dcg test

[Joe Farina]

For narrowband, I've been using room-temp (ambient temp. 20C) 70, 91, and 100% IPA for 5 minutes each. My coatings are thick. Rallison seems to have favored the use of a "tuning bath" i.e., the first alcohol bath: ".....A near ideal tuning bath has a specific gravity of .86 when it is warmed to about 55 degrees C." I am definitely keeping this in mind, but so far, I have not varied the alcohol baths. I do get the impression that the tuning bath can be used to get either a red or blue shift, but this was not detailed in the papers I have. Probably there is too much variation in DCG parameters to make the specifics meaningful, actual lab tests need to be done. As I recall, Rallison said somewhere that .86 specific gravity IPA roughly corresponds to 70% IPA. Does that sound right? I've found that skipping the 70% does produce a broadband result (the "mbdcg from last weekend" just had 91 and 100%). I'm not aware that hot IPA causes shrinkage, but I would expect it to produce more of a broadband result.

[MilanKarakas]

For narrowband, I've been using room-temp (ambient temp. 20C) 70, 91, and 100% IPA for 5 minutes each. My coatings are thick. Rallison seems to have favored the use of a "tuning bath" i.e., the first alcohol bath: ".....A near ideal tuning bath has a specific gravity of .86 when it is warmed to about 55 degrees C." I am definitely keeping this in mind, but so far, I have not varied the alcohol baths. I do get the impression that the tuning bath can be used to get either a red or blue shift, but this was not detailed in the papers I have. Probably there is too much variation in DCG parameters to make the specifics meaningful, actual lab tests need to be done. As I recall, Rallison said somewhere that .86 specific gravity IPA roughly corresponds to 70% IPA. Does that sound right? I've found that skipping the 70% does produce a broadband result (the "mbdcg from last weekend" just had 91 and 100%). I'm not aware that hot IPA causes shrinkage, but I would expect it to produce more of a broadband result.

Yes, seems that .86 SG is about 70% alcohol, but not sure at which temperature (room or elevated?).

I am not sure about hot vs. cold alc. bath, since my last holograms are milky so my whole attention was focused on this issue. Just noticed that if hologram is overexposed, last hot alcohol bath move it in the UV spectra. Or at least I got that impression.

Maybe this is because I am recording at 450 nm, and it is already too close to the visible end of the spectra anyway. At first, I can see the hologram in the hot alc. bath beginning as red, but after a while and especially after drying, it become violet or invisible and lost somewhere in the UV.

Changing recording geometry helps a bit to prevent too much blue shift. But I am recording transmission holograms, and don't know does it will helps to the reflection holograms as well. It is close to Brewster angle, but slightly more tilted, so that plate get less light (when observed from the laser perspective, cross section is narrower), yet not much 'wood grains'.

Oh, btw.... I remember Rallison recommending more dichromate for bluer hologram (and less dichromate for redder hologram). Maybe we should to try this method. I know, it is pain in the neck having low power laser and low sensitivity of the plates, but if this helps to prevent moving color centers in the wrong directions, maybe it is worth prolonging (already long) exposures?

Best--
milan

[Tony DCG]

Oh, btw.... I remember Rallison recommending more dichromate for bluer hologram (and less dichromate for redder hologram). Maybe we should to try this method. I know, it is pain in the neck having low power laser and low sensitivity of the plates, but if this helps to prevent moving color centers in the wrong directions, maybe it is worth prolonging (already long) exposures?

Yes this is correct. This is one way I do red
Also longer bath times (narrow band), short bath times (a few seconds) and hot temps.

Thanks for the photo Joe, made a big difference.