WHITE LIGHT LASERS

[Martin]

http://www.lumalaser.com/overview_JenLas.htm

http://www.pi4.uni-stuttgart.de/NeueSei ... t_apps.pdf

[Colin Kaminski]

www.lumalaser.com/overview_JenLas.htm

This is getting close to what we need, too bad it is pulsed operation and has no coherence specs.

[Sergio]

www.lumalaser.com/overview_JenLas.htm

This is getting close to what we need, too bad it is pulsed operation and has no coherence specs.

The second link states pulsed continuous operation and a perfect TEM00 mode, based on Raman laser I wonder what is the temporal coherence and how to calculate this?

[Colin Kaminski]

I don't have my library handy but I seem to remember that the shorter a pulse the shorter its coherence length. The pulse train is > 20 ps pulses. The main problem is that there is no guarantee that successive pulses are the same frequency. It is common in single pulse lasers to have the laser switch modes on a random double pulse.

[Joe Farina]

For color holography, I would personally stay away from white-light lasers, for a variety of reasons. Most importantly, the control of RGB ratio is essential, and if you can't do this to the individual beams (beore they are combined), then it would create a problem. (Of course, if a laser has a variable RGB ratio, that might be a different story, but the laser would still need to be tested for holographic-quality coherence, which is not an easy requirement to be met.)



Adjustment of the RGB ratio may be necessary for each batch of plates, unless we are able to produce emulsion that is very consistent (Bjelkhagen stessed this point during his Lake Forest lecture in the mid-90's, as the RGB ratio had to be adjusted for each batch of PFG-03C plates he used). Although Bjelkhagen seems to have briefly tried a white-light (mixed-gas) laser, he quickly moved back to individual lasers, and that's what Gentet uses also. Vary rarely do I see white-light lasers used in color holography, and I believe the reason for this is the RGB control issue.

[Martin]

For color holography, I would personally stay away from white-light lasers, for a variety of reasons. Most importantly, the control of RGB ratio is essential, and if you can't do this to the individual beams (beore they are combined), then it would create a problem. (Of course, if a laser has a variable RGB ratio, that might be a different story, but the laser would still need to be tested for holographic-quality coherence, which is not an easy requirement to be met.)

Adjustment of the RGB ratio may be necessary for each batch of plates, unless we are able to produce emulsion that is very consistent (Bjelkhagen stessed this point during his Lake Forest lecture in the mid-90's, as the RGB ratio had to be adjusted for each batch of PFG-03C plates he used). Although Bjelkhagen seems to have briefly tried a white-light (mixed-gas) laser, he quickly moved back to individual lasers, and that's what Gentet uses also. Vary rarely do I see white-light lasers used in color holography, and I believe the reason for this is the RGB control issue.

I agree. RGB mixing seems to be a very tricky business.
However, if you look at the pdf file, the summary says:

White light lasers are a new class of lasers, emitting not just a single color, but rather covering a wide rang of the wavelength spectrum. White light lasers, covering the whole visible range from blue, green, yellow, red, into the infrared, have been developed.

So there's hope, at least for the future, that the quarrel about the most appropriate RGB wavelengths for color holography will find an end. The project described in pdf file suggests there might be real broadband laser sources available (they mention a spectrum from 460 - 1600nm). Some day a color hologram may come close to the color rendition of a Lippmann photograph.

[Sergio]

Martin i would suggest read the article : http://www.opticsexpress.org/DirectPDFA ... N=33362981



Onto Demonstration of a silicon Raman laser, I guess the way you think on Lippmann process greatly influentiate and demonstrate the possibility here, as the Lippmann process is limited to a narrow space emulsion thickness the raman laser is limited to a short temporal pulse, so we need to consider the time bandwidth broaduct (Δτ.Δν) factor over the broadband spectrum.



Note the pulses are reproducible at a constant rate and the temporal profile of each pulse is Gaussian, so the reproduction may give the "coherence length", of course the ref/object beams must be adjusted or you will lost the coherence also geting "zebra" images, but you idea on Lippmann analogy makes the system work for contact copies and rest to know the true temporal laser coherence for a off-line holography.

[Martin]

Martin i would suggest read the article : http://www.opticsexpress.org/DirectPDFA ... N=33362981

Onto Demonstration of a silicon Raman laser, I guess the way you think on Lippmann process greatly influentiate and demonstrate the possibility here, as the Lippmann process is limited to a narrow space emulsion thickness the raman laser is limited to a short temporal pulse, so we need to consider the time bandwidth broaduct (Δτ.Δν) factor over the broadband spectrum.

Note the pulses are reproducible at a constant rate and the temporal profile of each pulse is Gaussian, so the reproduction may give the "coherence length", of course the ref/object beams must be adjusted or you will lost the coherence also geting "zebra" images, but you idea on Lippmann analogy makes the system work for contact copies and rest to know the true temporal laser coherence for a off-line holography.

I agree, making holograms with a continuous spectrum sounds like a naïve idea. I certainly don't know enough about lasers to judge if this is a mere pipe dream. Haven't we been told over and over again a laser essentially was an very narrow bandwidth light source!

Maybe I am reading too much into that paper. Anyway, the abstract of that pdf file says:

Excellent focusing properties and small divergence of the white light are some of the unique advantages. Additionally, spectral, temporal, and spatial coherence are especially beneficial properties of the white laser light.

From German patent (DE 10220871) I gathered their laser device uses glass fibers that serve to replace non-linear crystals to introduce a wavelength change.

[Joe Farina]

Some day a color hologram may come close to the color rendition of a Lippmann photograph.

That's an interesting thought, comparing the color rendition of a Lippmann photograph to a color hologram. The question arises: has anyone tried to measure the CRI of a Lippmann photograph? We may think that a Lippmann phograph has a very good CRI, but is this really the case?



To be honest, I don't know exactly how the CRI is established for a given illumination system. Or even if CRI can be applied to an imaging system like photograpy. (I would tend to think it could, however.) My intuition tells me that Lippmann photography does not achieve a CRI of 100.



I guess the idea behind the CRI is that a set of different color samples is illuminated with a certain kind of light, then the colors under that light are compared to the same colors under daylight. (I don't know exactly how "daylight" is defined however.) The closer the "match," then the closer the CRI approaches 100.



The other day I checked my Westinghouse "daylight" fluorescent bulb with my cheap spectrometer, and it verified three very sharp lines around 440, 540, and 610. (It was interesting to see a rather close correspondence between these wavelengths and the wavelengths of the white-light laser in the above link.) The color-rendering index of this light bulb is 94, which is very good. I wonder if a Lippmann photograph would achieve a CRI this high? We know how critical processing procedures are for both Lippmann photos and holograms.

[Paulos]

Some calculation, based on the specifications of this laser:

Pulse duration <10 ps, Output = 10W, Pulse Frequency = 80 MHz

so:

1. The length of each emitted beam is

(duration * speed of light) = (10*10EXP-12)*(300*10EXP6) = ... =3 mm !

This is equivalent to the coherence length, for the case the laser is single mode.

This make the laser unsuitable for holography.



2. The Energy of each pulse is also too low:

10 W / 80 MHz = ... = 0.125 uW (microwatt)!

And it is very doubtable that the pulses are the same frequency.