##
VOIGT

The
VOIGT function returns the intensity of an atomic absorption line profile (also known as a VOIGT profile) based on the Voigt damping parameter *
a*
and the frequency offset *
u,*
in units of the
Doppler width. The result is always floating-point and has the same structure as the arguments. Note that *
a*
and *
u*
should not both be vectors.

The returned line profile *
f*
(*
a*
,*
u*
) is defined as:

where *
H*
is the classical Voigt function:

The Doppler width *
D*
*
v*
_{
D}
(assuming no turbulence), is defined as:

where *
n*
_{
0}
is the line center frequency. The dimensionless frequency offset *
u*
and the damping parameter *
a*
are determined by:

Here, *
G*
is the transition rate:

where *
g*
is the spontaneous decay rate, and *
n*
_{
col}
is the atomic collision rate. See *
Radiative Processes in Astrophysics*
by G. B. Rybicki and A. P. Lightman (1979) p 291 for more information. The algorithm is from Armstrong, *
JQSRT 7*
, 85. (1967).

###
Calling Sequence

Result = VOIGT(*
A, U*
)

###
Arguments

####
A

The Voigt damping*
*
parameter.

####
U

The dimensionless frequency offset in Doppler widths.