O. L. Weaver

Saturated absorption spectroscopy of acetylene gas inside large-core photonic bandgap fiber

Saturated absorption spectroscopy is performed on the acetylene nu(1) + nu(3) band near 1532 nm inside photonic bandgap fibers of small (approximately 10 microm) and large (approximately 20 microm) core diameters. The observed linewidths are narrower in the 20 microm fiber and vary from 20 to 40 MHz depending on pressure and power. Variations in the background light transmission, attributed by others to surface modes, are significantly reduced in the 20 microm fiber. The optimum signal for use as a frequency reference in a 0.8 m long, 20 microm diameter fiber is found to occur at about 0.5 torr for 30 mW of pump power. The saturation power is found by modeling the propagation and attenuation of light inside the fiber.

A characterisation of the scattering data in the 3D inverse scattering problem

A necessary and sufficient condition is given for the given function A( theta , theta ,k) to be the scattering amplitude corresponding to a potential from a class Q and a condition is given for Newtons equation to have exactly one solution with the desired properties.

Independent center, independent electron approximation for dynamics of molecules and clusters

A formalism is developed for evaluating probabilities and cross sections for multiple‐electron transitions in scattering of molecules and clusters by charged collision partners. First, the molecule is divided into subclusters each made up of identical centers (atoms). Within each subcluster coherent scattering from identical centers may lead to observable phase terms and a geometrical structure factor. Then, using a mean field approximation to describe the interactions between centers we obtain AI∼∑k∏keiδkIAIk. Second, the independent electron approximation for each center may be obtained by neglecting the correlation between electrons in each center. The probability amplitude for each center is then a product of single electron transition probability amplitudes, aIki, i.e. AIk≊∏iaiki. Finally, the independent subcluster approximation is introduced by neglecting the interactions between different subclusters in the molecule or cluster. The total probability amplitude then reduces to a simple product of am...

Velocity dependence of the fragmentation of methane caused by fast proton impact

We have measured the relative cross sections of the different breakup channels of CH4 caused by 1 to 12 MeV H+ impact. The ion‐neutral channels are found to be independent of the collision velocity. Good agreement with previous measurements by Malhi et al. and with electron impact measurements is observed. On the other hand, the ion‐pair breakup channels show some dependence on the collision velocity. The ion‐pair data was compared with electron impact measurements at 1 and 10 keV. Significant deviations at the low electron impact energy can be seen. The ratio of double to single ionization of CH4 is about 1% and decreases slowly with the collision velocity. Triple ionization at these velocities is negligible.

Saturated absorption signals from acetylene gas inside photonic bandgap fiber

Saturated absorption spectroscopy signals inside a 20 mum diameter acetylene-filled photonic bandgap fiber are optimized for use as optical frequency references. Modeling of the light propagation along the fiber reveals a low saturation intensity.

Saturated Absorption Spectroscopy in Acetylene Filled Photonic Bandgap Fibers

Saturated absorption spectroscopy in acetylene filled photonic bandgap (PBG) fibers is investigated. Pressure and optical power are optimized to narrow the line width to allow this signal to be used as an optical reference.

An experimental method for evaluating the H2 and D2 contamination levels in a HD bottle

Abstract Studies of one- and two-electron processes in collisions with hydrogen molecules using the time-of-flight technique are simplified by using the heteronuclear HD isotope because the H+ and D+ fragments can be easily distinguished from each other. The difference in the time-of-flight of H+ and D+ enable the fragments to be measured in coincidence with each other. However, it is hard to determine the purity of the HD target, in particular the H2 contamination, because the H2+ molecular ions coincide with the D+ fragments. A method is suggested to determine the purity of a HD target to a precision of a few percent. This method is based on measuring the yield of very slow ( 1 MeV). The H2 contamination is then determined by subtracting the theoretically evaluated contribution of the ground-state dissociation of the HD+ molecular ion from the measured sum of both H+ and D+ low-energy fragments.

Direct determination of recoil ion detection efficiency for coincidence time-of-flight studies of molecular fragmentation

Abstract Molecular fragmentation of diatomic and small polyatomic molecules caused by fast ion impact has been studied. The evaluation of the cross sections of the different fragmentation channels depends strongly on the recoil ion detection efficiency, ϵ r (single ions proportional to ϵ r , and ion pairs to ϵ r 2 , etc.). A method is suggested for the direct determination of this detection efficiency. This method is based on the fact that fast H + + CH 4 collisions produce C 2+ fragments only in coincidence with H + and H + 2 fragments, that is, there is a negligible number of C 2+ singles, if any. The measured yield of C 2+ singles is therefore due to events in which the H + m of the H + m +C 2+ ion pair was not detected and thus is proportional to 1−ϵ r . Methane fragmentation caused by 1 MeV proton impact is used to evaluate directly the recoil ion detection efficiency and to demonstrate the method of deriving the cross sections of all breakup channels.