Expand laser beam with micoscope objective : which one ?

[thycore]

Hia Holofriends !

I've been using a 40x microscope objective for quite a while now, I harvested this objective from a cheap omegon microscope, it served me quite well but I believe it has reached its limits in terms of quality. Sparks/dots and aberrations are now too much for what I'm looking to achieve.

I cannot afford —yet— a spatial filter to clear my beam (and even if I had a spatial filter, my laser being a 17mW it would not be powerful enough to illuminate my scene once purged of 90% of its power through the pinhole, please correct me if I'm wrong : pinhole reduces laser power a lot)

So, I'm about to search for a new microscope objective, maybe a 100x this time but when I look for such things on eBay I can't choose.

What are these FLUOR objectives any doped lens, is this required for my application ?
What are these "OIL" stuff objectives ? Is it like a "liquid" lens ? would this not somehow "move/ripple/morph" during my CW laser shoot ?
What are these "planar" stuff objectives ? is it like some "collimated" objective which would *not help* me in my quest to "expand" my beam ?

Well folks, which microscope objective would you use with a 17mW HeNe laser to illuminate a 20x20cm scene ?

Thanks =)

[Din]

a 100X is far too divergent for a 20cm x 20cm (8in x 8in) plate. Depending on how far away is the plate/object from the objective, you may not need much more than a 20X, perhaps a 40X if you quite close to plate/object. The magnification factor (the "X") is a measure of the beam divergence. For display holography, you only need to diverge the beam roughly to cover the plate, or illuminate the complete object scene. Any more divergence simply wastes light. If you're between a metre and two metres, a 20X should expand the beam enough. There will be a Gaussian fall-off, where the beam at the edges is less intense, if you're concerned about this, get a 40X, but it'll waste all the light at the edges. For a 17mW laser, you need to conserve as much light as possible.

What are these FLUOR objectives any doped lens, is this required for my application ?

The FLUOR refers to an objective that produces a flat wavefront across the spectrum from ir to uv. This is important for fluorescent applications

What are these "OIL" stuff objectives ? Is it like a "liquid" lens ? would this not somehow "move/ripple/morph" during my CW laser shoot ?

The oil is placed inside the obective to diverge the light more than air would, due to the increased refractive index. The higher the refractive index, the more the beam diverges. The oil is packed and sealed, so, no, it will not ripple.

What are these "planar" stuff objectives ? is it like some "collimated" objective which would *not help* me in my quest to "expand" my beam ?

Again, the aim is to produce a flat wavefront. It's important in technical applications, such as HOE production, but, not as important in display holography.

[Ed Wesly]

"please correct me if I'm wrong : pinhole reduces laser power a lot"
At least 90% passes through if you work at it. Get the pinhole!

"maybe a 100x this time but when I look for such things on eBay I can't choose."
Good luck finding one! A lens from a CD or DVD player would probably give you a similar spread, if you are interested in having a very wide angle one.

OIL objectives are designed to couple optically to a microscope slide with an indexing matching fluid, which are usually oily.

610.jpg (191 KiB) Viewed 5242 times

This image is burned into my mind, from Seeing the Light, a book I used in teaching optics classes at 3 art schools ever since it was published. http://edweslystudio.com/nlutie/Bookshe ... Light.html It should be on the bookshelf of all who frequent here, as it explains a lot about optics in well thought out pictures. Plus their holography chapter is well-researched.

As far as the other objectives, I would need to go to https://www.edmundoptics.com/microscopy/ to answer them, so I leave that task up to you. Check out their spatial filters and think about how you could make something like that with what resources you have at hand.

Pinholes aren't that expensive, my go-to sources are Optimation or Lenox Laser, which are quite reasonable compared to Edmund, who probably gets theirs from them.

"Well folks, which microscope objective would you use with a 17mW HeNe laser to illuminate a 20x20cm scene ?"
Depends not only how much room you have on the table or the floor, and how far away you plan to have the replay light when looking at the hologram. Usually I use a 20X objective about 2 meters away from the plate.

Hope this helps!

[thycore]

Thanks for your kind information

I managed to buy the "Practical Holography IV" and this reading is really helpful. In this book they recommend either a double-concave lens, or a microscope objective x40, or a sphere lens as expander depending on the length of your holography bench.

Now I understand that maybe my holography lab is too small xD it would maybe simplier to set the laser source far from my table and expand it gently over 4-5 meters (instead of 90cm distance as I have now).

[Grayham]

Hi,

90cm is enough room to do some good work.
I've made some nice multi beam beam reflections on a 60 x 90 (2' x 3') breadboard with a spatial filter.
I've also made some OK single beams on a 12" square slab on an inner tube with a HeNe

My advice is to not be too binary and just use what works. A simple set up for me was to use a 10mm concave mirror with a short focal length.
This will cause the reflected beam to be diverged quickly from the focal point and as it's a mirror you can place it at the far end of the table and reflect the light back across the whole table. You can get quite a divergence in 90 cm.

Edmund optics and other suppliers do these mirrors. Ask them for a deal on the delivery as edmund overcharge

Grayham

[Valery]

I use homemade microlenses
see details
http://www.holographyforum.org/forum/vi ... 649#p68649

Valery

[John Klayer]

I use Toslink (or generic equivalent) optical cables. They are cheap 1 mm diameter multi mode fibers used for linking audio, TV, DVD, etc entertainment components together. Just shoot your laser beam into one end and use what comes out the other end for the reference beam. If needed, you can use a convex mirror for more divergence. This works really well for small holograms. I've made some impressive transmission holograms up to 4 X 4 inches this way. What I get is a nice image behind a slightly dirty looking plate.

If you insist on using a spatial filter, somewhere in the Holowiki is my simple design for one.