We designed and tested an alternating-Z tripler that consisted of two detuned, Type-1, potassium dihydrogen phosphate (KD*P) doublers and one KD*P mixer. The crystal thicknesses were, respectively, 13, 10 and 10 mm, and the detunings of the doublers were +420 and -520 µrad. All three crystals were fabricated from 80% deuterated KDP. Conversion efficiency was measured and calculated for input 1053- nm pulses with approximately rectangular waveforms and durations of either 1 or 6 ns, and for 20-ns pulses that exhibited intensity variation by a factor of 10. The measured peak conversion efficiency was more than 80%, and energy conversion efficiencies ranged from 62-80% depending on the waveform of the input pulse. The expected large dynamic range in input intensity, 9-10, was observed, and the measured and calculated efficiencies were in excellent agreement.

Summary form only given. The National Ignition Facility (NIF), currently under construction by the Department of Energy at Lawrence Livermore National Laboratory, is a megajoule class Nd:glass laser and target irradiation complex for investigating the physics associated with stockpile stewardship and inertial confinement fusion (ICF).

A standard third harmonic frequency converter consists of a single doubler crystal and a subsequent mixer crystal. This converter configuration has optimum performance for monochromatic temporally flat pulses. Significant degradation of conversion efficiency occurs when the input pulses have large intensity variations or applied bandwidth. Calculations have shown that dynamic range can be increased and bandwidth sensitivity reduced by adding a second doubler crystal and second mixer crystal, respectively.

The characteristics of the 3 omega focal spot are determined by the properties of the 1 omega beam and the frequency tripling process. The size of the 3 omega focal spot depends on the spectrum of spatial noise in the 1 omega beam. A perturbation theory for ripple transfer in frequency tripling is used to predict the characteristics of the 3 omega focalspot. The theory predicts that 1 omega phase noise grows 9X in power in the tripling process. This can cause a significant reduction in 3 omega energy delivered to the target. Results from Beamlet 3 omega focal spot characterization experiments are also presented.

The Beamlet laser is a nearly full-scale, single-aperture prototype of the driver design for the National Ignition Facility (NIF). As part of a test and validation plan for the NIF design, Beamlet was recently equipped with final focussing optics and diagnostics for the purpose of evaluating integrated component performance and equivalent target-plane irradiance conditions at the 0.351-mu m output wavelength specified for NIF targets. A 37-cm aperture two-crystal converter scheme generates the third harmonic of the Nd:glass 1.053-mu m wavelength with high efficiency. The efficiency of the converter has been characterized and is reported, along with detailed measurements of the near-field and far-field UV irradiance distributions at operating conditions up to and exceeding red-line levels for the NIF. Dependences of observed beam quality on critical laser parameters including output power, B-integral, and spatial filtering are discussed and compared with numerical simulations.

The Beamlet laser is a large aperture, flashlamp pumped Nd: glass laser that is a scientific prototype of an advanced Inertial Fusion laser. Beamlet has achieved third harmonic, conversion efficiency of near 80% with its nominal 35cm {times} 35cm square beam at mean 3{omega} fluences in excess of 8 J/cm{sup 2}(3-ns). Beamlet uses an adaptive optics system to correct for aberrations and achieve less than 2 {times} diffraction limited far field spot size.