  Manipulation of intense pulse propagation in gas-filled capillaries is
desirable for various high-field applications. Tuning the parameters of the
driving laser pulse and the working gas is the conventional approach, and it
provides limited capability of control. Here we demonstrate through numerical
simulations a practical scheme to control the propagation of intense pulses. A
weak ultraviolet pulse is launched into a capillary with a negative delay with
respect to a main infrared pulse. The pulses begin to temporally overlap due to
dispersion. As the main pulse self-compresses, the control pulse is strongly
red-shifted due to cross-phase modulation. The frequency shifts of the two
pulses mitigate pulse walk-off and allow an efficient coupling, substantially
extending the effective interaction length. This interesting phenomenon may
benefit applications such as high-order harmonic generation.
