Photonics West 2025

Holography related topics.
Martin
Posts: 134
Joined: Sat Apr 04, 2015 2:36 am

Re: Photonics West 2025

Post by Martin »

Din wrote: Mon Jan 27, 2025 9:30 am I think these Bragg gratings would have to be very narrow band. So, whether it could be possible with red diodes would depend on whether bandwidth is proportional to wavelength.
Absolutely. I guess it involves very thick volume Bragg gratings, recorded into PTR glass (photo-thermo-refractive glass). Since PTR glass is probably out of reach for most of us, I wonder to what extend alternative recording materials might be used. Of course most of these materials cannot rival glass when it comes to heat resistance/ coefficient of expansion etc. With high power lasers this certainly becomes a limiting factor. But what about lower powered lasers? I wonder if less restrictive recording materials might become an option - maybe something alike Denisyuk/Ganzherli did a while ago with processing-free dichromated glycerol gelatin layers.There might be other candidates for such a task as well.

Furthermore, would stacked layers be an option? What happens if we stacked 10 pieces of Covestro film between two glass plates? How good would they perform optically - big question mark since there would be several pieces of PET or TAC film present in that structure.

Din wrote: Mon Jan 27, 2025 9:30 am I'm a little intrigued by:
Martin wrote: Mon Jan 27, 2025 7:36 am We extended the approach to coherently combine several blue diodes in order to increase the total output power.
Wouldn't all the blue diodes have to have the same spectral profile within the bandwidth?
Probably so. I would go for just one diode. Would it not be nice turning a cheap laser diode into a precious long coherence length laser?
Din
Posts: 509
Joined: Thu Mar 12, 2015 4:47 pm

Re: Photonics West 2025

Post by Din »

Martin wrote: Tue Jan 28, 2025 12:13 pm There might be other candidates for such a task as well.
Lithium Niobate comes to mind. I don't think a 1 cm cube of niobate costs more than a few hundred dollars. It was insensitive compared to DCG, at POC in 1988, an Argon laser at 488 that took about 3 - 5 minutes to expose DCG took me about 20 minutes to expose a 1cm cube of LiNbo(3), so it would take a powerful laser. However, since 1988, such lasers are relatively easily available. Also, 20 minute exposures are not uncommon for Covestro.
Martin wrote: Tue Jan 28, 2025 12:13 pm Furthermore, would stacked layers be an option? What happens if we stacked 10 pieces of Covestro film between two glass plates? How good would they perform optically - big question mark since there would be several pieces of PET or TAC film present in that structure.
Not sure it would work unless both the Covestro layers and the PET/TAC were exactly the same thickness within perhaps λ/10, because otherwise there'd be scattering and refractions at each interface, and, if the rms of the Covestro/PET/TAC layers were greater than about half a micron, you'd effectively get prisms at the interfaces. Ive seen several attempts over the years of people trying to get emulsion thickness by interferometric techniques and they've never workd because the rms is too high, giving a variable twisted fringe structure. I don't think manufacturers of holographic film are too concerned about uniformity of the material and sub layers.
Martin wrote: Tue Jan 28, 2025 12:13 pm Would it not be nice turning a cheap laser diode into a precious long coherence length laser?
Yep. But, it would put a lot of companies we know out of business!
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