Raymond Andrew Hill

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There is a growing body of literature that points to the value of using the intensity measures of the backscattered laser light in addition to the pulse range measurements for studying a range of environments, including forests. However, there is a lack of literature that has validated the lidar intensity values captured in a campaign, and therefore limited(More)
A retroreflecting multipass cell consisting of two lenses and both on-axis and off-axis retroreflecting mirror assemblies has been constructed and tested. A gain in Raman scattered signal intensity of 20 has been attained in a focal volume 1.1 mm x 0.3 mm x 0.3 mm. A system employing off-axis paraboloids should provide somewhat higher gain and a diffraction(More)
In turbocharger application bleed air at impeller exit is typically used to seal bearing compartments and to balance axial thrust in the rotor. It was previously shown that this bleed air can have a significant impact on both compressor performance and stability. Experiments suggest that spike stall inception in centrifugal compressors can be formed by a(More)
An ultrarapid scanning spectrometer has been constructed that records spectra at a constant angle of diffraction. The spectral scanning is accomplished by the rotation of a high-speed rotating mirror (7.6 cm diam) that causes a collimated light beam to sweep across a plane grating, changing the angle of incidence. The full-aperture scanning range depends(More)
A holographic interferometer is described that is used in conjunction with a high-speed camera system (10,000 frames/sec) to record the temporal and spatial interactions of the laser gas medium and the resonator mode. In particular, a high-power CO(2) electric discharge convectively cooled laser-gas medium was interferometrically analyzed before, during,(More)
The difference between spherical and elliptical lighttrapping systems mentioned by Sturtevant ("in spherical systems, spherical aberration will produce a small axial migration of the foci") indicates that a spherical system cannot be used for a light-trapping cell (LTC II). The LTC II uses a coaxial flat-spherical mirror positioned midway between the foci(More)
A gated photon counting system, cavity-dumped argon-ion laser, and a multipass retroreflecting light cell have been combined in a system to enhance spontaneous Raman scattering in luminous background situations. Signal-to-background ratio (SBR) has been improved a factor of 450 over a single-pass cw system with cw power equal to the pulsed average power.(More)
A design for a new plane grating monochromator is described. The system employs a symmetrical configuration of off-axis paraboloids for both the collimator and camera mirrors. The entrance and exit slits are mounted on the same side of the grating and are curved in order to eliminate wavelength errors due to spectral line curvature. There is, in fact, a(More)