A magnetron IS a microwave laser.  Study the physics.  

How do i dírect the waves like the waves are directed in a optical laser, where the light is reflected between two mirrors, and then send out in one monocrome direction?
I know about horns, but how do i do it in a way like the optical system?

For what purpose?

There's a big difference between producing coherent radiated microwave energy and a coherent microwave "beam."

The former can be accomplished, the latter is not practical.  The diffraction limit of a 6ft aperture at 2.4 GHz is about 10 degrees.

TTFN

You can't focus Microwaves in a small size like a laser. You can focus it, but the wavelength is so much larger, your energy is focused proportionally in a much larger area. Hence take the spot size of a laser beam and multiply that size by the ratio of frequencies (light/microwave) and that's the spot size of microwaves you'd expect.

I've focused 2.5 ghz microwave oven energy into a 0.75" spot to heat a piece of chicken/cancerous tumor.  
kch

What you want is called a gyrotron. The high frequency of operation ~100GHz allows focusing of a microwave beam to a spot near the diffraction limit which is about the wavelength.

Higgler, you have said about three times that you focussed microwaves in this forum. Where is the work or anything like it documented? I wish to do similar things with 2.54. I also can't afford $300K for a gyrotron, but need to experiment.

This conversation is going all over the place.  First you are talking about lasers, then focusing, then low cost.  Tell us EXACTLY what you are trying to do.

ProfK

What we did was;
Standard small Microwave oven with rf power feed on the side (not the top), removed its'door, cheated the interlocks, added a waveguide to coax adapter (as an antenna to capture the rf energy), used a coax cable inside the oven from the waveguide to coax adapter and connected it to the N-f feedthru on a new door (we had a shop make a new aluminum door to protect us and add the N-f feedthru), we added a water filled tupperware inside to place the coax. to waveguide transition onto (plus it minimizes arcing). A xoax cable connected to the N-f on the the door went to a notch antenna feed 12" diameter elliptical reflector antenna. We only used about 50-100 watts of output power to demonstrate cooking the chicken.

kch

Higgler, if your goal is to treat things like a surface cancer, it seems like there would be a lot of power lost in reflection from the antenna to air and air to skin.  Skin/flesh is probably a pretty high dielectric constant.  I would look at some sort of flexible metal-coated dielectric waveguide where you can hold the open end of the waveguide right on top of the tumor.  That way the energy in the dielectric waveguide goes right into the high dielectric flesh without so much of a reflection.

Thanks higgler and biff44. Sorry to steal thread.