Simultaneous spatial and temporal focusing for axial scanning

Abstract

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.

Temporally focused wide-field two-photon microscopy: Paraxial to vectorial

“…We find that it is more important to maintain the assumption that 0 k k ≠ whereas the diffracted angle can be assumed to be small. This is in contrast to previous literature [2,12]. In this paper, we will present TF2p microscopy using the paraxial and vectorial approaches and compare the validity of both approaches through experiment.…”

“…This being the case, the effect of the OTF is such that the non-DC frequencies attenuate with defocus for the image of a bead whereas the DC term is always present and does not attenuate with defocus for the image of a thin plane. It has been demonstrated [12,13] that the plane can be scanned along the optical axis simply through the introduction of a chirp to the excitation beam. Since paraxial theory indicates dependence upon 2 1 M (see Eq.…”

“…This property has been exploited in temporal focusing to shift the position of the focal plane along the z-axis effectively creating an axial scan through optical means [12,13]. This is done by deliberately up-chirping or down-chirping the beam.…”

“…At present the analysis of TF2p microscopy has been restricted to a pulse that is relatively long [2,12,14,15] in which the spectrum of the pulse is taken to be small such that…”

Three-dimensional random access multiphoton microscopy for functional imaging of neuronal activity

“…In such techniques, scanning different axial planes requires the objective lens to be physically moved with an actuator, such as a stepper motor or a nanopositioner, a process which is temporally limited by the combined inertia of objective lens and actuator. Several methods have been developed to quickly change the focal position, and thus allow for axial scanning, including deformable mirrors 25 , variable focus liquid-filled lenses 26 , and simultaneous spatial and temporal focusing 27,28 . However, none have the ability to simultaneously scan in the lateral dimension, and none have been demonstrated to functionally image parameters of neuronal activity.…”