Lenses for holography?

[Anthony P]

Getting back into holography. Most set ups require 1 or 2 diverging lenses. Are there pros and cons to AR coatings? Also, from past experience, longer FL lenses take quite a bit of space to illuminate object. Is there any reason not to use very short FL concave lenses ( -6mm or -9mm). First set-ups will be split beam reflection, green plates, DPSS green laser(125mW), isolation table is 3'x5'.

 

[diachi]

Don't see why there'd be any cons to AR coatings other than increasing cost.

Can't comment on short FL lenses, seeing as I'm not a holographer. Couple others here are and would know.

 

[paul1598419]

It is better to use a FS convex mirror instead of lenses to spread your beams out. Lenses introduce noise into your holograms that may require the use of spacial filtering to correct for it. It is important that your laser have a long coherence length as this will effect your outcomes a lot too. If you just have to use lenses, you don't need very short FL lenses as they will spread the beam out too much in a very short space and you want to keep light leaks to a minimum which will be difficult to do if your beams are spread out further than they need to be.

 

[Anthony P]

It is better to use a FS concave mirror instead of lenses to spread your beams out. Lenses introduce noise into your holograms that may require the use of spacial filtering to correct for it. It is important that your laser have a long coherence length as this will effect your outcomes a lot too. If you just have to use lenses, you don't need very short FL lenses as they will spread the beam out too much in a very short space and you want to keep light leaks to a minimum which will be difficult to do if your beams are spread out further than they need to be.

Thanks Paul. That makes a lot of sense. Never thought of using concave mirrors before... I will try it. I have done red holograms before. I started with the kit from Intergraf (Dr Jeong) and added mirrors and lenses etc. I noticed Thor Labs sells green plates and developing chemicals. This is the direction I am leaning towards.

 

[paul1598419]

By red holograms, I assume you are referring to transmission holograms. The reflection ones made with red He-Ne lasers turn out green as the emulsion shrinks and makes the hologram come out in a lower wavelength. I wish you luck with your 532nm holography as all holography is a work in progress. I've been doing it since 1980 and I still learn new things all the time.

 

[Anthony P]

Interesting. By red I meant that I used red sensitive plates and 8mW polarized HeNe. They always seemed more impressive when viewed with the green laser. It is an old dpss from laser glow named after a deity ( forget which one).

 

[paul1598419]

If you need a laser to view your holograms, they are transmissions ones. Reflection holograms can be viewed in ordinary light. The difference is in the setup when you make the hologram. Instead of having both the reference beam and the object beam strike your photographic plate from the same side, you have the reference bean strike the front on the plate and the object beam strike the back. Also, I misspoke in my earlier post. To use a mirror to spread the beam, you need a FS convex mirror. Sorry for that. You will always use a red sensitive plate when using a 633nm He-Ne laser, no matter what type of hologram you are making. I would be concerned with the coherence length of your 532nm laser as that is most important to make a quality hologram.

 

[Anthony P]

If you need a laser to view your holograms, they are transmissions ones. Reflection holograms can be viewed in ordinary light. The difference is in the setup when you make the hologram. Instead of having both the reference beam and the object beam strike your photographic plate from the same side, you have the reference bean strike the front on the plate and the object beam strike the back. Also, I misspoke in my earlier post. To use a mirror to spread the beam, you need a FS convex mirror. Sorry for that. You will always use a red sensitive plate when using a 633nm He-Ne laser, no matter what type of hologram you are making. I would be concerned with the coherence length of your 532nm laser as that is most important to make a quality hologram.

Enlightening as always, Paul. Do you have a recommendation for green laser. This project is still in planning stage and spatial coherence has been a concern. I plan to do more research. I have a 20 mW 488 argon which would be a great beam, but I would have to set up laser in different room for vibration isolation ( mega cooling fan). Also I will check the sensitivity of plates to 488.

 

[diachi]

https://www.holographyforum.org/forum/

There's also a holography Facebook group that might offer further insight.

 

[paul1598419]

Yes, even air currents in your holography setup will ruin your hologram. For that reason I have never tried to use an argon laser to make a hologram. If you are unsure of your setup, try making a Michelson interferometer. If you can get stationary interference lines your setup is fine. If you can't see the lines at all, look for problems.

There are 532nm lasers with long coherence lengths, but they are lower power ones and generally more expensive. You can find one that outputs 20 mW, which in green is plenty, with very long coherence lengths. Some have coherence lengths in hundreds of meters.

 

[diachi]

Yes, even air currents in your holography setup will ruin your hologram. For that reason I have never tried to use an argon laser to make a hologram. If you are unsure of your setup, try making a Michelson interferometer. If you can get stationary interference lines your setup is fine. If you can't see the lines at all, look for problems.

There are 532nm lasers with long coherence lengths, but they are lower power ones and generally more expensive. You can find one that outputs 20 mW, which in green is plenty, with very long coherence lengths. Some have coherence lengths in hundreds of meters.

Sometimes get a Coherent Compass 215 or 315 on eBay for cheap. They'll do the job well.

 

[paul1598419]

Check this 75 mW 530nm laser for your holography. It has the necessary coherence length. Offer him $75.00 for it. Or maybe less and he will counter with $75.00.

www.ebay.com/itm/233004200040

 

[Anthony P]

Check this 75 mW 530nm laser for your holography. It has the necessary coherence length. Offer him $75.00 for it. Or maybe less and he will counter with $75.00.

www.ebay.com/itm/233004200040

Thanks Paul... offer made. Thank you as well, diachi. I am wondering if the 100mW 532 I already have is adequate. I could set up interferometer. Is there a way to test coherence length?
As far as convex mirrors I will just buy a couple at different FL to experiment with. I am now thinking about a very old Scientific American article about sputtering your own mirrors. Now that would be a real science project! I find it fascinating how those guys from the past used ingenuity and determination to do all sorts of things: making their own mirrors, telescope lenses from glass discs, high voltage rectifier from a motorized and timed contact, etc. I wonder if some resourceful individual will figure a way to make your own laser diodes at home.

 

[Anthony P]

Been doing some reading and set up interferometer. If I understand correctly, distinct and even amplitude and spacing indicates high temporal coherence which equates to long coherence length. There were no noticeable differences in brightness from line to line. Also the line were smoothly shaped which indicates spatial coherence. Bottom line is that it is worth a try. This is an experimental science. I will repeat experiment with the new laser when it arrives and with some cheap diode lasers that I would expect to show distortions.

 

[paul1598419]

Your interference lines will also depend on the sability of your optical bench and air currents in the room. If your setup is very good you may see even lines in your interference pattern, but even a great laser will give you a poor interference pattern if there is something wrong in your bench. The lines will likely crawl even if your bench is very stable and you have no air currents. The Michelson interferometer is the way I troubleshoot my bench before I try to make my first hologram.

 

[Anthony P]

I am thinking of building a "good" interferometer. Seriously considering a cube beam splitter with mirrors attached to sides. Only question is should the cube be polarized or not?
As far as the table goes, my shop was designed and built around it 20 years ago. The legs are 4" concrete filled pipes that sink 3' into the ground. They penetrate the floor through rubber roof flashings and hold a heavy wooden table. There are 4 tractor tire inner tubes that can be inflated to float a 3'x5', 500lb concrete slab. It preformed very well years ago when I made a variety of transmission holograms (got the terminology straight this time).
The project for today is to change one of the tubes. Although the table was designed for this task, it still is going to be a real chore.

update: Wow! Got lucky. Just had to replace schrader valve.