Manipulating the polarization state of an intense laser beam in a plasma using a less intense auxiliary laser.

Manipulating the polarization of intense laser beams in plasmas was recently proposed [1] and subsequently achieved in proof-of-principle laboratory experiments [2,3] that demonstrated the feasibility of plasma-based photonics devices such as plasma-Pockels cells or polarizers. However, both the theory and experiments were carried out in the linear regime of polarization mixing, whereby the ``pump'' beam that was used to introduce birefringence in the plasma was much more intense than the ``probe'' beam whose polarization was being manipulated. The absence of a means of surpassing the linear regime is the major hurdle that has to date prevented the practical applications of these concepts. In this presentation, we propose a novel solution to this fundamental problem. Our method enables the practical application of plasma-based photonic devices in a regime where the intensity of the probe beam significantly exceeds that of the pump. This is achieved by taking advantage of a particular geometrical arrangement that preserves the polarization state of the pump while allowing the polarization of the probe to be manipulated arbitrarily. We present a non-linear, two-dimensional analytical solution for this interaction geometry, and discuss the implications of this non-linear regime for the plasma-polarizer and plasma-Pockels cell concepts. [1] P. Michel et al., PRL 113, 205001 (2014). [2] D. Turnbull et al., PRL 116, 205001 (2016). [3] D. Turnbull et al., PRL 118, 015001 (2017).