Method for the optoinjection of exogenous material into a recipient biological cell, wherein the cell comprises a cell membrane which encloses it, the method comprising: (a) placing a biological cell on a planar surface of a substrate, the cell having a basal surface resting on the planar surface of the substrate and an apical surface opposite the basal surface and in contact with a fluid solution which contains exogenous material; (b) transmitting a sub-ns pulsed laser beam through a variable convergence/divergence collimator, the collimator comprising a lens with focal length tunable by means of a variable amplitude control electrical signal; (c) directing the laser beam, having passed through the collimator, through an objective lens configured to focus the laser beam along an optical axis in a focal spot, the optical axis defining an axial direction substantially perpendicular to the planar surface of the substrate, such that the focal spot is positioned along the axial direction; (d) setting the electric control signal to a first amplitude value which defines a first focal length of the lens, corresponding to a first axial position z i of the focal spot along the optical axis, wherein the first amplitude value of the control signal is selected such that the first axial position z i is above the apical surface of the cell at a first axial distance from the planar surface of the substrate, and (e) moving the focal spot towards the cell along the axial direction by continuously varying the electric control signal from the first amplitude value to a second amplitude value, the second amplitude value defining a second focal length corresponding to a second axial position z f of the focal spot, wherein the second amplitude value of the control signal is selected such that the second axial position is positioned inside the cell, at a second axial distance from the planar surface of the substrate, less than the first axial distance, such that the focal spot traverses the membrane of the cell during the descent of the focal spot towards the cell producing a pore in the membrane, which allows the fluid solution containing exogenous material to enter the cell. (a) placing a biological cell on a planar surface of a substrate, the cell having a basal surface resting on the planar surface of the substrate and an apical surface opposite the basal surface and in contact with a fluid solution which contains exogenous material; (b) transmitting a sub-ns pulsed laser beam through a variable convergence/divergence collimator, the collimator comprising a lens with focal length tunable by means of a variable amplitude control electrical signal; (c) directing the laser beam, having passed through the collimator, through an objective lens configured to focus the laser beam along an optical axis in a focal spot, the optical axis defining an axial direction substantially perpendicular to the planar surface of the substrate, such that the focal spot is positioned along the axial direction; (d) setting the electric control signal to a first amplitude value which defines a first focal length of the lens, corresponding to a first axial position z i of the focal spot along the optical axis, wherein the first amplitude value of the control signal is selected such that the first axial position z i is above the apical surface of the cell at a first axial distance from the planar surface of the substrate, and (e) moving the focal spot towards the cell along the axial direction by continuously varying the electric control signal from the first amplitude value to a second amplitude value, the second amplitude value defining a second focal length corresponding to a second axial position z f of the focal spot, wherein the second amplitude value of the control signal is selected such that the second axial position is positioned inside the cell, at a second axial distance from the planar surface of the substrate, less than the first axial distance, such that the focal spot traverses the membrane of the cell during the descent of the focal spot towards the cell producing a pore in the membrane, which allows the fluid solution containing exogenous material to enter the cell.