This is version 2.2 or so of my holography apparatus. Go read the description of version 2.0 first, this'll be mostly covering the new hardware...
Click on the image above, to see close-up images of the various bits.
The table as two configurations: transmission hologram master, and H1H2 copy. This is H1H2 copy mode. H1H2 refers to Hologram number 1 (the original), being copied to Hologram number 2. This is also called an image-plane hologram, in that what this arrangement does is make a hologram of a hologram, but with the image crossing the plane of the film, so it "sticks out".
First, the table is on innertubes now. Hopefully that'll improve its vibration isolation. Right now the primary result is that the table goes down nearly a quarter of an inch as the air pressure changes.
Then, I have a new beam splitter... Its a polarizing cube (seen in the middle, under the Plexiglas. What the cube does is takes the vertically polarized component of the incoming light, and lets it go straight, while the horizontally polarized component gets reflected. The knurled bit is a half wave plate which rotates the polarization of the incoming laser light (which must be polarized already). Change the angle means change the beam ratio. The big advantage is that there are no losses, all the light is reflected. So if one has a BIG laser, the optics won't melt.
Then, we have a collimating lens. Usually people use a parabolic mirror, but this thing came up surplus for about 1/2 to 1/3 what a mirror would cost, so I grabbed it. It weighs 11 pounds all by itself.
So, what happens is the light comes in, goes straight through the beam splitter, goes through a 40x microscope objective, bounces off the big mirror in the far left corner, goes through the big lens, and thats the collimated reference beam.
The reference beam then bounces off the mirror in the lower left, and hits the film holder. There are actually two film holders... they are mirror images of each other. The one on the right holds the H1 original, and the one on the left holds the H2 copy. They take 8 3/8 inch square pieces of glass, just like the other angled film holder, which can be seen folded up behind the other two film holders. The angled one is used for transmission holograms. (Note how its lined up with the reference beam.)
The H1 original is illuminated by the light reflected by the beam splitter, which goes through a 10x microscope objective and a pair of baffles. The baffles cut off the light in the cone that would otherwise hit outside of the mask on the H1 film holder.
The reason for all the baffles is that the illumination beam is bright. If it hits the film in the H2 holder directly, it will produce massive diffraction gratings, and pretty much ruin the hologram. (Why can't my holograms ever be that bright? :-P )
The illumination beam continues to be a problem after it passes through the H1 as well. There is a mirror taped to the big lens to keep the beam out of the reference beam optics. (And more baffles, which were removed for the pictures.)
This arrangement actually needs quite a bit more baffling. Look at all the light coming off the beam splitter. That will be producing extra images in the hologram, and generally fogging things. I've been meaning to make a big foam-core box to enclose the reference beam optics.