Maksymilian Pluta Institute of Applied Optics

A fringe displacement during the exposure process in scanning beam interference lithography (SBIL) systems leads to wavefront errors in linear gratings. The exact orientation of the fringe pattern along the scan direction is also essential for the production of high-quality gratings. In this paper, we report on the development of a fringe stabilization system with a separate measuring beam, which can precisely determine the fringe movement during the exposure of the photoresist and simultaneously record the orientation of the fringe pattern. This is specifically designed to minimize low-frequency phase errors originating in the lithography writing head itself, which can be a dominant source of instability independent of the stage positioning. Using polarization camera based phase-shifting interferometry, we determine the phase offset between the two interfering beams in real time, and thus reduce the fringe movement to single-digit nanometers by moving a piezo-actuated mirror. In addition, we can use the area-based phase measurement to align the setup and track the rotation of the fringe spot during exposure. In combination with a nano positioning and measuring machine, a fringe observation system was implemented that can precisely record the fringe displacement in the substrate plane. This allows the performance of the fringe stabilization system to be quantified.

As terahertz (THz) technology rapidly develops, room temperature THz detectors with high sensitivity and wide bandwidth are urgently required. Rydberg atoms are very sensitive to external electric fields, and offer a promising approach for THz detection with exceptional sensitivity. In this paper, we propose a method for measuring the THz field with the frequency of 0.17 THz using 85Rb Rydberg atoms. By analyzing the probe laser transmission spectrum and atomic population, the electromagnetically induced transparency (EIT) and Autler-Townes (AT) splitting effect are explained by the presence and splitting of the Rydberg dark states; the THz field, coupling laser and probe laser play a crucial role in the EIT signal; and the EIT spectral transmission will increase when the atomic population of the excited state decreases. Moreover, a method was demonstrated to improve the THz detection sensitivity by changing the eigenfrequencies of the Rydberg dark states with THz detuning. This work finds the relationship between EIT-AT effect and atomic population of Rydberg atoms caused by THz wave and provides what we believe to be a new method to improve the detection efficiency.

Abstract This study investigates age-related changes in visuomotor functions by analyzing gaze path velocity (pixels per second). The research included 50 participants aged 7 to 83 years, divided into four groups: children (7–14 years), young adults (19–39 years), middle-aged adults (45–58 years), and older adults (62–83 years). Eye movements were tracked during a visual scanning task. Statistical analyses, including one-way ANOVA, post-hoc Tukey HSD tests, and effect size calculations (η²), evaluated group differences. Significant differences in gaze path velocity were found across groups. Children had an average velocity of 150.44 px/s, serving as a baseline. Young adults showed a substantial increase (365.97 px/s), and middle-aged adults reached the highest velocities (423.48 px/s), indicating peak visuomotor function. Older adults demonstrated a decline (256.15 px/s), reflecting age-related neuroplasticity reductions. A nonlinear trajectory, modeled by a second-degree polynomial equation (R² = 0.89), peaked at age 46.3 years (Vmax = 406.03 px/s). This pattern reflects rapid growth in childhood, stabilization in middle age, and decline in later life. The findings underscore the importance of age-specific interventions, optimized user interfaces, and neurodegenerative diagnostics. Future studies should expand on sample size and consider health and lifestyle factors to enhance understanding of visuomotor variability.

Light-based in-vivo brain imaging relies on light transport over large distances of highly scattering tissues. Scattering gradually reduces imaging contrast and resolution, making it difficult to reach structures at greater depths even with the use of multiphoton techniques. To reach deeper, minimally invasive endo-microscopy techniques have been established. These most commonly exploit graded-index rod lenses and enable a variety of modalities in head-fixed and freely moving animals. A recently proposed alternative is the use of holographic control of light transport through multimode optical fibres promising much less traumatic application and superior imaging performance. We present a 110 μm thin laser-scanning endo-microscope based on this prospect, enabling in-vivo volumetric imaging throughout the whole depth of the mouse brain. The instrument is equipped with multi-wavelength detection and three-dimensional random access options, and it performs at lateral resolution below 1 μm. We showcase various modes of its application through the observations of fluorescently labelled neurones, their processes and blood vessels. Finally, we demonstrate how to exploit the instrument to monitor calcium signalling of neurones and to measure blood flow velocity in individual vessels at high speeds.

In imaging geometries, which employ wavefront-shaping to control the light transport through a multi-mode optical fibre (MMF), this terminal hair-thin optical component acts as a minimally invasive objective lens, enabling high resolution laser-scanning fluorescence microscopy inside living tissues at depths hardly accessible by any other light-based technique. Even in the most advanced systems, the diffraction-limited foci scanning the object across the focal plane are contaminated by a stray optical signal carrying typically few tens of % of the total optical power. The stray illumination takes the shape of a randomised but reproducible speckle, and is unique for each position of the focus. We experimentally demonstrate that the performance of imaging a fluorescent object can be significantly improved, when resulting images are computationally post-processed, utilising records of intensities of all speckle-contaminated foci used in the imaging procedure. We present two algorithms based on a regularised iterative inversion and regularised direct pseudo-inversion respectively which lead to enhancement of the image contrast and resolution.

Abstract Highly sensitivity Surface Plasmon resonance (SPR) sensor consisting of Ag-Pt bimetallic films sandwiched with 2D materials Black Phosphorus (BP) and Graphene over Pt layer in Kretschmann configuration is analyzed theoretically using the Transfer Matrix Method. Numerical results shows that upon suitable optimization of thickness of Ag-Pt and number of layers of BP & graphene, sensitivity as high as 412º/RIU can be achieved for p-polarized light of wavelength 633 nm. This performance can be tuned and controlled by changing the number of layers of BP and graphene. Further, the addition of graphene and heterostructures of black phosphorus not only improved the sensitivity of the sensor but keep the FWHM of the resonance curve much smaller than the conventional sensor utilizing Au as plasmon metal and hence improved the resolution to a significant extent. We expect that this new proposed design will be useful for medical diagnosis, biomolecular detection and chemical examination.

The optical properties of colloidal near-infrared (NIR) emitting gold nanoclusters (AuNCs) are thoroughly investigated at variable temperatures and excitation powers. Both absorption and photoluminescence (PL) excitation spectra reveal optical transitions expected from literature models of thiolated AuNCs - with the exception of the lowest energy transition which has the form of a featureless absorption tail partially overlapping with the PL band. The absorption cross section is determined via the PL saturation and PL modulation techniques to be in the range of 2-3 × 10-14 cm2 for excitation at 405 nm (relatively large value for such small clusters) and decreases ∼20 times toward 633 nm. Slow transient quenching (perfectly reversible) of PL is observed when the excitation power exceeds the saturation threshold, i.e. when the probability of achieving the second absorption in an excited AuNC before its relaxation is significant. A stable PL quenched level is reached within a fraction of a minute or a few minutes after the start of the excitation. Similar time intervals are needed for AuNCs to relax back to the original state in the dark. By comparing thermally-induced and light-induced PL decreases and PL kinetics speed up, we conclude that the transient quenching is due to heating caused by the dissipated excitation power. The light-induced PL amplitude reduction is much stronger (up to ∼80% under 405 nm, 60 W cm-2 excitation) than changes in PL decay time (∼20%), which is due to PL blinking and PL switching-off in a fraction of the AuNC ensemble. The potential application of these AuNCs in nanothermometry is discussed.

The paper concentrates on the micro-interferometric techniques that utilize a light source of the continuously tuned wavelength. The technique is called, after the light source, the variable wavelength interferometry. It can be implemented in transmitted or reflected-light modes and is useful in testing fibers, micro-structures and optical elements like retarders (wave plates). The emitted spectrum has to be continuous. When the measurement procedure advances the selected wavelength must be determined with high accuracy, which ultimately defines uncertainty of the optical path difference to be measured. The continuous character of the light source is the linking element with previously published Part I of the paper that focused on confocal sensors.