Laser Optics

nomiss · Post by **nomiss** » Thu Feb 09, 2012 3:54 pm

Ok so im having some trouble ordering supplies for my Holography lab. I have a Coherent Compass 315M-100 DPSS 532nm Laser Single Longitudinal Mode but I'm not sure what mirrors, diffusers and beam splitters to order. Any help with what I should order for this specific laser? for example, does this laser require different mirrors and beam splitters compared to a standard HeNe laser?

holorefugee · Post by **holorefugee** » Fri Feb 10, 2012 2:40 am

How many mirrors do you plan to use in your set up?

Jem · Post by **Jem** » Fri Feb 10, 2012 7:35 am

nomiss wrote:Ok so im having some trouble ordering supplies for my Holography lab. I have a Coherent Compass 315M-100 DPSS 532nm Laser Single Longitudinal Mode but I'm not sure what mirrors, diffusers and beam splitters to order. Any help with what I should order for this specific laser? for example, does this laser require different mirrors and beam splitters compared to a standard HeNe laser?

With 100mW of light you've got a reasonable amount to play with, so you can afford to lose a bit of light and keep costs down for your initial setup.

Your mirrors need to be 'front surface mirrors' and you can find these in large sheets (8" x 6") on Ebay and cut them down to size. One sheet will make you many mirrors

. Standard front surface mirrors will probably be around 97% to 98% efficient. As you progress you can replace these mirrors with dielectric mirrors, either broadband coated or coated to the specific wavelength of laser you're using, these are usually >99% efficient.

As for beam splitters it depens on what you have in mind for your setup, you can either use a partially silvered glass plate or go with polarised beamsplitter cubes (PBS cubes). Partially silvered glass plates would be the cheapest option to get you started, but eventually you'll probably decide to go the PBS cube route. PBS cubes are wavelength dependant, you'll need ones for 532nm. Same goes for halfwave plates (you'll need these with your PBS cube to make a variable beamsplitter), again, you'll need halfwave plates specifically for 532nm light.

Standard front surface mirrors will work reasonably well with pretty much any wavelength in the visible spectrum (400nm to 700nm ish).

If you're interested I have a 'Jodon' variable beamsplitter for sale

, see here...

http://holoforum.org/forum/viewtopic.ph ... odon#p2303

Cheers

Jem

holorefugee · Post by **holorefugee** » Sat Feb 11, 2012 4:00 am

If you have questions about Gem's post please ask. It was an advanced and brief reply. I t was correct if you had mad lots of holograms.

Dinesh · Post by **Dinesh** » Sat Feb 11, 2012 9:50 am

nomiss wrote:Ok so im having some trouble ordering supplies for my Holography lab. I have a Coherent Compass 315M-100 DPSS 532nm Laser Single Longitudinal Mode but I'm not sure what mirrors, diffusers and beam splitters to order. Any help with what I should order for this specific laser? for example, does this laser require different mirrors and beam splitters compared to a standard HeNe laser?

Nomiss, if you've never made a hologram before I'd suggest you start with the simplest, most basic setup . This is called a "Single Beam Denisyuk". It consists of just a lens and, optionally, a single mirror. The idea is that you simply expand the raw, laser beam to envelop your plate, place your object behind the plate, and zap it. If you have a small table or a large plate size, you may need to bend the beam with a mirror. Otherwise, simply expanding the beam directly from the laser is enough and all you need is a lens that expands the beam enough. A single diverging (negative) lens with a focal length twice the diameter (f/2, if you understand the jargon) will cover about 5 inches over a distance of about 12 inches. This simple geometry will teach you a lot about stability requirements, processing methods and just basic technique. The kind of things that can be holographed and the orientation of the object are also important factors. Make sure your object is solid and is solidly placed and is also uniformly reflective. Orientate the object such that the majority of the reflected light falls back onto the plate.

If you need to bend the beam, any front surface will do for a start, as Jern says. It doesn't have to be wavelength specific at this stage, just be sure it's front-surface. If you place the lens after the mirror, the mirror can be quite small, since it just reflects the raw laser beam. In this case, the mirror can be an inch or so.

I'd strongly recommend Fred's book: "Holography Handbook" by Fred Unterseher. Most of us on this forum started out with Fred's book, including myself. I'd also look into Integraf's Holokit (http://www.integraf.com/holography_kit_2.htm ). It containsd evrything you need to start making a hologram.

Once you get past the initial hurdles and get a feel for the techniques, you can go further, make more complex setups and more complex optics.

BobH · Post by **BobH** » Sat Feb 11, 2012 11:50 am

I recommend the Saxby book way before the Holography Handbook. The latter doesn't even mention polarization, and the sandbox table is an obsolete approach that does work but nobody (save a few) uses.

Jem · Post by **Jem** » Sun Feb 12, 2012 7:45 am

holorefugee wrote:If you have questions about Gem's post please ask. It was an advanced and brief reply. I t was correct if you had mad lots of holograms.

Yes, it was probably over the top.. Didn't realise he was new, sorry 'nomiss'

nomiss · Post by **nomiss** » Mon Feb 13, 2012 2:00 pm

So what do you think about this set up? I will be lasing with a Coherent Compass 315M-100 DPSS 532nm Laser which is Single Longitudinal Mode. I plan on using a Single Beam Denisyuk setup and U08 ultimate Holography Plates. I am not sure on what type of table to build. I have room up to a 4x8 table but i don't know if I should go that big. As for the size of my holograms, I plan to experiment with some 2.4x2.4 plates and do my final project on 8x10 plates. As for a conceptual idea, I was thinking of lasign a series of train cars and then displaying them in a row so when put together they would resemble a train. What do you guys think about this setup/idea?

Dinesh · Post by **Dinesh** » Mon Feb 13, 2012 3:04 pm

nomiss wrote: I am not sure on what type of table to build. I have room up to a 4x8 table but i don't know if I should go that big.

For a 2.5 x 2.5, you don't need a very large table, a 2ft x 2ft is probably enough. But if you intend to go to an 8x10 plate size, you will need something larger. It really depends on the complexity of your shot. A single beam Denisyuk of a scene about 6in deep on an 8x10 plate using the lens I mentioned earlier (the negative f/2) would need about a 3ft x 3ft at least, assuming the laser was on the table. Some people place the laser off the table. To do an H1/H2 shot, again assuming the laser was on the table, would probably require 4ft x 4ft, but a 4ft x 6ft would probably be a little more comfortable to work with. Having said that, I've heard of extremely compact tables making fairly complex shots (Hi Colin!). However, in conclusion, I'd say that a 4ft x 6ft table should be ample for your immediate needs. Remember to have a station for processing that can also be quite dark. Some people box their plates and go into another room, and some people cordon off part of the table room for a processing station.

nomiss wrote: As for a conceptual idea, I was thinking of lasign a series of train cars and then displaying them in a row so when put together they would resemble a train. What do you guys think about this setup/idea?

The depth of the image depends on the coherence length of your laser. I don't know what that is for your laser. Dave? Generally, you don't want to go to the limit of the coherence length, as the brightness falls off quite fast as you approach the end of your coherence. So, if you have a coherence length of 3 ft, I wouldn't shoot anything deeper than 2 feet. So, you have to figure out how deep is going to be the depth of these cars behind the plate. The cars themselves cannot be free rolling on rails, that would cause too much motion. I'd use hot glue to glue the cars down onto a surface. Also, if the cars have wheels attached to shafts below the car, you may want to glue the wheels to the main body. Just before you shoot, tap all parts of the object (the cars, the wheels, any doodads and thingummy's that stick out of the cars etc) gently with your fingernails. If you hear a sharp tone or a ringing tone, you may have motion problems. When you tap with your nails, you want to hear a dull thud kind of sound. Be aware that the laser beam is a Gaussian profile. That means that the beam strength falls off quite fast at the edges. For uniformity, I'd cover the entire scene within the middle third of the beam diamater. So, if you plate were placed in landscape (the 10in length is the viewing horizontal), then the beam needs to spread about 25 inches across.

nomiss · Post by **nomiss** » Mon Feb 13, 2012 3:21 pm

Sorry if I wasn't as clear before. My plan is to purchase a set of 9 8x10 plates and make each individual plate have a single train car on it. Then I plan to display the plates right next to each other so it would be like this. [][][][][][] I would probably use 5-6 plates and hence 5-6 train cars. This way I would be able to display a train over a pieced together hologram that would be 50-60 inches long and eight inches tall. This concept would create a train from a side perspective but if i wanted to add depth I could angle the cars at the same angle each time and move them farther back each time to create the perception of distance. What do you think about this idea about piecing together multiple holograms?