blue laser diode

Holography related topics.
soda
Posts: 38
Joined: Mon Oct 08, 2018 4:05 am

Re: blue laser diode

Post by soda »

You are right, the blue part is most complicated. If eye sensitivity is taken in to account, 532nm frequency doubled Nd:YAG/YVO (or 530 OPSL) is perfect. I found, that 633nm HeNe is somewhat better than 640nm diode, color rendition is indistinguishable by my eye, but eye is little bit more sensitive to 633nm and my emulsion too, I need to increase by 1/4 dye amount. My SilverX emulsion sensitized by ascorbate / pinacyanol and isocyanine have sensitivity roughly 2, 3, 1.5mJ/cm2 for RGB respectively, Ultimate is more than 10x sensitive (and 100x more expensive).
Blue is another story: In theory 445 - 450nm is optimum. Also LED for reconstruction light peaking at this wavelenght, what surprise if the chip is from the same material as LD :-)) PL450 is single TE mode, which favours it over Nichia 1W 445nm diode. 20mW will be reliable, enough for AgX, W's 40 is unbeliveable. Diodes are generally sensitive to enviroment changes and backreflections, other types of lasers are typically more stable. From difraction efficiency and eye sensitivity point of view longer wavelenght is prefered, especially for silver halide materials, 473nm DPSSL (Nd:YAG doubled line) will be best choice, but my 10mW BWtec resist to any attemps to SLM operation - reason when I dealing with diodes. 488nm argon/OPSL will be good solution, if deep blue is omitted. HeCd, dye LASER, etc. are nowadays unreliable and exotic light sources.
Joe Farina
Posts: 804
Joined: Wed Jan 07, 2015 2:10 pm

Re: blue laser diode

Post by Joe Farina »

For your silver emulsion, 1.5mJ sensitivity in the blue is excellent. I'm not sure about my color DCG material, but it probably needs more than 30mJ in the blue. I've often wondered about the necessity of keeping close to 450nm for the blue component of RGB holography. The literature seems to say that it's optimum. Yet, you and Y. Gentet like 473nm DPSS for your silver materials. So I guess the practical difference between 457 and 473 might not be significant, and there may be advantages to 473 from a holographic standpoint. The longer wavelength of 473 would have less scattering compared to 457. I noticed that scattering with the Melles-Griot 457 was quite substantial, and that wavelength seemed to pick up a lot of noise from small particles (dust, etc.). Years ago, I saw a side-by-side comparison of two holograms at Lake Forest of two RGB holograms, both identical, except that one was done with 442, the other with 488. I honestly couldn't tell the difference (although the guy next to me said he could tell a subtle difference). I guess if the object/scene contains blue that is short, less that 473 for example, and that blue component is important, it might be noticeable. But in nature and many natural pigments, I think blue has less real significance compared to red and green. On the other hand, blue should definitely help to "whiten" white. The laser cost of usable 473nm light might be high, possibly comparable to Melles BLD/BLS, I haven't seen many such lasers available over the years, and have never used one. I'm considering a Sapphire at 488nm, mainly to brighten whites. Prices on eBay are looking pretty good lately.
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