A method for producing electromagnetic radiation using a laser driven plasma accelerator, the method comprising: firing a first laser pulse and generating a plasma region, said first laser pulse penetrating at least partially into said plasma region to create a plasma density wake in said plasma region; and providing a group of charged particles in the plasma region arranged so as to be accelerated in the plasma density wake of the first laser pulse, said method comprises: reflecting the first laser pulse after said first laser pulse has at least partially penetrated into said plasma region, to give a reflected laser pulse travelling in opposite direction to the group of charged particles; wherein reflecting the first laser pulse comprises generating a plasma mirror by the interaction of a rising edge of the first laser pulse with an obstacle, wherein the plasma mirror is a dense plasma having a higher density than the plasma region to be able to reflect back the first laser pulse while the plasma region can be penetrated by the first laser pulse; arranging said reflected laser pulse to interact with said group of charged particles so as to generate an electromagnetic radiation by obtaining a spatial and temporal overlap between said reflected laser pulse and said group of charged particles, so that said charged particles travelling in the electromagnetic field of the reflected laser pulse, oscillate and emit synchrotron-like radiation; and deviating the group of charged particles after the generation of said electromagnetic radiation by providing a magnet in the path of the charged particles, the magnet being able to deflect the group of charged particles out of the path of the electromagnetic radiation thereby allowing for a separation of electromagnetic radiation from charged particles. firing a first laser pulse and generating a plasma region, said first laser pulse penetrating at least partially into said plasma region to create a plasma density wake in said plasma region; and providing a group of charged particles in the plasma region arranged so as to be accelerated in the plasma density wake of the first laser pulse, said method comprises: reflecting the first laser pulse after said first laser pulse has at least partially penetrated into said plasma region, to give a reflected laser pulse travelling in opposite direction to the group of charged particles; wherein reflecting the first laser pulse comprises generating a plasma mirror by the interaction of a rising edge of the first laser pulse with an obstacle, wherein the plasma mirror is a dense plasma having a higher density than the plasma region to be able to reflect back the first laser pulse while the plasma region can be penetrated by the first laser pulse; arranging said reflected laser pulse to interact with said group of charged particles so as to generate an electromagnetic radiation by obtaining a spatial and temporal overlap between said reflected laser pulse and said group of charged particles, so that said charged particles travelling in the electromagnetic field of the reflected laser pulse, oscillate and emit synchrotron-like radiation; and deviating the group of charged particles after the generation of said electromagnetic radiation by providing a magnet in the path of the charged particles, the magnet being able to deflect the group of charged particles out of the path of the electromagnetic radiation thereby allowing for a separation of electromagnetic radiation from charged particles.