High preformance DPSS Laser- a New Video

[mixedgas]

A division of the parent company of the company I work for sells some unique crystals. There are only two vendors for the material in the world.

There are other processes for wavelength shifting such as Raman shifting. The materials are expensive, require a really high grade of input light, and are not something Asian vendors can access.

What it is, is well, mum....

I'm sending him parts for a crude yellow this week using a DPSS technique.

It took a lot of work to find the optics to start to support yellow, with doubling 1121, I only have two sets.

Steve

[planters]

What are your plans for obtaining orange without using a 444nm pump source? The only DPSS oranges I know of (604nm and 607nm) uses a 444nm pumped Pr:YLF / Pr:PAYAC (respectively).

The problem as I understand it with Pr3+ is that there is a high absorption of the orange light in the crystal on the order of 1.5%/ pass and so they will heat under moderate pumping. That is why I believe Kvant's 200mw orange is limited in power rather than the available pump power.

As Steve said and I agree with him, I am more interested in the lower gain YAG lines and the raman shifting technique to generate these colors between green and red. Even though they require somewhat more exotic coatings and some unusual crystals the design is essentially the same as in my video.

When you demagnify, as well as reducing spot size, do you reduce intensity or change other beam characteristics?

No you don't. This really straight forward. I discuss this in my spatial filtering video. The two positive lenses that create the focus for the filter can be selected to magnify or de-magnify the beam to best fit a scanner's aperture. The consequence is a trade off of improving divergence as the beam is maximized in size. There is no other down side other than cost, added beam line length and the absorption of the lenses themselves.

Certainly, for any commercial laser where you do not have access to the internal focusing optics there is a chance that these were not optimized or shifted over time. In this case you can use a lens pair to very slightly readjust the focus or if you are going to operate the laser at a known distance then optimize the focal point to that distance. The trade off here is that the divergence beyond this focus or beam waist will worsen more quickly, but until you move the laser the light will never get that far. The result can be a marked improvement in the spot size of the laser for this specific distance.

[Galvonaut]

No you don't. This really straight forward. I discuss this in my spatial filtering video. The two positive lenses that create the focus for the filter can be selected to magnify or de-magnify the beam to best fit a scanner's aperture. The consequence is a trade off of improving divergence as the beam is maximized in size. There is no other down side other than cost, added beam line length and the absorption of the lenses themselves.

Certainly, for any commercial laser where you do not have access to the internal focusing optics there is a chance that these were not optimized or shifted over time. In this case you can use a lens pair to very slightly readjust the focus or if you are going to operate the laser at a known distance then optimize the focal point to that distance. The trade off here is that the divergence beyond this focus or beam waist will worsen more quickly, but until you move the laser the light will never get that far. The result can be a marked improvement in the spot size of the laser for this specific distance.

So ideally, if I were using this method in a dome, would it be best to keep the source in the centre of the dome in order to keep the termination as close to the focal point as possible?

Is this similar to photographic lenses where if the focal point is less than the focal length, you best depth of field is 50% into the field, otherwise it is 75% (IIRC)?

I am finding this a little confusing as I thought coherent light was always 'in focus' or at least focussed @ infinity?

Thanks

Keith

[planters]

Lasers are not "food of the gods" just better tamed light. Your description of running @ the center of the dome is spot on. That would be the best way to get a tight beam and the smallest spot. For the very tightest beam you would want to still focus on the screen, but if the beam was so fat at the laser that you could get a blinding far field spot then the cone shaped beam might not look very bright. As you telescope the beam down in diameter at the laser the far field will expand and the beam becomes more cylindrical. To get specific with typically available projection lasers, not the "Z-fold", a 3-5mm exit beam matches well with 10-20M beam length and focused as tight as possible for the termination distance. Coherent light has nothing to do with the focus, but rather the in -sync amplitude of the photon's wave (I just love when this gets a little quantum). These diodes are so poor as lasers that these waves are already out of step within a mm of the facet.

[Galvonaut]

I'm glad it's only 'a little quantum'! Although I love reading about quantum effects, most of it goes straight over my head!

Is it the non-synchronised amplitude of the photons that causes the unstable speckled beam image that is common with all of the beams I have seen?

Can photon amplitude phase be manipulated using wave plates or polarising filters, or are we stuck with whatever comes out of the aperture?

I hope you don't mind all of these questions? - I'm on a bit of a learning curve and getting well and truly stuck into it!

[planters]

Is it the non-synchronised amplitude of the photons that causes the unstable speckled beam image that is common with all of the beams I have seen?

I don't know if you intended this, but Touche'! It actually is the coherency that IS the cause of this speckled pattern. The process is subtle and in reviewing it I think the link to Wikipedia does it better than I could:

http://en.wikipedia.org/wiki/Speckle_pattern

The reason I believe you still see this even with lasers such as diodes that are operating way beyond their coherency length is that as the narrow but not zero frequency (color) waves continue to propagate, there is some fraction that remain in lock step and others that due to their slightly different frequency, will re-converge in a repeating beat. At some point the coherency becomes so poor, and this is good for television makers, that the speckle disappears.

Can photon amplitude phase be manipulated using wave plates or polarizing filters, or are we stuck with whatever comes out of the aperture?

Oh yes! But I'm going to pass the torch on this one to those here who actually do just that for a living.

I hope you don't mind all of these questions? - I'm on a bit of a learning curve and getting well and truly stuck into it!

Not at all. This is precisely why lasers are so much fun.

[Galvonaut]

Hehe, thanks Planters. Great info

[sugeek]

Planter's I always enjoy the videos thanks for posting this I really enjoyed watching! Also thanks to Steve for his support in your efforts!

-Adam

[The_Doctor]

Lasers are not "food of the gods" just better tamed light.

A useful remark. I noticed that even a small bare 6V tungsten lamp will put out some coherent light. Meaning, the speckle is detectable if you look at the reflection of the lamp on white gloss paint in a dark room, and move carefully and slowly to pick out the way it appears to move with you in same direction, as laser speckle does. It's weak, but very beautiful, it has a kind of mallard feather like separation of colours in it too. Now, either speckle is not solely caused by coherence in the original source, OR even small hot objects thought of as purely spontaneous in emission do include small amounts of coherent light. One of those statements must be true. My money's on the second. Which is interesting, because it implies that natural laser light might be more common than we think, just hard to spot given how much of it isn't coherent or stimulated in the right way.

All that said, if the speckle has more to do with the wavefronts formed by (or preserved during) reflection by rough surfaces, then the implication may be that laser-cavity-like behaviour may exist for light caught in it, regardless of the source of that light. At which point it gets beyond me so I'll leave it there.

[The_Doctor]

These diodes are so poor as lasers that these waves are already out of step within a mm of the facet.

Which diodes? I assumed that they varied a great deal, that some have good coherence length and longitudinal mode, and were used by holographers. One of which specifically seeks them out and publishes test results:
http://redlum.xohp.pagesperso-orange...eanalysis.html

Interesting (though his needs are different from ours, mostly), he despises the Mitsubishi 300 mW diode. But I have found his page useful to gauge single mode diodes for good predictable behaviour. So many things can kill them early, especially when risking reflections off optics and strong drive currents, that his page is a wise study before choosing a single mode diode to experiment with for anything.