POLAR—Sets polarization of a beam if spin-tracking is enabled

13.80 POLAR—Sets polarization of a beam if spin-tracking is enabled

Sets polarization of a beam if spin-tracking is enabled
Parallel capable? : yes
GPU capable? : no
Back-tracking capable? : no
Spin-tracking capable? : yes


Parameter Name	Units	Type	Default	Description

POLARIZATION		double	0.0	desired polarization

VX		double	0.0	x component of vector for polarization direction

VY		double	0.0	y component of vector for polarization direction

VZ		double	0.0	z component of vector for polarization direction

MODE		STRING	twostate	mode of spin vector generation (twostate, narrowcone, widecone)

ON_PASS	NULL	long	0	If <0, polarization is unchanged; otherwise, pass on which polarization is changed.

GROUP		string	NULL	Optionally used to assign an element to a group, with a user-defined name. Group names will appear in the parameter output file in the column ElementGroup

This element assigns spin vectors to the particles to provide a specified degree of polarization P in a specified direction = ⃗
V ∕V , where ⃗
V = (V X,V Y,V Z). It has no effect if spin_tracking=0 in run_setup.

There are four available modes, controlled by the MODE parameter:

twostate — All spin vectors are along or - , with the two states being randomly assigned so as to approximately produce the specified polarization. For example, for P = 0.85 (85% polarization) 92.5% of the spins vectors are and 7.5% are - .
vonmises-fisher — This is the preferred method when random spin directions are desired. The distribution is a biased gaussian that intersects the unit sphere. The gaussian parameter is chosen so that the desired polarization is achieved. The method and code were adapted from a discussion with ChatGPT.
narrowcone — All spins are oriented in the direction , but with a polar angle θ such that cosθ = P. The azimuthal angle is uniformly distributed over [0,2π).
widecone — All spins are oriented in the direction , but with a randomly-chosen, uniformly-distributed polar angle θ in the range [0,θ₁], with θ₁ chosen so that that ⟨cosθ⟩ = P. The azimuthal angle is uniformly distributed over [0,2π).

POLYSERIES

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