Holographyforum.org / holowiki.org

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.

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.

[quote=dannybee post_id=71858 time=1595779695 user_id=2167]
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?
[/quote]
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.

[quote=dannybee post_id=71857 time=1595779582 user_id=2167]
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
[/quote].
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').

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? 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

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? 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 ji

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?

There are two ways of checking your theory that the dyes in the film are more absorptive at 640nm:

1. Record a grating on silver halide film with the diode. This will eliminate the laser itself.

2. Record a grating on silver halide, simultaneously [i]behind[/i] a sheet of the polymer. But, be sure you use the same exposure you would have used on the silver halide alone. If you're right that the dyes are absorptive at 640nm, then insufficient light will get to the silver halide film behind the polymer, and the resulting hologram (on silver, remember) will be weak or non-existent.

One more thing to consider: photopolymer requires at least threshold irradiance [mW/cm2] in order to record anything. If yoour diode is weak, making the exposure longer does not help. (Contrary to silver halide, where you can usually compensate weak laser by longer exposure.) I did not test HX200 at 640 nm, but it should work.

according to the transmission of the polymer in 640nm is much less transmission than a hene, so that the problem with that 640nm it needs more light to go through the dye for a reflection, it would be ok for a transmission but a bit low for a reflection. if this is the same stuff as liti they probably have the red diode closer to the plate. but with hene it allows enough light to go through the polymer

Geola is selling Bayer/Covestro panchromatic HX200 photopolymer. Don’t know if they’re also selling some other photopolymer as well... if you’re referring to HX200, it’s definitely sensitive at 640nm. I’ll leave it to you to research online😊.