Phase-quadrature quantum imaging with undetected photons.

Sensing with undetected photons allows access to spectral regions with simultaneous detection of photons of another region and is based on nonlinear interferometry. To obtain the full information of a sample, the corresponding interferogram has to be analyzed in terms of amplitude and phase, which has been realized so far by multiple measurements followed by phase variation. Here, we present a polarization-optics-based phase-quadrature implementation in a nonlinear interferometer for imaging with undetected photons in the infrared region. This allows us to obtain phase and visibility with a single image acquisition without the need of varying optical paths or phases, thus enabling the detection of dynamic processes. We demonstrate the usefulness of our method on a static phase mask opaque to the detected photons as well as on dynamic measurement tasks as the drying of an isopropanol film and the stretching of an adhesive tape.

Towards efficient structure prediction and pre-compensation in multi-photon lithography: publisher's note.

This publisher's note contains a correction to [Opt. Express30, 28805 (2022)10.1364/OE.462775].

Towards efficient structure prediction and pre-compensation in multi-photon lithography.

Microscale 3D printing technologies have been of increasing interest in industry and research for several years. Unfortunately, the fabricated structures always deviate from the respective expectations, often caused by the physico-chemical properties during and after the printing process. Here, we show first steps towards a simple, fast and easy to implement algorithm to predict the final structure topography for multi-photon lithography - also known as Direct Laser Writing (DLW). The three main steps of DLW, (i) exposure of a photo resin, (ii) cross-linking of the resin, and (iii) subsequent shrinkage are approximated by mathematical operations, showing promising results in coincidence with experimental observations. For example, the root-mean-square error (rmse) between the unmodified 3D print of a radial-symmetrically chirped topography and our predicted topography is only 0.46 µm, whereas the rmse between this 3D print and its target is 1.49 µm. Thus, our robust predictions can be used prior to the printing process to minimize undesired deviations between the target structure and the final 3D printed structure. Using a Downhill-Simplex algorithm for identifying the optimal prediction parameters, we were able to reduce the rmse from 4.04 µm to 0.33 µm by only two correction loops in our best-case scenario (rmse = 0.72 µm after one loop). Consequently, this approach can eliminate the need for many structural optimization loops to produce highly conformal and high quality micro structures in the future.

Calibration sample for arbitrary metrological characteristics of optical topography measuring instruments.

Areal optical surface topography measurement is an emerging technology for industrial quality control. However, neither calibration procedures nor the utilization of material measures are standardized. State of the art is the calibration of a set of metrological characteristics with multiple calibration samples (material measures). Here, we propose a new calibration sample (artefact) capable of providing the entire set of relevant metrological characteristics within only one single sample. Our calibration artefact features multiple material measures and is manufactured with two-photon laser lithography (direct laser writing, DLW). This enables a holistic calibration of areal topography measuring instruments with only one series of measurements and without changing the sample.

Automated aberration correction of arbitrary laser modes in high numerical aperture systems.

Controlling the point-spread-function in three-dimensional laser lithography is crucial for fabricating structures with highest definition and resolution. In contrast to microscopy, aberrations have to be physically corrected prior to writing, to create well defined doughnut modes, bottlebeams or multi foci modes. We report on a modified Gerchberg-Saxton algorithm for spatial-light-modulator based automated aberration compensation to optimize arbitrary laser-modes in a high numerical aperture system. Using circularly polarized light for the measurement and first-guess initial conditions for amplitude and phase of the pupil function our scalar approach outperforms recent algorithms with vectorial corrections. Besides laser lithography also applications like optical tweezers and microscopy might benefit from the method presented.

Cryopreservation does not alter main characteristics of Good Manufacturing Process-grade human multipotent mesenchymal stromal cells including immunomodulating potential and lack of malignant transformation.

BACKGROUND AIMS: The immunomodulating capacity of multipotent mesenchymal stromal cells (MSCs) qualifies them as a therapeutic tool in several diseases. However, repeated transplantation with products of reproducible characteristics may be required. This could be achieved with cryopreserved aliquots of Good Manufacturing Practice (GMP)-grade MSCs. However, the impact of cryopreservation on the characteristics of GMP-MSCs is ill defined. METHODS: We produced fresh and cryopreserved MSCs from human donors with a xenogen-free GMP protocol. Immunogenicity and immunomodulating capacity were tested in co-culture with putative recipient-specific peripheral blood mononuclear cells (PBMCs). Risk of malignant transformation was assessed in vitro and in vivo. RESULTS: Cryopreservation had no impact on viability and consensus criteria of MSCs. In co-culture with PBMCs, MSCs showed low immunogenicity and suppressed mitogen-stimulated proliferation of PBMC irrespective of cryopreservation. Cytogenetic aberrations were not observed consistently in fresh and cryopreserved products, and no signs of malignant transformation occurred in functional assays. MSC products from an elderly pretreated donor showed reduced functional quality, but imminent failure of functional criteria could be detected by an increased population doubling time in early passages. DISCUSSION: This study is the first systematic analysis on cryopreservation of xenogen-free human bone marrow-derived GMP-MSCs. The data support that cryopreservation does not alter the characteristics of the cells and thus may allow the generation of products for serial transplantation. In addition, the protocol allowed early detection of MSC products with low functional capacity.