High-energy photon generation from self-organized plasma cavities in field-enhanced laser-preplasma interactions

The interaction of an ultraintense Nd:glass laser pulse with a near-critical plasma self-organizes into a highly efficient <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mi>γ</a:mi> </a:math> -ray source. Three-dimensional particle-in-cell simulations demonstrate that relativistic self-focusing, aided by a self-generated electron cavity, enhances the laser intensity by more than an order of magnitude, driving the system into the radiation-reaction-dominated regime, i.e., one where the electrons lose a substantial amount of their energy as hard radiation. Peak photon emission occurs near 0.5 times the relativistic critical density, with a <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mi>γ</b:mi> </b:math> -photon yield exceeding <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mn>20</c:mn> <c:mo>%</c:mo> </c:mrow> </c:math> of the laser energy. Compared to Ti:Sa lasers of the same power, the longer duration of Nd:glass laser pulses leads to an order of magnitude increase in <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mi>γ</d:mi> </d:math> -photon number in the extreme conversion efficiency regime, making them particularly well suited for photonuclear physics applications. These findings point to a robust and scalable mechanism for compact, ultrabright <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mi>γ</e:mi> </e:math> -ray generation in the multipetawatt regime.