45 research outputs found
The performance of arm locking in LISA
For the laser interferometer space antenna (LISA) to reach it's design
sensitivity, the coupling of the free running laser frequency noise to the
signal readout must be reduced by more than 14 orders of magnitude. One
technique employed to reduce the laser frequency noise will be arm locking,
where the laser frequency is locked to the LISA arm length. This paper details
an implementation of arm locking, studies orbital effects, the impact of errors
in the Doppler knowledge, and noise limits. The noise performance of arm
locking is calculated with the inclusion of the dominant expected noise
sources: ultra stable oscillator (clock) noise, spacecraft motion, and shot
noise. Studying these issues reveals that although dual arm locking [A. Sutton
& D. A Shaddock, Phys. Rev. D 78, 082001 (2008).] has advantages over single
(or common) arm locking in terms of allowing high gain, it has disadvantages in
both laser frequency pulling and noise performance. We address this by
proposing a hybrid sensor, retaining the benefits of common and dual arm
locking sensors. We present a detailed design of an arm locking controller and
perform an analysis of the expected performance when used with and without
laser pre-stabilization. We observe that the sensor phase changes beneficially
near unity-gain frequencies of the arm-locking controller, allowing a factor of
10 more gain than previously believed, without degrading stability. We show
that the LISA frequency noise goal can be realized with arm locking and
Time-Delay Interferometry only, without any form of pre-stabilization.Comment: 28 pages, 36 figure
Phase measurement device using inphase and quadrature components for phase estimation
A phasemeter for estimating the phase of a signal. For multi-tone signals, multiple phase estimates may be provided. An embodiment includes components operating in the digital domain, where a sampled input signal is multiplied by cosine and sine terms to provide estimates of the inphase and quadrature components. The quadrature component provides an error signal that is provided to a feedback loop, the feedback loop providing a model phase that tends to track the phase of a tone in the input signal. The cosine and sine terms are generated from the model phase. The inphase and quadrature components are used to form a residual phase, which is added to the model phase to provide an estimate of the phase of the input signal. Other embodiments are described and claimed
Experimental Demonstration of Time-Delay Interferometry for the Laser Interferometer Space Antenna
We report on the first demonstration of time-delay interferometry (TDI) for
LISA, the Laser Interferometer Space Antenna. TDI was implemented in a
laboratory experiment designed to mimic the noise couplings that will occur in
LISA. TDI suppressed laser frequency noise by approximately 10^9 and clock
phase noise by 6x10^4, recovering the intrinsic displacement noise floor of our
laboratory test bed. This removal of laser frequency noise and clock phase
noise in post-processing marks the first experimental validation of the LISA
measurement scheme.Comment: 4 pages, 4 figures, to appear in Physical Review Letters end of May
201
Techniques for Solution- Assisted Optical Contacting
A document discusses a solution-assisted contacting technique for optical contacting. An optic of surface flatness Lambda/20 was successfully contacted with one of moderate surface quality, or Lambda/4. Optics used were both ultra-low expansion (ULE) glass (Lambda/4 and Lambda/20) and fused silica (Lambda/20). A stainless steel template of the intended interferometer layout was designed and constructed with three contact points per optic. The contact points were all on a common side of the template. The entire contacting jig was tilted at about 30 . Thus, when the isopropanol was applied, each optic slid due to gravity, resting on the contact points. All of the contacting was performed in a relatively dusty laboratory. A number of successful contacts were achieved where up to two or three visible pieces of dust could be seen. These were clearly visible due to refraction patterns between the optic and bench. On a number of optics, the final step of dropping isopropyl between the surfaces was repeated until a successful contact was achieved. The new procedures realized in this work represent a simplification for optical contacting in the laboratory. They will both save time and money spent during the contacting process, and research and development phases. The techniques outlined are suitable for laboratory experiments, research, and initial development stages
Progress in Interferometry for LISA at JPL
Recent advances at JPL in experimentation and design for LISA interferometry
include the demonstration of Time Delay Interferometry using electronically
separated end stations, a new arm-locking design with improved gain and
stability, and progress in flight readiness of digital and analog electronics
for phase measurements.Comment: 11 pages, 9 figures, LISA 8 Symposium, Stanford University, 201
High-Speed Digital Interferometry
Digitally enhanced heterodyne interferometry (DI) is a laser metrology technique employing pseudo-random noise (PRN) codes phase-modulated onto an optical carrier. Combined with heterodyne interferometry, the PRN code is used to select individual signals, returning the inherent interferometric sensitivity determined by the optical wavelength. The signal isolation arises from the autocorrelation properties of the PRN code, enabling both rejection of spurious signals (e.g., from scattered light) and multiplexing capability using a single metrology system. The minimum separation of optical components is determined by the wavelength of the PRN code
The Physics of LIGO
In the spring term of 1994, I organized a course at Caltech on the The Physics of LIGO (i.e., the physics of the Laser Interferometer Gravitational Wave Observatory). The course consisted of eighteen 1.5-hour-long tutorial lectures, delivered by members of the LIGO team and others, and it was aimed at advanced undergraduates and graduate students in physics, applied physics and in engineering and applied sciences and also at interested postdoctoral fellows, research staff, and faculty
Inhibition of Toxic Shock by Human Monoclonal Antibodies against Staphylococcal Enterotoxin B
BACKGROUND: Staphylococcus aureus is implicated in many opportunistic bacterial infections around the world. Rising antibiotic resistance and few alternative methods of treatment are just two looming problems associated with clinical management of S. aureus. Among numerous virulence factors produced by S. aureus, staphylococcal enterotoxin (SE) B is a secreted protein that binds T-cell receptor and major histocompatibility complex class II, potentially causing toxic shock mediated by pathological activation of T cells. Recombinant monoclonal antibodies that target SEB and block receptor interactions can be of therapeutic value. METHODOLOGY/PRINCIPAL FINDINGS: The inhibitory and biophysical properties of ten human monoclonal antibodies, isolated from a recombinant library by panning against SEB vaccine (STEBVax), were examined as bivalent Fabs and native full-length IgG (Mab). The best performing Fabs had binding affinities equal to polyclonal IgG, low nanomolar IC(50)s against SEB in cell culture assays, and protected mice from SEB-induced toxic shock. The orthologous staphylococcal proteins, SEC1 and SEC2, as well as streptococcal pyrogenic exotoxin C were recognized by several Fabs. Four Fabs against SEB, with the lowest IC(50)s, were converted into native full-length Mabs. Although SEB-binding kinetics were identical between each Fab and respective Mab, a 250-fold greater inhibition of SEB-induced T-cell activation was observed with two Mabs. CONCLUSIONS/SIGNIFICANCE: Results suggest that these human monoclonal antibodies possess high affinity, target specificity, and toxin neutralization qualities essential for any therapeutic agent
Website Identity Notification: Testing the Simplest Thing That Could Possibly Work
Users are used to authenticating themselves to websites, but not for websites to authenticate to them. One readily available mechanism that may help users make safer online decisions lies in website certificates that contain website identity information. Fraudulent websites are now short-lived and present valid certificates without any identity information. Our goal was to create and test the effectiveness of simpler certificate interfaces, made to help users differentiate between identity-verified websites and those without such verification, and thus, potentially fraudulent. We conducted a study with a certificate interface prototype with simple identity notification types. Our findings suggest that presenting identity information to users can help them differentiate between real and potentially fraudulent websites. Some users were suspicious of the notifications and incorrectly felt that they could make decisions based on website appearance, so building user background knowledge is essential