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Kristiaan Meerlo wrote: ↑Sun Aug 04, 2019 7:36 am I wanted to use a apodizing filter to get a better uniform object light to make a reflection hologram. Is that a bad idea? Does it affect the polarisation or other laserlight parameters?

No, it won't make any difference to any laser property, besides, of course, beam profile. Whether it's a good or bad idea depends on the apodizing function. If you're trying to flatten the Gaussian, the apodizing function needs to be an inverse Gaussian, (T = 1 - exp(-ar²)).

I’m no expert on reflections but I would think, if it’s a Denisyuk, that, since diffuse objects tend to scatter & change the polarization anyway, the answer would be no negative effect. Even if the filter does change the polarization, it’s the same basic polarized or randomly polarized diverged beam going through and reflecting/scattering back through the emulsion in the reflected direction and, I would think, some portion of the beam will remain in phase... Separately, you can always use a known orientation polarizing filter in a rotation mount to observe the polarization change/effect of a diverged beam passing through the polarizing filter with and without the apodizing filter inserted in the beam path. If the apodizing filter is a glass/film sandwich instead of directly on the glass of the filter, if the film base is polyester instead of triacetate, it will be birefringent and cause polarization problems easily seen with the aforementioned polarizing filter test. Please post results of your interesting testing!

I wanted to use a apodizing filter to get a better uniform object light to make a reflection hologram. Is that a bad idea? Does it affect the polarisation or other laserlight parameters?