Sprecher
Beschreibung
Many applications require an ultrafast laser source with excellent long-term stability. One example is laser plasma acceleration (LPA), where the properties of the drive laser pulse directly determine those of the accelerated electron beam. Therefore, the highest possible laser stability is required for reliable long-term operation of the LPA. In the high-energy drive lasers of LPA, even the low-energy seed plays a role in defining the final pulse and the performance of the accelerator. While optical parametric chirped pulse amplifiers (OPCPA) are an excellent choice for seeding such high-intensity lasers due to their inherent spectral flexibility, excellent temporal contrast and compactness, achieving high stability has traditionally been a challenge in OPCPA. The main reason for this is that the pulse characteristics are intricately coupled, making precise control of these pulses difficult. For example, one amplifier stage can influence subsequent stages, making it often unintuitive to tune an OPCPA system for specific output characteristics, and simple feedback loops that stabilise individual laser properties - such as pulse energy - can interfere and introduce unwanted fluctuations in other properties - such as spectral characteristics.
As an alternative approach, we present results from the optimisation of a multi-stage OPCPA system using evolutionary strategies, and demonstrate centralised feedback control of the laser system that simultaneously stabilises multiple output parameters. Enabled by this approach, the laser exhibits exceptional long-term spectral and energy stability, with <50 pm wavelength stability and <0.2% rms energy jitter over several days of operation.
