A device for characterizing a high-power laser beam, characterized in that it comprises: - a plate partly delimiting at least a space for the propagation of the laser beam to be characterized, comprising an area of entry of the laser beam to be characterized, an area of exit of a high-energy ion beam and supporting: - a removable target-carrier that is located in a focusing area passed through by a focal axis on which is located an optical focal point of a concentrating mirror and that carries several targets each configured to emit at least protons following a shooting of the laser beam to be characterized, - motorized positioning means adapted to place each target individually on the focal axis of the mirror, - motorized translation means of the target-carrier, substantially parallel to the focal axis of the concentrating mirror in the focusing area, configured to be able to place and immobilize a target at different points on either side of the position of the focal point, - a module for optically determining the position, in the focusing area and along the focal axis, of a front face directed towards the focusing mirror for a target positioned on the focal axis, - an interface module that is connected to the positioning means, to the translation means of the target-carrier and to the module for determining the position of each target and that is adapted to, based on instructions received, place successively the targets, one after each other, on the focal axis at determined points and to measure and transmit the position on the focal axis of each target, - a mirror for concentrating the laser, located downstream from the entry area and configured to focus an incident light beam to an optical focal point located in the focusing area and on a focal axis of the mirror, - a mass spectrograph located downstream from the area of exit of the high-energy ions and that is configured to measure the energy of the emitted protons, - a control unit that is connected to the interface module and to the spectrograph and that is adapted to record, for each shooting on a target, the position of the target along the optical axis and the energy of the protons emitted following the shooting, the characterisation device being characterized in that it comprises a reflecting mirror configured to reflect at least 90 % of the laser beam to be characterized towards the focusing area and to transmit a part at least of an adjustment laser beam, whose source is located at the opposite of the focusing area with respect to the reflecting mirror and whose optical axis is substantially merged with the optical axis of the laser beam to be characterized after reflection on the reflecting mirror. - a plate partly delimiting at least a space for the propagation of the laser beam to be characterized, comprising an area of entry of the laser beam to be characterized, an area of exit of a high-energy ion beam and supporting: - a removable target-carrier that is located in a focusing area passed through by a focal axis on which is located an optical focal point of a concentrating mirror and that carries several targets each configured to emit at least protons following a shooting of the laser beam to be characterized, - motorized positioning means adapted to place each target individually on the focal axis of the mirror, - motorized translation means of the target-carrier, substantially parallel to the focal axis of the concentrating mirror in the focusing area, configured to be able to place and immobilize a target at different points on either side of the position of the focal point, - a module for optically determining the position, in the focusing area and along the focal axis, of a front face directed towards the focusing mirror for a target positioned on the focal axis, - a removable target-carrier that is located in a focusing area passed through by a focal axis on which is located an optical focal point of a concentrating mirror and that carries several targets each configured to emit at least protons following a shooting of the laser beam to be characterized, - motorized positioning means adapted to place each target individually on the focal axis of the mirror, - motorized translation means of the target-carrier, substantially parallel to the focal axis of the concentrating mirror in the focusing area, configured to be able to place and immobilize a target at different points on either side of the position of the focal point, - a module for optically determining the position, in the focusing area and along the focal axis, of a front face directed towards the focusing mirror for a target positioned on the focal axis, - an interface module that is connected to the positioning means, to the translation means of the target-carrier and to the module for determining the position of each target and that is adapted to, based on instructions received, place successively the targets, one after each other, on the focal axis at determined points and to measure and transmit the position on the focal axis of each target, - a mirror for concentrating the laser, located downstream from the entry area and configured to focus an incident light beam to an optical focal point located in the focusing area and on a focal axis of the mirror, - a mass spectrograph located downstream from the area of exit of the high-energy ions and that is configured to measure the energy of the emitted protons, - a control unit that is connected to the interface module and to the spectrograph and that is adapted to record, for each shooting on a target, the position of the target along the optical axis and the energy of the protons emitted following the shooting,