The Nulling Interferometry Cryogenic Experiment (NICE) is an experimental testbed for the beam combiner of the Large Interferometer For Exoplanets (LIFE) space mission. Until now, progress on NICE has been confined to an ambient bench, where we have recorded progress in deep (<10^-5) nulls at wavelengths between 4 and 5 microns at 300 K. However, the ultimate goal and requirement of NICE is to repeat these measurements at the sensitivity levels expected for a planetary system, requiring deep cryogenic conditions at 15 K. Here, we describe the “Ice Cube” cryostat, a small version of the future NICE cryostat that is used for component and subsystem level cryogenic testing. This is interfaced with a measurement setup using a segmented aperture interferometer and a wavefront sensor. We will also describe the testing campaign for understanding the material and mounting challenges that will be faced when translating the warm bench to cryogenic operations.

A metasurface-based wide-band (400-1500nm) blazed grating is modeled by in-house Finite Element model with 3D topology optimization, leading to a pillar-structure exhibiting 57% average diffraction efficiency over the 2-octave band.

The aim of this lecture is to show how the consideration of very specific measurement requirements, related to segmented surfaces and metasurfaces, has enabled a generalist multilateral shearing interferometer to evolve into new innovative devices. This has enabled state-of-the-art performance to be achieved, in particular by exploiting in the design a priori knowledge of the objects to be measured. Performance is illustrated here by a comparison of measurements on a canonical object, a PTT-111 deformable mirror from the company Iris AO, with a reference Phase Shifting Interferometer from the community.

We present a new interferometer to measure piston, tip and tilt of segmented mirrors, using the combination of an optical grating and a microlens array. Since this interferometer is able to collect all the incident light and to operate with a large spectra bandwidth, it is particularly suitable to operate in low light level conditions, for example for the co-phasing of segmented primary mirrors like James Webb Space Telescope. We tested our new device on a 37-segment deformable mirror and obtained an accuracy better than lambda/100. The measurement is self-referenced and errors can be estimated on the measurement itself thanks to closure relationships.

L’interférométrie à décalage multilatéral est une technique d’analyse optique aux multiples applications. Basée sur un procédé simple, extension avantageuse de l’interférométrie à décalage, elle a permis de développer un grand nombre de dispositifs, chacun adapté à un besoin particulier de mesure. Elle correspond à un changement de paradigme qui voit maintenant les utilisateurs chercher à approcher au mieux des objets d’intérêt à analyser sans les perturber, en respectant au mieux les conditions environnementales. Le fait de se spécialiser dans un type de mesure permet en particulier d’introduire des connaissances a priori qui aident à la qualité de la mesure.

CBC (Coherent Beam Combining) is a key technology for the realisation of intense lasers. In this context, PISTIL (PISton and TILt interferometry), a precise metrology tool for measuring segmented wave surfaces, has been developed and used in particular to characterise and diagnose CBC ultrafast and digital laser in the framework of the XCAN (X Coherent Amplification Network) project at the École Polytechnique. We propose here to use it in a way to help the optimisation of control techniques by including PISTIL in an XCAN type CBC laser simulator. This will allow an easy tuning of the control laws, outside the clean rooms in which these large lasers are deployed and without the need to start them up.

Optical metasurfaces allow the development of original and more and more complex optical functions. They are therefore facing a design and characterization problem. Indeed, they are more and more composed of complex patterns, with different types of antennas and non-periodic. This is why it is important to build libraries of nano-structures that can be used as building blocks to compose optical functions. Therefore, we propose a direct phase measurement metrology method for optical nanostructures. Using lateral shift interferometry, our technique allows to simultaneously characterize in amplitude and phase nano-antennas of all types, shapes and materials, and thus to experimentally establish a library of nano-antennas. Our method brings an additional tool in the design of nano-antennas, which completes the existing simulation tools, by allowing to test all types of nano-antennas.

Meta-optics allow the realization of new optical functions that are increasingly complex to realize and characterize locally. This is why we propose an interferometric method of systematic wavefront metrology of the meta-elements constituting a metasurface. This technique will allow the design of a library of nano-antennas, characterized in phase and amplitude. Once constituted, this library will allow the design of more complex optical functions. Tested for MIM (Metal-Isolating-Metal) metasurfaces, this technique can be applied to all metasurfaces.

One of the most promising solutions to access high power laser chains is to achieve a coherent combination of a large number of elementary lasers. To interfere constructively, these laser sources should be identical and operate under the same conditions. However, despite these efforts, differential delays appear in the course of time, which must be compensated for. While designing the required correction system, knowing the behavior of a laser as a function of the environmental conditions is not crucial, whereas having access to the differences in the behaviors of identical lasers is, leading to difficulties in modeling. The purpose of this paper is to illustrate how a large set of lasers can be simultaneously analyzed to estimate their variations and optimize a correction system. The X-Coherent Amplified Network laser relies on 61 fiber amplifiers, which are as identical as possible. This state of the art femtosecond digital laser therefore appears as an ideal candidate to study a large number of fiber lasers working under controlled conditions.

PISTIL (PISton and TILt) interferometry is a segmented wavefront metrology technique that can fulfill the role of being an independent phase analyzer for tiled laser arrays used in coherent beam combining (CBC). It presents a plug-and-play characteristics enabling others research or industrial applications such as metrology of segmented mirrors, MOEMS or measurement standards. It can operate onto complex optical benches. Alongside the PISTIL concept, we developed methods for phase extraction and meta-analysis, with best accuracy to rightfully address an end user needs in term of segmented wavefront diagnosis. We demonstrate those functionalities onto the HIBISCUS optical testbed equipped with a segmented mirror, specifically designed test data analysis pipelines and improve the control-command based on PISTIL wavefront analysis. In the current configuration, it can emulate CBC near field piston and tilt variations.

Coherent beam combining (CBC) opens the way to a new paradigm in laser architecture [1] . The quest to high peak and average power indeed faces several fundamental limitations (transverse amplified spontaneous emission in wide amplifiers, thermal management issues) which can be addressed when relying on numerous smaller scale reliable lasers coherently combined. Achieving CBC for a large number of amplifiers will not only rely on the use of an efficient phase-locking scheme but also on fiber management inside the laser head (such as accurate angular and lateral positioning, at µm or mrad levels), optics, and amplifiers management as well as laboratory environment control. An accurate diagnosis of the laser array is mandatory in order to get significant feedback on its design, and potentially improve or stabilize its behavior, either in phase-locked loop or in free run.

PISTIL (Piston and Tilt) is a recent interferometric system that computes the absolute piston and tip/tilt map of a segmented wavefront. Its high precision makes it usable as a metrology tool for wavefront sensing of coherently-combined laser arrays for example. This interferometer needs to correctly address high dynamic piston sensing, while dealing with fringes wrapping that leads to ambiguous phase estimations. We derived a mathematical combination for two measurements at different wavelengths and did a technical demonstration of it, using a IRIS-AO PTT111 Deformable Mirror as a segmented wavefront generator. We have verified that the loss of accuracy is slightly increased for a larger piston compared to a previous study, and we got a standard error of lambda/160 with a Peak-to-valley of lambda/50. This technique could be extended to a broader spectrum.

The purpose of this paper is to show that the Shack-Hartmann wavefront sensor (SHWFS) gives access to more derivatives than the two orthogonal derivatives classically extracted either by estimating the centroid or by taking into account the first two harmonics of the Fourier transform. The demonstration is based on a simple model of the SHWFS, taking into account the microlens array as a whole and linking the SHWFS to the multi-lateral shearing interferometry family. This allows for estimating the quality of these additional derivatives, paving the way to new reconstruction techniques involving more than two cross derivatives that should improve the signal-to-noise ratio.

The PISTIL interferometry has been recently developed for the wavefront sensing of phase delays (pistons) and tilts of segmented surfaces, used in many domains such as astronomy, high-power lasers or ophthalmology. In this paper, we propose a two-wavelength version of this interferometer developed to bypass the dynamic range limitation of the ambiguous 2π phase wrapping. Principle of the technique is presented, along with experimental results obtained with a demonstration deformable mirror PTT-111 from Iris AO. Above wavelength pistons are measured with a precision and accuracy below λ/100, making the two-wavelength PISTIL interferometry a high-dynamic range technique. To prove these performances, we successfully compare the results in terms of precision and accuracy with those of a reference phase-shifting Interferometer, from a blind experimentation.

New architectures for telescopes or powerful lasers require segmented wave front metrology. This paper deals with a new interferometric wave front sensing technique called PISTIL (PISton and TILt), able to recover both piston and tilts of segment beams. The main advantages of the PISTIL technique are the absence of a reference arm and an access to the tilt information. An explanation of the principle, as well as an experimental implementation and the use of a segmented active mirror, are presented. Measurement errors of λ/200 for piston and 40 µrad for tilts have been achieved, well beyond performances requested for the above mentioned applications.

A new architecture for active coherent beam combining of a large number of fibers is demonstrated. The approach is based on a self-referenced quadriwave shearing interferometer and active control with arrays of electro-optic ceramic modulators. Coherent phase combining of 64 independent amplified fibers is obtained. This is to our knowledge the highest reported number of combined fibers. A Strehl ratio degradation less than 2dB is achieved with a residual phase error <λ/10 rms.

In this paper, we present the design of a very precise collimated fiber array that meets requirements for beam combining. Calculations permit to determine the tolerances toward key parameters and specify the components to manufacture. Thus, the collimated fiber array is composed of a high quality commercial microlens array and an especially dedicated fiber holder that we design and realize experimentally. Manufacture techniques for both the microlens and the holder are chosen to be collective and then compatible with a high number of fibers. With the collimated fiber array hence obtained, the individual beam quality was measured to be lambda/10 and the pointing accuracy is under 0.6 mrad. (c) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3537968]