Geola question

Holography related topics.
Din
Posts: 259
Joined: Thu Mar 12, 2015 4:47 pm

Re: Geola question

Post by Din » Sun Jul 26, 2020 2:43 pm

dannybee wrote:
Sun Jul 26, 2020 11:08 am
Thanks Dinesh you could also do this by measuring the intensity of the light going through and comparing it to the light coming in right?
No, unless you have a re-e -a-a-l-y sensitive meter. The reason is that the modulation is a non-linear function of the recording light This means that the efficiency, or brightness, of a hologram is sensitive to small changes in the recording light that could not be directly measured, unless the direct measuring system is very sensitive. But, you can measure the efficiency of the hologram as a result of small changes in the recording light.
dannybee wrote:
Sun Jul 26, 2020 11:06 am
My hene is 18mw and my 640 diode is 25mw spread to about 5x7 at the plate film is a 4x4 .. this setup works fine with the hene & and the 532nm. ... a nice even spread of yellow , and like lobaz said maybe a 640nm and this amount of spread of red light is not meeting the required amount because of the transmission curve of this polymer
.
It looks like you have about 100 uW at the plate for the diode. This may be too small. It has nothing to do with the transmission curve of the polymer, it has to do with the charge potential. What this means is the charge - electrons - is 'held back' to the polymer, and you have to 'kick it out' of the influence of the polymer before it begins to record. Basically, this polymer works because electrons are stripped away from the polymer, and begin to migrate towards the bright fringes (I think, it could migrate to the dark part). At any rate, there are electrons that migrate to one part of the fringe, leaving a charge separation between the two parts of the fringe. But, in order to start moving, they have to overcome a barrier.

Consider you're in a bowling alley. Normally, you roll the ball towards the pins. It doesn't matter how slowly you roll the ball, eventually, it will hit the pins. But, something has caused a bulge in the alley, and you have to take the ball over and beyond the bulge. If you do not roll the ball sufficiently forcefully, the ball will not go over the bulge, it will simply roll back towards you. This has nothing to do with the width of the alley (the "transmission curve').

Martin
Posts: 95
Joined: Sat Apr 04, 2015 2:36 am

Re: Geola question

Post by Martin » Mon Jul 27, 2020 1:07 am

You may switch on an auxiliary incoherent light source during recording. This lowers the threshold energy required to initiate polymerization for the holographic (laser) exposure. It involves a lot of testing and fine tuning though.

lobaz
Posts: 272
Joined: Mon Jan 12, 2015 6:08 am
Location: Pilsen, Czech Republic

Re: Geola question

Post by lobaz » Mon Jul 27, 2020 6:16 am

The easiest would be to try recording a small Denisyuk hologram, with beam spread to a small area, say diameter 3 cm. That should make irradiance strong enough.

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