Haydn Martin

Focus variation microscopy is a non-contact technique for surface topography measurement, which utilizes the limited depth of focus of a microscope to allow the topography of a surface to be determined after it has been scanned through the focal plane. Recently, approaches using a chromatic dependence of the focal plane location, realized using multiple glass elements in a custom objective, have been developed that remove the need to physically scan elements. Here, we demonstrate how a metalens can be used to simultaneously deliver the focusing and wavelength-dependent focal shift required with only a single lightweight element, opening up the path to the development of ultra-compact lightweight focus variation instrumentation.

Metasurfaces allow the manipulation of light without the size and weight of traditional optical elements, and offer a path to the type of ultra-compact optical systems needed if optical sensors are to be integrated within manufacturing chains without disrupting them. Here we look at the use of a spatially interleaved metasurface as a method to extend the spectral range over which high-resolution measurements can be obtained with an off-axis metasurface lens. Such a spectrometer exploits chromatic abberation to separate out different wavelengths of light, however the abberation will lead to a degredation in the resolution. By spatially interleaving two such devices the measurement range over which the abberation is minimised can be extended, leading to a more useful device.

In order to calculate the electromagnetic fields that are produced after light passes through a metasurface, simulation methods such as the Finite-Difference Time-Domain method are often employed. While these provide a good approximation to the fields, the level of detail at which the volume of space that the light is propagating in needs to be modelled and the time for which simulations need to run, mean that as the area of the metasurface is increased these simulations rapidly become unwieldy. In this paper we show how the result of a FDTD simulation of a unit cell can be used to generate a good approximation of the vectorial field that large area metasurfaces will generate, but using a fraction of the computational resources. This approach can provide an intermediate design step, allowing potentially interesting designs to be rapidly identified or discarded.

The development of ultra-compact lightweight optical instrumentation that can be used on-machine and to carry out in-process measurements is vital in realizing improved manufacturing processes, increasing the quality of parts being made while saving time and energy by reducing scrappage rates. Only incremental progress is being made in developing suitable instrumentation based on conventional components such as traditional refractive elements as fundamental limits in terms of size and weight are already reached. Here we demonstrate a chromatic confocal sensor that utilizes the natural chromatic aberration found with a basic hyperbolic metalens to realize an ultra-compact and simple probe. Further, we demonstrate how this can be combined with a compact specklemeter as the detection element, thus realizing the whole sensing system in a compact manner. Even with the proof-of-principle instrument in its preliminary and unoptimised state we achieve the successful recovery of the location of a scatterer as it is scanned over a 227 μm range, with a standard deviation of error in the position of 1.37 μm. Sensors of this form can be deployed in areas where traditional instrumentation would typically impede the manufacturing processes, increasing the number of processes that can have metrology applied directly and providing real-time feedback to improve manufacturing outcomes.

Monitoring strain is important in precision engineering applications that require maintaining the precise alignments of structures over time, such as those found in machine tools and metrology frames. We present a fiber-optic strain measurement technique based upon broadband interferometry that is variously configurable in terms of gauge length and sensitivity. This is achieved by the use of an unbalanced interrogation interferometer configuration that alleviates the cavity length limit imposed by the temporal coherence of the system. We also demonstrate that dispersion in fiber sensors based on intrinsic Fabry–Perot interferometers must be considered to optimize performance. The possibility of multisensor interrogation using the same optical system is also reported.

Screening manufactured products that are conducted faster to enhance the contemporary manufacture processes and quality is possible by implementing enhanced quality control. Such quality control of manufactured products has increased the market for process-focused precision metrology that can execute evaluations faster while providing significant feedback for the manufacturing system. This investigation examines spatial dispersive interferometry’s potential for producing accurate surface profile measurements by emphasizing vertical range measurements and identifying a system that can enable them to increase incrementally while maintaining the results’ quality. Thus, this investigation selected Fourier transform profilometry (FTP) to assess surface profile measurements, as it provides the most reliable and fastest outcome data regarding this sensor. Exploring new surface scanning methods is important, as crucial weaknesses hinder several common approaches. As optical metrology sensors are bulky, difficult to establish, and expensive, the investigation will prove that FTP can resolve these restrictions. The investigation uses the synthetic wavelength approach for addressing vertical measurement limitation concerning optical systems for extending surface step height’s vertical measurement range. Though it was observed that the FTP technique surmounts the vertical height limitations, certain limitations were also noted, with all outcomes considering key variables, including the scanning objective lens, system resolution, the spectrometer resolution, and diffraction grating. Future examinations must examine a wider vertical range to expand the snapshot spatial dispersive interferometry process’s scope. Further, the step-height repeatability is enhanced, showing a good outcome range from 22 to 20 nm.

Interferometric instruments with dispersion introduced in the reference arm have previously been created, as the controlled dispersion can be used to generate a signal that contains a clearly identifiable point, the location of which relates to the position of the scattering surface in the measurement arm. In the following, we illustrate that the linear approximations that have been used previously can lead to significant errors, and that second-order terms need to be included in order to correct this. These corrections are vital if these instruments are to be used for metrological applications.