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The designed [M(OH)2]3(IO3)(SeO4)·H2O (M = Ga and In) feature ∞[MO2(OH)2]3− layers composed of M3O6(OH)9 trimeric units capped by SeO4 and IO3 groups from different sides of the layers. They exhibit moderate SHG effects and large LIDT values.

The first metal iodate-phosphates, namely, Cd2(IO3)(PO4) and Cd1.62Mg0.38(IO3)(PO4), display novel crystal structures and comprehensive SHG performance.

LaBS3 possesses a large SHG effect, high laser-induced damage threshold, wide band gap, and high thermal stability.

A new paradigm for designing high-performance PM NLO crystals: a novel PM fresnoite oxychalcogenide, Ba2SnSSi2O7, has been successfully designed and obtained by the isomorphous substitution strategy, on the basis of the NPM parent Ba2TiOSi2O7.

Herein, a novel metal polyiodate, namely, Ba4Ag5(IO3)6(I3O8)3(I4O11)2, has been prepared by using H3PO4 (≥85 wt% in H2O) as the reaction medium.

Cd4REO(BO3)3 (RE = Sm, Eu, Tb) obtained by introducing non-centrosymmetric (NCS) groups into borates have high stability and good SHG signals and fluorescence performance.

A promising nonlinear optical material, CaCe(IO3)3(IO3F)F, containing both IO3− and IO3F2− anions, has been reported.

The first NLO-active metal iodate-phosphates, namely, Cd

VELOX-CI was launched on December 16, 2015 into the near-equatorial orbit. It is the second micro-satellite of Satellite Research Center (SaRC) in Nanyang Technological University in Singapore. VELOX-CI is designed to explore the potential of using the commercial-off-the-shelf (COTS) GPS receivers for RO mission for the first time. Three GPS antennas are located at the zenith, forward-velocity, and after-velocity directions. In total, VELOX-CI collected 240 radio occultation (RO) missions (570 h) from 2015 to 2018 with mission durations ranging from 0.5 to 16.7 h. The lowest penetration altitude from the COTS receivers reaches 6 km. In this paper, the RO performance of the VELOX-CI is evaluated and validated with both ground-based and space-based measurements. Tropospheric and ionospheric profiles obtained from VELOX-CI are also compared with assimilative atmospheric models and empirical ionospheric models, respectively. Results show that with proper sampling frequencies (5–20 Hz), the refractivity error estimated by VELOX-CI RO is below 5% at altitudes below 25 km compared to reanalysis model estimations and radiosonde measurements. The observed ionospheric peak density and height show reasonable ranges for both daytime and nighttime. This study demonstrates the capability of COTS receiver in observing atmospheric and ionospheric parameters. In the future, utilizing COTS receivers with lower-cost low Earth orbit (LEO) satellite missions can largely increase the data volume of RO and enhance our capability in monitoring the Earth's atmosphere. Economic Development Board (EDB) The research work and VELOX-CI mission are supported by Singapore Economic Development Board (EDB).

Through systematic experiments, two novel mercury iodate sulfates, namely, Hg

A new phase-matchable nonlinear-optical material, Na

An organic-inorganic hybrid polyiodate, namely, [o-C

A novel mixed-anion NLO crystal, namely, Bi4O(I3O10)(IO3)3(SeO4), containing a brand-new "pinwheel-like" I3O105- polyiodate anion group was constructed from the trimeric condensation of IO43- monomers. Bi4O(I3O10)(IO3)3(SeO4) exhibits a complex 3D topological structure and gives a moderate second harmonic generation (SHG) signal about 1.1 times that of KH2PO4 (KDP).

Once injected into the orbit, the satellites operate in space all the time and they are exposed under very harsh space environment such as extreme temperature variation in vacuum condition, radiation etc. As a satellite requires significant amount of investment, it is desired to understand its lifespan and performance degradation before a replacement satellite is launched. The degradation process of an electronic component is strongly related to the thermal, radiation and pressure conditions in the low earth orbit. This research focuses on the degradation and fault monitoring of the electronics components in the DC-DC converters of satellite power system. The main contributions of this research are listed below.  Developed a low sampling rate online power converter circuit parameter estimation method. The estimation accuracy is compatible with the conventional high sampling rate methods as indicated in both simulation and experimental results.  Derived the interleaved boost converter’s state space model to include the most important parasitic effects.  Developed a grouped immigration algorithm to accelerate the solution convergence rate in highly inter-relative multi-variable problems using biogeography based optimisation (BBO). The degradation in the converters are detected through the online parameter estimation. The previously reported fault detection methods for the DC-DC converter require a sampling frequency to be at least 25 times of the switching frequency. In this thesis, the new parameter estimation methods are developed based on the averaged converter circuit model. This allows the measurements to be taken only once in every few switching cycles. Therefore, this method can be implemented using low cost and low power processer. This is particular important for miniaturized satellites which have limited power budget due to the limited area of the solar array available for the satellite. The low sampling rate method has been verified through simulation and experimental study for a buck converter. The average estimation error for the circuit components are less than 5.17% in the simulation and 7.5% for the experimental results. The parameter estimation method can be extended to other converter topologies. To provide redundancy in the power system, the multi-phase interleaved converter has been developed for various applications. Such feature is useful for satellite to eliminate single point failure. To develop an online parameter monitoring system, a general state space based interleaved DC-DC converter averaged model is formulated in this thesis. Moreover, the number of measurements and unknowns in this model are scalable . As additional unknowns are added into the optimization problem for multiphase interleaved converter, the convergence rate of the conventional BBO approach dropped. To accelerate the convergence rate of BBO with moderate calculation complexity, the grouped immigration method is proposed in this research. Results have demonstrated that the convergence rate improved significantly such that the estimation error deviation for the circuit component is less than 2% and the averaged error is less than 7% when the function evaluation is restricted to 200,000. Thus it outperformed the conventional BBO method, in which the estimation error is greater than 100% due to premature termination under the same function evaluation limit. Doctor of Philosophy (EEE)

The first alkali-metal vanadium iodate fluoride, CsVO

The search for new non-centrosymmetric (NCS) crystals with wide energy-gaps (Eg) and strong second-harmonic generation (SHG) responses has become one of the greatest challenges in the mid- and far-infrared (MFIR) nonlinear optical (NLO) field. In this work, a novel quaternary NCS material Sr5ZnGa6S15 (SZGS), which contains a complex 3D anionic framework and possesses the optical properties required for the MFIR NLO applications, especially the good balance between wide Eg (3.15 eV) and large SHG response (dij = 1.2 × AgGaS2), has been discovered for the first time. Moreover, the result of theoretical calculation further indicates that the 3D [ZnGa6S15]10− framework makes definitive contributions to the NLO properties. All these studies demonstrate that SZGS is a promising NLO candidate in the MFIR region.

To develop new mid-infrared (MIR) nonlinear optical (NLO) materials, which can overcome the low laser damage threshold (LDT) of the commercial MIR-NLO crystals (AgGaS2 , AgGaSe2 and ZnGeP2 ) and simultaneously keep the large NLO susceptibility, is necessary for high-power MIR laser frequency conversion technology. To improve the LDT, a new strategy of increasing lattice stability was adopted. Here, the strongly covalent structural unit of the PS4 tetrahedron was introduced into AgGaS2 (AGS), and that led to the isolation of the first compound in AgI -GaIII -PV -S system, namely, AgGa2 PS6 (Cc). It retains a large SHG efficiency (1.0×AGS) with phase-matchable ability, and also exhibits an improved LDT (5.1×AGS), indicating AgGa2 PS6 is a new promising MIR-NLO crystal. Moreover, a novel 3D framework of [Ga2 PS6 ]- , with triangular-shaped channels, as well as interesting single triangular geometry of AgS3 -both of which are very rare in reported sulfides-was discovered in AgGa2 PS6 . Furthermore, theoretical calculations, and lattice energy and thermal expansions analyses suggest that the PS4 group makes a large contribution to the large SHG efficiency and high LDT.

A large nonlinear optical (NLO) coefficient and a wide band gap are two crucial but contradictory parameters that are difficult to achieve simultaneously in a single infrared (IR) NLO compound. A salt-inclusion chalcogenide (SIC), Li[LiCs

A new nonlinear optical material, the first fluoride selenite nitrate PbCdF(SeO

The Regional Ionosphere Mapping and Autonomous Uplink (RIMAU) mission is a constellation of six CubeSats in an equatorial orbit, making Radio Occultation (RO) measurements of the atmosphere and in-situ Ionospheric measurements to characterize the ionosphere over equatorial South-East Asia in near real time. RIMAU builds on the success of the VELOX-CI mission developed and operated at the Satellite Research Centre (SaRC) at Nanyang Technological University, which carried a commercial-off-the-shelf GPS receiver and have been operating successfully since December 2015. RIMAU will carry GPS receivers for RO and an Ionospheric payload, the Compact Ionosphere Probe (CIP) developed by National Central University of Taiwan, consisting of a planar Langmuir probe, retarding potential analyser and Ion trap/drift meter. RIMAU-1 is scheduled to be in operation by 2021 with the full constellation scheduled for flight by 2023. A secondary objective of RIMAU is to provide a Low Earth Orbiting nanosatellite platform for communication with remote sensors in the region. RIMAU-1 will demonstrate communication with remote water sensors monitoring water pollutants and uplink from ground based GPS sensors to adjust the sampling rate for the Ionospheric probe during periods of high scintillation. Understanding the occurrence and impact of Ionospheric irregularities is critically needed for equatorial countries like Singapore. In this paper, we present a novel idea to combine ground based and space based Ionospheric observations to monitor in near-real time the Ionosphere over the Singapore region to characterize Ionospheric disturbances and their impact on communication and navigation systems. The main data products from these measurements will be vertical profiles of the Total Electron Content (TEC) in the ionosphere, atmospheric temperature and humidity profiles in the troposphere. RIMAU TEC measurements will be combined with ground based TEC measurements from ~ 60 GPS receivers in the SE Asia region, operated by the Earth Observatory of Singapore to produce 3D maps of the Ionosphere.

Noncentrosymmetric (NCS) mixed-metal chalcogenides have attracted significant attention lately because of their structural multiplicities, strong second-harmonic-generation (SHG) efficiencies ( d

New middle and far-infrared (MFIR) nonlinear optical (NLO) chalcogenides have been receiving increasing attention for their great importance in military and civil fields. In addition, the current challenge in the efforts for identifying a promising MFIR NLO material lies in achieving simultaneously large second-harmonic generation (SHG) intensity and high laser-induced damage threshold (LIDT) in the same material. In this study, two quaternary non-centrosymmetric (NCS) sulfides, BaAg

Partial substitution of iodate anions in La(IO

To develop new mid-infrared (MIR) nonlinear optical (NLO) materials, which can overcome the low laser damage threshold (LDT) of the commercial MIR-NLO crystals (AgGaS

In this paper, we studied the changes in the photoluminescence spectra of the Ar + ion implanted mono-crystalline sapphire annealed at different atmospheres and different temperatures. Single crystals of sapphire (Al 2 O 3 ) with the (1 0 1¯ 0) (m-samples) orientation were implanted at 623 K with 110 keV Ar + ions to a fluence of 9.5×10 16 ions/cm 2 . Photoluminescence measurement of the as-implanted sample shows a new emission band at 506 nm, which is attributed to the production of interstitial Al atoms. The intensity of emission band at 506 nm first increased then decreased with increase in annealing temperature. For the same annealing temperature, the intensity of PL peak at 506 nm of the sample annealed in air was higher than the sample annealed in vacuum. The experimental results show that the intensity of the PL peak at 506 nm of Ar-implanted sapphire can be enhanced by subsequent annealing with an enhancement of nearly 20 times. The influence of thermal annealing of the Ar-implanted samples on the new 506 nm emission band was discussed.

In the present paper the authors report a research on testing the nonlinear optical performance of optical materials in visible and infrared band. Based on the second order nonlinear optic principle and the photoelectric signal detection technology, the authors have proposed a new testing scheme in which a infrared OPO laser and a method for separating the beams arising from frequency matching and the light produced by other optical effects were used. The OPO laser is adopted as light source to avoid the error of measurement caused by absorption because the double frequency signal of the material is in the transmittance band Our research work includes testing system composition, operational principle and experimental method. The experimental results of KTP, KDP, AGS tested by this method were presented. In the experiment several new infrared non-linear materials were found. This method possesses the merits of good stability and reliability, high sensitivity, simple operation and good reproducibility, which can effectively make qualitative and semi-quantitative test for optical material's nonlinear optical properties from visible to infrared. This work provides an important test -method for the research on second order nonlinear optical materials in visible, infrared and ultraviolet bands.