Miikka Kangas

THE BACKGROUND EMISSION ANISOTROPY SCANNING TELESCOPE (BEAST) INSTRUMENT DESCRIPTION AND PERFORMANCES

The Background Emission Anisotropy Scanning Telescope (BEAST) is a millimeter wavelength experiment designed to generate maps offluctuations inthecosmicmicrowave background (CMB). The telescope is composed of an off-axis Gregorian optical systemwith a 2.2 mprimary thatfocuses the collected microwave radiation onto an array of cryogenically cooled high electron mobility transistor (HEMT) receivers. This array is composed of six corrugated scalar feed horns in the Q band (38 to 45 GHz) and two more in the Ka band (26 to 36 GHz) with one of the six Q-band horns connected to an ortho-mode transducer for extraction of both polarizations incident on the

Galactic foreground contribution to the BEAST cosmic microwave background anisotropy maps

We report limits on the Galactic foreground emission contribution to the Background Emission Anisotropy Scanning Telescope (BEAST) Ka- and Q-band CMB anisotropy maps. We estimate the contribution from the cross-correlations between these maps and the foreground emission templates of an H? map, a destriped version of the Haslam et al. 408 MHz map, and a combined 100 ?m IRAS DIRBE map. Our analysis samples the BEAST ~10? declination band into 24 one-hour (R.A.) wide sectors with ~7900 pixels each, where we calculate (1) the linear correlation coefficient between the anisotropy maps and the templates; (2) the coupling constants between the specific intensity units of the templates and the antenna temperature at the BEAST frequencies; and (3) the individual foreground contributions to the BEAST anisotropy maps. The peak sector contributions of the contaminants in the Ka-band are of 56.5% free-free with a coupling constant of 8.3 ? 0.4 ?K R-1, and 67.4% dust with 45.0 ? 2.0 ?K MJy-1 sr-1. In the Q band the corresponding values are of 64.4% free-free with 4.1 ? 0.2 ?K R-1 and 67.5% dust with 24.0 ? 1.0 ?K MJy-1 sr-1. Using a lower limit of 10% in the relative uncertainty of the coupling constants, we can constrain the sector contributions of each contaminant in both maps to <20% in 21 (free-free), 19 (dust), and 22 (synchrotron) sectors. At this level, all these sectors are found outside of the b = 146 region. By performing the same correlation analysis as a function of Galactic scale height, we conclude that the region within b = ?175 should be removed from the BEAST maps for CMB studies in order to keep individual Galactic contributions below ~1% of the maps rms.

A modular 100-GHz high-gain scalar corrugated nonbonded platelet antenna

A compact 100-GHz corrugated platelet array antenna has been developed based on a corrugated feed design for the background emission anisotropy scanning telescope (BEAST). The antenna results in a gain of 20 dB, and a bandwidth across the full range of W-band 75-110 GHz. The sidelobes are down by about - 25 dB, a requirement comparable to feed horns used for observation of the cosmic microwave background. The design and fabrication presented in this paper is straightforward and inexpensive. A feature is that because the plates are not permanently bonded, the horn can be disassembled and modified to change its properties.

A 31 pixel flared 100-GHz high-gain scalar corrugated nonbonded platelet antenna array

A compact 100-GHz corrugated platelet antenna array has been developed based on a corrugated feed design for the background emission anisotropy scanning telescope (BEAST) optics. The antennas in the array result in a gain of 20 dB, and a bandwidth across the full range of W-band 75-110 GHz. The side lobes are down by about -25 dB, a requirement comparable to feed horns used for observation of the cosmic microwave background. The design and fabrication presented in this letter is straightforward and inexpensive. A feature is that because the plates are not permanently bonded, the horn can be disassembled and modified to change its properties such as addition of flare plates or modified rib structures.

Optical modeling for a laser phased-array directed energy system

We present results of optical simulations for a laser phased array directed energy system. The laser array consists of individual optical elements in a square or hexagonal array. In a multi-element array, the far-field beam pattern depends on both mechanical pointing stability and on phase relationships between individual elements. The simulation incorporates realistic pointing and phase errors. Pointing error components include systematic offsets to simulate manufacturing and assembly variations. Pointing also includes time-varying errors that simulate structural vibrations, informed from random vibration analysis of the mechanical design. Phase errors include systematic offsets, and time-varying errors due to both mechanical vibration and temperature variation in the fibers. The optical simulation is used to determine beam pattern and pointing jitter over a range of composite error inputs. Results are also presented for a 1 m aperture array with 10 kW total power, designed as a stand-off system on a dedicated asteroid diversion/capture mission that seeks to evaporate the surface of the target at a distance of beyond 10 km. Phase stability across the array of λ/10 is shown to provide beam control that is sufficient to vaporize the surface of a target at 10 km. The model is also a useful tool for characterizing performance for phase controller design in relation to beam formation and pointing.

Directed energy planetary defense

Asteroids and comets that cross Earth’s orbit pose a credible risk of impact, with potentially severe disturbances to Earth and society. Numerous risk mitigation strategies have been described, most involving dedicated missions to a threatening object. We propose an orbital planetary defense system capable of heating the surface of potentially hazardous objects to the vaporization point as a feasible approach to impact risk mitigation. We call the system DE-STAR for Directed Energy System for Targeting of Asteroids and exploRation. DE-STAR is a modular phased array of kilowatt class lasers powered by photovoltaics. Modular design allows for incremental development, test, and initial deployment, lowering cost, minimizing risk, and allowing for technological co-development, leading eventually to an orbiting structure that would be developed in stages with both technological and target milestones. The main objective of DE-STAR is to use the focused directed energy to raise the surface spot temperature to ~3,000K, allowing direct vaporization of all known substances. In the process of heating the surface ejecting evaporated material a large reaction force would alter the asteroid’s orbit. The baseline system is a DE-STAR 3 or 4 (1-10km array) depending on the degree of protection desired. A DE-STAR 4 allows for asteroid engagement starting beyond 1AU with a spot temperature sufficient to completely evaporate up to 500-m diameter asteroids in one year. Small asteroids and comets can be diverted/evaporated with a DESTAR 2 (100m) while space debris is vaporized with a DE-STAR 1 (10m).

MEMS-based tunable filters for compact IR spectral imaging

Arrays of independently tunable MEMS Fabry-Perot filters have been developed that enable spectral tuning over the range of 11 - 8 microns with a filter bandwidth of ~ 120 nm. Actuation is provided using a MEMS driver IC that is hybridized to the MEMS chip. Combining the filter array with an IR FPA enables spatially-resolved spectral tuning in a compact architecture. Tunable spectral response data from the first integrated tunable filter / FPA device are presented.

Local phase control for a planar array of fiber laser amplifiers

Arrays of phase-locked lasers have been developed for numerous directed-energy applications. Phased-array designs are capable of producing higher beam intensity than similar sized multi-beam emitters, and also allow beam steering and beam profile manipulation. In phased-array designs, individual emitter phases must be controllable, based on suitable feedback. Most current control schemes sample individual emitter phases, such as with an array-wide beam splitter, and compare to a master phase reference. Reliance on a global beam splitter limits scalability to larger array sizes due to lack of design modularity. This paper describes a conceptual design and control scheme that relies only on feedback from the array structure itself. A modular and scalable geometry is based on individual hexagonal frames for each emitter; each frame cell consists of a conventional lens mounted in front of the fiber tip. A rigid phase tap structure physically connects two adjacent emitter frame cells. A target sensor is mounted on top of the phase tap, representing the local alignment datum. Optical sensors measure the relative position of the phase tap and target sensor. The tap senses the exit phase of both emitters relative to the target normal plane, providing information to the phase controller for each emitter. As elements are added to the array, relative local position data between adjacent phase taps allows accurate prediction of the relative global position of emitters across the array, providing additional constraints to the phase controllers. The approach is scalable for target distance and number of emitters without loss of control.

A 100-GHz high-gain tilted corrugated nonbonded platelet antenna

A compact 100-GHz corrugated platelet array antenna with an internal tilt has been developed based on a untilted platelet antenna design similar to W-band electroformed horns for the background emission anisotropy scanning telescope (BEAST). The antenna results in a gain of 20 dB, and a beam launching bandwidth across the full range of W-band 75-110 GHz as measured by a vector network analyzer (VNA), with beam tests performed at 90 GHz. The side lobes are down by about -25 dB, a requirement comparable to feed horns used for observation of the cosmic microwave background. The design and fabrication presented in this paper is straightforward and inexpensive. One innovative feature of this array is that the horn can be disassembled and modified to change its properties since the plates are not permanently bonded. A second innovative feature is the ability to direct the horns with an internal tilt without significantly adversely affecting sidelobes and cross-polar pickup. This is useful for large focal plane arrays of detectors where horns must be directed toward a central region such as a telescope mirror.

Imaging the cosmic microwave background: The BEAST experiment

We describe the Santa Barbara BEAST experiment, a balloon borne telescope to image the Cosmic Microwave Background (CMB) radiation anisotropy pattern. Some aspects of the map making pipeline are also discussed.