Fully coherent, wake and ASE-suppressed 15 μj, 120 fs amplified high order harmonic pulse demonstrated with 1D time-dependant Bloch-Maxwell code

Seeding plasma-based soft-x-ray lasers (PBSXR) with high order harmonics (HOH) is a promising way to obtain fully coherent, short (hundreds of femtoseconds), tens of microJoules pulses. Nevertheless, up to date only 1 μJ, 1 ps pulses have been demonstrated seeding plasmas created from gas targets1 and solid targets.2 As the amplification process couples plasma hydrodynamics, atomic processes and the propagation of electromagnetic fields, a careful optimization of seed and amplifier properties is essential to reach multi-microJoule, hundreds of fs regime. Recent papers3-5 showed that short and wide (up to 1 mm) plasmas present an optimal gain zone and up to 20 μJ could be extracted when seeding. Nevertheless, the temporal duration and profile of the output beam is still not optimal. Simulations show that the HOH is weakly amplified whereas most of the energy is within a long (several picoseconds) wake induced by the HOH.6, 7 In addition to this, these simulation pointed out the presence of deleterious Amplified Spontaneous Emission (ASE). In order to obtain intense pulses useful for practical applications is crucial to reduce the duration to hundreds of fs and obtain ASE-suppressed, structure-free (ideally only an amplified HOH) pulses. Using the 1D Bloch-Maxwell code DeepOne8 we will show that fully coherent, wake and ASE-suppressed, 15 μJ, 120 fs pulse can be obtained when optimizing at the same time both the seed and the plasma conditions.