Talk:Ruby laser

Paragraph removed from article

I removed this:

At first, ruby lasers used natural rubies, making the commercial and scientific use of lasers a very expense venture. However, the application of lasers become more viable with the invention of the synthetic ruby by John M. Burdick in 1949 (U.S. Patent 2488507), working for Linde Air Products, which was at that time a division of Union Carbide.

since it pre-dates the actual invention of the laser. --Bob Mellish 21:29, 22 May 2007 (UTC)

Not to mention that it was totally wrong. Natural rubies contain far too many impurities and defects for laser operation. Even the rubies which Charles Townes used in his masers were synthetic.Zaereth (talk) 00:54, 14 November 2008 (UTC)

Photo is a bit wrong

I don't know if its important enough to mention, but the illustration of the first laser is slightly incorrect. The ruby Maiman used in his first laser was cube shaped. Also, a perfect, (synthetic), ruby will cleave into a perfect square whith exteremly flat ends, eliminating the need for extensive polishing and shaping, which made it the perfect choice for Maiman to use.Zaereth (talk) 01:00, 14 November 2008 (UTC)

You might be right, but do you have a source for this? (I don't have access to Maiman's original paper.) The illustration is copied from one in a reliable source. (Of course reliable sources can be wrong.) A cleaved cube doesn't seem optimum for a ruby laser. The square cross-section prevents uniform pumping from the spiral flash lamp. While the ends can be cleaved very flat, it's not clear to me that they will be parallel enough for the device to work. To make a working laser with flat reflectors, they have to be parallel to very high precision.--Srleffler (talk) 18:16, 29 December 2010 (UTC)

Sorry, that information came from something I once mis-read. The ruby used by Maiman was in fact just like the illustration. My bad there. Ruby will cleave according to the structure of it's crystal matrix, and in fact will cleave with great parallelism, but that at best would only provide a starting point for the precision polishing needed. Also, having reviewed the source which that information came from, and comparing it to other sources, I wouldn't consider it to be very reliable. Better sources indicate that Maiman's use of ruby most likely came from a combination of his extensive research into its fluorescence and the fact that he already had a good supply of it.

From my own OR, some lasers with plane/plane mirrors can operate with the parallelism off by a couple of seconds of arc. However, there seem to be many variables which affect that. If the beam can make several passes before walking off of the path there will usually be some amount of gain. With a high gain medium, like my dye laser, the effect appears to be much greater than it is with my Nd:YAG laser. Cavity length versus diameter is another factor. The farther apart I place the mirrors, the greater the level of parallelism needed. Output power and beam profile, though, greatly improve the closer I get to perfect alignment. The interesting thing, to me, when this happens is that the beam profile is filled interference fringes, indicating exactly how far off the parallelism is.

I was very new to Wikipedia when I wrote that, and have since learned to double-check my facts before opening my mouth. It's amazing how often I can prove myself wrong. :-D Zaereth (talk) 20:34, 29 December 2010 (UTC)

Lede section

This is purely a safety concern, but it may be worthy to note in the lede that if someone intends to "watch carefully" the target area of a high pulsed power laser, they had better have the proper safety glasses on. Even reflected radiation can be harmful, especially at optical wavelengths. Zaereth (talk) 17:10, 28 April 2009 (UTC)

I took it out. While Wikipedia is not a how-to guide and doesn't necessarily have to give safety tips, the comment on how to observe millisecond pulses seemed unnecessary to me. Note that your suggestion wouldn't work: if you're wearing ruby laser safety glasses, you likely aren't going to see the pulses.

Reflected radiation is not necessarily harmful. Diffuse reflections of class III and lower lasers should be safe. Ordinary safety practices would require laser goggles anyway, however. --Srleffler (talk) 03:44, 29 April 2009 (UTC)

Thanks, I think, by not recommending a possibly dangerous situation, that your solution solves the problem just fine. just enought red light from a 30 joule pulse from my Kentek laser gets through my green safety goggles to make it visible, but perhaps they're not dark enough. (A fog machine is much more spectacular anyhow.) I know looking at the spot from my 200 milliwatt green pointer hurts my bare eyes in less than a minute, realizing there are many variables, such as distance from and reflectivity of the target.Zaereth (talk) 17:24, 29 April 2009 (UTC)

Continuous ruby laser

This article now mentions only pulsed ruby lasers, as invented by Maiman in 1960. However the article on 2009 Nobel laureate Willard Boyle says that he developed a continuous ruby laser with Don Nelson in 1962. Should this be mentioned in another section? Are present-day ruby lasers pulsed or CW or both? What are the uses of each? Dirac66 (talk) 20:19, 11 October 2009 (UTC)

I wasn't aware that it was even possible to make a CW ruby laser. Ruby lasers are generally pulsed. --Srleffler (talk) 20:52, 11 October 2009 (UTC)

Thanks. Perhaps the CW version didn't work well enough to be useful, so isn't well-known? Dirac66 (talk) 03:04, 12 October 2009 (UTC)

That's very interesting to me, as I've always read that ruby can't be operated continuously the way that other crystals can, but I can't recall exactly why. I think ruby can be pulsed at a high enough rate to appear as CW, but has a very long fluorescence lifetime, 2 milliseconds I believe. Zaereth (talk) 16:40, 12 October 2009 (UTC)

Part of it is because ruby is a three-level lasing medium, which makes it difficult to get the material above the lasing threshold. There may be more to it though—I don't recall. Other 3-level media can be made to lase CW, although it is not easy.--Srleffler (talk) 02:45, 13 October 2009 (UTC)

Apparently it's true. However, all sources I've seen so far point to Leon Goldman as the inventor, who was a pioneer in laser medicine. These were very low energy and often used for tattoo removal and to induce healing. Sources indicate that due to technical problems, and with the invention of other laser types, medicine moved away from this. (I find this very interesting now, for I noticed years ago that a fresh wound treated with a green laser pointer healed much faster than one that has not.) This year, however, a new diode pumped CW ruby laser has been released onto the market. Zaereth (talk) 18:22, 12 October 2009 (UTC)

OK, I see from Zaereth's answers that CW ruby lasers exist and have been used in the past, so they could be mentioned in the article which now says flatly that "Ruby lasers produce pulses ..." Perhaps this statement needs a qualifier "Most" or "The most useful" at the beginning, plus a mention of the CW work. One could add the reasons given by SRLeffler why pulsed lasers are preferred. Not being a laser expert, I will not attempt to edit this article myself.

As for Goldman as inventor, what the book linked by Zaereth actually says is that Goldman first used the CW ruby laser for medical applications. This is not the same as inventing the CW ruby laser. I searched Wiki for Leon Goldman and found him described as a surgeon, in the article on his daughter - Senator Dianne Feinstein#Early life! It seems more plausible that a physicist (Willard Boyle) would have developed the laser, and that a surgeon (Goldman) then applied it to medicine. Dirac66 (talk) 03:15, 13 October 2009 (UTC)

We shouldn't be speculating here. We should add something about CW lasers, but only what can be supported by reliable sources.--Srleffler (talk) 03:57, 13 October 2009 (UTC)

This policy applies to articles more than to talk pages. Yes, articles should avoid speculation and depend on reliable sources. The "more plausible" comment was not intended to be inserted in the article now, but rather to incite one of you to recheck who invented what. I agree that we do not have a reliable source at this time. Dirac66 (talk) 14:17, 13 October 2009 (UTC)

I notice that the article on Willard Boyle does not say that he developed a continuous-wave ruby laser, but rather that he developed the first "continuously operating" one. These are not necessarily the same thing. A laser that produces a continuing series of pulses is "continuously operating", but not CW.--Srleffler (talk) 03:57, 13 October 2009 (UTC)

Ah, I had wondered about that. Thank you for the clarification. In Boyle's case, the source for "continuously operating" is not highly reliable either - the Wiki article has a "citation needed", though there is a mention in the CBC news report ("Canadian scientist ..."). Again, someone familiar with lasers can look for more reliable sources to check who did what exactly. I am glad to have started a useful discussion; yes, better sources are needed to get it right. Dirac66 (talk) 14:17, 13 October 2009 (UTC)

I will be more than happy to give this some more research, but my time is fairly limited right now. I only took about 10 minutes to check google, and didn't yet thoroughly read the sources, so I may be incorrect on the inventor. But I am definitely curious. Zaereth (talk) 16:14, 13 October 2009 (UTC)

Ok, it took a little more in depth research this time, but I finally came up with some specifics about this laser. It appears, according to Bell Labs, that this laser was actually invented by Boyle. After looking at the other sources, I believe you're correct Dirac, that Goldman was merely a pioneer in its use. This source here provides some specifics about the design and operation, which is far different than any other laser configuration that I've ever seen. See page 74. Hope that helps. Zaereth (talk) 19:56, 13 October 2009 (UTC)

Good work! To summarize, we now appear to have reliable sources for two facts, which I will quote in the words of the sources:

(1) From your latest two sources, Boyle and Nelson "developed the continuously operating ruby laser" in 1961. (2) From the source linked just after your mention of Goldman, "The CW ruby laser was the first laser used for medical applications by Goldman et al. in the early 1960s". I think both facts are of interest for the article.

However given SRLeffler's point that continuously operating is not necessarily CW, it is not yet clear (at least to me) whether Goldman used the same laser that Boyle and Nelson developed, so we should avoid saying so without a reason. (It is not easy to get all the details correct.) Dirac66 (talk) 02:06, 14 October 2009 (UTC)

Agreed, we shouldn't make any assumptions. I have not yet found any specifics on the laser Goldman used, other than it was the first used in medicine. These sources could be added to the Boyle article too, if the source provided there is not reliable enough.Zaereth (talk) 17:46, 14 October 2009 (UTC)

As I suspected, Nelson and Boyle's laser was "continuously operating", but not CW:

"Continuous" in the normal sense means that the laser operates for lengthy periods, for instance, for minutes or hours. It does not necessarily mean that the emission is stable. For the continuously pumped ruby laser of NELSON and BOYLE, for instance, it consisted of a sequence of pulses, the so-called spikes. Such a sequence of pulses may

be explained as relaxation oscillations.

—Gürs, K. (1965). "Solid state lasers with CW emission". Zeitschrift für Angewandte Mathematik und Physik. 16 (1). Birkhäuser Basel: 49–62. doi:10.1007/BF01589043. ISSN 0044-2275. {{cite journal}}: Unknown parameter |month= ignored (help)

Nelson and Boyle's paper:

• Nelson, D. F.; Boyle, W. S. (1962). "A Continuously operating ruby optical maser". Appl. Opt. 1 (S1): 99–101.

Their ruby is tiny: 0.61 mm in diameter by 11.5 mm long. It was cooled with liquid nitrogen. The output is an irregular train of spikes ("relaxation oscillations"). They did not at the time understand why.--Srleffler (talk) 04:00, 14 October 2009 (UTC)

So would that be what is now called quasi-CW? Zaereth (talk) 17:46, 14 October 2009 (UTC)

I'm trying to figure out how to incorporate this information in a paragraph or two, but don't want to confuse "continuous" with "continuous wave." I've found many sources which refer to "continuous wave ruby," "continuous operating ruby," and a few "quasi-cw ruby." (That last source seemed a bit dubious.) I don't have a hard copy of Koechner's book, and can't access the desired pages from it on google.

One of the books I find to be extremely good when it comes to laser info is Principle's of lasers, by Oratio Svelto, in which he explicitly states on page 37 that, "Ruby laser's can also run cw, transversely pumped by a high-pressure mercury lamp, or longitudinally pumped by an argon-ion laser." According to the book, and confirmed in Koechner's book on page 2, relaxation oscillations are normal even in pulsed ruby, unless the system is q-switched so that the population inversion can reach high values before lasing begins.

So it's obvious that one source uses the term cw ruby, but not quasi-cw. I don't know if Koechner's Solid state laser engineering has any more info on it. I'm not exactly sure if quasi-cw is the correct term for ruby, as it seems that it is more like a pure three-level medium than what is described as quasi three-level. Honestly, I'm not too clear on the what the difference between cw and quasi-cw in terms of output, although there is a clear difference in input. I'm tempted to simply call it continuously operating and leave it at that ... perhaps also giving a brief explanation of the relaxation oscillation effect. Does anyone have any ideas on how to word this? Zaereth (talk) 01:58, 9 June 2010 (UTC)

A CW laser produces continuous output while it is operating; the output may have relaxation oscillations or other noise, but does not drop to zero. Every CW laser has relaxation oscillations when it is first turned on. Ideally, these don't cause lasing to cease, and the amplitude of the relaxation oscillations rapidly decays until the laser is operating with constant output, exactly at threshold. A quasi-CW laser is continuously pumped, but does not produce continuous output. Instead it produces a continuous train of pulses, with the intensity dropping essentially to zero between pulses.

Since Svelto says the lasers can operate CW, you can say that and cite his book to back it up. --Srleffler (talk) 04:51, 9 June 2010 (UTC)

Thanks for clearing that up for me! The continuous "train of pulses" definitely sounds like ruby's output. Even pulsed ruby will deliver a train of pulses, within the profile of one large pulse, essentially dropping to zero between them. I'll mull this over for a few more days, check a few more sources, and try to add something about it next week. Again, thanks for your assistance. :-D Zaereth (talk) 16:39, 9 June 2010 (UTC)

I'm glad to see that my question on Boyle's role has been answered today, and also that CW and pulsed have now been straightened out. Thanks. Dirac66 (talk) 01:01, 17 June 2010 (UTC)

You're welcome. I'm glad that I could help. Zaereth (talk) 17:43, 18 June 2010 (UTC)

2010 demo of Maiman's original laser

I think that the section added today about the 2010 demonstration of Maiman's original laser would be better placed in the article on Maiman. Dirac66 (talk) 18:43, 22 May 2010 (UTC)

I think this article could use a history section, that discusses Maiman's work. The new material added today could be included in that section.--Srleffler (talk) 20:17, 22 May 2010 (UTC)

I agree. This article could definitely use some expanding. The history is fascinating, and I read up on quite a bit of it, during a bit of research I did for the section above this one. Besides Maiman, being the first to build a working unit, I think the contributions to the field by Townes, Schawlow, and Gould should not be overlooked. I'll work on expanding this article when time permits. Zaereth (talk) 17:18, 24 May 2010 (UTC)

Well, yes, a history section is certainly a good idea, and the 2010 demonstration could be its last paragraph. One source for the history is this site which is linked from the article on Theodore Maiman. The page The race to build a laser describes Maiman's work in the paragraph Hughes Laboratories. If I understand correctly, Maiman's essential contribution was to use a pulsed energy source when Schawlow etc. were unsuccessfully trying continuous sources. Dirac66 (talk) 19:46, 24 May 2010 (UTC)

As I recall, there was considerable debate over whether ruby, which worked so well in masers, would even work at all as a laser medium, and Schalow was very much convinced that it wouldn't. Gould, on the other hand, came up with the pulsed idea first, (as I recall), and after Maiman's laser was dwmonstrated, there was a huge battle over the patent rights. I believe Gould won the patent for pulsed lasers, but I'll have to go back and read it again. The sources I have are The history of the laser By Mario Bertolotti and How the laser happened: adventures of a scientist By Charles H. Townes, which I believe are availabe on Google Books. Nearly everyone was surprised by the peak powers produced. Zaereth (talk) 20:12, 24 May 2010 (UTC)

Note that Wikipedia does cover the general context of laser history at Laser#History. This article needs to concentrate on the specific history of the ruby laser and Maiman, which get all of two sentences in the other article. Dirac66 (talk) 20:22, 24 May 2010 (UTC)

Agreed. I'm all for relevance and organization. Zaereth (talk) 20:32, 24 May 2010 (UTC)

pink ruby vs red ruby

This article currently claims that someone "stated that pink ruby, having a lowest energy-state that was too close to the ground-state, would require too much pumping energy for laser operation, suggesting red ruby as a possible alternative."

This raises several questions that the article does not adequately address.

• Was that person approximately correct that pink ruby requires a lot of pumping energy, and Theodore Maiman brute-forced the problem by supplying lots of energy? Or did it turn out that pink ruby actually required less energy to lase than that person expected?
• Is there a significant difference in "lowest energy-state" between "pink ruby" and "red ruby"?
• Compared to building a laser with a "pink ruby", would a "red ruby" work better, about the same, worse, or not at all?

--68.0.124.33 (talk) 15:23, 23 July 2010 (UTC)

Ruby lasers are still made with pink ruby. I don't know how it compares to red ruby. Pink ruby requires enormous amounts of pumping energy compared to better laser media such as Nd:YAG. You make a ruby laser by pumping the gain medium very hard, such that you deplete the ground state of the medium. "Brute force" is a good description. --Srleffler (talk) 17:07, 23 July 2010 (UTC)

These are some complex questions, which I may nat be able to completely answer without some research. In particular, I'm not sure why pink ruby seems to be used by far more than red. I would guess that a higher concentration of dopant in red ruby would give some better conversion efficiency, but then again, since ruby absorbs some of its lasing light, the higher concentration of dopant may increase this absorption beyond a usable point. (User:Srleffler seems to know quite a bit about these aspects of lasers, so perhaps he (she?) could answer this.)

To answer some of your other questions; yes, ruby does require a huge amount of intensity to bring it to threshold. Ruby is considered a three-level laser, but it actually has four energy-state levels. The lowest energy state is so close to the ground level that they are simply considered to be one level. What this means is that the energy drops from level two back to level one (decays) so quickly that it is very difficult to get any energy out of these lower levels (depopulate) and into the higher levels where lasing can occur (population inversion). Maiman realized that pumping with a huge amount of energy was not enough, but also that the energy had to be delivered had to be concentrated into a very smalll amount of time. Maiman felt that doing this could depopulate the ground state by at least 50%, which was just enough for an inversion.

Charles Townes is credited with coming up with the idea for the laser. His brother-in-law, Arthur Schawlow, helped him solve the problem of parasitic mode reflections by suggesting an open resonator. They were the top scientists in the field at that time, so everyone interested in lasers listened to them very carefully. According to Townes, they were the type of scientists that wanted to work everything out on paper first, so they would be 100% sure it would work before building it. At first they thought that red ruby might be worth further study, but quickly abandoned ruby altogether and began examining other materials. Most everyone agreed with these two (who wouldn't) and stopped looking into ruby, except Maiman. Maiman was more of a "hands-on" scientist --an experimentalist-- who more or less went ahead with his gut instinct in the face of opposition. After purchasing three different flashtubes, though, he measured their output, and chose the smallest one because the intensity level (power) was high enough to achieve an inversion.

I don't know if red ruby is better or worse, but most lasers I've seen use pink ruby. I know this does not fully answer you question, but don't have time to fully research the difference right now. I hope this heps though. Zaereth (talk) 17:40, 23 July 2010 (UTC)

What is the object below the ruby rod in the first image?

Diagram of the first ruby laser.

The image at the top of this page shows a small, apparently glass, tube running parallel to the ruby rod. It is between the lower part of the rod and the surrounding flash tube. It appears to have an electrical wire running back to the contacts on the right.

This object does not appear in the actual model shown later, nor in any of the other images. It is not described in the text or any of the image captions here or the commons.

Anyone know what this is? I suspect it is the capacitor shown in some diagrams, but I'm not certain. Maury Markowitz (talk) 14:33, 8 October 2023 (UTC)

It would have to be the trigger wire, and whatever surrounding it is probably just for insulation to keep the high-voltage trigger pulse from shorting out against the aluminum body. For more, see: flashtube. Zaereth (talk) 16:13, 8 October 2023 (UTC)

It's certainly not the capacitor. Modern flashtubes don't require an external trigger, but perhaps Maiman's did. --Srleffler (talk) 20:28, 8 October 2023 (UTC)

I'm sure his probably did, because his was before series triggering or simmer-voltage triggering was even invented. There wasn't much scientific study of flashtubes before Maiman, and these other triggering techniques were developed afterwards specifically for lasers, some of them by Schawlow. There's no other reason to have three wires. Zaereth (talk) 20:51, 8 October 2023 (UTC)

Yeah it's definitely the trigger wire. You can find a schematic with it labeled here. You can also see it in the picture to the right. Rather crude construction in my opinion, looks like it was just insulated with wax. Zaereth (talk) 22:09, 10 October 2023 (UTC)

So the black cylinder on the right that the wire connected to is not a capacitor? Anyone know what it is? Maury Markowitz (talk) 12:33, 14 October 2023 (UTC)

The yellow block would have to be the capacitor. The black cylinder would be the trigger transformer. Of course, this drawing was by the US Government in 1997, as Maiman's original laser had all the electronics separate, but those are the two main things needed to operate a flashtube. Maiman's laser was much smaller than it looks in the pics. It was only about 4 inches long, and maybe 2 inches in diameter. It could fit in the palm of your hand. It wasn't until the advent of semiconductors in the 1970s that the electronics became small enough to fit inside such small units. My guess is that he would probably have been using paper capacitors similar this, which is about 3 times the size of his laser head. There are many other differences too, for example, his laser did not have separate mirrors. Maiman used wet-deposition of silver-nitrate to apply coatings of silver directly to the ends of his rod. But it is a close approximation. Zaereth (talk) 14:03, 14 October 2023 (UTC)

Ok, last question: in this case the trigger wire runs near the tube only on one side, how did this result in the entire tube ionizing? Maury Markowitz (talk) 18:48, 1 November 2023 (UTC)

It can definitely work that way, although it typically requires a higher trigger voltage than if the wire, called the "reference plane", follows the entire length of the lamp. In a helical tube, that's not always practical though. The gas in the lamp ionizes due to the rising electrostatic field created by the trigger pulse, which simply knocks loose the electrons from some of the atoms. This causes the gas to glow faintly as most of those ions recombine with their electrons almost immediately. However, some of them will start forming spark streamers from one or both electrodes, and if the streamers connect, the lamp will discharge. For example, most of the flashtubes shown on my user page were triggered by simply using a stun gun held very near the glass in just one point. In most instances, using 150,000 volts, this was plenty, without the use of a reference plane at all. However, it wasn't as reliable as having a reference plane, and sometimes it didn't work. Having a longer plane like Maiman used helps bring that field closer to the electrodes which in turn makes the triggering more reliable. Zaereth (talk) 19:16, 1 November 2023 (UTC)

Got it, thanks! If you're willing, perhaps you might add a one-line mention of the tube and its purpose in the article? Maury Markowitz (talk) 18:46, 2 November 2023 (UTC)

Possibly, but I don't know where. This is all pretty basic flashtube operation, but nothing that's specific to ruby lasers, or lasers in general. The flashtube article already describes this in enough detail, I think. Maiman just purchased a GE flashtube that was originally meant for photographic use, most likely, and I'd be willing to bet he got his power supply from them as well. Then he simply modified his laser to fit it. But its the same way nearly all photographic flashtubes and strobe lights work, and that level of detail is likely best suited to the flashtube article. The big problem is that none of the sources seemed particularly interested in how the flashtube itself worked. The focus is always on the laser operation and usually ignores the flashtube operation. That was 20 year-old technology by the time Maiman built his laser, so I would want to avoid adding a lot of OR to this article unless we can find it in sources. Plus, an encyclopedia is not a how-to manual but a quick reference guide.

The best way, I think, is to simply modify the image by adding some arrows that point to the various parts, so we can label them in the caption, for example, A- flashtube, B - Ruby rod, C - Reflector cavity, D - trigger wire, etc... How does that sound. Zaereth (talk) 22:20, 2 November 2023 (UTC)