RESUMO
The advanced radiographic capability (ARC) laser system, part of the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, is a short-pulse laser capability integrated into the NIF. The ARC is designed to provide adjustable pulse lengths of â¼1-38ps in four independent beamlets, each with energies up to 1 kJ (depending on pulse duration). A detailed model of the ARC lasers has been developed that predicts the time- and space-resolved focal spots on target for each shot. Measurements made to characterize static and dynamic wavefront characteristics of the ARC are important inputs to the code. Modeling has been validated with measurements of the time-integrated focal spot at the target chamber center (TCC) at low power, and the space-integrated pulse duration at high power, using currently available diagnostics. These simulations indicate that each of the four ARC beamlets achieves a peak intensity on target of up to a few 1018W/cm2.
RESUMO
We provide the first account of the second-order susceptibility of quartz down to 10 mum (1000 cm(-1)) and show how this data may be used along with the sum-frequency response of an amorphous gold surface to elucidate the nonlinear susceptibility of any material in the mid-infrared region. Crystalline quartz is an established material for use in second-harmonic and sum-frequency generation studies of new systems, on account of its well-characterized linear and nonlinear optical properties. Previous knowledge of its nonlinear susceptibility has been limited to its transparent region, wavelengths shorter than about 3 mum. Longer wavelength chi((2)) values for quartz are particularly important for techniques such as vibrational sum-frequency spectroscopy which are expanding into the mid-IR with the increasing availability of widely tunable infrared laser sources.
RESUMO
Visible-infrared sum-frequency spectroscopy is ideally suited to the study of surfaces and interfaces. This paper introduces new sum-frequency spectroscopy instrumentation that we have developed with two novel features: (1) stable and robust infrared generation in the 900-3100 cm(-1) (11-3.2 microm) region using an amplified Ti : sapphire oscillator with a home-built OPG/OPA, and (2) continuous tuning over either 900-2700 cm(-1) (11-3.7 microm) or 1800-3100 cm(-1) (5.5-3.2 microm) in a single experiment. All practical details of baseline correction issues due to the picosecond pulses (including variation in infrared (IR) energy, spatial and temporal overlap, Fresnel coefficients) are addressed while demonstrating signal throughout this region from an amorphous gold surface. A sum-frequency spectrum from an oriented polymer is shown as a complete example of the data treatment, which reveals the vibrational modes accessible in this wavelength region.
