Nik's Pr:YLF 640, 607 and 523 nm Laser Project

Hi all, Nik here.

It’s great to see that there are people around which are interested in Pr:Ylf lasers! I think that blue diode pumped rare earth ion lasers (Pr, Dy, Sm, etc.) are really fascinating since they all enable multiple transitions in the visible spectrum whilst being pumped by relatively cheap blue diodes. Even direct yellow transitions exist! I suggest giving this article a read: https://onlinelibrary.wiley.com/doi/epdf/10.1002/lpor.201500290
Of course, for hobbyists, getting our hands on the crystals is the most difficult part… Anyways, if you have any questions, I will give my best to answer them even though I am not an expert in this field…

Greetings from Germany!
Nik

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Hi Nik, thank you so much for joining and posting!

I would love to see a photo of the crystal you used in your project, I know, it’s just a tiny crystal, but am interested, if you have one to share which shows it close up enough.

Do you have any idea why 4lasers.com shows a diagram of a configuration on their web site with two pump diodes at 442 nm and two at 444 nm PBS cube combined? I don’t understand why they would have the diodes at different wavelengths like that if the sweet spot is close to or at 444 nm.

Chris. I’m from Alaska but working in Qatar.

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Welcome Nik.
It’s great to have you here.
Pr:YLF lasers are amazing, and it is only a shame that crystals and optics are not as accessible.
None of us here are experts, however I don’t doubt you have good experience and knowledge on the topic. We are currently investigating the production of a high powered 607nm system. So any help on the matter would be greatly received.

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Hi Niklas & welcome to forum!
Nice to see same minded folks here, I’m currently a bit away from lasers / posting here due my further engineering studies but I’m maintaining forum & looking that system runs smoothly… -No ad’s or tracking on this platform… We’re trying to keep everything UCD (User-centered design) as much as possible. :slight_smile:

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Thank you all so much for the warm welcoming!

Regarding the 442nm diode: The absorption peak of Pr:YLF slightly depends on polarization. I think the original paper by Tanaka et. al says it best:

Tanaka et al : https://doi.org/10.1364/AO.57.005923
The absorption of anisotropic Pr:YLF crystal is polarization dependent, and the absorption peak wavelength locates at ∼444 and ∼442 nm for polarization parallel to the crystal’s c and a axes, respectively. Therefore, we adopted LDs emitting nominally at 444 and 442 nm for better absorption efficiency.

I will go and take a photo of the crystal when I get home this evening. It is 2x2mm and 6mm long. At the power levels I use, active cooling is not necessary.

The thread you referred to is quite long but seems very interesting nonetheless! I’ll give it a read and see if I can contribute :slight_smile:

Cheers! Nik

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No problem Nik. :slight_smile:
Thanks a lot. You just solved an issue to was troubling both me and Chris. So one polarisation is more efficient at one of those wavelengths. Is there a way of determining what polarisation you have coming from the diode to know which one you need to control at 442nm etc? Because we know that having a 1/2 waveplate switches the polarisation to the opposite plane but we don’t know if it is s or p still.

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I think I might have solved this question. So whatever beam is reflected with a PBS appears to be s polarised and transmitted p polarised. Haven’t found a diagram that differs yet. So it appears 444nm is for p, and 442nm for s.

So I have modified the setup like so.

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Nik, thank you for helping with some of those questions, looking forward to the picture you offered. I haven’t purchased a crystal yet, but purchased some 1/2 wave rotators for the project yesterday. I already have some broadband VIS PBS cubes which should work I bought a couple of years ago. Mirrors are something I still need to HR 607-pass 444 and an OC for 607. I will probably buy the cylinder lens pairs from optlasers.

Those mirrors can be ordinary dichroics. As long as they have good specs at those wavelengths then they will work. I have accounted for Opt lasers cylindricals funny enough.

Can you let me know the size of the PBS please? Also any specs for the ones you have?

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The only mirror that is absolutely crucial will be that output coupler. It must be at 607 and not have enough gain for the 640nm line. And we need to get the ROC correct for the cavity we want.

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I prefer optlasers for some things, but you can’t count on their stock being there when they say they have it, must ask. Lasertack is pretty good, for some things I will only buy from him simply because no one else offers them I can find. I sure wish I knew who was making the knife edge assemblies he sells, the assemblies are perfect, wonderful machining.

A member over at PL just posted today he has Pr:YLF crystals and optics in stock: View Profile: Phritzler - Photonlexicon Laser Forum

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Well, like you said there is no rush. But definitely want a plan put together before you proceed with expensive purchases.

I wonder how much he charges for pr ylf?

Phillip. I think this guy might be on LPF too.

I sent a PM for the prices he offered.

Edit: Received an answer, prices look good. I asked him if I can post the prices he is offering me here, sometimes prices offered to hobbyists differ from their regular price and if so, I won’t post here.

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Huh. I actually know Phillip! He’s from Austria, is the CEO of a (smaller) company there. Very nice guy, I got my pump diode from him. His prices are very reasonable indeed.

Here’s the photo of the crystal, as I said its 2x2x6mm. The black block next to it is a TO-92 packaged LM35 temperature sensor. I used a very small amount of thermal glue to fix it in place. Indium foil or something like that is better but at my pump powers crystal overheating was not a problem.

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Very cool. And thanks for the photo. Chris will be happy. Unfortunately I’m about to get some shut eye now. But thanks. I like the idea of a temp sensor.

As for Phillip he does seem like a friendly and helpful guy.

Nik, look what came in the mail here:

OC mirrors on order, maybe will come end of August. Diodes are NUBM44 at 444 nm.

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Initially, I thought the crystal was much more amber, but that was a sticky holding it down to the membrane in the box. Upon casual observance in normal lighting the crystal appears almost colorless but does have a light yellow tint.

Photo flash brings out the yellow tint.

4x4x7 mm crystal.

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Beautiful crystal! I am very much looking forward to seeing it lase :slight_smile:
I have been thinking - on and off - about a building a laserpointer out of my crystal and optics, even though I don’t really need it. Would be an interesting challenge though.

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We’re currently working on that challenge now. It is rather challenging to say the least. A lot of thought has had to go into this project. But we’re making good progress. We’re using wavelength selected NUBM44’s so I am currently trying to get the best focal match for the crystal. I’ve been doing a lot surrounding the optical side. And building stuff has been working on the electronics. And Chris has been ordering and sourcing parts.

We are predominantly working on 607nm.

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