The demand for large coated flat and curved optics is growing for applications in automotive (windshields, LIDAR windows) or space (spectrally resolved imaging, FSO Lasercom). Their large size leading to high Transmitted wavefront error (TWE) and their sensitivity to wavelength require new metrology instruments. We propose measuring the TWE of such optics with a quadriwave lateral shearing interferometer (QLSI) based wave front sensor, in a double-pass configuration. We present the instrument ability to measure optics in their full transmission spectral band. We also discuss the best strategy to characterize large TWE optics in dynamic ranges exceeding tens of microns.
Smartphones, AR/VR and ADAS optics are challenging to qualify due to their short focal length, high chief ray angle and numerical aperture. Wave front sensing measures the optical aberration and the associated Zernike coefficients, which are used to understand manufacturing errors. In this paper, we propose to use a quadriwave lateral shearing wave front sensor, which is able to characterize such samples without any intermediate optics. This configuration makes the qualification process comprehensive and fast. We will present examples of commercial and calibrated optics with CRA larger than 35°.
We present an optical metrology instrument for measuring the transmitted wavefront error (TWE) of coated or uncoated optics having large aberrations.
Fizeau interferometry is a standard technique to measure TWE. However, the dynamic range is limited and measuring large aberrations requires the use of computer-generated holograms or null lenses, which increases both cost and time dedicated to precise alignment.
The chosen solution is based on a quadriwave lateral shearing interferometer (QWLSI) wavefront sensor. QWLSI is an achromatic technique, meaning that it measures optical path differences at any wavelength without any need for recalibration at specific wavelengths. Moreover, QWLSI directly measures phase derivatives unlike Fizeau interferometers that measure phase. Therefore, QWLSI has, by design, a better wavefront error dynamic range for TWE and also reflected wavefront error measurements.
The proposed optical solution was characterized using samples previously measured using an interferometer from Zygo. Comparisons were made on samples having 5 µm defocus P-V and 3 µm astigmatism.
Finally, measurements were made on optics presenting more than 20 µm peak-to-valley (P-V) of defocus aberration. Measuring this sample with a classical interferometer is not possible and our solution provided TWE measurements without using any relay optics.
We present an optical metrology instrument for measuring both transmitted and reflected wavefront error (TWE and RWE) of coated or uncoated optics over a diameter of 4 inches in the SWIR range. Depending on the coating transmittance and reflectance, the measurements were done at different wavelengths from 1100 nm to 1650 nm.
Fizeau interferometry is a standard technique to measure the TWE and RWE of uncoated optics. But in the case of coated optics (bandpass filters for example) measurement of TWE is not possible because the optics may not transmit the interferometer laser light. Moreover, for measurements at different wavelengths, a dedicated interferometer has to be built for each different wavelength.
The chosen solution is based on a quadriwave lateral shearing interferometer (QWLSI) wavefront sensor. QWLSI is an achromatic technique, meaning that it measures optical path differences at any wavelength without any need for recalibration at specific wavelengths. Consequently, various sources at different wavelengths can be used with the same instrument and metrology bench. In addition, QWLSI measures the derivative of phase contrary to interferometer that measures phase. Therefore, QWLSI has by design a better WFE dynamic range for TWE and RWE measurement. Moreover, an achieved accuracy below 30 nm RMS is perfectly adapted to optical metrology measurement.
The optical solution is a standard double pass configuration composed of a collimator and a beam expander to adapt the size of the beam to the aperture of the SWIR wavefront sensor. Different sources between 1100 nm and 1650 nm were integrated.
We present an optical metrology instrument for measuring both transmitted and reflected wavefront error (TWE and RWE) of coated or uncoated optics over a diameter of 5 inches. Depending on the coating transmittance and reflectance, the measurements have to be done at different wavelengths.
Interferometer is a standard instrument to measure the TWE and RWE of uncoated optics. But in the case of coated optics (bandpass filters for example) measurement of TWE is not possible because the optics may not transmit the interferometer laser light.
The chosen solution is based on a quadriwave lateral shearing interferometer (QWLSI) wavefront sensor. QWLSI is an achromatic technique, meaning that it measures OPD at any wavelength without any need for recalibration at specific wavelengths. Consequently, various sources at different wavelengths can be used with the same instrument and metrology bench. In addition, QWLSI measures the derivative of phase contrary to interferometer that measures phase. Therefore, QWLSI has by design a better WFE dynamic range for TWE and RWE measurement. Moreover accuracy (below 15nm RMS) and repeatability (below 2nm RMS) is perfectly adapted to optical metrology measurement.
The optical solution is a standard double pass configuration composed of a collimator and a beam expander to adapt the size of the beam to the wavefront sensor aperture. We use LED sources to avoid any noise due to interferences within the optics, which occur with coherent light. We can use different wavelength between 400nm and 1100nm. We can optimize the longitudinal chromatic aberration by moving a lens from the beam expander.
We characterized the bench according to the ISO 5725 standard for different wavelengths. Its precision was tested with different samples (filters and mirror). The precision on TWE was found to be below 2nm RMS.
Elastic Light Scattering (ELS) is an innovative technique to identify bacterial pathogens directly on culture plates. Compelling results have already been reported for agri-food applications. Here, we have developed ELS for clinical diagnosis, starting with Staphylococcus aureus early screening. Our goal is to bring a result (positive/negative) after only 6 h of growth to fight surgical-site infections. The method starts with the acquisition of the scattering pattern arising from the interaction between a laser beam and a single bacterial colony growing on a culture medium. Then, the resulting image, considered as the bacterial species signature, is analyzed using statistical learning techniques. We present a custom optical setup able to target bacterial colonies with various sizes (30-500 microns). This system was used to collect a reference dataset of 38 strains of S. aureus and other Staphyloccocus species (5459 images) on ChromIDSAID/ MRSA bi-plates. A validation set from 20 patients has then been acquired and clinically-validated according to chromogenic enzymatic tests. The best correct-identification rate between S. aureus and S. non-aureus (94.7%) has been obtained using a support vector machine classifier trained on a combination of Fourier-Bessel moments and Local- Binary-Patterns extracted features. This statistical model applied to the validation set provided a sensitivity and a specificity of 90.0% and 56.9%, or alternatively, a positive predictive value of 47% and a negative predictive value of 93%. From a clinical point of view, the results head in the right direction and pave the way toward the WHO’s requirements for rapid, low-cost, and automated diagnosis tools.
We report here on the ability of elastic light scattering in discriminating Gram+, Gram- and yeasts at an early stage of growth (6h). Our technique is non-invasive, low cost and does require neither skilled operators nor reagents. Therefore it is compatible with automation. It is based on the analysis of the scattering pattern (scatterogram) generated by a bacterial microcolony growing on agar, when placed in the path of a laser beam. Measurements are directly performed on closed Petri dishes.
The characteristic features of a given scatterogram are first computed by projecting the pattern onto the Zernike orthogonal basis. Then the obtained data are compared to a database so that machine learning can yield identification result. A 10-fold cross-validation was performed on a database over 8 species (15 strains, 1906 scatterograms), at 6h of incubation. It yielded a 94% correct classification rate between Gram+, Gram- and yeasts. Results can be improved by using a more relevant function basis for projections, such as Fourier-Bessel functions. A fully integrated instrument has been installed at the Grenoble hospital’s laboratory of bacteriology and a validation campaign has been started for the early screening of MSSA and MRSA (Staphylococcus aureus, methicillin-resistant S. aureus) carriers.
Up to now, all the published studies about elastic scattering were performed in a forward mode, which is restricted to transparent media. However, in clinical diagnostics, most of media are opaque, such as blood-supplemented agar. That is why we propose a novel scheme capable of collecting back-scattered light which provides comparable results.
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