Speaker
Description
While laser wakefield accelerators (LWFAs) are promising compact betatron radiation sources, controlling the stability of electron injection and radiation efficiency remains a critical challenge. Temporal pulse shaping through higher-order spectral phase control offers a pathway to manipulate laser-plasma interaction dynamics and optimize betatron radiation generation.
In this study, we systematically investigate the effects of group-delay dispersion (GDD) and third-order dispersion (TOD) on electron acceleration and betatron radiation using a 150 TW Ti:sapphire laser system. The relative spectral phase was precisely scanned using an acousto-optic programmable dispersive filter (AOPDF, Dazzler) around an empirically optimized reference condition corresponding to the minimum pulse duration of 24 fs, which is defined as relative GDD = 0 and TOD = 0. This condition is referred to as the transform-limited (TL) reference pulse in this study. The dispersion was scanned within the ranges of GDD from $-500$ to $+500$ fs$^2$ and TOD from $-5000$ to $+5000$ fs$^3$ while interacting with a gas mixture of He and 1% N$_2$.
The temporal pulse profiles under different spectral-phase conditions were characterized using SPIDER measurements. Our measurements reveal that specific asymmetric temporal pulse profiles significantly alter electron acceleration and betatron radiation characteristics. In particular, at GDD = 0, the hardness indices obtained from Ag/Ti and Mo/Ti filter ratios increased for negative TOD and reached their maximum values at TOD = $-3000$ fs$^3$, indicating an enhancement of the high-energy component of betatron radiation compared with the TL reference pulse. These experimental trends are further supported by particle-in-cell simulations using FBPIC under dispersion conditions matched to the experimental scan range. The simulation results indicated that negative TOD conditions can increase the critical energy and photon yield of betatron radiation by modifying laser pulse evolution in plasma. The enhancement of betatron radiation is associated with laser pulse steepening in plasma and stronger transverse betatron motion of the injected electrons.
These results demonstrate that active higher-order spectral phase control is not merely a tool for pulse compression, but a crucial optimization parameter for improving the efficiency of compact laser-plasma betatron radiation sources.
| Working group | WG1 |
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