Newb question about DPSS

[spark001uk]

OK so be gentle, as although I've been dabbling in lasers for some time now I'm still learning the ins and outs of optics and the complex processes that go on right from the diode, to optics and solid state pumping and the likes.
My question is this - I understand that a common 532nm green DPSS starts with an 808nm diode pumping the Nd, then the resulting 1064nm halving to 532nm through the KTP. So, if you took away the Nd, and fired the 808nm directly through the KTP, would you get 404nm out? Or is it not as simple as that, and why?
Still learning here so any explanation will be gratefully absorbed !

 

[paul1598419]

No. The reason is the wavelength absorption of KTP is 1.06 um. It is necessary to have your wavelength be within 5.6 angstroms of this primary wavelength. Citation: Solid-State Laser Engineering by Walter Koechner, p 500.

 

[spark001uk]

Ah I see. So the ktp is made for the job then. I'm guessing that the fact I haven't seen a 404 dpss means there isn't a suitable material in existence then?

 

[CurtisOliver]

Not exactly made for the job, but crystals are coated to their specified application. What matters is phase matching range. KTP doesn't allow phase matching of 808nm, therefore you will not get 404nm from a KTP based system.
As for there not being a suitable crystal out there for it, there are other options. LBO,BBO and BiBO to name a few.
The problem with direct doubling of semiconductors is they have a larger linewidth. Also when you pump a solid state crystal with semiconductors the output beam quality is independent of the pump beam quality. This is not the case when a semiconductor is directly doubled, so will have worse beam specs. 404nm DPSS's aren't common, as there is no application for them. There are 405nm diodes available that are more efficient and compact. Also the one reason why someone would opt for a DPSS over a diode is beam specs. The diode in this case would have superior beam quality. So there really is no point in 404nm DPSS's unless you are going for more power than currently available in diodes.

https://www.osapublishing.org/oe/abstract.cfm?uri=OE-16-4-2486

 

[spark001uk]

You're right about beam specs, that's the main thing I like about them, nice tight beams. Though my 303 green is doing something strange, after its had a bit of a warm-up the beam starts changing about 1sec after firing, the beam dims and the spot gets a bit wider. From what I can find out this is probably mode shifting?

 

[CurtisOliver]

Tidy and tight is how I like lasers too. As for your 303, it sounds like mode shifting to me.

 

[paul1598419]

It is more frequently called mode hopping. But, these not temperature compensated DPSS lasers often mode hope when the crystals get out of their temperature comfort zone. I do have some thermostatically controlled 532nm lasers and they remain stable for as long as you run them.

 

[spark001uk]

About 10yr ago I had a couple of then very expensive CNI dpss, one of 473nm and one of 593.5nm. I sold them on, which I now regret, wish I'd kept them. The orange one in particular was a very nice shade.

EDIT: I say then very expensive, but a quick look suggests they're now even more expensive if anything!

 

[Benm]

Well yeah, certainly the orange one would be something pretty rare to have, and there is no direct-diode available that produces 593 nm.

On the blue front i don't selling the 473 was a mistake as direct, single mode, diodes of similar color are now available on the market, and probably a lot cheaper per mW than the 473's ever were.

As in doubling 808 nm or light from any diode laser: This will always be troublesome, since you need very monochromatic light for the doubling process. The 1064 nm solid state laser is good enough to achieve this, and you can also have the doubler crystal -in- the 1064 nm lasing cavity, with a mirror on the output side that is very reflective to 1064 nm but transparant to 532 nm, so you keep the 1064 in the cavity due to the mirrors, giving it multiple chances to double in the crystal and then leave the cavity.

I guess this already sounds like a pretty complex setup, but it can be produced very cheaply and most 532 nm pointers work by this principle: the solid state laser and doubler crystal are a single assembly. Downside is that both are temperature sensitive, and their optimal efficiency may be at different temperatures. This is basically why handheld green lasers tend to do things like fluctuate in brightness and even mode hop. In a lab laser each component has thermal control and that gives you a really stable output.

 

[paul1598419]

Yeah, I've got a 473nm DPSS laser and a direct diode laser that measures 477nm. The head on my DPSS one is huge, but only puts out a maximum of 50 mW. My direct diode one is close to 130 mW. Much smaller too.

 

[spark001uk]

What's the DD Sanwu pocket range like, worth the money? I like the look and form factor, not sure what beam specs/lens quality is like etc though?

 

[Singlemode Laser]

As allready pointed out, your doubling crystal temperature needs to match the pumping wavelength, at the pumping light needs to be fairly narrow (~O.1 nm or so) or you will waste a lot of your pumping power. That's the reason why usually solid state lasers (DPSS) with narrow emmision lines are used in compact setups. But if you have more space (and money) you can build narrow pump sources from (1600nm to ~ 400nm) and you can buy crystals for these wavelength range too.

Singlemode

 

[diachi]

What's the DD Sanwu pocket range like, worth the money? I like the look and form factor, not sure what beam specs/lens quality is like etc though?

Build quality is top-notch on the pocket series. I have two, fantastic little lasers.

 

[spark001uk]

Build quality is top-notch on the pocket series. I have two, fantastic little lasers.

Yes I'm considering getting a couple too. I was thinking definitely a 505, I love the look of that colour, and I'm sure it's even better in real life, as is the case most of the time with laser light, the camera rarely does it full justice.