qspec.inverse_doppler  (  f_atom ,  f_lab ,  alpha ,  mode = 'raise-raise' ,  return_mask = False  )[source]

The velocity $$\begin{aligned}v &= \frac{c}{s}\left[\cos(\alpha) \pm (f_\mathrm{atom}/f_\mathrm{lab})\sqrt{s - 1}\right]\\[2ex] s &= (f_\mathrm{atom}/f_\mathrm{lab})^2 + \cos(\alpha)^2\end{aligned}.$$ For angles $-\pi/2 < \alpha < \pi/2$, there can be two solutions. Depending on the combination of f_atom, f_lab and alpha, the situation may be physically impossible. Specify mode to choose the desired behavior.

Parameters:

f_atomarray_like

The frequency of light $f_\mathrm{atom}$ in the atom's rest frame (arb. units).

f_labarray_like

The frequency of light $f_\mathrm{lab}$ in the laboratory frame ([f_atom]).

alphaarray_like

The angle $\alpha$ between the velocity- and the light-vector in the laboratory frame (rad).

modestr

The mode how to handle nan values and ambiguous velocities. Available options are:

• "raise-raise": Raise an error if there are nan values or if the velocity is ambiguous.
• "raise-small": Raise an error if there are nan values and return the smaller velocity.
• "raise-large": Raise an error if there are nan values and return the larger velocity.
• "isnan-raise": Ignore nan values and raise an error if the velocity is ambiguous.
• "isnan-small": Ignore nan values and return the smaller velocity.
• "isnan-large": Ignore nan values and return the larger velocity.

return_maskbool

Whether the mask where the velocity is ambiguous is returned as a second argument.

Returns:

vndarray | tuple[ndarray, ndarray]

The velocity $v$ required to shift f_lab to f_atom. Optionally returns the mask where the velocity is ambiguous (m/s).

Raises:

ValueError

mode must be "raise-raise", "raise-small", "raise-large", "isnan-raise", "isnan-small", or "isnan-large". For additionally raised errors, see the description of the mode parameter.