This PDF file contains the front matter associated with SPIE Proceedings Volume 11873 including the Title Page, Copyright information, and Table of Contents.

Free-form micro-optical arrays (FMOAs) gain increasing interest because they can overcome some limitations of rotationally symmetric optical components and because of the benefits of their microscopic dimensions. They enable better performance and compactness of optical devices. However, the complex and segmented surface shapes bring many challenges, from design to fabrication to quality control. In particular, for FMOA designs that contain many individual free-form elements, their manufacturability assessment is far from trivial. Here, we present computer-aided design (CAD)-based tools that analyze FMOA designs for manufacturing constraints so that critical parts can be identified at an early stage, reducing time-consuming and costly adjustments at a later stage. The CAD tools are of great support to quickly and reliably analyze FMOA designs containing several hundred individual elements in an automated manner. They have been developed as user-oriented tools that require little software knowledge and display the results with great visual clarity

We investigate the feasibility of a full-silica transmission grating acting as a wave plate at the wavelength of 351 nm as an alternative to an anisotropic crystal. We report on the design, manufacturing process and optical characterization carried out. We evidence the possibility to obtain a full-silica component exhibiting at 351 nm a high damage threshold and a phase retardance ranging between lambda/5 and lambda/4 associated with a diffraction efficiency above 94%.

The paper describes methods for manufacturing of diffractive optical elements by means of only "dry" processes starting from direct laser writing on titanium-containing films. According to first approach, direct laser writing onto thin Ti film forms surface oxide mask. Reactive ion etching removes non-oxidized Ti film and develops "latent" oxidized image. Subsequent thermal annealing of the oxidized Ti structure in air makes the mask more stable for following reactive ion etching of fused silica substrate to ensure proper phase depth of the binary diffractive structure. This makes it possible to avoid liquid etching, which reduces the yield and accuracy. The phase structure of the diffractive elements manufactured using the described method consists of the grooves etched in the fused silica substrate between ridges covered by TiO₂ between them. We found out also that covering the Ti film by very thin Si layer helps to increase laser energy absorption at direct writing and creates quite resistant masking layer TiSi₂ for the reactive ion etching. Preliminary estimates show that dual layer Si/Ti films can be used to create amplitude reflective DOEs. Possible application area for the developed methods is manufacturing of the diffractive optical elements used for precision generation of reference wavefronts in interferometric measurements of spherical and aspherical surfaces.

The refractive index is the most important property of optical glass. Therefore, refractive index measurement is a key characterization method also for process control. The requirements for refractive index control demand a fast and accurate measurement method for production control and a very high accurate measurement method for tightest requirements. For refractive index measurement two different measurement setups are common: the v-block refractometer for economic refractive index control up to the fifths digit and the spectral goniometer for high precision index measurement over a broad wavelength range from 185 nm to 2.325 μm up to the sixth digit. Providing Sellmeier dispersion equation data for individual measurements enables accurate interpolation of index data for arbitrary wavelengths for high precision applications. To cope with specific production requirements and the required high reliability of the measurements SCHOTT develops its own measurement setups. Both, the v-block system and the high precision spectral goniometer have been updated in recent time. To evaluate the accuracy SCHOTT participates in international round-robin tests. SCHOTT is also participating in the standardization of refractive index measurement methods for the optical industry. In this paper the current status of refractive index measurement of optical glasses at SCHOTT is presented.

In the past 20 years, a new generation of telescopes with large primary mirrors has appeared, based on the segmented mirrors design. The Thirty meter Telescope and the European Southern Observatory (ESO) Extremely Large telescope (ELT) are now under construction. They have, respectively, a 30m aperture and a 39m aperture. To cope with these apertures, they both have a large monolithic secondary mirror. These two convex aspherics are the TMT secondary mirror, a 3.1 m convex hyperboloid, and the ELT secondary mirror, a 4.25 m diameter aspheric with an asphericity of 2 mm. The surface measurement of these mirrors is challenging and auxiliary optics, like Test Plates (TP) and Computer Generated Holograms , are needed. In this paper, we present the Interferometry Test Bench, designed at Safran Reosc to polish and validate the ELT secondary mirror (ELT M2). The test bench is composed of three main components: a temporal phase shift interferometer, a Test Plate and the ELT M2 mirror on its polishing support. We perform interferometry between the concave face of the test plate and the mirror surface, forming an analogue to a Fizeau interferometer. The interferometer, named IRIDE, was designed and manufactured by Safran Reosc. It is a temporal phase shift interferometer, where environmental vibrations are addressed by increasing the interferograms acquisition rate. The interferometer has a low coherence light source, to reduce parasitic fringes. The Test Plate is a ZERODUR® meniscus lens fabricated at Safran Reosc. . Its concave surface is an off-axis isophase portion of the ELT M2 mirror and it is the Fizeau cavity’s reference surface. The ELT M2 mirror blank is mounted on its support for metrology and polishing (SMP). The SMP supports the mirror blank and interfaces it with the turning table. A measurement of the entire ELT M2 clear aperture is composed of 12 sub pupils measurements.

Final fused silica optics of high energy fusion class laser facilities are one of the components that limit the UV laser energy available for experiments. These final optics suffer from laser-induced damage. Some solutions are available to limit laser damage growth and to increase optics lifetime. However, to use them, it is necessary to be able to detect damage initiation as soon as possible, and to follow damage growth efficiently. An imaging system and a lighting source make the observation of laser damage sites possible after each laser shot without removing the optical components. Laser damage detection algorithms exist but they are not sufficiently efficient to provide reliable monitoring of damage growth over time because of small repositioning fluctuations of the optical system. An effective solution based on digital image correlation and brightness/contrast corrections is proposed to detect and follow laser damage sites as soon as they initiate in an automatic way. The effectiveness of the presented method is compared to the widely used method that is based on the analysis of local signal-to-noise ratio.

Optical systems often employ off-axis optics to prevent obscuration or because of geometric constraints. Measuring these optics in conventional interferometric setups is challenging: for cases other than off-axis parabolas, a CGH has to be used and setup size grows with the off-axis distance and radius of curvature. Measuring large convex surfaces is particularly difficult. Measurements of theses surfaces using a DUI NMF600 S cylindrical non-contact measurement machine will be demonstrated, showing flexibility, high point density, short measurement times and no setup cost.

We propose a method to design the null-screen on a cylindrical surface when the surface under test is a freeform, this implies that the surface is described by a complex analytical expression. Also, the method avoids overlapping objects in the image plane this assures the appropriate correlation between the object and the image points. The surface under study was designed using Zernike polynomials and it was built through a 3D printer and CNC machine. To retrieve the surface sagitta, in previous work, we obtained the best-fitting surface using a probabilistic algorithm. In this work, we propose to measure the slopes of the test surface in the x and y directions, and by integration, we calculated the sagitta of the test surface. We present a comparison between both methods to show which of them recovers the shape of the surface more accurately.

High intensity lasers in the 10-PW range require large optics (up to 600 mm diameter) with very high surface quality. In our case we have been facing troubles coming from very small wavefront defects at high spatial frequencies; defects that were not visible when checking with a Fizeau-type interferometer that was providing a PSD record. These very small defects were creating high-contrast Talbot fringes when propagating our laser beam. We decided to check carefully how the focal spot of our laser beam was affected and this was the reason why we decided to build collimators. Our collimator is a classical Newton-type telescope that can be used either off-axis or on- axis with a low central occultation (< 12%). The beam comes from a collimated laser source that is focused through a 30-μm pinhole by a microscope objective (x 20) in order to obtain a "clean" spatial distribution. In the collimated part, optical densities calibrated at the operating wavelength(s) are inserted in order to control the intensity in the focal spot. An operating range of 10 orders of magnitude is obtained with a source emitting 5 mW. The measurement is made in the focal plane of the component to be tested with a CCD camera. In cooperation with Aperture Optical Sciences Inc., the collimator was tested with known components and results compared with other available systems. Finally, we are able to identify and to measure periodic defects as low as l/2500 and to connect them with their PSD value.

In this work, we use a null-screen corneal topographer with a semiradial spot pattern by using a mobile device’s camera to obtain images of the reflected pattern with the main aim of obtaining the corneal topography. First, we discuss how to integrate the system to calibrate it by testing a reference surface where we obtain optical parameters such as the radius of curvature and the conic constant, as well as elevation, sagittal curves, and meridional curvature maps with this method. Finally, we show some prelaminar measurements of the topography of some human corneas.

Bifocal diffractive-refractive intraocular lenses (BDRIOL) are used in ophthalmology to replace natural lenses that are clouded by cataracts. In Russia, the REPER-NN enterprise developed a BDRIOL manufacture technology on the base of a liquid photopolymer frontal polymerization placed between two transparent fused silica moulds. One of them has a spherical shape, the other has a flat surface with a diffractive optical element (DOE). In our BDRIOL design the diffractive structure depth changes so that the energy distribution over the foci weakly depends on the pupil diameter. Zeroth and first orders efficiencies should almost the same. Measurement of this distribution is complicated due to the diffractive profile depth corresponds to the operation of a polymer lens in the eye and is significantly greater than required for working in air. We have proposed to use temporal planarization of the diffractive mould to measure energy distribution over foci. The diffractive structure is filled with a material that provides approximately the same module of refractive index difference with fused silica as between the polymer and vitreous body of the eye. This difference is adjusted by the temperature and time selection at the photoresist baking. The sign inversion of the refractive index difference in comparison with the operating conditions in human eye changes the DOE focus to positive. The paper discussed specific photoresist treatment, refractive index measurement and preliminary results of the developed method.

Diffractive Optical Elements (DOEs) are amplitude and/or phase masks that can be applied to light beams to modify their phase and/or intensity distribution. They are applied in holography, beam shaping, generation of exotic beams (Hermite-Gauss, Laguerre-Gauss, Gauss-Bessel, accelerating or vortex beams, etc.), generation of custom intensity profiles (top-hat, lines, figures, etc.), atomic physics, quantum optics, etc. They can be implemented using Spatial Light Modulators (SLMs) or micro-structured materials. Femtosecond laser writing is a very promising technique for fabricating photonic and micro-optics devices in metallic and dielectric materials. It consists on the removal (ablation) or modification of the irradiated material. Due to the short pulse duration of fs pulses, the energy is deposited in a localized region by nonlinear absorption mechanisms, allowing a very precise control of the material removal/modification. Compared to other methods, it has many advantages like a reduction of the amount of energy required to fabricate devices, and the absence of pollutant chemicals, becoming one of the most environmentally friendly fabrication techniques. One technique for implementing amplitude modulation DOEs is using dielectric samples covered with a metal thin film (few hundreds of nm thick). Then, the metallic film is selectively removed by laser ablation. This allows the engraving of a binary amplitude mask, where the remaining metallic coating reflects the electric field while the exposed dielectric area supports its transmission. Hence, these masks may work in both transmission and reflection. Although laser processing of DOEs has been successfully proved, some challenges still remain and should be addressed to optimize their behaviour. Several problems may arise during the laser ablation process. One of the problems treated in this contribution is the effect of damage on the dielectric substrate under the metallic coating. This happens since the light used to remove the metallic layer can also affect the dielectric sample, producing damage, variations of the material lattice or compositional changes, thus altering its refractive index. This variation may affect the effect of the DOE when it is used in transmission configuration. Another issue related to the ablation process is the different ablation strategies to engrave a given spatial distribution. Here, the laser is driven to process a matrix of points, or it can work in raster mode across the sample. We will analyze these two effects to properly understand the limitations of the technique and to find some useful strategies to overcome them when engraving DOEs through laser ablation.

We use the null-screen method to evaluate in a qualitative and quantitative way the shape of a parabolic trough solar collector. When a parabolic trough solar collector is fabricated can occur that the manufacturing errors are large. In some cases, when using the null screen method, the objects in the image plane are overlapped. This problem is solved adequately by placing the CMOS sensor and LCD null-screen in off-axis positions. Also, we propose to display a suitable null-screen on the LCD screen. In the first evaluation the null screen is composed of few object points, in the next evaluation, we change the distribution of objects that compose the null screen with the aim of increasing the measurement points. Finally, the data corresponding to each evaluation is merged in only one set of evaluation data to calculate the surface sagitta from slope measurements of the test surface in the x and y directions.

In this work, we analyze the advantages and limitations of the systems of low speeds of frames per second (fps) for the estimation of the vibrations measurements in systems where optical techniques are used. The acquisition systems with low fps are interesting because they are not expensive. In this way, the aim of this work is to compute the limit speed to obtain good resolutions in data collection. Laser triangulation technique is implemented to determine the natural frequency of vibration of a system using a cantilever beam, as a standard example. The results are compared, with a commercial accelerometer.