The importance of laser wavelength in driving ICF targets

We have reexamined the role that laser wavelength plays in driving inertial confinement fusion (ICF) targets, concentrating on the ArF (193 nm laser wavelength), KrF (248 nm) excimer lasers and the frequency-tripled glass Nd:glass laser (351 nm). We look at different analytic frameworks that provide predictions for the wavelength scaling of many important target parameters, and compare these models to the results of our radiation-hydrodynamics simulations. Newer, updated scalings relevant for current ICF scenarios are found. Generally, smaller drive wavelengths couple to plasmas more efficiently and thus require less energy and power to drive targets to ICF relevant conditions. The shorter wavelength drivers also have additional important advantages like increased bandwidth and the ability to be easily 'zoom' their focal spots to match an imploding target. Potential disadvantages of shorter wavelengths like laser imprint effects and the potential for the Landau-Darrieus instabilty are considered and shown to be either minor and/or easily remediated. We then examine the importance of the laser driver for targets designed to produce significant gain for sub-megajoule laser energies. The sensitivity of high gain targets to laser plasma instabilities (using linear theoretical thresholds) and hydrodynamic instabilities (using both theory and 2D implosion simulations) is explored, and we show how these instabilities limit the design space of allowed laser drive wavelength and pellet geometry (initial aspect ratio).