Showing papers by "Jason Glenn published in 1997"

Laser micromachining of silicon: a new technique for fabricating high quality terahertz waveguide components'

Abstract: One of the main obstacles encountered in designing low noise, high efficiency, heterodyne receivers and local oscillator sources at submillimeter wavelengths is the quality and cost of waveguide structures At wavelengths shorter than 400 micrometers, rectangular waveguide structures, feedhorns, and backshorts become extremely difficult to fabricate using standard machining techniques We have used a new laser milling technique to fabricate high quality, THz waveguide components and feedhorns Once metallized, the structures have the properties of standard waveguide components Unlike waveguide components made using silicon wet-etching techniques, laser-etched components can have almost any cross section, from rectangular to circular Under computer control, the entire waveguide structure (including the corrugated feedhorn!) of a submillimeter-wave mixer or multiplier can be fabricated to micrometer tolerances in a few hours Laser etching permits the direct scaling of successful waveguide multiplier and mixer designs to THz frequencies Since the entire process is computer controlled, the cost of fabricating submillimeter waveguide components is significantly reduced With this new laser etching process, the construction of high ' The Lincoln Laboratory portion of this work was performed under a cooperative research and development agreement (CRDA) with the University of Arizona Opinions, interpretations, conclusions, and recommendations are those of the author and are not necessarily endorsed by the United States Government

Millimeter-wave spectropolarimetry of evolved stars: evidence for polarized molecular line emission

Abstract: We present spectropolarimetry of CS J = 2-1 emission from the evolved stars IRC +10216 and CRL 2688 and spectropolarimetry of the HCN J = 1-0 transition from CRL 2688. We detected a line-averaged linear polarization of ~1% toward IRC +10216 on three separate occasions. We found no evidence for velocity dependence of the polarization within the emission line. A deviation from spherical symmetry in the radiative transfer of the envelope is implied because polarization was detected toward the central star. The polarization position angle of about -70° is orthogonal to the envelope elongation apparent in previous observations. Polarizations of 5.1% ± 1.5% (1 σ) and less than 0.9% (3 σ), respectively, were derived for CS and HCN from CRL 2688.

HCO+ Spectropolarimetry and Millimeter Continuum Polarimetry of the DR 21 Star-forming Region* **

Abstract: We report the results of a search for linear polarization in emission lines toward the outflow lobes of DR 21 (HCO+J = 1-0), Mon R2 (HCO+ J = 1-0), and IRAS 16293-2422 (CS J = 2-1). Theoretical models suggest linear polarization in optically thin emission lines may be present at the level of a few percent in these regions. However, no polarization was detected. An upper limit of 0.4% can be placed on the polarization toward DR 21 and Mon R2, and 1.2% toward IRAS 16293-2422. Using published HCO+ interferometry of DR 21, we argue that the lack of polarization is probably due to the presence of clumpy, turbulent gas, which is unresolved by our beam (70'' FWHM). Diminished polarization by multiple scattering cannot be ruled out. We also present new λ = 1.3 mm and λ = 2 mm continuum polarimetry of the DR 21 dust core. Polarizations of P = 1.7% ± 0.2% and P = 0.77% ± 0.13%, respectively, were detected. The λ = 2 mm polarization is lower than the ~2.0%-2.5% previously reported at millimeter and submillimeter wavelengths. However, with the unpolarized free-free component of the flux density from H II regions in the star-forming core removed, the level of polarization is consistent with the previous observations. Based on our observations and those previously reported, there is no clear dependence of level of polarization on beam size in the inner ~30'' of the dust core. The λ = 2 mm polarization position angle, 2° ± 5°, is rotated ~20° with respect to the previous measurements. If the rotation is real, it implies the magnetic field on this expanded scale (42'' FWHM beam) is more perpendicular to the general elongation of the dust cloud than it is within the inner 20'' of the dust core.

Cyclops: A single beam 1.3 millimeter polarimeter

Abstract: We present the design of a broad band, 1.3 mm polarimeter for astronomical observations and the results of first light observations at the Heinrich Hertz Telescope (HHT). The systematic polarization of the instrument plus telescope is 1.1%. The observed linear polarization of DR 21,P=1.65%±0.14% andθ=16°±2°, is consistent with previous measurements. Our 0.9% upper limit on the linear polarization of Cepheus A is the first 1.3 mm measurement reported. With Cyclops it is possible to map the magnetic fields in several of the brightest molecular cloud dust cores in the Milky Way. We comment on the expected performance of an achromatic Rexolite half-waveplate for λ=800µm to 1.3 mm.