Calvin E. Thompson

Optics damage inspection for the NIF

Two optics damage inspection system will be implemented on the NIF, one to inspect optics within the laser and transport sections and the other to inspect the final optics at the target chamber. Both system use dark-field imaging technology to enhance defect contrast. Details of each system design will be provided. A functional optics damage inspection system prototype, using dark-field imaging technology, is currently in operation on the Beamlet laser. This system provides us with the opportunity to measure non- ideal optical surfaces expected to be present on NIF. Prototpye details and performance will be presented.

Effect of bandwidth on beam smoothing and frequency conversion at the third harmonic of the Nova laser

We present the results of experiments performed on the Nova laser system to determine the effect of bandwidth on third harmonic (3(omega) ) frequency conversion and beam smoothing by spectral dispersion (SSD). Our experiments utilized a wide bandwidth fiber optic cross- phase modulated (XPM) source and a narrower bandwidth microwave modulated (FM) source, each centered at 1053 nm (1 (omega) ). A significant fraction (> 50%) of the 1(omega) XPM bandwidth was transferred to the 3(omega) beam (22 cm-1 yields 36 cm-1), yielding 0.13% bandwidth at 3(omega) . The maximum intrinsic narrowband 3(omega) frequency conversion obtained using a type-II/type-II KDP crystal array was 62%. The intrinsic efficiency obtained at the Nova 10-beam chamber is typically > 65%. Frequency conversion was essentially unaffected by the 2 cm-1 bandwidth obtained from FM source. However, the 5 - 16 cm-1 of bandwidth from the XPM source reduced the conversion efficiency to approximately 24%. We have developed broadband frequency conversion codes and broadband pulse simulations to model our results, and have obtained good agreement with experiment.

Low-dispersion optical fiber highly transparent in the UV spectral range

The National Ignition Facility performs fusion experiments using ultraviolet (351 nm) light. High-bandwidth, low-attenuation optical fibers are required to transport subnanosecond, UV laser diagnostic signals from the target chamber area to recording instruments located in adjacent rooms, with some fiber runs approximately 65 m in length. Special optical fibers are developed and fabricated to perform this task, since no existing commercially available fibers possess all of the required characteristics. These large-core (435 µm) fibers have optical dispersions less than 0.9 psec/m and attenuations less than 150 dB/km at 351 nm.

Alignment and diagnostics of the National Ignition Facility laser system

The NIF laser system will be capable of delivering 1.8 MJ of 351 nm energy in 192 beams. Diagnostics instruments must measure beam energy, power vs. time, wavefront quality, and beam intensity proifle to characterize laser performance. Alignment and beam diagnostics are also used to set the laser up for the high power shots and to isolate problems when performance is less than expected. Alignment and beam diagnostics are multiplexed to keep the costs under control. At the front-end the beam is aligned and diagnosed in an input sensor package. The output 1053 nm beam is sampled by collecting a 0.1% reflection from an output beam sampler and directing it to the output sensor package (OSP). The OSP also gets samples from final focus lens reflection and samples from the transport spatial filter pinhole plane. The output 351 nm energy is measured by a calorimeter collecting the signal from an off-axis diffractive beam-sampler. Detailed information on the focused beam in the high-energy target focal plane region is gathered in the precision diagnostics. This paper describes the design of the alignment and diagnostics on the NIF laser system.

Beamlet focal plane diagnostic

This paper describes the major optical and mechanical design features of the Beamlet Focal Plane Diagnostic system as well as measurements of the system performance, and typical data obtained to date. We also discuss the NIF requirements on the focal spot that we are interested in measuring, and some of our plans for future work using this system.

Design progress for the National Ignition Facility laser alignment and beam diagnostics

Earlier papers have described approaches to NIF alignment and laser diagnostics tasks. Now, detailed design of alignment and diagnostic systems for the National Ignition Facility (NIF) laser is in its last year. Specifications are more detailed, additional analyses have been completed, Pro- E models have been developed, and prototypes of specific items have been built. In this paper we update top level concepts, illustrate specific areas of progress, and show design implementations as represented by prototype hardware. The alignment light source network has been fully defined. It utilizes an optimized number of lasers combined with fiber optic distribution to provide the chain alignment beams, system centering references, final spatial filter pinhole references, target alignment beams, and wavefront reference beams. The input and output sensor are being prototyped. They are located respectively in the front end just before beam injection into the full aperture chain and at the transport spatial filter, where the full energy infrared beam leaves the laser. The modularity of the input sensor is improved, and each output sensor mechanical package now incorporates instrumentation for four beams.

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 (

Precision operation of the Nova laser for fusion experiments

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.

Characterization of third-harmonic target plane irradiance on the National Ignition Facility Beamlet demonstration project

The operation of a Neodymium glass laser of a special design for fusion experiments is improved by a better pulse synchronization, the gain stabilization, and the laser diagnostics. We used sensor upgrading and antifriction coating of focusing lenses. The pointing accuracy of the Nova laser meets now our goal for precision operation. (AIP)