Pulsed "multi mode"?

Simple answers are here! For Theory look in General Holography.
holo_cyware

Pulsed "multi mode"?

Post by holo_cyware »

I am wondering if in pulsed holography (not rubby but the 532 green) some kind of stabilisation for the laser is needed, or for the 20 ns pulse there is no such thing as "multimode"?

In other words, say I get a 1J capable Nd:YAG laser. If I shot it thru a KTP, would the resulted green capable of providing me with a "bread slices free" hologram or not? Is there some extra stabilisation needed?
Ed Wesly

Pulsed "multi mode"?

Post by Ed Wesly »

It all revolves around how single-frequency the beam is before the frequency doubler. An intra-cavity doubler is regarded as the more efficient way to do things.
JohnFP

Pulsed "multi mode"?

Post by JohnFP »

A pulsed laser can have a non gausian profile (muli mode temperally) or muliple lines lasing (multi mode transversly) or non polarized (no brewsters or polarization filters). Pretty much all things that need to be controlled for making a hologram has to be present (or controleed) in the pulsed laser.
Dutchelm05

Pulsed "multi mode"?

Post by Dutchelm05 »

JohnFP wrote:A pulsed laser can have a non gausian profile (muli mode temperally) or muliple lines lasing (multi mode transversly) or non polarized (no brewsters or polarization filters).
Your right on all accounts but KTP should only lase in one polarization (unless it is a brifrigent crystal) if I remember correctly. IMO at 20ns you might have a good chance of it being single mode temporally (no thermal lensing), but I doubt you would be spatailly. We would have to see what your cavity looks like i.e curvature of OC and HR, distances, etc.

You can lase it external cavity but as Ed said it is not as effecient. You would need to be careful of the type of crystal you use since some are more brifrigent than others at high peak energy. Is this q-switched? A 20ns flash lamp pulse at one jolue is pretty amazing.

Good Luck,
JohnFP

Pulsed "multi mode"?

Post by JohnFP »

So Tony, does that mean the KTP is polarization sensitive? That is, you need to orientate the crystal with the polarization of the laser? Or does the crystal act as a polarizer (brewster windows or something)?
Dutchelm05

Pulsed "multi mode"?

Post by Dutchelm05 »

So Tony, does that mean the KTP is polarization sensitive? That is, you need to orientate the crystal with the polarization of the laser? Or does the crystal act as a polarizer (brewster windows or something)?

Well its been a while, but KTP (at least intra-cavity) is preferentially polarized. On one of the sides of the crystal there is nomally an arrow which indicates orientation. If I remember correctly, it's doubling is only using one polarization of the YAG, (which is sometimes why they use a quater wave plate intracavity). You also have to match the phase angle as well, which requires temperature regulation and XYZ tuning.

In some systems I worked on, we used a rotating waveplate and polarizer to attenuate the beam (externally) so the polarization was important.

I don't know if you ever heard of a laser called the Greenlight (you may not be old enough to worry about your prostate :) ) but that is one of the systems I helped developed many years ago. It is a high power KTP (100 watts average)
JohnFP

Pulsed "multi mode"?

Post by JohnFP »

Thanks Tony. I worked for years with pulsed lasers but we never had a need to frequency double them.

Just a few more synaptic connections added. :wink:
Colin Kaminski

Pulsed "multi mode"?

Post by Colin Kaminski »

holo_cyware wrote:I am wondering if in pulsed holography (not rubby but the 532 green) some kind of stabilization for the laser is needed, or for the 20 ns pulse there is no such thing as "multimode"?

In other words, say I get a 1J capable Nd:YAG laser. If I shot it thru a KTP, would the resulted green capable of providing me with a "bread slices free" hologram or not? Is there some extra stabilization needed?
Normally a TEM00 pulsed laser has a first stage that is designed simply to be TEM00. Then the power comes from amplifying stages later on. I made a SSY work in TEM00 and it took adding a pinhole and reducing its power significantly.

To get a Single Longitudinal Mode is not as hard. The only sliced bread pulsed holograms I have seen have been from double pulses.
holo_cyware

Pulsed "multi mode"?

Post by holo_cyware »

That's what I assumed; the pulse duration is simply to short to ruin the hologram. That also may mean that every pulse has a different "pattern" of frequencies, maybe unique, the crystal temperature being the most important factor, hence bread lines for a two-pulse exposure.
Dutchelm05

Pulsed "multi mode"?

Post by Dutchelm05 »

holo cyware,
Any way you can share what kind of system delievers 1 joule at 20ns?
What rod size is that?
Is it q-swtiched?
Just curious.
Thanks,
Tony
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