Measurement of ultra-low optical absorption in mirror substrates for the next-generation gravitational wave detectors

A key element for the next-generation gravitational wave interferometers are optical substrates characterized by a very low absorption level in the infrared at cryogenic temperatures (a few part per million per cm). In this respect the precise characterization of optical losses is mandatory. However the target absorption levels are so small that a direct measurement is challenging. Moreover there are currently no developed protocols for such characterization in cryogenic conditions. In this thesis we propose to build a setup for this purpose based on the measurement of the heating of a test substrate due to the absorbed power of an IR laser. The final absorption measurement will be performed with the use of an innovative method, compared to the ones that are commonly used in literature, the Modulation Calorimetry technique. The silicon absorption coefficient estimate that is obtained in the experiment that is presented in this thesis will be compared to the only existing measurement of the coefficient in analogous environmental conditions that is currently present in literature and the consequences of this findings on the Einstein Telescope design will be analyzed

Optical absorption of Si at 1550 nm at cryogenic temperatures

The new generation of gravitational wave interferometers are conceived to work at cryogenic temperatures to improve the signal-to-noise ratio by reducing unwanted noise sources associated to thermal excitations in the mirror test masses. Due to its favorable behavior at low temperatures, Silicon (Si) is nowadays considered as the most promising candidate to fabricate the suspended masses. However, another key requirement that needs to meet the design specifications is that the Si substrates remain very transparent at the operation conditions, with optical losses of the order of 1 ppm or below. In spite of the fact that Si is a widely investigated material, there are very scarce studies of its behavior at low temperature when such extremely small absorption levels are involved. In this thesis we propose to optimize and exploit a newly designed set-up to measure Si optical absorption with very high sensitivity and in cryogenic conditions. The experiment consists in measuring the temperature increase of a Si sample when the latter is illuminated by a high-power laser beam at the target wavelength (1550 nm).The new generation of gravitational wave interferometers are conceived to work at cryogenic temperatures to improve the signal-to-noise ratio by reducing unwanted noise sources associated to thermal excitations in the mirror test masses. Due to its favorable behavior at low temperatures, Silicon (Si) is nowadays considered as the most promising candidate to fabricate the suspended masses. However, another key requirement that needs to meet the design specifications is that the Si substrates remain very transparent at the operation conditions, with optical losses of the order of 1 ppm or below. In spite of the fact that Si is a widely investigated material, there are very scarce studies of its behavior at low temperature when such extremely small absorption levels are involved. In this thesis we propose to optimize and exploit a newly designed set-up to measure Si optical absorption with very high sensitivity and in cryogenic conditions. The experiment consists in measuring the temperature increase of a Si sample when the latter is illuminated by a high-power laser beam at the targe

Using the Hottest Particles in the Universe to Probe Icy Solar System Worlds

We present results of our Phase 1 NIAC Study to determine the feasibility of developing a competitive, low cost, low power, low mass passive instrument to measure ice depth on outer planet ice moons, such as Europa, Ganymede, Callisto, and Enceladus. Indirect measurements indicate that liquid water oceans are likely present beneath the icy shells of such moons (see e.g.,the JPL press release "The Solar System and Beyond is Awash in Water"), which has important astrobiological implications. Determining the thickness of these ice shells is challenging given spacecraft SWaP (Size, Weight and Power) resources. The current approach uses a suite of instruments, including a high power, massive ice penetrating radar. The instrument under study, called PRIDE (Passive Radio Ice Depth Experiment) exploits a remarkable confluence between methods from the high energy particle physics and the search for extraterrestrial life within the solar system. PRIDE is a passive receiver of a naturally occurring radio frequency (RF) signal generated by interactions of deep penetrating Extremely High Energy (> 10^18 eV) cosmic ray neutrinos. It could measure ice thickness directly, and at a significant savings to spacecraft resources. At RF frequencies the transparency of modeled Europan ice is up to many km, so an RF sensor in orbit can observe neutrino interactions to great depths, and thereby probe the thickness of the ice layer

Nanoscale magnetophotonics

This Perspective surveys the state-of-the-art and future prospects of science and technology employing the nanoconfined light (nanophotonics and nanoplasmonics) in combination with magnetism. We denote this field broadly as nanoscale magnetophotonics. We include a general introduction to the field and describe the emerging magneto-optical effects in magnetoplasmonic and magnetophotonic nanostructures supporting localized and propagating plasmons. Special attention is given to magnetoplasmonic crystals with transverse magnetization and the associated nanophotonic non-reciprocal effects, and to magneto-optical effects in periodic arrays of nanostructures. We give also an overview of the applications of these systems in biological and chemical sensing, as well as in light polarization and phase control. We further review the area of nonlinear magnetophotonics, the semiconductor spin-plasmonics, and the general principles and applications of opto-magnetism and nano-optical ultrafast control of magnetism and spintronics

Generation of high power single-cycle and multiple-cycle terahertz pulses

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 131-141).In this thesis, we present experimental methods and results of tabletop generation of high power single-cycle and frequency-tunable multiple-cycle terahertz (THz) pulses pumped with near-infrared ultrashort optical pulses at 1 kHz and 10 Hz repetition rates. Single-cycle THz pulses with sub-picosecond duration and more than 50 pJ pulse energy, and multiple-cycle THz pulses with picosecond duration and more than 10 pJ pulse energy, are achieved respectively. These THz outputs are very close approximations to Gaussian beams, and can be well collimated and focused into samples for time-resolved spectroscopic experiments. This may allow for explorations in coherent nonlinear spectroscopy in the THz region such as the photon echo and multidimensional spectroscopy, revealing novel phenomena in solids, liquids, gases, and complex materials.by Zhao Chen.S.M

Rapid Fluctuations in Solar Flares

Topics addressed include: X-rays; radio and microwaves; thermal response; plasma physics; and future plans

Assessment of Coordination and Proprioception in Youth With Autism Spectrum Disorder

Autism spectrum disorder (ASD) is characterized by social and communicative delays. It is known that those with ASD exhibit lower activity levels and decreased proprioception to some extent. The biomechanics of movement in ASD has not been assessed thoroughly enough to provide information on ASD specific movement patterns, and no studies have been performed examining work and recovery. The purpose of this study is to examine whether 1) inter-limb and intra-limb coordination patterns during walking and running differ between youth with ASD and neurotypical sex, age, and BMI-matched controls. Youth with ASD (N=8) and their BMI, age, and sex matched controls (N=8) performed walking at their self-selected speed and also at a standardized speed of 1.3 m/s for at least five trials each. An eight-camera motion capture system was used to collect three-dimensional (3D) kinematics for each subject. After in-lab data collection, subjects were given an accelerometer to wear to measure physical activity levels over a span of at least four days. To analyze the data, angle-angle plots were constructed for the left upper-arm and right thigh, and right shank-foot. Vector coding was used to obtain coupling angle and coupling angle variability information. No significant differences existed in coordination patterns or physical activity levels between the two groups. Upper-arm dominance and antiphase upper arm/thigh patterns were significantly related to minutes of vigorous physical activity (Rho: -0.63, p\u3c0.01 & Rho: 0.58, p=0.02, respectively). According to these results, there are no differences in coordination between those with and without ASD

Gigahertz Bandwidth and Nanosecond Timescales: New Frontiers in Radio Astronomy Through Peak Performance Signal Processing

Abstract In the past decade, there has been a revolution in radio-astronomy signal processing. High bandwidth receivers coupled with fast ADCs have enabled the collection of tremendous instantaneous bandwidth, but streaming computational resources are struggling to catch up and serve these new capabilities. As a consequence, there is a need for novel signal processing algorithms capable of maximizing these resources. This thesis responds to the demand by presenting FPGA implementations of a Polyphase Filter Bank which are an order of magnitude more efficient than previous algorithms while exhibiting similar noise performance. These algorithms are showcased together alongside a broadband RF front-end in Starburst: a 5 GHz instantaneous bandwidth two-element interferometer, the first broadband digital sideband separating astronomical interferometer.  Starburst technology has been applied to three instruments to date. Abstract Wielding tremendous computational power and precisely calibrated hardware, low frequency radio telescope arrays have potential greatly exceeding their current applications.  This thesis presents new modes for low frequency radio-telescopes, dramatically extending their original capabilities.  A microsecond-scale time/frequency mode empowered the Owens Valley Long Wavelength Array to inspect not just the radio sky by enabling the testing of novel imaging techniques and detecting overhead beacon satellites, but also the terrestrial neighborhood, allowing for the characterization and mitigation of nearby sources of radio frequency interference (RFI).  This characterization led to insights prompting a nanosecond-scale observing mode to be developed, opening new avenues in high energy astrophysics, specifically related to the radio frequency detection of ultra-high energy cosmic rays and neutrinos. Abstract Measurement of the flux spectrum, composition, and origin of the highest energy cosmic ray events is a lofty goal in high energy astrophysics. One of the most powerful new windows has been the detection of associated extensive air showers at radio frequencies. However, all current ground-based systems must trigger off an expensive and insensitive external source such as particle detectors - making detection of the rare, high energy events uneconomical.  Attempts to make a direct detection in radio-only data have been unsuccessful despite numerous efforts. The problem is even more severe in the case of radio detection of ultra-high energy neutrino events, which cannot rely on in-situ particle detectors as a triggering mechanism. This thesis combines the aforementioned nanosecond-scale observing mode with real-time, on-FPGA RFI mitigation and sophisticated offline post-processing.  The resulting system has produced the first successful ground based detection of cosmic rays using only radio instruments. Design and measurements of cosmic ray detections are discussed, as well as recommendations for future cosmic ray experiments.  The presented future designs allow for another order of magnitude improvement in both sensitivity and output data-rate, paving the way for the economical ground-based detection of the highest energy neutrinos.</p

Flare emission observed in high resolution and comparison with numerical modeling

As one of the most intense activities on the solar surface, flares have been extensively observed and studied ever since the first report. The standard model of solar flares has been established and commonly accepted. However, many limitations from the researching tools have left some of the problems unsolved or controversial. For example, the density of electrons in the corona is lower than it is required to activate the observed emission in HXR, and the mechanism that these electron beams can penetrate down to lower chromosphere is unclear. Many theoretical scenarios were suggested, and more observations had been in need. Multi-wavelength observations are powerful tools in revealing the details of solar flares. Following the improvement of research instruments, such as spacecraft, telescopes, charged-coupled devices (CCDs) and computing devices, we are able to make better use of the emissions for understanding the flare. For instance, Goode Solar Telescope in Big Bear Solar Observatory (BBSO/GST), equipped with a 1.6-meter major mirror, has been dedicated to solar observation. With a resolution up to about 0.03 arc-second per pixel, it is capable of providing detailed information of fine structures in solar flares. Interface Region Imaging Spectrograph (IRIS) offers images in the ultraviolet (UV) together with spectrograms over several wavelength windows, including tens of spectral lines that are powerful in diagnosing the flaring atmosphere. Solar Dynamic Observatory (SDO) records solar full-disk images in multiple wavelengths, from the extreme ultraviolet (EUV) to the visible continuum, covering a wide range of temperatures. Moreover, thanks to the improvement of computing power, more plausible codes are developed to calculate the flaring atmosphere. Taking advantages of the high-resolution instruments and novel numerical modeling packages, the dissertation work cover several topics, from the energetics of white-light emission in macro-scope to the sub-arcsecond features on flare ribbons in multiple wavelengths and the corresponding modeling. As summarized below, the major results provide additional and important constraints in understanding the flare emission and instructive for future observations and developing of new modeling: Using the SDO/HMI images and RHESSI hard X-ray (HXR) spectra, the relationship between white-light (WL) and HXR emissions id found. The correlation between HXR power-law indices and WL emissions indicates the importance of non-thermal electrons\u27 energy distribution in stimulating the WL flares. This suggests the direct heating mechanism accounts for the core of the compact WL flares. The WL flares, which are considered to be in the most violent class, and solar energetic particle (SEP) events are under survey, and no clear correlation is found between them. Straightforward speculation is that the acceleration process could be different for SEPs and the energetic electrons powering WLFs in the events analyzed. Emissions from chromospheric spectral lines, Mg II k line and Hα are observed using IRIS and BBSO/GST, respectively for the flare on 2015-06-22. Unique features of the line profiles are observed in narrow edge of the ribbon. Numerical study using combination code of RADYN and RH suggests the formation height and corresponding thermodynamic conditions of the distinct line feature. Inspired by a study of solar flares in He I 10830 A line that observed enhancement absorption in the frontiers of flare ribbons, we analyze the evolution of the line emission in numerical models and compare it with observations. The result suggests that the temperatures and free electron densities at heights of 1.3-1.5 Mm should be larger than ~104K and 6*1011cm3 are thresholds for the line to start being in emission. With the high-resolution vector magnetogram, in wavelength of 1.56 um that is from the lower layer of the atmosphere, a transient rotation of the local magnetic field is observed in the leading edge of 2015-06-22 flare ribbon. The azimuth angle rotates closer to the extrapolated potential field. This newly observed magnetic field activity may be related to the energetic electron beams, but cannot be well explained using existing models