Simultaneous spatial and temporal focusing for axial scanning.

We show theoretically and experimentally that simultaneous spatial and temporal focusing can scan the temporal focal plane axially by adjusting the group velocity dispersion in the excitation beam path. When the group velocity dispersion is small, the pulse width at the temporal focal plane is transform-limited, and the amount of shift depends linearly upon the dispersion. By adding a meter of large mode area fiber into the system, we demonstrate this axial scanning capability in a fiber delivery configuration. Because a transform-limited pulse width is automatically recovered at the temporal focal plane, simultaneous spatial and temporal focusing negates the need for any dispersion pre-compensation, further facilitating its integration into a fiber delivery system. A highly promising application for simultaneous spatial and temporal focusing is an axial scanning multiphoton fluorescence fiber probe without any moving parts at the distal end and without dispersion pre-compensation.