Lawrence Livermore National Laboratory (LLNL) has been developing compact solid state lasers since the 1990's. One of the first lasers to be developed utilized flashlamp pumped architecture and neodymium glass as the laser gain media. In the early 2000's, a diode pumped version of the original flashlamp pumped laser was designed and built, responding to the requirements that a laser system for the military be compact in both size and weight while creating significant power (~100 kW) for the missions envisioned. This paper will discuss the evolution of solid state lasers at LLNL and provide a glimpse into the types of capabilities that could be achieved in the near future.
The Solid-State, Heat-Capacity Laser (SSHCL) program at Lawrence Livermore National Laboratory is a multi-generation
laser development effort scalable to the megawatt power levels with current performance approaching 100 kilowatts. This
program is one of many designed to harness the power of lasers for use as directed energy weapons. There are many
hurdles common to all of these programs that must be overcome to make the technology viable. There will be a in-depth
discussion of the general issues facing state-of-the-art high energy lasers and paths to their resolution. Despite the relative
simplicity of the SSHCL design, many challenges have been uncovered in the implementation of this particular system.
An overview of these and their resolution are discussed. The overall system design of the SSHCL, technological strengths
and weaknesses, and most recent experimental results will be presented.
Correlation wave-front sensing can improve Adaptive Optics (AO) system performance in two keys areas. For point-source-based AO systems, Correlation is more accurate, more robust to changing conditions and provides lower noise than a centroiding algorithm. Experimental results from the Lick AO system and the SSHCL laser AO system confirm this. For remote imaging, Correlation enables the use of extended objects for wave-front sensing. Results from short horizontal-path experiments will show algorithm properties and requirements.
The Solid-State, Heat-Capacity Laser (SSHCL) program at Lawrence Livermore National Laboratory is a multigeneration laser development effort scalable to the megawatt power levels. Wavefront quality is a driving metric of its performance. A deformable mirror with over 100 degrees of freedom situated within the cavity is used to correct both the static and dynamic aberrations sensed with a Shack-Hartmann wavefront sensor. The laser geometry is an unstable, confocal resonator with a clear aperture of 10 cm x 10 cm. It operates in a pulsed mode at a high repetition rate (up to 200 Hz) with a correction being applied before each pulse. Wavefront information is gathered in real-time from a low-power pick-off of the high-power beam. It is combined with historical trends of aberration growth to calculate a correction that is both feedback and feed-forward driven. The overall system design, measurement techniques and correction algorithms are discussed. Experimental results are presented.
The Solid-State, Heat-Capacity Laser (SSHCL), under development at Lawrence Livermore National Laboratory (LLNL) is a large aperture (100 cm2), confocal, unstable resonator requiring near-diffraction-limited beam quality. There are two primary sources of the aberrations in the system: residual, static aberrations from the fabrication of the optical components and predictable, time-dependent, thermally-induced index gradients within the gain medium. A deformable mirror placed within the cavity is used to correct the aberrations that are sensed with a Shack-Hartmann wavefront sensor. Although it is more challenging than external correction, intracavity correction enables control of the mode growth within the resonator, resulting in the ability to correct a more aberrated system longer. The overall system design, measurement techniques and correction algorithms are discussed. Experimental results from initial correction of the static aberrations and dynamic correction of the time-dependent aberrations are presented.
Scene-based wave-front sensing (SBWFS) is a technique that allows an arbitrary scene to be used for wave-front sensing with adaptive optics (AO) instead of the normal point source. This makes AO feasible in a wide range of interesting scenarios. This paper first presents the basic concepts and properties of SBWFS. Then it discusses the application of this technique with AO to remote imaging, for the specific case of correction of a lightweight optic. End-to-end simulation results establish that in this case, SBWFS can perform as well as point-source AO. Design considerations such
as noise propagation, number of subapertures and tracking changing image content are analyzed.