Laser energetics and propagation modelling for the NIF

Abstract

Design, activation, and operation of modern high-energy, fusion-class lasers rely heavily on accurate simulation of laser performance. Setup, equipment protection, and data interpretation of the National Ignition Facility 1 (NIF) at Lawrence Livermore National Laboratory (LLNL) are being controlled by a Laser Performance Operations Model (LPOM) 2 , which, at its core, utilizes a Virtual Beam Line (VBL) simulation code to predict laser energetics, wavefront, near-and far-field beam profiles, and damage risk prior to each shot. This same simulation tool is being used widely to understand such diverse phenomena as regenerative-amplifier saturation, damage inspection system performance, fratricide risk from small-scale flaws in large optics, converter performance, and conjugate image formation.

The shaped pulses control and operation on the SG-III prototype facility

“…The first step is the calculation of 1ω pulse shape required at the frequency convertors [11]. Then the resultant 1ω pulse is used as input for a calculation that accounts for the distortion of the pulse caused by gain saturation in amplifiers [12]. The calculation yields the needed master oscillator pulse.…”

COMBINE*: An integrated opto-mechanical tool for laser performance modeling

“…The numerical optical code COMBINE computes stress induced birefringence with a link to the commercial finite element analysis code ANSYS Workbench. It also interfaces with optical codes codes Miró [4] and VBL [5] used for the development of high performance laser designs. This paper is organized as follows: first the physical principles of polarized electrical field propagation through a media along a light ray are recalled along with the quantities of interest which are depolarization, optical path length and Jones matrices.…”

“…Stresses change the indices of refractions and induce inhomogeneities and anisotropy. We present a modern, integrated analysis tool that efficiently produces reliable results that are used in our laser propagation tools such as VBL [5]. COMBINE is built on and supplants the existing legacy tools developed for the previous generations of lasers at LLNL but also uses commercially available mechanical finite element codes ANSYS or COMSOL (including computational fluid dynamics).…”

Algorithm for Fourier propagation through the near-focal region

“…To meet these stringent performance requirements, each beam includes hundreds of optical components and extends over an optical path of about 4.5 km, folded to fit into a facility equal in area to three football fields. Designing and operating a laser system of such length and complexity requires a sophisticated modeling capability based on Fourier beam propagation methods (F-BPM) for computational efficiency [3,4]. Other approaches have been suggested toward beam propagation and shaping in large laser systems [5][6][7].…”

“…The comparison for the top-hat shaped beam was done using the virtual beam line (VBL) numerical simulations, which are used on a daily basis for the operation and the modification of the NIF [3]. The VBL modeling code, implemented in Java, includes all the required laser physics and incorporates the optical characteristics of the NIF beams to predict their intensity distribution and temporal shape throughout the NIF chain.…”