Nonstationary polarization optical forces, considering the influence of dispersion and diffraction

TL;DR

The paper investigates nonstationary longitudinal polarization forces on neutral particles caused by the diffraction and dispersion of ultrashort laser pulses in air. It develops an exact analytical solution to the linear $3D+1$ paraxial equation for a Gaussian pulse, yielding explicit expressions for the pulse amplitude $A(x,y,\xi,t)$, its intensity $|A|^2$, the longitudinal force density $\vec{F}$, and the trapping potential $U$, showing that the force is negative and front-to-center attractive. The analysis highlights the roles of diffraction length $z_{dif}$ and dispersion length $z_{dis}$, including the case $z_{dis}=z_{dif}$ where intensity decays by a known factor at one length, illustrating how pulse evolution shapes trapping. The results, valid in the linear regime where nonlinear effects are negligible, point to potential applications in neutral particle laser accelerators and laser-driven fusion contexts, by providing a rigorous framework for predicting nonstationary optical forces in pulsed propagation.

Abstract

In the present work, the dynamic properties of an attractive longitudinal optical force and the applied potential, due to diffraction and dispersion of ultrashort laser pulses, propagating in air at distances of several diffraction and dispersion lengths, are presented. The results are based on an analytical solution of the linear 3D+1 paraxial amplitude equation and its application to the evolution in time of the longitudinal optical force. The current research provides valuable guidance for the development and creation of neutral particle laser accelerators with potential applications in the field of laser driven nuclear fusion.

Figures (2)

• Figure 1: (a) Trapping potential of initial Gaussian pulse for $t=0$, (b) Optical force of initial Gaussian pulse for $t=0$.
• Figure 2: (a) Trapping potential of laser pulse at $z_{dis}=z_{dif}$, (b) Optical force of laser pulse at $z_{dis}=z_{dif}$.