Conference Agenda

The demand for 100% inspection is increasing due to rising quality requirements in manufacturing. Multiwavelength Digital Holography (MDH) has emerged as a promising sensing technology capable of achieving both high throughput and high resolution. However, despite its potential, MDH has not yet been widely adopted in commercial metrology applications.

One of the key challenges in MDH system design is minimizing noise in the laser-illuminated optical imaging system. Due to the high coherence of laser light, digital holography systems are particularly sensitive to particle contamination and internal reflections within optical components.

We address this challenge by introducing a phase randomizing mirror (PRM) that controls coherent length by dynamically modulating the spatial profile of the illumination. Compared to conventional mechanical modulation methods, the PRM operates at significantly higher frequencies, enabling shorter exposure times. This results in a system that is not only high-throughput but also more resilient to environmental vibrations.

In this presentation, we will discuss the impact of the PRM on our newly developed phase-shifting digital holography system and demonstrate its application in real-world inspection scenarios.

Zernike polynomials are widely used to approximate optical aberrations and represent them in a compact, yet sufficiently accurate way. They are essential in precision optical manufacturing to characterize surface figure errors and wavefront aberrations of optical systems measured by interferometers or wavefront sensors. Zernike polynomials also describe freeform surfaces in optical design and are used in adaptive optics to correct for dynamic aberrations such as atmospheric turbulence.

The aberration coefficients of the polynomials are typically presented in tables or simple bar graphs that can be difficult to interpret at first glance. This work presents intuitive visualizations of Zernike aberrations that emphasize the magnitude and orientation of the dominant terms. Depending on the polynomial degree of the approximation, we use bubble plots or heat maps to represent low-order and mid-spatial frequency terms, respectively. In addition, we propose an alternative definition for the angular orientation of the paired polynomials with azimuthal orders m ≠ 0.

These graphical tools provide immediate visual feedback, benefiting tasks such as aberration compensator adjustment, real-time wavefront monitoring, and optical alignment. They can also improve the clarity of acceptance reports and measurement certificates.

We present a calibration method that correlates in-line measurement results from a digital holographic microscope (DHM) integrated into a two-photon polymerisation system (TPP) with offline results from a high-resolution laser scanning microscope (LSM). Our findings indicate that a single calibration step for a specific polymer is sufficient to reliably monitor the fabrication of various structures. In future, this approach will make it possible to adapt the production process to the manufactured structure geometry in real time.

Conventional interferometers provide uniform phase sensitivity across the measurement range. However, for applications involving small phase changes, amplifying the response within a specific phase range—at the expense of reduced sensitivity elsewhere—can be advantageous. A key example is the Gires-Tournois etalon, used in gravitational wave interferometers. In this work, we introduce an ultrasensitive phase measurement system based on time-holographic recording with a conventional Mach-Zehnder interferometer, operated near the intensity minimum at the dark output port. Phase fluctuations in the milliradian range around this point are converted into rad-sized dark output phases, with amplification factors exceeding 1,000. The adjustable imbalance between the interferometer arms controls this magnification, which is revealed by heterodyning the output with a frequency-shifted beam. Phase is digitally retrieved from the time-hologram using Fourier processing, with noise subtraction for correction. The system achieves phase sensitivities better than λ/3,000, enabling sub-nanometer precision for dimensional measurements. This versatile platform provides powerful tools for ultrasensitive phase measurements in a wide range of scientific and technological applications.

In this work we investigate the efficiency and accuracy of different perturbation methods, for the important case of a 1D periodic grating. These methods are potentially important in the study of the influence on optical performance of mid-spatial frequency errors on the surfaces of optical components.

The scope is limited to reflective optical systems. The perturbation methods are based on the Rayleigh hypothesis, boundary integral equations and volume integral equations. The Padé approximant is used to improve the convergence of the perturbation series. Results for a specific grating are included in a to be published paper and will be shown during the presentation.

Ptychography is a powerful computational imaging technique that

reconstructs both the complex object function and the illumination probe from

overlapping diffraction patterns. While it provides high-resolution, aberrationcorrected

imaging, its reliance on stepwise mechanical scanning limits acquisition

speed. In this work, we propose a fly-scan ptychographic approach that

enables continuous sample translation along arbitrary trajectories, significantly

reducing measurement time. To account for motion-induced decoherence, we

incorporate an object mode decomposition model combined with automatic differentiation

for accurate trajectory correction. This method enables diffractionlimited

reconstructions without the need for high-speed tracking, allowing fast

and precise measurements using standard ptychographic setups.