Blues?

[Daedal]

Ok... this is a very newbie question, but it;s been bugging me...

I know Greenies use frequency doubling with KTP/ND:YVO4 from 808nm. I also know that blue lasers use some kind of frequency doubling, but what exactly is the optic part of it all? I know for a fact that LBO is the preferred frequency doubling medium, I also know that KTP works but is far inefficient!

Some explanation and information would be much appreciated. As in the pump diode, efficiency and such.

Also, what is the same details for the yellow lasers?

Thanx;
DDL

 

[pseudonomen137]

Well, all start off with 808nm pumps. Dunno about general efficiency ranges, but in order from most to least efficienct you have green, blue, yellow.

Yellow and blue rely on other lines of Nd:YAG besides the regular 1064nm used for greenies. Without much knowledge on the specfics myself, I'll just drop soem basic info and keywords that you can use to research the rest on your own  

Blue DPSS is fundamentally similar to green DPSS in concept, but instead of using the 1064nm line of Nd:YAG, the cavity mirrors are coated so gain takes place at the 946nm line which is far less inefficient. As you were mentioning, from there any number of different NLOs (non-linear optics) can be used for the generating the second harmonic of 946nm - 473nm.

Yellow DPSS uses a cavity that promotes both the 1064nm and 1342nm lines of Nd:YAG, and these are pumped into KTP for sum-frequency generation.

So there you have some of the big fancy words, go look the rest up yourself ya lazy bum! jkjk

PS: Nd:YVO4 is used in these MCA hybrid crystals for our small portable greenies, but the big-boy greenies often use Nd:YAG, so you can see that across all of these lasers, 808nm pumps and Nd:YAG get pretty important!

 

[Daedal]

Thank you very much pseudonomen137. That was a great explanation, yet terse. In regards to the ND crystal, I messed up that part... But isn't KTP more effecient that both Nd crystals?

Either way... I found a very nice explanation of the Blue laser operation written up by Buffo over at the PL

http://www.photonlexicon.com/forums/showthread.php?t=2603

I did fond that yellow lasers are cheaper than blues in some places, and they are supposed to be more visible... makes me wanna get one.

Thanx again;
DDL

 

[pseudonomen137]

Per mw yellow are brighter. Don't confuse yellow DPSS with Red+green=yellow color mixing though. Prices on really weak yellow pens are cheaper than blue, but in general yellow is much more expensive than blue. If you're interested in buying either, send me a PM

As to the Nd crystals, those are used to up 808nm to 1064nm in the case of Nd:YVO4, or to take 808nm to 1064nm, 1342nm, 946nm, and others in the case of Nd:YAG (Nd:YVO4 is generally more efficient, but has worse thermal properties and so Nd:YAG is often used instead when you get into the watt range greenies).

KTP on the other hand is used for SHG (second harmonic generation) from the 1064nm or 946nm wavelengths, taking them to 532nm or 473nm, respectively.

To make a greenie, you need both a Nd:YVO4 or Nd:YAG AND KTP, not one or the other.

 

[pseudonomen137]

Just read buffos explanation, and just for the heck of it, here's a clarification on the "optical coatings" he's talking about:

With these crystals, they are capable of generating different wavelengths, however in order to actually laser, you need gain. Gain is the amplification you get by passing some of the light output back through the crystal with a mirror. When 808nm pumps Nd:YAG, to get it to lase at 1064nm, cavity mirrors are used that are passive to 808nm so it enters the cavity, but partially reflective to 1064nm so that some 1064nm gets reflected back in, causing the "stimulated emission of radiation" we all love.

For high efficiency, you want to have the right amount of gain for the 1064nm line while having the mirrors supress gain on the other lines so that pump energy is not wasted on unused lines. So those are the goals of the coatings basically: Let/keep 808nm in, reflect some of the lasing line back into the cavity and let some free in the form of laser radiation, and supress all other lines.

In the case of blue, its the same but the coatings are tailored for the 946nm line instead.

 

[Daedal]

Very well explained... I now honestly understand that it is cheaper to buy a premade blue, and probably impossible to make my own!

Although... think of how cool it would be to put the unfiltered output of the Nd crystal into a KTP crystal and watch different colors come out, or a mixture come out...

I assume that is possible of course


--DDL