A down telescope can help.
Or image the beam waist into the crystal then collimate it.
Beam==== ()---AO---()===== scanners = down telescope.
where () = a AR coated 50 mm FL lens as the "sweet spot" in the crystal is often smaller then the window. Put the two 50 mm lenses roughly 100 mm apart. Use a lens at least 15 mm in diameter so you avoid abberation. Or mech engs 140/75, or a cavity change operation, either will work.
140/75 will get you a larger range of beam diameters.
When I want to beat that 70% number, I have found it useful to have the AO on a mount that can tip and tilt as well as do height and bragg angle. Also don't overdrive the crystal. Use just as much RF as you need to get peak power, and then just a tiny amount more. Most drivers have a adjustment for that. The sweet spot is often closer to the transducer on the side of the crystal then in the center.
Steve
Last edited by mixedgas; 10-31-2009 at 12:29.
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