Development of a Differential Interferometric Technique for Measuring Magnetic Field Profiles in a Plasma Radiation Source

The current distribution in plasma radiation sources is both a yardstick for measuring the coupling efficiency of the generator, and a means of studying the implosion dynamics of the load. Since the current distribution cannot be directly measured, it must be deduced from the magnetic field profile. Magnetic field distributions, based on the Faraday rotation of polarized laser light, are typically determined from intensity measurements of two polarization components. They are therefore susceptible to background emission problems. A differential interferometric technique is proposed to infer the magnetic field form the phase difference between the right and left circularly polarized components of a laser beam traversing a plasma. The phase of the two circular polarizations will be simultaneously recorded using a two reference beam hologram. The two reference beam holographic recording allows heterodyne techniques to be used during reconstruction for enhanced sensitivity. This is two to three orders of magnitude more sensitive than a typical Faraday rotation measurement. A third reference beam will be used to record a no plasma hologram needed to measure the electron density distribution. This technique allows the magnetic field profile to be measured with better sensitivity and less susceptibility to background emission than Faraday rotation techniques. A successful program will provide the PRS community with the first measurement of a magnetic field distribution In a PRS load. This is critical to the design of such devices and the comparison with theory.