Generation, Detection, and Control of Ultrafast Nonlinear Optical Processes in High Energy Density Plasmas Using Spike Trains of Uneven Duration and Delay
The success of Inertial Confinement Fusion (ICF) is to achieve controlled thermonuclear burn in the laboratory which will lead to the commercialization of clean, carbon-free and safe Inertial Fusion Energy (IFE). Both ICF and IFE demand a detailed understanding of the rapidly evolving high energy density plasmas (HEDP) as intense lasers create and nonlinearly modify them. We will develop and test new design tools for novel ultrafast diagnostics that use nonlinear optical (NLO) techniques to ferret out the complex, nonlinear, kinetic, microscopic dynamics of HEDP. Measuring the slope of the velocity distribution function of a plasma electron or ion species in a velocity sector of interest is one such paramount goal. We will accomplish this by (i) adopting the appropriate method of generating a pump laser composed of spike trains of uneven duration and delay (STUD pulses), (ii) adopting the appropriate method of detecting and diagnosing the amplified transmission of a stimulated Raman or stimulated Brillouin scattered (SRS or SBS) probe beam, and (iii) utilizing the gain variations of the scattered signal to develop a detailed map of background plasma instabilities. This code will be tested using output from state of the art kinetic simulations to emulate the microscopic state of an HED plasma. High-repetition-rate, high-average-power future drivers of IFE will use STUD pulses in order to control undesirable instabilities adaptively. During this Phase I, we will develop and test a comprehensive new design code utilizing kinetic HEDP physics and ultrafast optics to modulate laser beams as on-off sequences in the picosecond time scale in a suite of designer STUD pulses. We will also design probe beams which by crossing the STUD-pulse-modulated pump will target a certain velocity sector and reveal the kinetic properties of the plasma via the rapid transmission modulations of its gain. Whether in SRS or SBS mode, the three-wave nonlinear optical interactions between pump, probe and an electron plasma wave (EPW) or an ion acoustic wave (IAW), will be used to reveal the slope of the velocity distribution function (VDF) of the electron or ion species. The marriage of these technologies of detailed plasma kinetic behavior, ultrafast optics modulation of pulses, and the detection of scattered light on that same time scale requires careful analysis and design of input on-off pulse trains which will reveal maximal information about the fast evolving plasma state in the smallest number of shots. The amplification or gain exponent of the probe with a pump that maintains the amplifier in the linear regime by turning itself off before nonlinearities distort this picture, is the central idea. The enabling technologies are microscopic kinetic plasma evolution detection via ultrashort pulse arbitrary-waveform generation and detection. The latter two have been popularized and developed for the telecommunications industry. We propose to adopt, extend the functionality, and assess the relative merits of a multitude of these techniques so that electron and ion VDFs of unstable plasmas can be measured in HEDP for the first time.
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Polymath Research Inc.
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