Ellipsometric measurement of magneto-optical Kerr rotation at normal incidence

[[abstract]]Two simple methods were introduced for measuring the magneto-optical Kerr rotation when the light is incident upon the surface of the magneto-optical media at zero degree angle of incidence. The methods can readily be implemented on an existing ellipsometer[[fileno]]2030150010035[[department]]電機工程學

Silicon nitride and silica quarter-wave stacks for low-thermal-noise mirror coatings

This study investigates a multilayer high reflector with new coating materials for next-generation laser interferometer gravitational wave detectors operated at cryogenic temperatures. We use the plasma-enhanced chemical vapor deposition method to deposit amorphous silicon nitride and silica quarter-wave high-reflector stacks and studied the properties pertinent to the coating thermal noise. Room- and cryogenic-temperature mechanical loss angles of the silicon nitride and silica quarter-wave bilayers are measured using the cantilever ring-down method. We show, for the first time, that the bulk and shear loss angles of the coatings can be obtained from the cantilever ring-down measurement, and we use the bulk and shear losses to calculate the coating thermal noise of silicon nitride and silica high-reflector coatings. The mechanical loss angle of the silicon nitride and silica bilayer is dispersive with a linear weakly positive frequency dependence, and, hence, the coating thermal noise of the high reflectors show a weakly positive frequency dependence in addition to the normal 1/ vf dependence. The coating thermal noise of the silicon nitride and silica high-reflector stack is compared to the lower limit of the coating thermal noise of the end test mirrors of ET-LF, KAGRA, LIGO Voyager, and the directly measured coating thermal noise of the current coatings of Advanced LIGO. The optical absorption of the silicon nitride and silica high reflector at 1550 nm is 45.9 ppm. Using a multimaterial system composed of seven pairs of ion-beam-sputter deposited Ti∶Ta2O5 and silica and nine pairs of silicon nitride and silica on a silicon substrate, the optical absorption can be reduced to 2 ppm, which meets the specification of LIGO Voyager

A User Authentication Scheme Using Physiological and Behavioral Biometrics for Multitouch Devices

With the rapid growth of mobile network, tablets and smart phones have become sorts of keys to access personal secured services in our daily life. People use these devices to manage personal finances, shop on the Internet, and even pay at vending machines. Besides, it also helps us get connected with friends and business partners through social network applications, which were widely used as personal identifications in both real and virtual societies. However, these devices use inherently weak authentication mechanism, based upon passwords and PINs that is not changed all the time. Although forcing users to change password periodically can enhance the security level, it may also be considered annoyances for users. Biometric technologies are straightforward because of the simple authentication process. However, most of the traditional biometrics methodologies require diverse equipment to acquire biometric information, which may be expensive and not portable. This paper proposes a multibiometric user authentication scheme with both physiological and behavioral biometrics. Only simple rotations with fingers on multitouch devices are required to enhance the security level without annoyances for users. In addition, the user credential is replaceable to prevent from the privacy leakage

Thickness-dependent crystallization on thermal anneal for titania/silica nm-layer composites deposited by ion beam sputter method.

Crystallization following thermal annealing of thin film stacks consisting of alternating nm-thick titania/silica layers was investigated. Several prototypes were designed, featuring a different number of titania/silica layer pairs, and different thicknesses (in the range from 4 to 40 nm, for the titania layers), but the same nominal refractive index (2.09) and optical thickness (a quarter of wavelength at 1064 nm). The prototypes were deposited by ion beam sputtering on silicon substrates. All prototypes were found to be amorphous as-deposited. Thermal annealing in air at progressive temperatures was subsequently performed. It was found that the titania layers eventually crystallized forming the anatase phase, while the silica layers remained always amorphous. However, progressively thinner layers exhibited progressively higher threshold temperatures for crystallization onset. Accordingly it can be expected that composites with thinner layers will be able to sustain higher annealing temperatures without crystallizing, and likely yielding better optical and mechanical properties for advanced coatings application. These results open the way to the use of materials like titania and hafnia, that crystallize easily under thermal anneal, but ARE otherwise promising candidate materials for HR coatings necessary for cryogenic 3rd generation laser interferometric gravitational wave detectors

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Experimental determination of thin film thickness by polarized light scattering

[[abstract]]Presents preliminary results on the investigation of Muller matrix characterization of thin film edge. The authors found that the angular distribution of some of the Muller matrix elements of silicon oxide film edge are very sensitive to edge height, i.e. film thickness. This property can be utilized to determine film thickness. By establishing a well calibrated curve between variation of certain matrix elements and thickness, routine measurement of film thickness can be made by measuring that particular matrix element and use the calibration curve to obtain the thickness[[fileno]]2030150010038[[department]]電機工程學

LOCK-IN GROWTH IN A RING LASER GYRO.

[[abstract]]The authors report an experiment on lock-in growth and their attempt to explain the phenomenon with a burn-in grating theory. They also hope to stimulate discussion and work in this area. The experiment is significant in two respects. First of all, the lock-in growth is relatively small and seems to be bounded and exhibits a saturation effect. Secondly, the increase in lock-in was reversible after an initial non-recoverable level was reached.[[fileno]]2030150010040[[department]]電機工程學

Tilt-target magnetron sputter for deposition of magnetooptical disk

[[abstract]]A 3.5-inch magnetooptical disk is made by tilting the TbFeCo target in a DC circular magnetron sputtering process. The composition of the recording layer is controlled by using the Tb-rich deposition area. The optimal tilt angle of our target for uniform radial composition distribution on the disk is found to be about 15°. A model was proposed to explain the observed Tb, Fe and Co content variation with the tilt angle of the target. The dynamic read/write test also showed that good carrier to noise ratio (CNR) was obtained at this angle. A new deposition process for magnetooptical (M-O) disk based on the tilt target method is proposed; it has the merits of enabling simultaneous deposition of multiple disks. The CNR of the disk made at 15° tilt angle is 53 dB.[[fileno]]2030150010029[[department]]電機工程學