order interference patterns.