This recent news article discusses a Jewish man who was ordered by a non-Jewish court to pay maintenance to his wife until he grants her a get (Jewish divorce document).
The man claimed in court that if he were to grant a get under the terms of this ruling, the get would in fact be invalid, as it would have been given under compulsion.
The judge rejected this argument. But what do halachic sources say?
If a non-Jewish court imposes payments until a get is given, would that invalidate a subsequently granted get? Under what circumstances is a 'compelled get' valid or invalid? What exactly are the parameters that define a 'compelled get'?
Ideally, I would like as comprehensive an answer as possible, but answers discussing specific scenarios are of course welcome. I would be particularly interested in answers addressing the case described in the linked article, where there does not seem to have been any involvement of a Beit Din (Jewish court) in the process.