In indirect-drive implosion experiments, cross-beam energy transfer (CBET) leads to energy exchange between the inner and outer laser cones, affecting irradiation symmetry. Therefore, quantitative assessment of the CBET transfer rate is of great importance. To address this, a method is proposed to calibrate the CBET transfer rate using multiple shots of stimulated Raman scattering (SRS) or stimulated Brillouin scattering (SBS) spectra and backscatter fractions measured by the FABS system in tuning experiments.

This method assumes that the background plasma conditions vary only slightly across different shots and that both CBET and laser–plasma instabilities (LPI) remain in the linear regime under the experimental conditions. In this linear regime, the CBET theoretical model provides the relationship between the transfer rate and laser power, while the Tang formula describes the response of the backscatter fraction to laser intensity.

By coupling these two relationships, the CBET transfer rate can be inferred from the experimentally measured SRS or SBS backscatter fractions. Furthermore, incorporating time-resolved spectral information enables the establishment of a time-dependent calibration of the CBET transfer rate. This approach relies solely on FABS diagnostic data from tuning experiments, requiring no additional probe beams or dedicated decomposition experiments. It is non-perturbative, straightforward to implement, and offers a direct, practical pathway for evaluating the CBET transfer rate.
 

laser plasma instabilities,Cross-Beam Energy Transfer,Stimulated Raman scattering (SRS)