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It's possible that your cube beamsplitters may have some kind of structure within them, ie cracks, bubbles etc. This would cause scattering and cause your freckles. I used a variable neutral density filter ( https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1393 ) simply because the studio I...

CMB (Cosmic Microwave Background) radiation is radiation in the ~1.9mm region, ie in the microwave region, that pervades space.It's the result of the Big Bang origin of the universe, and detecting it is important to validate and improve the Big Bang Theory. But, the extreme cold of space means that ...

Here is a hologram made by painting on the model. We shot this about 2015. Joy's procedure for testing appropriate paints was to illuminate each colour paint by all three lasers. Using a red paint as an example for red information from the model: 1. Choose a set of red paints and paint a white card ...

Ont thing I forgot to mention is that you need a lens before the screen to expand the combined beam so as to enlarge the interference pattern. The unexpanded beam is too small to see any structure.

That leads to another related question: Is there an easy way to measure coherence length of a laser? Thanks again. Yes. You set up a Michelson interferometer, and vary the path difference. I've drawn up a diagram. The beams splitter sends the beam along both path a and path b (black lines). On refl...

You may be interested in a white paper I wrote for Melles Griot

The solubility of potassium iodide in ethyl alcohol decreases as the concentration of ethyl alcohol increases*. Since the way the iodide reduces printout is by replacement of the bromide ion in emulsions with the iodide ion, the large number of bromide ions still in the emulsion (depending, of cours...

Do inhomogeneities in the glass or acrylic cause this? Basically, yes. Speckle is caused by phase differences due to index and thickness differences of components along the optical path, and the rms (root mean square) height of the surface. Because of the extreme coherence of laser light, if the rm...