H2 Reference Beam Angle for Image Plane Holograms

[John Sonley]

Dinesh, Joy - hopefully I've reduced the size of this image enough - it's as described in my posting of a few minutes ago

John

[Dinesh]

What do you think of that as a plan?

I think it'll help.

By the way, you don't need to hit the H1 at 60. If the laser is unpolarised, Brewster's angle makes no difference anyway. If the laser is polarised, reducing the H1 ref to about 50 will not give serious woodgrain. Brewster's for a material of index n is arctan(n), which for glass of index 1.5 is actually 56 odd degrees. The Brewster effect is not a Dirac function, it falls off slower than that! I've discovered that the woodgrain doesn't transfer to the H2 anyway. It's true that if the woodgrain is bad, there'll be a shadowy blur in front of the H2. However, if the woodgrain isn't too bad, the observer focuses on the H2 plane and doesn't notice the "woodgrain blur"

[John Sonley]

Dinesh - thanks for your observations
I have always used an angle of incidence of 30 Deg (60 Deg to plate normal) for the H1 ref beam in making my H1s - I guess it stemmed from following the Unterseher method - my 1st holography book.
Of course, once you have a number of H1s made like that then the H1 reconstruction angle is defined when making the H2 copy
Until earlier this year I did get noticablewood grain on my H1s - but as you say the wood grain doesn't reconstruct in the same manner as the pseudo image, although it will add to 'noise' in the finished H2.
I overcame the woodgrain by initially turning my Melles Griott 30mW HeNe, which is polarised, on its side, which sorted out the wood grain but the power output of the laser fell to about 18mW.
I put the laser back to it's normal position and inserted my newly acquired half wave plate - problem solved and now I make wood grain free H1s