"incredible detail, ad nauseam, and I hope the question has been laid to rest for many years to come."
For those of you who are fans of projectile vomiting, I added some illustrations that were not printed in the original paper but were slides that were shown when the paper was presented many moons ago.
Please enjoy!
http://nlutie.com/ewesly/CoherenceAddenda.html
Long Red Lasers
Forum rules
Finding new homes for holography-related items is encouraged. Even commercial enterprises with goods to offer are welcome as long as it is in the spirit of members helping members. If a for-sale post reads like an infomercial, though, you have probably crossed the line of acceptability.
Finding new homes for holography-related items is encouraged. Even commercial enterprises with goods to offer are welcome as long as it is in the spirit of members helping members. If a for-sale post reads like an infomercial, though, you have probably crossed the line of acceptability.
Long Red Lasers
"We're the flowers in the dustbin" Sex Pistols
Long Red Lasers
Thanks Ed. It is nice of you to take the time to add the information.
The theory in the paper is sound and it would be cool to repeat the testing with modern available HeNe laser models that had been screened on a beam profiling ststem to be over 95% TEM 00. The only real criticism Sam had of this paper is that the lasers used had weak tubes but you guys used what you had on hand at the time right? I have a good understanding of this topic now thanks to all the discussions and your paper as well as some serious thought about the bandwidth of the Neon line not changing mo matter how many modes oscillate under it. Of course these many modes will create high frequency beat noise however for holography this is not an issue.
Starting now I will test every laser I sell for holography on a 2 GHz con focal spectrum analyzer and provide the new owner with the information and a photo...how many modes and the approximate bandwidth. I already do that for single frequency lasers but after this thread maybe this would be interesting.
I have a really nice Melles Griot 25-LHP-925 system ready to ship. The laser is 17 mW minimum power spec new outputting 20.3 mW with a nice TEM 00 beam. The lab supply box (LPL915-070) is new old stock with a few hours on it and we will offer a full year warranty on this system for $750 plus shipping. I will put this on the con focal and see what the spectrum looks like and how many modes it takes to make the 20+ mW. Who wants a nice, long, stable red laser? Phil (813) 974-2378 pbergero@usf<dot>edu
The theory in the paper is sound and it would be cool to repeat the testing with modern available HeNe laser models that had been screened on a beam profiling ststem to be over 95% TEM 00. The only real criticism Sam had of this paper is that the lasers used had weak tubes but you guys used what you had on hand at the time right? I have a good understanding of this topic now thanks to all the discussions and your paper as well as some serious thought about the bandwidth of the Neon line not changing mo matter how many modes oscillate under it. Of course these many modes will create high frequency beat noise however for holography this is not an issue.
Starting now I will test every laser I sell for holography on a 2 GHz con focal spectrum analyzer and provide the new owner with the information and a photo...how many modes and the approximate bandwidth. I already do that for single frequency lasers but after this thread maybe this would be interesting.
I have a really nice Melles Griot 25-LHP-925 system ready to ship. The laser is 17 mW minimum power spec new outputting 20.3 mW with a nice TEM 00 beam. The lab supply box (LPL915-070) is new old stock with a few hours on it and we will offer a full year warranty on this system for $750 plus shipping. I will put this on the con focal and see what the spectrum looks like and how many modes it takes to make the 20+ mW. Who wants a nice, long, stable red laser? Phil (813) 974-2378 pbergero@usf<dot>edu
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holozone
Long Red Lasers
Hello Phil and all the other people discussing this problem,
I have logged in the first time after my initial posting and just see all this messages about coherence length - I don't want to start a "bad" discussion about phils lasers, please believe me! Sorry for that phil.
I start my work 25 years ago with a 2 mW HeNe and this device has approx. 60 cm usable cohrence length. I need more power and used many laser in the next years between 5 - 25 mW and yes more power is better, Phil, you are right. I always measure the coherence length of my lasers, for very long tubes it mostly drops to 12-17 cm, but this is still very usable with precise length adjustment of the different beams.
Long time ago I have mode an experiment with the coherence length of hene's, I put some laser energy with a lens in a fiber, wrap it around a stick and made a hologramm of this. The fiber losses light (because of the tight circles) so it "glows" illuminated by laser light from inside. I was surprised about the resulting hologramm: The image of the fiber was bright first, then gets dark, get bright again and so on, perhaps 5 times before the coherence were lost totally. The distance from the first bright area to the first dark are was approx. the coherence length divided by 1.5 (I think caused by the reduced speed of light in the fiber). So i think the modes were in phase first, then the gets out of phase, come in phase again and so on.
We normally use only the first area to make hologramms. So it is more complicated, then "long tube = short cohrence length", but as a rule of thumb (is this an english expression?):
perhaps something like this is true, Laserpower 0.5 - 2 mW: 2m - 50 cm, 5-15 mW: 35 - 20 cm 15 - 45 mw: 20 - 12 cm, > 45 mW ~ 10 cm (no etalon).
kind regards,
Marcus
P.S. Because this is the FOR SALE AREA and not DISCUSS SALES I apologize and say: This 17 mW System is perfect for starting making hologramms and the price is fair!
I have logged in the first time after my initial posting and just see all this messages about coherence length - I don't want to start a "bad" discussion about phils lasers, please believe me! Sorry for that phil.
I start my work 25 years ago with a 2 mW HeNe and this device has approx. 60 cm usable cohrence length. I need more power and used many laser in the next years between 5 - 25 mW and yes more power is better, Phil, you are right. I always measure the coherence length of my lasers, for very long tubes it mostly drops to 12-17 cm, but this is still very usable with precise length adjustment of the different beams.
Long time ago I have mode an experiment with the coherence length of hene's, I put some laser energy with a lens in a fiber, wrap it around a stick and made a hologramm of this. The fiber losses light (because of the tight circles) so it "glows" illuminated by laser light from inside. I was surprised about the resulting hologramm: The image of the fiber was bright first, then gets dark, get bright again and so on, perhaps 5 times before the coherence were lost totally. The distance from the first bright area to the first dark are was approx. the coherence length divided by 1.5 (I think caused by the reduced speed of light in the fiber). So i think the modes were in phase first, then the gets out of phase, come in phase again and so on.
We normally use only the first area to make hologramms. So it is more complicated, then "long tube = short cohrence length", but as a rule of thumb (is this an english expression?):
perhaps something like this is true, Laserpower 0.5 - 2 mW: 2m - 50 cm, 5-15 mW: 35 - 20 cm 15 - 45 mw: 20 - 12 cm, > 45 mW ~ 10 cm (no etalon).
kind regards,
Marcus
P.S. Because this is the FOR SALE AREA and not DISCUSS SALES I apologize and say: This 17 mW System is perfect for starting making hologramms and the price is fair!
Long Red Lasers
Thanks for your comments. The 45 mW 10 cm is low I think unless there are non TEM 00 modes contaminating the beam. The Physics and math say coherence length is C divided by bandwidth and C divided by 1.5 GHz is 20 cm. Real lasers can have less than 100% pure TEM 00 beams so the actual coherence length may be less depending on the tube bore diameter and mirror radius. I welcome these discussions and I did learn alot from this one. Best! Phil 
Now...who wants to actually buy a nice laser? Hey I have a "short and hot" Melles Griot polarized head doing 11-12 mW...who wants that one for $300? The tube inside is about 40 cm long maximum.
Now...who wants to actually buy a nice laser? Hey I have a "short and hot" Melles Griot polarized head doing 11-12 mW...who wants that one for $300? The tube inside is about 40 cm long maximum.
Long Red Lasers
So it has ben some time since the many discussions of the long red lasers. The coherence length is limited to 15-20 cm with no etalon in the cavity but if you mind the path length difference high power HeNe's work well. Who wants one? 
Phil and Sam
Phil and SamLong Red Lasers
Sam and I still have many high power HeNe lasers for holography. We have 25" long polarized heads outputting 18-20 mW with lab power supplies starting around $500. We laso have 1 meter class lasers outputing over 35 mW. Send me a message if interested1 Phil
Long Red Lasers
I have several 25" long JDS 1145P and MG 925 polarized heads and matching lab supplies available. I have one up on e Bay now for $500 but for people here how about $450 with free shipping? 18-20 mW, TEM 00, stable, 15 cm coherence length (or slightly longer). Send me a PM...or call me (813) 974-2378
Long Red Lasers
So who wants a high powered HeNe laser? Phil
PhilLong Red Lasers
Phil said:
http://nlutie.com/ewesly/PreambleResearch.html
You just might be surprised!
Or how about 38 cm or so? I guess it's beating a dead horse, but check out some of my latest researches:I have several 25" long JDS 1145P and MG 925 ... 15 cm coherence length (or slightly longer).
http://nlutie.com/ewesly/PreambleResearch.html
You just might be surprised!
"We're the flowers in the dustbin" Sex Pistols
Long Red Lasers
Interesting test Ed. I'm going to disagree with you though, about statement of the coherence length you showed. I'd have stated the coherence length of the 25mW He-Ne you tested to be about 20cm, and the 5mW laser to be about 24cm. That's +/-10cm and +/- 12cm respectively. I understand why you stated it as you did and this has often confused me. I may reproduce your test to give me an excuse to think about it more. 