by Din » Tue Jan 07, 2025 1:38 pm
If I understand you correctly, you are generating a fringe structure in software. You then print this fringe structure onto Kodak film, and then transfer the fringe structure onto Ultimate holographic film using laser light.
I don't think polarisation is an issue, since you're not exposing either the Kodak film or the Ultimate film with two beams. If I'm right, you're generating the fringe structure in a computer, either just as a set of lines or by using FT software. Polarisation only becomes an issue when recording with two beams, where the polarisation of one beam is π/2 rotated with respect to the other.
My thoughts are:
What is the spatial frequency of your computer-generated fringe structure? You say that your printer has an 8K resolution, but without the size of the print, it's not possible to determine spatial frequency in terms of lines/mm - the usual way of stating the holographic spatial frequency of a grating. The spatial frequency is given by sin(θ)/λ l/mm(assuming one beam is normal), or, in your case, sin(θ)/0.000633 l/mm. So, what is the sin(θ) you have simulated? As an example, if I recorded a grating with one normal beam and one beam at 30 deg with a HeNe laser, the spatial frequency would be ~790 l/mm.
The actual fringe structure, recorded by two beams in the conventional manner, is sinusoidal. If the printer cannot reproduce the sinusoidal nature of the fringes, and instead prints them as a square(-ish) variation, you'll lose efficiency. The reason is that the diffracted light is based on the sinusoidal components of the printed fringe structure, ie on the Fourier transform of the printed fringe structure.
What is the modulation, ie what is the intensity variation between fringe and not-fringe? The most important parameter in holographic efficiency is the modulation. If the modulation is low, the efficiency will be low. Generally, the modulation is given by:
M = {I(high) - I(low)}/{I(high) + I(low)}
where I(high) is the intensity of darkest part of the fringe, and I(low) is the intensity of the non-fringe.
I am curious, though, why you feel you have to transfer to a holographic film. If the print can take the spatial frequency, you can simply hit the transparency with laser light, you don't need to transfer to holographic film. In fact, it may be a cause of the low efficiency, since there is a loss of information due to the transfer gamma; you may be losing some of the higher frequencies.
If I understand you correctly, you are generating a fringe structure in software. You then print this fringe structure onto Kodak film, and then transfer the fringe structure onto Ultimate holographic film using laser light.
I don't think polarisation is an issue, since you're not exposing either the Kodak film or the Ultimate film with two beams. If I'm right, you're generating the fringe structure in a computer, either just as a set of lines or by using FT software. Polarisation only becomes an issue when recording with two beams, where the polarisation of one beam is π/2 rotated with respect to the other.
My thoughts are:
What is the spatial frequency of your computer-generated fringe structure? You say that your printer has an 8K resolution, but without the size of the print, it's not possible to determine spatial frequency in terms of lines/mm - the usual way of stating the holographic spatial frequency of a grating. The spatial frequency is given by sin(θ)/λ l/mm(assuming one beam is normal), or, in your case, sin(θ)/0.000633 l/mm. So, what is the sin(θ) you have simulated? As an example, if I recorded a grating with one normal beam and one beam at 30 deg with a HeNe laser, the spatial frequency would be ~790 l/mm.
The actual fringe structure, recorded by two beams in the conventional manner, is sinusoidal. If the printer cannot reproduce the sinusoidal nature of the fringes, and instead prints them as a square(-ish) variation, you'll lose efficiency. The reason is that the diffracted light is based on the sinusoidal components of the printed fringe structure, ie on the Fourier transform of the printed fringe structure.
What is the modulation, ie what is the intensity variation between fringe and not-fringe? The most important parameter in holographic efficiency is the modulation. If the modulation is low, the efficiency will be low. Generally, the modulation is given by:
M = {I(high) - I(low)}/{I(high) + I(low)}
where I(high) is the intensity of darkest part of the fringe, and I(low) is the intensity of the non-fringe.
I am curious, though, why you feel you have to transfer to a holographic film. If the print can take the spatial frequency, you can simply hit the transparency with laser light, you don't need to transfer to holographic film. In fact, it may be a cause of the low efficiency, since there is a loss of information due to the transfer gamma; you may be losing some of the higher frequencies.