A couple of questions on solid state lasers

[rp181]

Ok,
I have been reading up on solid state lasers, and have a couple of questions:

1) say yout have a 100W 808nm laser diode. When it goes through a YAG crystal, it is about 20% effeciant, that means output is ~20W 808nm. When its put through a frequency doubler (KTP i think), it becomes visable, how much power is lost in this process?

2)ive seen some diode bars that say for example: ratings: 100W CW and 150W QCW. Why does it have a rated QCW? i thought q switched was in the crystal, not pumping source.

3)I want too try to do thermal blooming (where a dot of light apears in air from ionizing). Since it is one point, would putting it through a crystal be necesarry? or just a focusing lens? How much power would i need on a QCW laser to make thermal blooming happen?

Thanks.

 

[RA_pierce]

Pumping a YAG crystal with a 808nm diode produces 1064nm light.
Pumping KTP with a YAG laser produces 532nm light.
So 808nm --> YAG or Nd:YVO4 = 1064nm --> KTP = 532nm

I'll leave the rest of this to someone who would be able to explain it better than I can...


Edit: I don't think you need visible light to produce the result you want. I think it can be done with IR lasers focused correctly and pulsed at the right frequency.

 

[pseudonomen137]

QCW means quasi-CW. Its accomplished via rapidly pulsing the input power to the diode array as opposed to a true optical pulse method (and yes, they have to be diode arrays/bars which use many diodes side-by-side. 100W cannot be accomplished by a single diode).

To do what you're asking though, the best would be a UV laser, but perhaps a cheap pulsed laser would do the trick. In any case, its gunna cost some notable cash!

 

[rp181]

why would a UV laser be better?

 

[ArRaY]

I´am just guessing, but i think it is because UV has a shorter wavelength and therefore carrys more energy.
And UV gets more absorbed by the air than higher wavelengths...

 

[GooeyGus]

I would look into the SSY-1 laser head on ebay. Its a yag/flashlamp assembly with optics and everything. It would probably be able to do what you're looking for when focused correctly. They're pretty potent

 

[keeperx]

http://www.freepatentsonline.com/4809291.html

 

[likewhat]

The easiest way to do what you want, air breakdown, is with avalanche ionization. There are other ways to do it but they are more expensive. Basically if you have a powerful laser pulse that is at least several nanoseconds long it will wiggle some free electrons with the extremely high electric field at the laser focus. These electrons will hit atoms with enough energy to ionize them and so on in that manner until a little ball of plasma is formed and then your pulse ends. This is usually accomplished with a Qswitched YAG fundemental (1064 nm) laser pulse that is a few nanoseconds long and maybe and intensity of around may 10^10 W*cm^-2.

Because this works by just grabbing free electrons and wiggling them the wavelength is unimportant, only the electric field is important, so you need the laser to be focused to a small spot and UV or whatever doesnt really help you.

There are other ionization mechanisms that become important if you get to higher intensities/field strengths. Multiphoton ionization and tunneling ionization becomes important around 10^12 - 10 ^14 W*cm^-2. This is where having a shorter wavelength is useful. If your wavelength is short enough (soft x-ray lasers) then they ionize basically anything neutral that they run into and you need a vacuum to propagate the beam.

 

[rp181]

Having it UV does kind of make sense, more energy in a small area.
Yesterday, i saw TI:Saphire lasers and regerative amplification, <10 femtoseconds and 5 mJ is 50 gigawatts according to wiki. I kind of get the method of streching the pulse, amplfying it, and compressing it back, does anyone know a page with more information on this?

 

[likewhat]

That is called chirped pulse amplification or CPA you can just google it to find whatever you need.