Module Polarizing Mirror

# VITESS Module Polarizing Mirror

The module pol_mirror simulates one plane mirror that might have different reflectivity curves for spin-up and spin-down neutrons. The transmitted or the reflected beam can be regarded. The co-ordinate system of the following module has to be set accordingly. Size, position and orientation of the mirror as well as the reflectivity curves for spin-up and spin-down neutrons have to be given. In addition, the spin quantization direction has to be defined.
The orientation of the mirror can only be set in 2 different ways: a) rotation about the y-axis starting from a horizontal orientation (in x-y-plane) b) rotation about the z-axis starting from a vertical orientation (in x-z-plane) Absorption is not considered. If absorption inside a mirror has to be taken into account or an orientation is needed that is not accessible in the way described, the more advanced module sm_ensemble has to be used.
The reflected fraction of the neutrons is calculated according to the formula
prefl= (aup*cos(&theta/2)2+ (adown*sin(&theta/2)2
&theta is the the polar angle relative to the quantization direction. aup = sqrt(Rup) is the square root of the reflectivity of spin-up neutrons and adown = sqrt(Rdown) the square root of the the reflectivity of the spin-down neutrons.
The orientation of the transmitted or reflected beam is given by
&thetaout,trans= 2 atan ( (1-adown) / (1-aup) * tan(&theta/2) )
&thetaout,refl= 2 atan ( adown/ aup* tan(&theta/2) )

### Parameters for module 'pol_mirror'

Parameter Unit | Description | Range or Values | Command Option
up-/down-reflectivity file | input data file containing the reflectivity curve R(Q) for spin-up and for spin-down neutrons resp. (in the same form as it is used for guide module) | - | -U -D
mode | criterion: use of transmitted or reflected beam. | transmission reflection | -T
length [cm] | length of the polarizing mirror (i.e. along beam axis) | >0 | -L
position X, Y, Z, [cm] | x-, y- and z-position of the center of the polarizing mirror (in the input frame) | any | -X -Y -Z
inclination [deg] | rotation angle of the polarizing mirror relative to the beam axis (see text) | [-180°,180] | -V
orientation | choice between vertical and horizontal orientation of the mirror (see text) | 'horizontal', 'vertical' | -O
analysis dir. X, Y, Z | x-, y- and z-component of the quantization direction | any | -a -b -c
output X, Y, Z, [cm] | x-, y- and z-position of the output frame (in the input frame) | any | -x -y -z
horiz. vert. rotation angle [deg] | rotation angle of the output frame relative to the input frame in horizontal and vertical direction | [-180°,180] | -h -v

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Last modified: Tue May 8 17:08:06 MET DST 2001