iData_Sqw2D: dynamic_range: crop the S(|q|,w) to the available dynamic range
for given incident neutron energy.
The dynamic range is defined from the momentum and energy conservation laws:
Ef = Ei - w is positive
cos(theta) = (Ki.^2 + Kf.^2 - q.^2) ./ (2*Ki.*Kf) is within [-1:1]
The incident neutron energy can be computed using:
Ei = 2.0721*Ki^2 = 81.8042/lambda^2 with Ki in [Angs-1] and lambda in [Angs]
conventions:
omega = Ei-Ef = energy lost by the neutron
omega > 0, neutron looses energy, can not be higher than p.ei (Stokes)
omega < 0, neutron gains energy, anti-Stokes
The scattering angle phi can be restricted to match a detection area
with the syntax:
sqw_Ei=dynamic_range(s, Ei, [angles])
The syntax:
[sqw_Ei, sphiw] = dynamic_range(s,...)
also returns the S(phi,w) data set, which shows the detected signal vs scattering
angle and energy transfer.
Input arguments can be given in order, or with name-value pairs, or as a
structure with named fields. In addition to Ei, one can specify 'lambda' or 'Ki'
e.g.:
sqw_Ei=dynamic_range(s, 'lambda', 2.36);
sqw_Ei=dynamic_range(s, 'Ki', 2.665);
syntax:
sqw_Ei =dynamic_range(s, Ei)
[sqw_Ei,sphiw]=dynamic_range(s, Ei)
[sqw_Ei,sphiw]=dynamic_range(s, Ei, [min_angle max_angle])
[sqw_Ei,sphiw]=dynamic_range(s, 'Ei', Ei, 'angles', [min_angle max_angle])
[sqw_Ei,sphiw]=dynamic_range(s, 'lambda', lambda)
input:
s: Sqw data set, e.g. 2D data set with w as 1st axis (rows, meV), q as 2nd axis (Angs-1).
Ei: incoming neutron energy [meV]
angles: scattering detection range in [deg] as a vector. Min and Max values are used.
'lambda','Ki': additional named arguments to specify the incident energy
output:
sqw_Ei: S(q,w) cropped to dynamic range for incident energy Ei.
sphiw: S(phi,w) angular dynamic structure factor for incident energy Ei.
Example: s=iData_Sqw2D('SQW_coh_lGe.nc'); dynamic_range(s, 14.8, [-20 135])
See also: iData_Sqw2D/Bosify, iData_Sqw2D/deBosify, iData_Sqw2D/symmetrize, iData_Sqw2D/scattering_cross_section
(c) E.Farhi, ILL. License: EUPL.