An Astigmatic Detection System for Polymeric Cantilever-based Sensors

We demonstrate the use of an astigmatic detection system (ADS) for resonance frequency identification of polymer microcantilever sensors. The ADS technology is based on a DVD optical head combined with an optical microscope (OM). The optical head has a signal bandwidth of 80 MHz, allowing thermal fluctuation measurements on cantilever beams with a subnanometer resolution. Furthermore, an external excitation can intensify the resonance amplitude, enhancing the signal- to-noise ratio. The full width at half maximum (FWHM) of the laser spot is 568 nm, which facilitates read-out on potentially submicrometer-sized cantilevers. The resonant frequency of SU-8 microcantilevers is measured by both thermal fluctuation and excited vibration measurement modes of the ADS

Tuning of Parameters for Robotic Contouring Based on the Evaluation of Force Deviation

The application of industrial robots with advanced sensor systems in unstructured environments is continuously becoming wider. A widely used type of advanced sensor systems is the force-torque sensor. Force-torque sensors are typically used for applications such as robot grinding, sanding, polishing, and deburring, where a constant force is exerted upon a workpiece. In this research, control parameters for exerting a constant force along a predefined path are evaluated in laboratory conditions. The experimental setup with the contouring force feedback is composed of a Fanuc LRMate six-degree-of-freedom industrial robot with an integrated force-torque sensor. Control parameters of the Contouring function within the Fanuc robot controller are tuned in four contouring experiments. The experiments conducted in this research are: i) flat beam, ii) flat beam with a rigid support, iii) wave shaped compliant plate, and iv) compliant flat plate. During the experiments, contouring parameters were altered in order to collect the feedback on the values of the force to be used for the evaluation of the force deviation. A fitness function for the evaluation of the force deviation and the tuning of the control parameters is presented. The fitness function enables a selection of initial control parameters which minimize the force deviation during the robot contouring process

Design of an Electro-Optic Beam Position Monitor for Unbunched Beams based on Frequency Domain DC Field Measurements

Continuous and accurate monitoring of the transverse position of a charged particle beam in an accelerator plays a crucial role in ensuring efficient operation of the accelerator and the success of the conducted physics experiments. This is typically achieved with Beam Position Monitors (BPMs) which are, however, insensitive to DC, or unbunched, beams. In such cases, other beam diagnostic tools are used, such as intercepting instruments which alter the properties of the passing beam. This feature poses a challenge for some experiments, e.g.Fixed Target Experiments at CERN, which rely on beams without any temporal structure. This thesis addresses the lack of DC-sensitive BPMs by exploring the use of Electro-Optic (EO) crystals as an alternative to traditional BPMs electrodes. The proposed technique requires four optical chains arranged symmetrically around the vacuum chamber. Each chains acts as an electrostatic field sensor composed of two EO crystals providing two different functionalities. One crystal, placed inside the vacuum chamber, encodes the intensity of the electrostatic field carried by the particle beam onto the polarisation state of the laser beam crossing the optical chain. The other EO crystal is installed outside the vacuum chamber and is modulated with a sinusoidal electric field. This allows the output signal to be analysed in the frequency domain, as well as setting a DC bias to control the system’s working point and to compensate for environmental changes of the crystal’s optical properties. A detailed study of low-frequency effects on the EO materials was carried out to evaluate the measurement error due to the collection of the space charge and the variation of the refractive indices due to temperature fluctuations. Laboratory measurements of the developed electrostatic field sensor, representing one BPM electrode, proved the feasibility of the proposed technique, comparing it to the analytical predictions obtained with a mathematical model of the setup. These measurements provided valuable insights into the performance of the system and further development and optimisation opportunities. The developed technology is not limited to particle accelerators, but can also find use in any application requiring DC field sensing in harsh environments without interfering with the measured field

Optical read-out techniques for the control of test-masses in gravitational wave observatories

This thesis discusses the development of optical read-out techniques, including a simple shadow sensor and a more elaborate compact homodyne interferometer, known as EUCLID. Both of these sensors could be utilised as part of a seismic isolation and suspension system of a ground-based gravitational wave observatory, such as Advanced LIGO. As part of the University of Birmingham’s commitment to the upgrade of the Advanced LIGO, it was responsible for providing a large quantity of sensor and actuator units. This required the development and qualification of the shadow sensor, through to production and testing. While characterising production units, an excess noise issue was uncovered and eventually mitigated; demonstrating that even for a ‘simple’ shadow sensor, ensuring a large quantity of units meet the target sensitivity requirement of 300 pm/rt-Hz at 1 Hz, is not a trivial exercise. Over the duration of this research, I played a key role in the design and fabrication of a novel compact interferometer. The objective of this work was to demonstrate that the interferometric technique offers a significant improvement over the existing shadow sensors and could easily be deployed in current, or future, generations of gravitational wave observatories. Encouraging sensitivities of approximately 50 pm/rt-Hz at 1 Hz, over operating ranges of approximately 6 mm have been achieved, whilst maintaining around 1 degree of mirror tilt immunity. In addition, this design overcomes many of the drawbacks traditionally associated with interferometers

Time-of-Flight Method for Automotive Interior Applications

There is a growing desire to make driving safer, easier and more comfortable. This thesis explored how optical sensors can be applied to automotive equipment. Optical sensing can be used to detect both the interior and exterior of a car. In the interior, one application that has been much studied is gesture control for infotainment systems. Gesture control is less distracting to the driver than, for example, control via touch screen. Time-of-Flight technology is most commonly used in optical distance sensors. As its name suggests, it measures the time it takes for light to travel from the transmitter to the target and back to the receiver. The principle of operation and the components involved are explained in the theoretical section of this thesis. Time-of-Flight can be used to measure distance alone or to measure a 3D depth image using multiple receivers. The Time-of-Flight sensor provides not only distance information but also the intensity of the light reaching the receiver. Intensity is one indicator of the reliability of the distance measurement. In the experimental part of this work, two distance sensors based on the Time-of-Flight method were investigated. One was the TMF8805 manufactured by ams and the other was the S13021- 1CT manufactured by Hamamatsu. Most commonly, touch sensors are based on capacitive sensing. However, it is not suitable for metallic surfaces. The aim was to investigate whether Time-of Flight sensors could optically detect the position of a finger on a touch surface. The requirements were sufficient measurement accuracy at distances between 0 and 300 mm, eye safety of the light source and a measurement duration of less than 20 ms. The TMF8805 met the requirements well in the range 0-200 mm. Thereafter, a clear dip in the measurement results was observed. When the manufacturer was consulted, it was explained that the problem was known and was due to a change in the algorithm when the measurement mode was changed at 200 mm. The S13021-1CT did not work as required. The thesis shows how the performance of the sensor was improved, for example by changing the light source. Ambient light caused problems for the operation of the sensor, and at distances below 50 mm the measurement results were anomalous. An attempt was made to minimize the effect of ambient light by using a bandpass filter, but when this was used the measured distance did not increase linearly with the actual distance. Another weakness of the sensor was that the measurement duration was too long. Further research would be needed under changing conditions to bring the application into production. The measurements carried out in this work were made under very stable laboratory conditions. In reality, the conditions in the car are highly variable in terms of temperature, ambient light and vibration. In addition, the reflectivity of the finger is not always constant. The range of skin tones is quite wide and the driver may also be wearing gloves. The influence of reflectivity on the success of the measurement should be taken into account more carefully

The LATT way towards large active primaries for space telescopes

The Large Aperture Telescope Technology (LATT) goes beyond the current paradigm of future space telescopes, based on a deformable mirror in the pupil relay. Through the LATT project we demonstrated the concept of a low-weight active primary mirror, whose working principle and control strategy benefit from two decades of advances in adaptive optics for ground-based telescopes. We developed a forty centimeter spherical mirror prototype, with an areal density lower than 17 kg/m2, controlled through contactless voice coil actuators with co-located capacitive position sensors. The prototype was subjected to thermo-vacuum, vibration and optical tests, to push its technical readiness toward level 5. In this paper we present the background and the outcomes of the LATT activities under ESA contract (TRP programme), exploring the concept of a lightweight active primary mirror for space telescopes. Active primaries will open the way to very large segmented apertures, actively shaped, which can be lightweight, deployable and accurately phased once in flight

Realization of an atomically thin mirror using monolayer MoSe2

Advent of new materials such as van der Waals heterostructures, propels new research directions in condensed matter physics and enables development of novel devices with unique functionalities. Here, we show experimentally that a monolayer of MoSe2 embedded in a charge controlled heterostructure can be used to realize an electrically tunable atomically-thin mirror, that effects 90% extinction of an incident field that is resonant with its exciton transition. The corresponding maximum reflection coefficient of 45% is only limited by the ratio of the radiative decay rate to the linewidth of exciton transition and is independent of incident light intensity up to 400 Watts/cm2. We demonstrate that the reflectivity of the mirror can be drastically modified by applying a gate voltage that modifies the monolayer charge density. Our findings could find applications ranging from fast programmable spatial light modulators to suspended ultra-light mirrors for optomechanical devices

High precision optical fiber alignment using tube laser bending

In this paper, we present a method to align optical fibers within 0.2 μm of the optimal position, using tube laser bending and in situ measuring of the coupling efficiency. For near-UV wavelengths, passive alignment of the fibers with respect to the waveguides on photonic integrated circuit chips does not suffice. In prior research, it was shown that permanent position adjustments to an optical fiber by tube laser bending meets the accuracy requirements for this application. This iterative alignment can be done after any assembly steps. A method was developed previously that selects the optimal laser power and laser spot position on the tube, to minimize the number of iterations required to reach the target position. In this paper, that method is extended to the case where the absolute position of the fiber tip cannot be measured. By exploiting the thermal expansion motion at a relatively low laser power, the fiber tip can be moved without permanent deformation (only elastic strain) of the tube. An algorithm has been developed to search for the optimal fiber position, by actively measuring and maximizing the coupling efficiency. This search is performed before each bending step. Experiments have shown that it is possible to align the fiber with an accuracy of 0.2 μm using this approach