Hello all,
To design the real Fresnel lens one needs to use “Fresnel 1” in Non-sequential mode. But I have no idea on how to calculate the following parameters for Fresnel 1
a)Pitch
b)Radius
c)coeff r^2, Coeffr^4 and so on.
I calculated these parameters easily in sequential mode. But in Non-sequential mode I dont know which parameter in optimization tab controls it. The below image is for reference.
Does anybody know how to calculate it?
Best answer by David
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+4
For the Fresnel1, the radius, conic, and higher order coefficients have the same function as in an even asphere in sequential or non-sequential and the fresnel2 in non-sequential. They are generally made variable and optimized to achieve the imaging requirements. I think this was discussed in previous posts.
The +Depth/-Frequency, Pitch, and Thickness control the physical structure of the lens. There is a good explanation of these in the help documentation. Since they describe the actual structure, they are limited by the manufacturing capabilities and influence optical behavior such as scattering. I can’t help with this because I have no experience with the fabrication of Fresnel lenses. There is likely to be published information on this in books and on line. Or perhaps someone with experience in this can comment further.
+4
Hi Sathya,
Here is a bit more information. I looked at the specifications of the Edmund 46-614 Fresnel lens:
I then built a non-sequential design with a Source Ellipse shining a collimated beam on a Fresnel1 lens, with a detector positioned where the focus should be. There is no equivalent to the EFFL operand in non-sequential, but the lens is thin, so I just positioned the detector one focal length (4”) from the lens.
The Fresnel1 parameters are taken directly from the spec:
The pitch is set at 2 degrees. This is the angle from vertical of the inactive faces. It’s probably a reasonable guess.
A merit function was built using the wizard. It optimizes for minimum RMS spot on the detector and also for full power on the detector. The power requirement keeps the optimizer from minimizing the spot by putting only a single ray on the detector. The Radius, Conic, and 4th order term were made variable. (The 2nd order with the conic is redundant.) It is necessary to set the ray trace control to ignore errors.
This might not be the exact design of the Edmund part, but it’s likely the best we can do without detailed specs from them.
Here is an interesting article on Fresnel lenses: Optical Design Using Fresnel Lenses
I have attached a ZAR.
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