I would say: No.
And why would you want to ‘force focus on it until the user closes it’?
Let’s say I am your user and I need to calculate some values and place them into your app. The calculator opens, I can do some math, but I cannot enter anything into any application, including yours, because you ‘forced the focus’ on the calc. I need to close it, enter my value, open calc again to do another calculation, close the calc again.
Have fun.
---- Andy
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station.