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/*******************************************************************************
*
* McStas, neutron ray-tracing package
* Copyright 1997-2002, All rights reserved
* Risoe National Laboratory, Roskilde, Denmark
* Institut Laue Langevin, Grenoble, France
*
* Component: Pi_2_rotator
*
* %IDENTIFICATION
* Written by: Erik Knudsen (erkn@fysik.dtu.dk)
* Date: 8/4-2008
* Origin: Risoe
*
* Ideal π/2-rotator
*
* %Description
* Simple, idelized, component that turns the polarization exactly π/2 around the specified vector
* vector (rx,ry,rx).
* The geometry of the component is realized as a box, where the the spin is rotated at the z-midpoint.
*
* %PARAMETERS
* xwidth: [m] width of the component
* yheight: [m] height of the component
* zdepth: [m] thickness of the component
* rx: [] x-component of the rotation axis
* ry: [] y-component of the rotation axis
* rz: [] z-component of the rotation axis
*
* %LINKS
*
* %END
****************************************************************************/
DEFINE COMPONENT Pol_pi_2_rotator
SETTING PARAMETERS(xwidth=0.1, yheight=0.1, zdepth=0.01, rx=0,ry=0,rz=1)
SHARE
%{
%}
DECLARE
%{
%}
INITIALIZE
%{
double rr=scalar_prod(rx,ry,rz,rx,ry,rz);
if (rr!=1){
rx=rx/sqrt(rr);
ry=ry/sqrt(rr);
rz=rz/sqrt(rr);
}
%}
TRACE
%{
double t1,t2=0;
double rxs_x,rxs_y,rxs_z,rdots;
/*check to see if we actually hit the component*/
if(!box_intersect(&t1, &t2, x, y, z, vx, vy, vz,xwidth, yheight, zdepth))
{
ABSORB;
}
/*if so, propagate to the halfway point - i.e. the z-center fo the turner*/
PROP_DT((t2-t1)/2.0);
/*now turn spin and set SCATTERED, This to get a reference pt in mcdisplay*/
/*rodrigues' formula gives a rotation of v around u as: v_rot=cos(phi)v + sin(phi) u x v +(1-cos(phi)) (u.v)u*/
rdots=scalar_prod(rx,ry,rz,sx,sy,sz);
vec_prod(rxs_x,rxs_y,rxs_z,rx,ry,rz,sx,sy,sz);
sx=rxs_x+ rdots*rx;
sy=rxs_y+ rdots*ry;
sz=rxs_z+ rdots*rz;
SCATTERED;
%}
MCDISPLAY
%{
box((double) 0.0,(double) 0.0,(double) 0.0,
(double)xwidth,(double)yheight,(double)zdepth,0, 0, 1, 0);
%}
END
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