Low-frequency on-demand targeting strategy for high-repetition-rate LPP-EUV platforms

During the debugging and alignment phases of high-repetition-rate laser-produced plasma (LPP) extreme ultraviolet (EUV) platforms, continuous high-frequency targeting (e.g., 30 kHz) generates massive amounts of target debris, leading to the rapid contamination of expensive optical components. However, constrained by the physical mechanisms of continuously pumped MOPA lasers, directly reducing the operating frequency to mitigate debris induces severe amplified spontaneous emission (ASE) effects, risking fiber damage. To address this fundamental conflict, this paper proposes a low-frequency on-demand targeting strategy tailored for high-repetition-rate LPP-EUV platforms. The core of this strategy lies in the combination of an intentional misalignment logic and a buffer pulse compensation mechanism. By introducing a 15 μs feedforward misalignment delay, non-target laser pulses are shifted in the time domain to precisely pass through the vacuum gaps between falling targets. This maintains the high-frequency steady state of the laser while achieving physical misses. To overcome the transient energy degradation caused by the sudden transition from the misaligned state back to the targeting state, buffer pulses are pre-injected to reconstruct the population inversion within the gain fiber, ensuring a 100% energy recovery for the target pulse. High-speed shadowgraphy experiments demonstrate that the macroscopic kinematic recoil morphology of the targets perfectly corroborates the microscopic step-like energy recovery process. By strictly ensuring the hardware safety of high-power lasers, this strategy successfully enables high-quality low-frequency (e.g., 1 Hz) on-demand targeting on a high-repetition-rate platform, providing a versatile solution for the clean debugging of LPP-EUV light sources.