Hi ,
Suppose an aperture is illuminated by laser ,and i'm interested in its negative by optics means.
I need to maintain the waveform coherence of the negative image to be processed at Fourier optics.
Does anyone has a way without using interferometer ?
for example:
input image output image:
1 1 1 0 0 0
1 0 1 0 1 0
1 1 1 0 0 0
I thought of this setup:
pass the laser beam through beam splitter.
one of the beam passes through the aperture and then through a waveplate of half wavelength.
Then the two beams are recombined at beam combiner.
This way the waveforms are substracted.
Thank you
Gil, I don't quite understand your question. When I think of image, I think of irradiance that implies a square law function that eliminated phase. Note that the diffraction from and image (in amplitude space) and it's inverse are identical if the image is an even function. Otherwise, inverting the diffraction of the inverted image (in amplitude space) is the same but the frequency coordinated are inverted (flipped).
The question you seem to asking is if the coherent optical field passes through a square or circular aperture is compared to the diffracted optical filed passing by an obscuration with the same size and shape, what's the difference in the observed (ie irradiance) pattern in the Fourier plane. The answer is that they are identical. Try a search on Babinet's Principle.
The true Fourier transform integrates over an infinite spatial and/or spatial frequency extent. Simulations can't simulate infinity. There are many windowing techniques to attempt to circumvent this issue or you might try "zero padding," but this is another case where reality and theory diverge. Theory gives insight but the world requires broader considerations.
Hi James.
Following our discussion.
I've implemented the idea on matlab ,and it works well.
But when simulating on Zemax, the babinet principle doesn't appear.
for example, diffraction pattern due to single slit and laser.
An inverted situation of blocker at the same dimension as the slit... doesn't have an effect.
Please advise.
Gil
Physical optics, beam propagation and diffraction are difficult to model in Zemax. How did you get to a Fourier plane, ie the far field condition or Fraunhofer diffraction? Try putting the slit at the front focal plane of and ideal lens (using a long focal length to get a slow, large F/no lens) and checking the irradiance at the back focal plane. This is the fundamental basis of Fourier optics.
The focal length should be about 8x to 10x the lens diameter. The lens diameter must be over twice the size needed to pass the divergence due to the slit which is theta = 2*lambda/width to the first zero in the diffraction pattern. I would choose a reasonable slit width to get maybe 10 degrees and calculate the rest.
I ran some simulation using FRED from Photon Engineering. If Zemax using Gaussian beamlets to simulate beam propagation, then the beamlets' interaction with the slit may give artifacts due to secondary ray clipping. So note that even these types of simulations are difficult.
- Badges
- Science topic
- Similar topics
- Computer Science
- Images