Picosecond amplification images the energy transfer between two laser beams
Picosecond amplification images the energy transfer between two laser beams lead image
Energy exchange between overlapping laser beams in plasma, also called Cross Beam Energy Transfer (CBET), is detrimental to inertial confinement fusion experiments, but can be used in plasma photonics. Researchers in France investigated how CBET amplification induces changes of the spatial distribution polarization in the focal spot of a picosecond pulse amplified by a nanosecond pump. Understanding the effect may lead to predictably modifying energy transfers to change a solid target.
Reported in Physics of Plasma, simultaneous camera imaging experimentally reveals the dispersion, previously only simulated, of polarization modifications of the picosecond-pulse hot spots, called speckles, after amplification.
The light scatter from CBET shows the shared polarization component of two beams exchanging energy. CBET can then induce polarization modifications of the picosecond-beam speckles, directly related to their amplification. Analysis of the speckled amplification pattern within the picosecond-beam’s focal spot provides a new result to compare with CBET models. These results provide a better understand of CBET, allowing researchers to moderate and predict energy transfer outcomes by identifying only the polarization modifications made by CBET, and not by the plasma.
After laser formation of a plasma, two interaction beams, a nanosecond beam and a picosecond beam with equal wavelength (λ=526.5 nanometers), were sent into the high-temperature (about 7 million degrees Kelvin) preformed plasma. The incident intensities and target position were varied to gather different mean amplifications of the picosecond beam by CBET. Two cameras captured focal spot images, and amplification of each speckle were detected from intensity peaks in the picosecond beam focal spot.
The results of light spatial distribution analysis are consistent with models of beam amplification after CBET beam interaction and give confirmation to ongoing efforts to better control the energy transfer for multiple intense laser beams in plasma.
Source: “Polarization modification of a spatially randomized picosecond-pulse beam during its amplification by a nanosecond pump,” by C. Neuville, K. Glize, P.-E. Masson-Laborde, P. Loiseau, S. Hüller, A. Debayle, C. Baccou, M. Casanova, C. Labaune, and S. Depierreux, Physics of Plasmas (2017). The article can be accessed at https://doi.org/10.1063/1.4998657 .
