Michael W. Kartz

Modeling of adaptive optics-based free-space communications systems

We introduce a wave-optics based simulation code written to model a complete free space laser communications link, including a detailed model of an adaptive optics compensation system. We present the results obtained by this model, where the phase of a communications laser beam is corrected, after it propagates through a turbulent atmosphere. The phase of the received laser beam is measured using a Shack-Hartmann wavefront sensor, and the correction method utilizes a MEMS mirror. Strehl improvement and amount of power coupled to the receiving fiber results for both 1 km horizontal and 28 km slant paths will be presented.

Adaptive optics system for solid state laser systems used in inertial confinement fusion

Using adaptive optics we have obtained nearly diffraction-limited 5 kJ, 3 nsec output pulses at 1.053 micrometer from the Beamlet demonstration system for the National Ignition Facility (NIF). The peak Strehl ratio was improved from 0.009 to 0.50, as estimated from measured wavefront errors. We have also measured the relaxation of the thermally induced aberrations in the main beam line over a period of 4.5 hours. Peak-to-valley aberrations range from 6.8 waves at 1.053 micrometer within 30 minutes after a full system shot to 3.9 waves after 4.5 hours. The adaptive optics system must have enough range to correct accumulated thermal aberrations from several shots in addition to the immediate shot-induced error. Accumulated wavefront errors in the beam line will affect both the design of the adaptive optics system for NIF and the performance of that system.

Performance of a high-resolution wavefront control system using a liquid crystal spatial light modulator

We have developed a high-resolution wavefront control system based on an optically addressed nematic liquid crystal spatial light modulator with several hundred thousand phase control points, a Shack-Hartmann wavefront sensor with two thousand subapertures, and an efficient reconstruction algorithm using Fourier transform techniques. We present quantitative results of experiments to characterize the performance of this system.

High-resolution wavefront control using liquid crystal spatial light modulators

Liquid crystal spatial light modulator technology appropriate for high-resolution wavefront control has recently become commercially available. Some of these devices have several hundred thousand controllable degrees of freedom, more than two orders of magnitude greater than the largest conventional deformable mirror. We will present results of experiments to characterize the optical properties of these devices and to utilize them to correct aberrations in an optical system. We will also present application scenarios for these devices in high-power laser systems.

Wavefront correction system based on an equilateral triangular arrangement of actuators

We are developing an adaptive optics system that is based on an array of actuators arranged with subapertures that are equilateral triangles. The wavefront sensor is a video Hartmann sensor that also uses an equilateral array of lenslets. The controller hardware uses a VME bus. The design minimizes the generation of reflected wavefronts higher than first order across each lenslet for large excursions of actuators from positions where the mirror is flat and, thus maximizes the precision of the slopes measured by the Hartmann sensor. The design is also immune to the waffle mode that is present in the reconstructors of adaptive optics systems where actuators are arranged in a square array.

Real-time control system for adaptive resonator

Sustained operation of high average power solid-state lasers currently requires an adaptive resonator to produce the optimal beam quality. We describe the architecture of a real-time adaptive control system for correcting intra-cavity aberrations in a heat capacity laser. Image data collected from a wavefront sensor are processed and used to control phase with a high-spatial-resolution deformable mirror. Our controller takes advantage of recent developments in low-cost, high-performance processor technology. A desktop-based computational engine and object- oriented software architecture replaces the high-cost rack-mount embedded computers of previous systems.

Production of high-intensity laser pulses with adaptive optic wavefront correction

We have developed a Ti:sapphire/Nd:glass laser system which produces > 1.25 PW peak power. An irradiance of 1020 - 1021 W/cm2 is achieved utilizing an on-axis parabolic mirror, with adaptive optic wavefront correction. Experimental results will be described.

The Beamlet laser system as a prototype for the National Ignition Facility (NIF)

Summary form only given. The National Ignition Facility is designed to ignite inertial-confinement fusion (ICF) targets using 1.8 MJ of ultraviolet (351 nm) laser light generated by frequency tripling the output of 192 neodymium glass laser beams. The Beamlet laser system is a full scale scientific prototype of one of the 192 NIF beamlines. Because the estimated cost of the NIF facility is substantial (

Real-time geo-registration of imagery using cots graphics processors

1.1 billion) it is imperative that the performance be cost optimized. This implies operation as close as possible to power and energy extraction limits imposed by fundamental physical constraints. Control of beam quality in the NIF and the Beamlet prototype is enhanced through the use of a deformable mirror. Beamlet employs a sophisticated suite of laser diagnostic systems to measure beam quality.