Lunar soil properties and soil mechanics. Flow in porous media under rarefied gas conditions. Research phase: Fluid conductivity of lunar surface materials

Theoretical and experimental research on fluid conductivity of lunar surface materials is summarized. Theoretical methods were developed for the analysis of transitional and free-molecular flows, and for analysis of lunar permeability probe data in general. Experimental studies of rarefied flows under conditions of a large pressure gradient show flows in the continuum regime to be responsible for the largest portion of the pressure drop between source and sink for one dimensional flow, provided the entrance Knudsen number is sufficiently small. The concept of local similarity leading to a universal nondimensional function of Knudsen number was shown to have approximate validity; flows in all regimes may be described in terms of an area fraction and a single length parameter. Synthetic porous media prepared from glass beads exhibited flow behavior similar in many regards to that of a natural sandstone; studies using artificial stones with known pore configurations may lead to new insight concerning the structure of natural materials. The experimental method involving the use of segmented specimens of large permeability is shown to be fruitful

Measurements of mass and momentum flux in non-ideal molecular beams

Momentum transfer and mass determinations for nonideal molecular beam - fluid mechanic

Investigation of kilovolt ion sputtering quarterly progress report

Radioactive tracer technique to measure yield and angular distribution of cesium ion sputtered coppe

Investigation of kilovolt ion sputtering Quarterly progress report, Feb. - Apr. 1966

Sputtering of single crystals of electrode material under cesium and mercury ion beam bombardmen

Investigation of kilovolt ion sputtering quarterly progress report

Investigation of cesium ion sputtering of monocrystalline copper using radioactive tracer techniqu

Investigation of kilovolt ion sputtering Quarterly progress report, May - Jul. 1966

Aluminum sputtering, and neutron activation analysis after cesium ion bombardmen

The nonlinear optical properties of gallium arsenide pertaining to terahertz generation

Gallium arsenide shows excellent promise for terahertz generation using mid infrared. This is for two reasons. First, the indices of refraction for the terahertz (nTHz=3.61 at 1 THz) and mid infrared (nopt=3.431 at 2 μm) are close allowing a long interaction length. Second, the linear absorption is low at terahertz frequencies (αTHz=.5 to 4.5 cm⁻¹ for 1 to 3 THz). Since gallium arsenide is a direct bandgap material, multiphoton absorption and nonlinear refraction are issues for efficiency and system design in the mid infrared. In fact, linear absorption makes this material opaque at or below 870 nm. Additionally, two photon absorption is quite pronounced between 870 nm and 1.74 μm. I will present the theory then the experimental data for two and three photon absorption (870 nm to 1.74 μm and 1.74 μm to 2.61 μm, respectively) as well as for nonlinear refraction. The three photon absorption has a minimum at 2 μm in the spectral range of 1.74 to 2.61 μm thus it is the preferred wavelength for terahertz generation. At 2 μm the anisotropy in the three photon absorption was almost 50 %. The nonlinear refraction remains fairly constant in this range as expected. However at 2 μm the anisotropy in nonlinear refraction was only 16% as compared with the predicted factor of 2. Qualitatively, the anisotropic behavior of the nonlinear refraction still conforms to the expected symmetry class of zincblende crystals. Terahertz time domain spectroscopy will be discussed on both theoretical and experimental levels. The results will show that terahertz generation is promising in the mid infrared range for wavelengths 2 μm and above. At 2 μm I demonstrate the advantages of a quasi-phase matched structure. One, the inverting structure generates a narrow band source. Additionally, shaped domains map to the terahertz electric field allowing shaped pulses. Also, of benefit is the increase in power production from having a longer effective interaction path in the crystal

Generation of terahertz pulses with arbitrary elliptical polarization

We employ two different methods to generate controllable elliptical polarization of teraherz (THz) pulses. First, THz pulses are generated via optical rectification in nonlinear crystals using a pair of temporally separated and perpendicularly polarized optical pulses. The THz ellipticity is controlled by adjusting the relative time delay and polarization of the two optical pulses. We generate mixed polarization states of single-cycle THz pulses using ZnTe, and elliptically polarized multicycle THz pulses in periodically poled lithium niobate crystals. Second, we generate elliptically polarized THz pulses by making a THz “wave plate” using a combination of a wire-grid THz polarizer and a mirror to transform linearly polarized multicycle THz pulses into elliptical polarization.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87838/2/221111_1.pd