Offline estimation of decay time for an optical cavity with a low pass filter cavity model

This Letter presents offline estimation results for the decay-time constant for an experimental Fabry–Perot optical cavity for cavity ring-down spectroscopy (CRDS). The cavity dynamics are modeled in terms of a low pass filter (LPF) with unity DC gain. This model is used by an extended Kalman filter (EKF) along with the recorded light intensity at the output of the cavity in order to estimate the decay-time constant. The estimation results using the LPF cavity model are compared to those obtained using the quadrature model for the cavity presented in previous work by Kallapur et al. The estimation process derived using the LPF model comprises two states as opposed to three states in the quadrature model. When considering the EKF, this means propagating two states and a (2x2) covariance matrix using the LPF model, as opposed to propagating three states and a (3×3) covariance matrix using the quadrature model. This gives the former model a computational advantage over the latter and leads to faster execution times for the corresponding EKF. It is shown in this Letter that the LPF model for the cavity with two filter states is computationally more efficient, converges faster, and is hence a more suitable method than the three-state quadrature model presented in previous work for real-time estimation of the decay-time constant for the cavity

Towards online ageing detection in transformer oil: a review

Transformers play an essential role in power networks, ensuring that generated power gets to consumers at the safest voltage level. However, they are prone to insulation failure from ageing, which has fatal and economic consequences if left undetected or unattended. Traditional detection methods are based on scheduled maintenance practices that often involve taking samples from in situ transformers and analysing them in laboratories using several techniques. This conventional method exposes the engineer performing the test to hazards, requires specialised training, and does not guarantee reliable results because samples can be contaminated during collection and transportation. This paper reviews the transformer oil types and some traditional ageing detection methods, including breakdown voltage (BDV), spectroscopy, dissolved gas analysis, total acid number, interfacial tension, and corresponding regulating standards. In addition, a review of sensors, technologies to improve the reliability of online ageing detection, and related online transformer ageing systems is covered in this work. A non-destructive online ageing detection method for in situ transformer oil is a better alternative to the traditional offline detection method. Moreover, when combined with the Internet of Things (IoT) and artificial intelligence, a prescriptive maintenance solution emerges, offering more advantages and robustness than offline preventive maintenance approaches

A high-power laser transmitter for ground-based and airborne water-vapor measurements in the troposphere

A gain-switched high-power single-frequency Ti:sapphire laser was developed. It is pumped with a frequency-doubled diode-pumped Nd:YAG laser. The laser fulfills the requirements for a transmitter of a water-vapor differential absorption lidar (DIAL), intended for accurate high temporally- and spatially-resolved measurements from the ground to the upper troposphere. The laser was developed using thermal, resonator-design, spectral, and pulse-evolution models. There were layouts assembled for operation at 935 nm and 820 nm optimized for airborne and groundbased measurements, respectively. A birefringent filter and an external-cavity diode laser as an injection seeder are controlling the spectral properties of the transmitter. With a frequency stability of 99.7 %, the total error from the laser properties is smaller than 5 % for water-vapor measurements in the troposphere. The laser beam profile is near-Gaussian with M2 < 2. The achieved laser power was 4.5 W at 935 nm and 7 W at 820 nm at repetition rate of 250 Hz. These values are the highest reported for a single-frequency Ti:sapphire laser. As a part of a ground-based water-vapor DIAL system, the transmitter was deployed during the measurement campaign COPS (Convective and Orographically-induces Precipitation Study). Comparisons with radiosondes confirmed a high precision of the acquired water-vapor day- and nighttime measurements.Ein verstärkungsgeschalter leistungsstarker monofrequenter Ti:Saphir-Laser, der mit einem frequenzverdoppeltem diodengepumpten Nd:YAG Laser gepumpt ist, wurde entwickelt. Der Laser erfüllt die hohen Anforderungen eines Transmitters für ein Wasserdampf-Differential-Absorption-Lidar (DIAL), der mit hoher zeitlicher und räumlicher Auflösung Messungen innerhalb der Troposphäre durchführen soll. Für die Entwicklung des Lasers wurden Modelle für die thermischen Eigenschaften, das Resonatordesign, das Emissionspektrum sowie den Pulsaufbau verwendet. Es wurden Laseraufbauten gefertigt, die für den Einsatz bei 935 nm für Flugzeug-Plattformen bzw. 820 nm für bodengestützte Messungen optimiert sind. Ein doppelbrechender Filter und ein External-Cavity-Diodenlaser als Injection-seeder sorgen für die hohe Güte der spektralen Eigenschaften des Senders. Mit einer Frequenzstabilität 99,7 % ist der Gesamtfehler der Wasserdampfmessungen in der Troposphäre, der durch die Eigenschaften des Lasers bedingt ist, kleiner als 5 %. Werte der mittleren Ausgangsleistung von 4,5 W bei 935 nm und 7 W bei 820 nm sind die zur Zeit höchsten, die von einem monofrequenten Ti:Saphir-Laser mit nahezu gaussförmigem Strahlprofil und M2 < 2 erreicht wurden. Als Teil eines bodengestützten Wasserdampf DIALs, wurde der Transmitter während der Messkampagne COPS (Convective and Orographically-induces Precipitation Study) verwendet. Vergleiche von Messungen bei Tag und bei Nacht mit Radiosondenaufstiegen zeigten gute Übereinstimmungen

Sensitivity and performance of the Advanced LIGO detectors in the third observing run

On April 1st, 2019, the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), joined by the Advanced Virgo detector, began the third observing run, a year-long dedicated search for gravitational radiation. The LIGO detectors have achieved a higher duty cycle and greater sensitivity to gravitational waves than ever before, with LIGO Hanford achieving angle-averaged sensitivity to binary neutron star coalescences to a distance of 111 Mpc, and LIGO Livingston to 134 Mpc with duty factors of 74.6% and 77.0% respectively. The improvement in sensitivity and stability is a result of several upgrades to the detectors, including doubled intracavity power, the addition of an in-vacuum optical parametric oscillator for squeezed-light injection, replacement of core optics and end reaction masses, and installation of acoustic mode dampers. This paper explores the purposes behind these upgrades, and explains to the best of our knowledge the noise currently limiting the sensitivity of each detector

Sensitivity and performance of the Advanced LIGO detectors in the third observing run

On April 1st, 2019, the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), joined by the Advanced Virgo detector, began the third observing run, a year-long dedicated search for gravitational radiation. The LIGO detectors have achieved a higher duty cycle and greater sensitivity to gravitational waves than ever before, with LIGO Hanford achieving angle-averaged sensitivity to binary neutron star coalescences to a distance of 111 Mpc, and LIGO Livingston to 134 Mpc with duty factors of 74.6% and 77.0% respectively. The improvement in sensitivity and stability is a result of several upgrades to the detectors, including doubled intracavity power, the addition of an in-vacuum optical parametric oscillator for squeezed-light injection, replacement of core optics and end reaction masses, and installation of acoustic mode dampers. This paper explores the purposes behind these upgrades, and explains to the best of our knowledge the noise currently limiting the sensitivity of each detector

Sensitivity and performance of the Advanced LIGO detectors in the third observing run

On April 1st, 2019, the Advanced Laser Interferometer Gravitational-Wave Observatory (aLIGO), joined by the Advanced Virgo detector, began the third observing run, a year-long dedicated search for gravitational radiation. The LIGO detectors have achieved a higher duty cycle and greater sensitivity to gravitational waves than ever before, with LIGO Hanford achieving angle-averaged sensitivity to binary neutron star coalescences to a distance of 111 Mpc, and LIGO Livingston to 134 Mpc with duty factors of 74.6% and 77.0% respectively. The improvement in sensitivity and stability is a result of several upgrades to the detectors, including doubled intracavity power, the addition of an in-vacuum optical parametric oscillator for squeezed-light injection, replacement of core optics and end reaction masses, and installation of acoustic mode dampers. This paper explores the purposes behind these upgrades, and explains to the best of our knowledge the noise currently limiting the sensitivity of each detector. © 2020 authors. Published by the American Physical Society

Semiconductor Optical Amplifier for Next Generation of High Data Rate Optical Packet-Switched Networks

This chapter provides an overview of considerations for the development of semiconductor optical amplifiers (SOA) for the next generations of packet-switched optical networks. SOA devices are suitable candidates in order to realize high-performance optical gates due to their high extinction ratio and fast switching time. However such devices also introduce linear and nonlinear noise. The impact of SOA devices on several modulation formats via theoretical model, numerical simulation, and experimental validation is studied. Impairments introduced by SOAs are considered in order to derive some general network design rules

Wavefront modelling and sensing for advanced gravitational wave detectors

The Advanced Laser Interferometer Gravitational-wave Observatory (aLIGO) directly detected gravitational waves for the first time on the 14th of September 2015. In 2017 the detection of gravitational waves from a binary neutron star merger was subsequently followed up by observations by optical and radio astronomers — the first time an astrophysical event was observed by two completely separate astrophysical signals. This marked the beginning of multi-messenger astronomy. Since then 90 astrophysical events have been observed using gravitational waves. To increase the rate of event detection the sensitivity of gravitational wave detectors must be improved. Current state of the art gravitational wave detectors are optical interferometers in the dual recycled Fabry-Perot Michelson (DRFPMI) configuration with quantum squeezed light injected to reduce vacuum noise. Future plans to improve the sensitivity further rely on increasing the circulating laser power and improving the efficiency of quantum squeezing. Squeezing efficiency is drastically reduced by optical losses in the interferometer of which mode mismatch is a large component. Higher laser power introduces larger thermal distortions in the interferometer, which increase mode mismatch. This thesis covers topics relevant to optical modelling of coupled cavity interferometers such as the DRFPMI with a focus on mode mismatch. Novel applications in aLIGO commissioning based on existing mode mismatch sensing techniques using the output mode cleaner (OMC) are presented. A new mode mismatch sensing technique based on transverse higher order mode sidebands is demonstrated on an optical tabletop and its applications to mode mismatch sensing in aLIGO is discussed. A new optical modelling framework based on linear canonical transformations and signal flow graph theory is also presented.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 202