  Photon subtraction from squeezed states is a powerful scheme to create good
approximation of so-called Schr\"odinger cat states. However, conventional
continuous-wave-based methods actually involve some impurity in squeezing of
localized wavepackets, even in the ideal case of no optical losses. Here we
theoretically discuss this impurity, by introducing mode-match of squeezing.
Furthermore, here we propose a method to remove this impurity by filtering the
photon-subtraction field. Our method in principle enables creation of pure
photon-subtracted squeezed states, which was not possible with conventional
methods.
