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
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