polarization ( h )

Calculate the polarization of the beam from a image file header or a hardware connection.

Polarisation by Bragg reflection is 100% at 90 degrees 2 theta, since the component in the direction of the diffraction is completely blocked.

For an unpolarized beam that is polarized by a horizontal-plane graphite crystal ("perpendicular") the following holds in the ideal case:

I-hor-out = I-hor-in                   = I0
I-ver-out = I-ver-in * sin^2(2*theta)  = I0*cos^2(2*theta)

here "theta" is the diffraction angle on the monochromator.

For the denzo polarization parameter this means:

I-ver-out - I-hor-out   I0 * (cos^2(2theta)-1)    -sin^2(2theta)
p=  --------------------- = ---------------------- = ---------------
I-ver-out + I-hor-out   I0 * (cos^2(2theta)+1)   1+cos^2(2theta)

Theta=4.72/6.08/13.28 for agka/moka/cuka (according to Dirk Parlevliet). i.e. sin(theta)=0.1490*lambda, 2d=1/0.1490, d=3.355704 According to Web-Elements for C, c=6.711 Angstrom, or d(002)=3.355

so p=-0.0137 for AgKa, p=-0.0227 for MoKa, and p=-0.1111 for CuKa.

For a "parallel" monochromator, the sign is opposite.