Focusing microwaves to form plasma 'cavitations' in air...

[Sataure]

Hello,

 

I remembering watching a video from SIGGRAPH 2006 of this Japaneses research firm using IR lasers to form "holograms" in the air by making small bubbles of plasma in the air which produce light visible to the human eye for a split second, acting much like a pixel. The plasma bubbles were produced by focusing the infrared light from the laser to a point at some distance in the air.

 

I've asked someone who has also done this and they had stated that an energy density of 200mJ per 10ns can create this effect.

 

I don't have the money for a Nd:YAG laser to try this myself, but I was wondering if other forms of electromagnetic radiation can create these plasma balls.

 

I know microwave ovens are easy to come by and many have a lot of power available.

 

Would it be possible to focus the microwave radiation out of a magnetron using a parabolic metallic reflector to a point some distance away and create a plasma ball in the air, much like using a laser?

 

Would microwaves have sufficient energy densities available (for instance is it possible to pulse magnetrons fast enough to get 200mJ of energy within 10 nanoseconds?)

 

Thanks!

[Rocket Man]

iirc, you can't focus microwaves using parabolas in the size of the microwave chamber, the wave length is too big.

you'd need a decent sized dish, metres across would do, then of course you have teh problem of the size of your focal point. you need power density, not just power.

 

a standard microwave can put out about 700W.

200mJ in 10ns is 200 million watts. (that's why it's a pulsed laser with an incredibly fine focus)

 

you can sustain a ball of plasma in a microwave with a piece of aluminium and a glass/pyrex fish bowl but i'm assuming you want something a little more refined

[swansont]

iirc, you can't focus microwaves using parabolas in the size of the microwave chamber, the wave length is too big.

you'd need a decent sized dish, metres across would do, then of course you have teh problem of the size of your focal point. you need power density, not just power.

 

a standard microwave can put out about 700W.

200mJ in 10ns is 200 million watts. (that's why it's a pulsed laser with an incredibly fine focus)

 

you can sustain a ball of plasma in a microwave with a piece of aluminium and a glass/pyrex fish bowl but i'm assuming you want something a little more refined

 

Comparing power isn't the right thing to do. You may have 200 million watts, but it's still 200 mJ of energy. You don't need 200 MW to run the system.

 

You could conceivably make a power buildup cavity (i.e. a resonant chamber) with the microwaves and get very large power densities inside. Doing it in free space with a travelling wave will require a pulse time that is several periods and spatially several wavelengths. 10 ns might be possible, but 3 Ghz is 10 cm. Not a small spot.

[Sataure]

I see. I guess this effect, if wishing to use minimal resources, is strictly bound to near light spectrum and beyond.

 

Thanks for the help.

[THX-1138]

And regardless of the device creating the effect, it's not likely to be the sort of 'hologram' you can walk through (e.g., the operative in Serenity). At least not and retain perfect health..