Final report on LDRD project 105967 : exploring the increase in GaAs photodiode responsivity with increased neutron fluence.

A previous LDRD studying radiation hardened optoelectronic components for space-based applications led to the result that increased neutron irradiation from a fast-burst reactor caused increased responsivity in GaAs photodiodes up to a total fluence of 4.4 x 10{sup 13} neutrons/cm{sup 2} (1 MeV Eq., Si). The silicon photodiodes experienced significant degradation. Scientific literature shows that neutrons can both cause defects as well as potentially remove defects in an annealing-like process in GaAs. Though there has been some modeling that suggests how fabrication and radiation-induced defects can migrate to surfaces and interfaces in GaAs and lead to an ordering effect, it is important to consider how these processes affect the performance of devices, such as the basic GaAs p-i-n photodiode. In this LDRD, we manufactured GaAs photodiodes at the MESA facility, irradiated them with electrons and neutrons at the White Sands Missile Range Linac and Fast Burst Reactor, and performed measurements to show the effect of irradiation on dark current, responsivity and high-speed bandwidth

Microfabricated wire arrays for Z-pinch.

Microfabrication methods have been applied to the fabrication of wire arrays suitable for use in Z. Self-curling GaAs/AlGaAs supports were fabricated as an initial route to make small wire arrays (4mm diameter). A strain relief structure that could be integrated with the wire was designed to allow displacements of the anode/cathode connections in Z. Electroplated gold wire arrays with integrated anode/cathode bus connections were found to be sufficiently robust to allow direct handling. Platinum and copper plating processes were also investigated. A process to fabricate wire arrays on any substrate with wire thickness up to 35 microns was developed. Methods to handle and mount these arrays were developed. Fabrication of wire arrays of 20mm diameter was demonstrated, and the path to 40mm array fabrication is clear. With some final investment to show array mounting into Z hardware, the entire process to produce a microfabricated wire array will have been demonstrated

Enantiomerically selective vapochromic sensing

a b s t r a c t The double salt materials platinum(II)tetrakis-R-␤-methylphenethylisocyanide tetracyanoplatinate(II) (R-1) and platinum(II)tetrakis-S-␤-methylphenethylisocyanide tetracyanoplatinate(II) (S-1) have been synthesized with highly enantiomerically pure isocyanide ligands. The vapochromic behavior of R-1 and S-1 has been studied in the presence of a chiral probe vapor to determine if enantiomerically selective sensing is possible with these materials. The wavelength of maximum emission values ( max ) for solidstate vapoluminescence spectra of R-1 and S-1 in the presence of enriched R-and S-2-butanol vapor differ by approximately 10 nm while the max values for R-1 and S-1 under nitrogen are nearly identical. Principal component analysis has been performed on datasets that consist of a series of vapoluminescence spectra of R-1 and S-1 as a function of the R/S-2-butanol ratio. Plots of principal component one versus R/S-2-butanol ratio show mirror image trends for R-1 relative to S-1. While care must be taken to control water vapor and monitor R-1 and S-1 for possible decomposition, the reported results nevertheless show that R-1 and S-1 are capable of enantiomerically selective vapochromic sensing

SPECTROSCOPY WITH COMB-REFERENCED DIODE LASERS

Author Institution: Department of Chemistry, Stony Brook University, Stony Brook, New York 11794; Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, OK 72019-2061Extended cavity diode lasers have been stabilized by locking to components of an erbium-doped fiber laser-based frequency comb with a 250 MHz comb spacing centered at 1.5$\mu m$. We find the Allan variance of the diode laser frequency relative to the single comb component to which it is locked is of the order of a few Hz. For the system as a whole, the absolute frequency accuracy is approximately 1.5 parts in 10$^{12}$. In order to characterize the system more completely, we have recorded saturation dip absorption spectra of several transitions in the $\nu_1 + \nu_3$ combination band of acetylene near 6530 cm$^{-1}$. We find good agreement with published absolute frequency measurements for these transitions, which have been used as secondary frequency standards in the past. Aside from extremely precise saturation dip measurements such as these, comb-stabilized lasers should permit excellent measurements of Doppler-broadened lineshapes, both to compare with theory and for analytical applications. Progress along these lines will be reported at the meeting. Acknowledgments: T. J. Sears gratefully acknowledges support from a Brookhaven National Laboratory program development grant that enabled this work and also support for research at Brookhaven National Laboratory which was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences

FREQUENCY-COMB REFERENCED, SUB-DOPPLER SPECTROSCOPY OF HOT BANDS OF ACETYLENE IN THE REGION OF THE ν1+ν3\nu_1+\nu_3 COMBINATION BAND

Author Institution: Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973; Department of Chemistry, Stony Brook University, Stony Brook, New York 11794; Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973; Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973To take full advantage of recent improvements in the accuracy obtained in collision-induced absorption line shape measurements of the acetylene $\nu_1+\nu_3$ combination band, independent and accurate knowledge of the positions of weaker, overlapping hot band transitions is required. We have used cavity-enhanced saturation-absorption spectroscopy together with a frequency-comb referenced, extended cavity diode laser to determine Doppler-free transition frequencies for the $\nu_4$ and $\nu_5$ hot band transitions in this region . A laser intensity dependent asymmetry in the sub-Doppler saturation line shape is observed, and will be discussed in terms of the intra-cavity beam geometry. Acknowledgments: Work at Brookhaven National Laboratory was carried out under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences