My polarisation problems

[John Sonley]

Well - continuing-on from another Forum ...
I've turned my HeNe on it's side (90 deg) and lo and behold - I've lost the woodgrain effect, so my polarisation must have been wrong for the set-up I've always used! -and so I've made 350 holograms 'the wrong way round'

So why hasn't it seemed a problem?

The holograms I make are the H2 image plane white light viewable type - made from H1 masters. In projecting the pseudoscopic image from the H1 into the space where the H2 film (temporarily laminated on to glass with paint thinner) will be, I guess the wood grain effect, which isnt very apparent but which is certainly there, doesn't become re-constructed - but I guess may well add unwanted noise to the resultant H2

- but why don't I get the woodgrain effect from the glass on to which the H2 is temporarily laminated .. I've made some superb (self praise is no praise) H2s, clear, noise free ..... but why are they OK if my laser's wrong way round!

BRgds

John

[Vidar]

Hi John - In my setups there is a distinct difference in woodgrain if I by mistake have forgotten to rotate my laser. Do you get a huge difference in intensity downstream If you rotate a polarized sunglass in the beam?

[JohnSonley]

Hi Vidar - yes my laser is clearly polarised - if I put one lens of a pair of polarised sunglasses in it's beam and turn the glasses then the emergent beam goes from full light to zero light when I turn the glasses through 90 deg.

I just don't understand why I get such good H2 white light viewable holograms if I have my laser oriented so that I get woodgrain effects on the H1 master - why don't I get the same effect on the H2, which is temporarily laminated to glass
BRgds

John

[Johnfp]

Hey John. Can you describe your H1 set up and your H1 to H2 set up? Specifially is the reference overhead or side lighting, is the object on it's side or right side up, etc.

[John Sonley]

Hi John - I use the Untersheyer method.
I make my H1s with the subject normally oriented and the side reference beam coming in at an angle of 30 deg to the film
I make my H2s by tilting both the H1 master and H2 copy film, which remain parallel to one another, away from the reference beam, which is positioned at a slightly lower level in my sandbox such that the collimated reference beam strikes the emulsion side of the H2 copy film, temp. laminated on to glass, at about 40 - 50 deg

It sounds complicated - but if you've a copy of Untersheyer (not certain of spelling here) + two other authors, look up Image Plane Reflection Hologram

BRgds

John

[Johnfp]

Hey John, I do have that book and will need to locate it and look up the techniques. But I think you are mixing two different technique and this may be why the woodgrain is evident in one set up but not the other.

In making your H1's you have the object standing upright but are bring the reference beam in from the side of the plate at 30 degrees. Essentially using a side reference but the object is rotated 90degrees from the reference angle. Correct?

Now in making your copy you tilt the plates back and bring the beam in from the bottom. This would require that you turn the H1 by 90degree and now your are using a bottom reference angle. This would turn your object such that it is now lying on its side. If the H2 is also being lit from the bottom then this would make a final hologram that would need side lighting to see the object right side up. Is this correct?

If both these statements are correct then only one of the set ups, H1 side reference or H2 bottom reference would be correct in it's polarization orientation with relation to the laser's polarization.

I'm also a little concerned why you are not using brewsters angle for your reference beams. 56 Degrees off the normal. Which I think if your are using 30degrees from the edge to the normal then that is pretty close to brewsters.

A good test in either set up is to look at the reflection off a plain piece of glass onto the wall or ceiling. Now tilt the plate back and forth with respect to the reference beam angle and there will be one place where barely no reflection is to be seen. THis is your best angle. If you do not see any difference in the reflected light then you probably need to rotate your laser 90degrees.

Again, with the two set up having different reference orientation with respect to the laser, it seems you would have to rotate your laser 90 degrees when swithing from one set up to the other.

I will find that book tonight and take a peek at it. I've only read that book 100 time but just can't picture which set-ups you are using.

[John Sonley]

John - just come back to this forum - sorry for the delay

Rather than try to describe in text form the complexity of my set-ups. do you have an e-mail address that I could send to you a few .jpg images.
I think this would be simpler and less ambiguous

BRgds

John

John - you can view some general shots of my holography laboratory by viewing my web site
www.johnsonley.myzen.co.uk

[Johnfp]

holograms3d at yahoo dot com

[Johnfp]

A trick for photographing holograms is to take a white card and set it up next to your hologram oriented the same as your hologram. Then focus on the card (hold shutter half way down) and then while still holding the shutter half way move the view over to the hologram and finish depressing the shutter. With some practice you get nice photographs. Also, to adjust the light level, you may need to focus just 1/4, 1/2 or 3/4 of the way on the white card. This also sets you light level.

[Dinesh]

I just don't understand why I get such good H2 white light viewable holograms if I have my laser oriented so that I get woodgrain effects on the H1 master - why don't I get the same effect on the H2, which is temporarily laminated to glass

Because, possibly:

the H2 film (temporarily laminated on to glass with paint thinner)

The paint thinner is acting like an index-matching fluid.