This is a function of a 2-crystal monochromator. If the Bragg planes of the two crystals are exactly parallel, that's canned being tuned. Let's say you have Si111 crystals. Not only is the 111 allowed, but so are the 333, 444, ... Thus, if you're set for 3keV, you'll also get some at 9keV, 12keV, etc. This is often a Bad Thing, especially when measuring spectra in transmission. Now, the rocking curves for the harmonics are narrower than for the fundamental, meaning that if you tilt one of the crystals a little bit with respect to the other, you'll still pass the fundamental (111) but mostly reject the harmonics. That's what 'detune' means. I hope that's clear. Next installment: "Glitch" :-) mam On 6/21/2012 2:19 PM, Enyuan Hu wrote:
Dear all,
I'm new to the community and I was wondering if I can ask some basic questions here. I heard the beamline scientist mention "tune" and "detune" and I saw in some materials say "detune to get rid of high order harmonics", but what is "harmonics"? and why it's necessary to detune to get rid of high order harmonics? I'd really appreciate it if we can discuss this a little bit. Thanks.
Enyuan
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit