Tantalum oxide and silicon oxide mixture coatings deposited using microwave plasma assisted co-sputtering for optical mirror coatings in gravitational wave detectors.

This work presents the characterization of the optical and mechanical properties of thin films based on (T a 2 O 5)1-x (S i O 2)x mixed oxides deposited by microwave plasma assisted co-sputtering, including post-annealing treatments. The deposition of low mechanical loss materials (3×10-5) with a high refractive index (1.93) while maintaining low processing costs was achieved and the following trends were demonstrated: The energy band gap increased as the S i O 2 concentration was increased in the mixture, and the disorder constant decreased when the annealing temperatures increased. Annealing of the mixtures also showed positive effects to reduce the mechanical losses and the optical absorption. This demonstrates their potential as an alternative high-index material for optical coatings in gravitational wave detectors using a low-cost process.

Broadband infrared absorber based on a sputter deposited hydrogenated carbon multilayer enhancing MEMS-based CMOS thermopile performance.

Based on pulsed DC sputter deposition of hydrogenated carbon, an absorber optical coating with maximized broadband infrared absorptance is reported. Enhanced broadband (2.5-20 µm) infrared absorptance (>90%) with reduced infrared reflection is achieved by combining a low-absorptance antireflective (hydrogenated carbon) overcoat with a broadband-absorptance carbon underlayer (nonhydrogenated). The infrared optical absorptance of sputter deposited carbon with incorporated hydrogen is reduced. As such, hydrogen flow optimization to minimize reflection loss, maximize broadband absorptance, and achieve stress balance is described. Application to complementary metal-oxide-semiconductor (CMOS) produced microelectromechanical systems (MEMS) thermopile device wafers is described. A 220% increase in thermopile output voltage is demonstrated, in agreement with modeled prediction.

Amorphous dielectric optical coatings deposited by plasma ion-assisted electron beam evaporation for gravitational wave detectors.

Coating thermal noise (CTN) in amorphous coatings is a drawback hindering their application in precision experiments such as gravitational wave detectors (GWDs). Mirrors for GWDs are Bragg's reflectors consisting of a bilayer-based stack of high- and low-refractive-index materials showing high reflectivity and low CTN. In this paper, we report the characterization of morphological, structural, optical, and mechanical properties of high-index materials such as scandium sesquioxide and hafnium dioxide and a low-index material such as magnesium fluoride deposited by plasma ion-assisted electron beam evaporation. We also evaluate their properties under different annealing treatments and discuss their potential for GWDs.

Optical and structural properties of gradient (Ti,Co)Ox thin-film coatings with a resistive switching effect.

In this work, the optical and structural properties of gradient (Ti,Co)Ox coatings with a resistive switching effect have been outlined. They were prepared using multi-magnetron sputtering and, despite the high cobalt content, they were transparent and had a high refractive index. The gradient Co-addition resulted in the receiving of fine crystalline T i O 2-anatase and C o 3 O 4 forms in the amorphous surrounding. Observed resistance switching was a fully repeatable effect, and its occurrence in gradient (Ti,Co)Ox coatings has not reported earlier. The prepared gradient coatings exhibit great potential as transparent electronic devices with the resistance switching effect. Such memory effects in transparent thin-film coatings open new possibilities for the manufacturing of innovative memory elements in the future.

Development of measurement system and analysis method for characterization of linear variable bandpass filters.

An automated measurement system was developed to characterize the spatial gradient, linearity of the spatial gradient, bandwidth and transverse uniformity of a linear variable filter (LVF). To demonstrate this, the LVF fabricated in our group has been measured and analyzed. Simulations for beam spot size effects on measurements were performed for various LVF spectral peak profiles with results indicting significant averaging effect due to beam spot size and this is consistent with experiment results. Moreover, to fit the peak profile more accurately, a modified Pearson VII function was proposed and demonstrated high capability to express complex shapes of peaks mathematically. This provides a methodology for deconvoluting the original LVF peak profile from a measured averaged peak profile and has been verified using actual measured data.

Breath emulator for simulation and modelling of expired tidal breath carbon dioxide characteristics.

BACKGROUND: In this work we describe a breath emulator system, used to simulate temporal characteristics of exhaled carbon dioxide (CO2) concentration waveform versus time simulating how much CO2 is present at each phase of the human lung respiratory process. The system provides a method for testing capnometers incorporating fast response non-dispersive infrared (NDIR) CO2 gas sensing devices - in a clinical setting, capnography devices assess ventilation which is the CO2 movement in and out of the lungs. A mathematical model describing the waveform of the expired CO2 characteristic and influence of CO2 gas sensor noise factors and speed of response is presented and compared with measured and emulated data. OBJECTIVE: A range of emulated capnogram temporal waveforms indicative of normal and restricted respiratory function demonstrated. The system can provide controlled introduction of water vapour and/ or other gases, simulating the influence of water vapour in exhaled breath and presence of other gases in a clinical setting such as anaesthetic agents (eg N2O). This enables influence of water vapour and/ or other gases to be assessed and modelled in the performance of CO2 gas sensors incorporated into capnography systems. As such the breath emulator provides a means of controlled testing of capnometer CO2 gas sensors in a non-clinical setting, allowing device optimisation before use in a medical environment. METHODS: The breath emulator uses a unique combination of mass flow controllers, needle valves and a fast acting switchable pneumatic solenoid valve (FASV), used to controllably emulate exhaled CO2 temporal waveforms for normal and restricted respiratory function. Output data from the described emulator is compared with a mathematical model using a range of input parameters such as time constants associated with inhalation/ exhalation for different parts of the respiratory cycle and CO2 concentration levels. Sensor noise performance is modelled, taking into account input parameters such as sampling period, sensor temperature, sensing light throughput and pathlength. RESULTS: The system described here produces realistic human capnographic waveforms and has the capability to emulate various waveforms associated with chronic respiratory diseases and early stage detection of exacerbations. The system has the capability of diagnosing medical conditions through analysis of CO2 waveforms. Demonstrated in this work the emulator has been used to test NDIR gas sensor technology deployed in capnometer devices prior to formal clinical trialling.

Simulation analysis and preparation of a high optical density laser protection filter.

High optical density (OD) filters have been widely used in space observation, optical detection, and laser protection. However, the lack of high OD value filters is restricting their application. This paper reports the formulation of a three-dimensional mesh model that can help predict the effects of pinhole defects, thickness error, and uniformity on the transmittance and OD value of optical filters. A laser protection filter (LPF) with a high OD value was prepared on fused silica using a microwave plasma-assisted pulsed DC reactive sputtering technique. The transmittance and OD value of the LPF were measured. Comparing the designed, measured, and simulated results, we found that the thickness error and uniformity of the layers mainly affected the passband transmittance of the LPF and had little effect on the OD value of the blocking band. In contrast, the pinhole defects were the main factor that decreased the OD value of the blocking band. The average OD values of the prepared LPF in the blocking bands of 527-532 and 755-833 nm were 8.832 and 10.191, respectively. By comparing the transmittance and OD value of the simulated and measured results, we found that the LPF has ${\pm 1}\% $±1% uniformity error and 0.5% pinhole ratio. Suggestions for preparing high OD optical filters are provided, and further improvements are summarized.

Low-cost hyper-spectral imaging system using a linear variable bandpass filter for agritech applications.

Hyperspectral imaging for agricultural applications provides a solution for non-destructive, large-area crop monitoring. However, current products are bulky and expensive due to complicated optics and electronics. A linear variable filter was developed for implementation into a prototype hyperspectral imaging camera that demonstrates good spectral performance between 450 and 900 nm. Equipped with a feature extraction and classification algorithm, the proposed system can be used to determine potato plant health with ∼88% accuracy. This algorithm was also capable of species identification and is demonstrated as being capable of differentiating between rocket, lettuce, and spinach. Results are promising for an entry-level, low-cost hyperspectral imaging solution for agriculture applications.

Durable infrared optical coatings based on pulsed DC-sputtering of hydrogenated amorphous carbon (a-C:H).

Optical properties of low-temperature pulsed DC-sputter deposited ($ {\le} {70° {\rm C}}$≤70°C) hydrogenated carbon are presented. Increasing hydrogen incorporation into the sputter deposited carbon significantly decreases infrared optical absorption due to a decrease in deep absorptive states associated with dangling bonds. Hydrogen flow is optimized (hydrogen flow 3 sccm), achieving the best compromise between increased infrared transmittance and hardness for durable coating performance. Optical, environmental, and durability performance of pulsed DC-sputtered carbon incorporated in multilayer (a-C:H/Ge) infrared antireflective coatings indicates suitability as a durable infrared optical coating for commonly used infrared substrates, including temperature sensitive chalcogenide glass.

Modeling and validation of uniform large-area optical coating deposition on a rotating drum using microwave plasma reactive sputtering.

Magnetron sputter deposition onto a rotating drum is a method applied to high-throughput large-area optical coating deposition, where film physical thickness uniformity is an important parameter. Techniques have been developed, such as masking/substrate movement, in order to improve sputtered film uniformity. In this study, a model is described and validated for predicting film uniformity. Experimental data show excellent agreement with modeled simulations, with and without a modified sputtering mask. Practical application is demonstrated in maximizing uniformity over an individual substrate size of 100 cm2 for a high-optical-density visible/near-infrared dual-band laser protection filter.

Reactive dynamics analysis of critical Nb2O5 sputtering rate for drum-based metal-like deposition.

Drum-based metal-like film deposition for oxide was investigated using single wavelength in situ monitoring. The data were used to investigate the oxidation mechanism using combined second-order kinetic and parabolic models. A critical Nb2O5 deposition rate of 0.507 nm/s was found at drum rotation of 1 rev/s. However, Nb2O5 samples prepared at varying deposition rates showed that the deposition rate must be much lower than the critical deposition rate to achieve reasonable absorption. Thus simulation for the volume-fraction of metal in the oxide layer was done using effective medium approximation and a distribution function. Simulation gave high agreement with experimental results and allows the prediction of extinction coefficients at various deposition rates.