Broadband Laser Ranging (BLR) is a new diagnostic being developed in collaboration across multiple USA Dept. of Energy (DOE) facilities. Its purpose is to measure the precise position of surfaces and particle clouds moving at speeds of a few kilometers per second. The diagnostic uses spectral interferometry to encode distance into a modulation in the spectrum of pulses from a mode-locked fiber laser and uses a dispersive Fourier transformation to map the spectral modulation into time. This combination enables recording of range information in the time domain on a fast oscilloscope every 25-80 ns. Discussed here are some of the hardware design issues, system tradeoffs, calibration issues, and experimental results. BLR is being developed as an add-on to conventional Photonic Doppler Velocimetry (PDV) systems because PDV often yields incomplete information when lateral velocity components are present, or when there are drop-outs in the signal amplitude. In these cases, integration of the velocity from PDV can give incorrect displacement results. Experiments are now regularly fielded with over 100 channels of PDV, and BLR is being developed in a modular way to enable high channel counts of BLR and PDV recorded from the same probes pointed at the same target location. In this way instruments, will independently record surface velocity and distance information along the exact same path.
During the fabrication of an aspherical mirror, the inspection of the residual wavefront error is critical. In the program of a spaceborne telescope development, primary mirror is made of ZERODUR with clear aperture of 450 mm. The mass is 10 kg after lightweighting. Deformation of mirror due to gravity is expected; hence uniform supporting measured by load cells has been applied to reduce the gravity effect. Inspection has been taken to determine the residual wavefront error at the configuration of mirror face upwards. Correction polishing has been performed according to the measurement. However, after comparing with the data measured by bench test while the primary mirror is at a configuration of mirror face horizontal, deviations have been found for the two measurements. Optical system that is not able to meet the requirement is predicted according to the measured wavefront error by bench test. A target wavefront error of secondary mirror is therefore analyzed to correct that of primary mirror. Optical performance accordingly is presented.
A novel fiber-optic probe measures the velocity distribution of an imploding surface along many lines of sight. Reflected
light from each spot on the moving surface is Doppler shifted with a small portion of this light propagating backwards
through the launching fiber. The reflected light is mixed with a reference laser in a technique called photon Doppler
velocimetry, providing continuous time records.
Within the probe, a matrix array of 56 single-mode fibers sends light through an optical relay consisting of three types of
lenses. Seven sets of these relay lenses are grouped into a close-packed array allowing the interrogation of seven regions
of interest. A six-faceted prism with a hole drilled into its center directs the light beams to the different regions. Several
types of relay lens systems have been evaluated, including doublets and molded aspheric singlets. The optical design
minimizes beam diameters and also provides excellent imaging capabilities. One of the fiber matrix arrays can be
replaced by an imaging coherent bundle.
This close-packed array of seven relay systems provides up to 476 beam trajectories. The pyramid prism has its six
facets polished at two different angles that will vary the density of surface point coverage. Fibers in the matrix arrays are
angle polished at 8°to minimize back reflections. This causes the minimum beam waist to vary along different
trajectories. Precision metrology on the direction cosine trajectories is measured to satisfy environmental requirements
for vibration and temperature.
Paul Wine, J. Nicovich, Anthony Hynes, Robert Stickel, R. Thorn, Mian Chin, Jeffrey Cronkhite, Christie Shackelford, Zhizhong Zhao, Edward Daykin, Cornelius van Dijk, Shouzhi Wang, Jill Steidl
Some recent studies carried out in our laboratory are described where laser flash photolytic production of reactant free radicals has been combined with reactant and/or product detection using time-resolved optical techniques to investigate the kinetics and mechanisms of important atmospheric chemical reactions. Discussed are (1) a study of the radical-radical reaction O + BrO yields Br + O2 where two photolysis lasers are employed to prepare the reaction mixture and where the reactants O and BrO are monitored simultaneously using atomic resonance fluorescence to detect O and multipass UV absorption to detect BrO; (2) a study of the reaction of atomic chlorine with dimethylsulfide (CH3SCH3) where atomic resonance fluorescence detection of Cl is employed to elucidate the kinetics and tunable diode laser absorption spectroscopy is employed to investigate the HCl product yield; and (3) a study of the aqueous phase chemistry of Cl2- radicals where longpath UV absorption spectroscopy is employed to investigate the kinetics of the Cl2- + H2O reaction.
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