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Recent advances in self-frequency-doubling crystals

steve001

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In post #24 are you saying the Yb:YAB crystal's lasing at 1016nm, 1090nm and 1125nm? I took the quote as those being the pump wavelengths and the lasing lines were 510nm and 530nm. It sure seems that those are pump wavelengths to me and much too high to be a candidate for the 575nm crystal or the 565nm crystal.
That's why I stated it with a caveat. But this second article uses a 976 nm diode "Self frequency doubling ytterbium laser" to see why Curtis and me think this is some type of ytterbium laser.
 

LSRFAQ

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When it takes three months to a full year some times to run a Czochralski batch, no one will be in a hurry to grow these, as the only use is medical and low end medical analysis, and lifetimes have NOT been promising with the very high energy densities the Chinese are using. Other then for eye surgery and some dermatology applications, 532 is "Good Enough" and everything else medical that needs that wavelength use OPSL anyways.

We know it is SFD.

I had a nice chat with a employee of a major crystal grower at a recent conference, he concurs with my analysis of the material, word for word. His employer, decided that wasting machine time on a very low sales volume, high risk crystal was not worth their time. It is a Yb based material, although not one of the ones mentioned above.

The chief scientist at said company was well aware of SFD, but could not justify tying up the best machines in the western world on a freaky batch with no sales possibilities.

Steve



Steve
 
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steve001

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When it takes three months to a full year some times to run a Czochralski batch, no one will be in a hurry to grow these, as the only use is medical and low end medical analysis, and lifetimes have NOT been promising with the very high energy densities the Chinese are using. Other then for eye surgery and some dermatology applications, 532 is "Good Enough" and everything else medical that needs that wavelength use OPSL anyways.

We know it is SFD.

I had a nice chat with a employee of a major crystal grower at a recent conference, he concurs with my analysis of the material, word for word. His employer, decided that wasting machine time on a very low sales volume, high risk crystal was not worth their time. It is a Yb based material, although not one of the ones mentioned above.

The chief scientist at said company was well aware of SFD, but could not justify tying up the best machines in the western world on a freaky batch with no sales possibilities.

Steve



Steve
Perhaps some Chinese company with offer dpss yellow lasers if the layout is straight forward like the 532 nm dpss are. I suspect they would be expensive, but I remember well when a 5mW green pointer cost $450 in the late 90's. Before that I've heard that cost as much as $2000.

It seems from my reading the schematics of such lasers require convoluted paths to function unlike the green dpss lasers. Do you know if constructing such a laser is practical.
 
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LSRFAQ

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1121 nm has 1/20th the gain of 1064. 1121 in ND:YAG s really one line out of three 112x nanometer lines very close together, so you need a etalon intracavity to select the most powerful line on a big 561. unless you like frequency hopping. So a 20 mW 561 yellow needs the same pump and frame as a half watt 532 plus an extra precision optic or two.. So no one will make a microchip yellow, it cannot handle the heat density. Lasing 1121 needs active stabilization of the KTP and diode temps, and a means of suppressing 1064 and 1080 which will try to lase no matter what. Which means optics with a 32 layer coating instead of a 11 layer coating. With the exception of the 1064+1389 sum frequency orange, none of these other lines are easy to make in a small form factor. 20 mW of the sum frequency mixed orange needs 4-6x the pump power of a 532 of the same time. All these components have low yields compared to a component that are in high production rates.

It all comes down to economics. Medical yellow at 577 needs a minimum of 5 watts to ensure 3 watts at the patient delivery without being serviced for two years. That means active cooling and a big OPSL that needs a 35-40 amp pump diode. Yellow for confocal microscopy needs around 100 mW to deliver enough power (0-5 mW) to the sample, stabilized to .05% in amplitude or better thus removing that use from the cheap category. I keep my eyes on the yellow confocal laser at work, if it ever fails my employer is out 15,000$ plus 3200 for the service call to install a new one. It has a an AOM on it to level the output power precisely.

The optimum medical laser wavelengths were found with dye lasers years ago. The dye laser was cheap compared to the vastly improved patient treatment that resulted, and no one wants to do new five year clinical trials. So the OPSL or whatever gets tuned to the classical 577 nanometers and a FDA 401K form that says the new laser is substantially equal to the old dye laser performance is submitted. Short practical trial and certification, and your done, without a new clinical trial. Hence no need for "NEW" wavelengths in anything but surgical or dental.

Video projection if they want yellow for the fourth color, well, they use a very large VECSEL array, so its a floodlight.

There is very little demand in the low cost sector for a tiny yellow. Most lab applications need an incredibly stable yellow, and so far the SFD has proven anything but stable. Since there has been no easy yellow, very few applications for yellow are commercially viable. It is a chicken or egg first situation. If a cheap yellow appeared with tem00, and perfect amplitude stabilization, an application might be found. When a medical laser costs 300,000$ due to liability, clinical trials, and support infrastructure, in the US, paying Coherent 25,000$ for a eye surgery or derm grade medical OEM module is while not cheap, chickenfeed compared to the other costs.

It all comes down to economics. Most of the laser development papers linked on this forum are a development exercise for a doctorial degree to teach some one graduate level optics. Maybe (my estimate) 1 in 1000 get looked at for a commercial application. Since only 1 in 7 small businesses get past two years of existence, a new startup making a new laser and marketing it has about the same odds of getting to play in professional baseball for a minor league team.

We still buy and use HENEs at work for a reason. Not to pick on CNI, but as the largest, most professional maker of Chinese Lasers, I have only ever seen one mass produced US instrument (not laser show) with their lasers inside in 15 years. I am seeing Chinese high power CO2 making it into the US.

OPSL needs a dedicated MOCVD production line and is locked up through patents world wide. Only a few groups are sophisticated enough to even try, let alone be funded to compete in that arena. All those years of Ion Laser sales profits went to developing Ion's replacement, among other things. So the old workhorse visible laser sales wisely paid the for the development of new things.

:-(
Steve
 
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steve001

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1121 nm has 1/20th the gain of 1064. 1121 in ND:YAG s really one line out of three 112x nanometer lines very close together, so you need a etalon intracavity to select the most powerful line on a big 561. unless you like frequency hopping. So a 20 mW 561 yellow needs the same pump and frame as a half watt 532 plus an extra precision optic or two.. So no one will make a microchip yellow, it cannot handle the heat density. Lasing 1121 needs active stabilization of the KTP and diode temps, and a means of suppressing 1064 and 1080 which will try to lase no matter what. Which means optics with a 32 layer coating instead of a 11 layer coating. With the exception of the 1064+1389 sum frequency orange, none of these other lines are easy to make in a small form factor. 20 mW of the sum frequency mixed orange needs 4-6x the pump power of a 532 of the same time. All these components have low yields compared to a component that are in high production rates.

It all comes down to economics. Medical yellow at 577 needs a minimum of 5 watts to ensure 3 watts at the patient delivery without being serviced for two years. That means active cooling and a big OPSL that needs a 35-40 amp pump diode. Yellow for confocal microscopy needs around 100 mW to deliver enough power (0-5 mW) to the sample, stabilized to .05% in amplitude or better thus removing that use from the cheap category. I keep my eyes on the yellow confocal laser at work, if it ever fails my employer is out 15,000$ plus 3200 for the service call to install a new one. It has a an AOM on it to level the output power precisely.

Video projection if they want yellow for the fourth color, well, they use a very large VECSEL array, so its a floodlight.

There is very little demand in the low cost sector for a tiny yellow. Most lab applications need an incredibly stable yellow, and so far the SFD has proven anything but stable. Since there has been no easy yellow, very few applications for yellow are commercially viable. It is a chicken or egg first situation. When a medical laser costs 300,000$ due to liability, clinical trials, and support infrastructure, in the US, paying Coherent 25,000$ for a eye surgery or derm grade medical OEM module is while not cheap, chickenfeed compared to the other costs.

It all comes down to economics.

Steve
Apparently yellow in a portable form doesn't warrant economic consideration by large companies. However, as noted by Paul it appears there is a market for yellow low output lasers. And like Singlemode Laser I'll be optimistic.

P.S. I'd be happy with one lasing 555-561 nm in the mean time.
 
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paul1598419

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That is amazing as my 574nm yellow is incredibly stable in power and wavelength. Even after my heat sinking the output transistor and driver IC and adding a fan to the driver to remove the heat from pumping it more than twice as hard when I first received it. Now, I know they are having issues with getting stable crystals for new ones, but the one they sent me is just great. I can find no issues with it at all.
 
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It is great to read two so different options from LSRFAQ and Paul. Both are well supported. Since I am a realistic optimist I stick with Paul and hope for a new batch of these lasers soon. LSRFAQ points about the small market, research only and s.o. are usually also my arguments but since the chinese already demonstrated and sold these crystals I hope they did their share of market analysis (fingers cross ;)

Singlemode



Ps: Here an example of a research paper where the rare wavelength diodes hit the market (or should I say the lp forum) and then someone had the idea to apply them in atomic physics ;)

https://arxiv.org/abs/1810.11434
 

LSRFAQ

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In the US that crystal run would cost 35,000-50,000$. So even converted to Riminbi, That is a NOT a cheap growth shot.
I've got a dying one, my friend has a dying one and one better engineered one that is almost stable. Mine is developing a color center in the crystal. I'll move the crystal some day and realign it. I'm glad you have a stable one, but so far the jury is still out for most of us.

Steve
 
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paul1598419

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Yeah, I am aware of the problems. When I first got mine I thought that it might be a very inexpensive way to get yellow. It seems that only very few of these are very stable and the crystals are hit and miss whether you will get a very good one or one that is bound to fail. I wish that my first impression had panned out, but I cannot complain about the laser I received and now, I am even more grateful that I got this one.
 

WizardG

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Yeah, I am aware of the problems. When I first got mine I thought that it might be a very inexpensive way to get yellow. It seems that only very few of these are very stable and the crystals are hit and miss whether you will get a very good one or one that is bound to fail. I wish that my first impression had panned out, but I cannot complain about the laser I received and now, I am even more grateful that I got this one.
I'll second that sentiment. A few here thought I paid too much as I went through a fourth party seller, but now the price seems very reasonable.......for the unicorn of laser crystals!
 

paul1598419

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If you got a good one too, hang onto it. It looks like it might be quite awhile before these issues with the crystals are resolved.
 

Nexgen

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I have good crystal to. Managed to get peak around 80mw with re-alignment.
 

paul1598419

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Just because you got more power by changing the alignment, it doesn't mean you have a better beam quality. In Walter Koechner's book, "Solid-State Laser Engineering", he explains how TEM values other than optimum often cause the beam power to be greater. Lots of good information about solid state lasers in that book.
 

WizardG

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And so it begins.....My OPT has just decided to go from TEM00 to TEM01. I noticed the beam looked different last night so I threw a lens in front of it and yep, two symmetrical lobes on the wall. Power is now too unstable to measure. About all its good for now is a lumia. 8-(
 

Nexgen

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And so it begins.....My OPT has just decided to go from TEM00 to TEM01. I noticed the beam looked different last night so I threw a lens in front of it and yep, two symmetrical lobes on the wall. Power is now too unstable to measure. About all its good for now is a lumia. 8-(
I was able to go through 5 of these units and none of them were TEM00, I don’t think yours gonna drop in power, do you have LPM to measure the power?

I got this tiny crystal and I see no power drops here. Let’s hope to see some more units in the future.

I guess we have to ask our Chinese guy, as he always replies “I will let you know next week”
 

WizardG

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I was able to go through 5 of these units and none of them were TEM00, I don’t think yours gonna drop in power, do you have LPM to measure the power?

I got this tiny crystal and I see no power drops here. Let’s hope to see some more units in the future.

I guess we have to ask our Chinese guy, as he always replies “I will let you know next week”

Mine started out very nicely TEM00. Now I've got TEM01 with the 'lobes' flickering like mad. I'll need to bring it to work and let the guys in the lab measure it for me but it looks very unstable now. Hopefully development of these crystals will continue.
 




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