Rudy Barette

Successful evaluation for space applications of the 2048×1080 DMD

Next-generation infrared multi-object spectrographs (MOS) for ground-based and space telescopes could be based on MOEMS programmable slit masks. This astronomical technique is used extensively to investigate the formation and evolution of galaxies. ESA has engaged a study for a technical assessment of using a DMD from Texas Instruments for space applications. The DMD features 2048 × 1080 mirrors on a 13.68μm pitch, where each mirror can be independently switched between an ON (+12°) position and an OFF (-12°) position. For MOS applications in space, the device should work in vacuum, at low temperature, and each MOS exposure would last for typically 1500s with micromirrors held in a static state (either ON or OFF). A specific thermal/vacuum test chamber has been developed for test conditions down to -40°C at 10-5 mbar vacuum. Imaging capability for resolving each micromirror has also been developed for determining degradation in any single mirror. Our first tests reveal that the DMD remains fully operational at -40°C and in vacuum. A 1038 hours life test in space conditions, Total Ionizing Dose radiation, thermal cycling and vibrations/shocks have also been successfully completed. These results do not reveal any concerns regarding the ability of the DMD to meet environmental space requirements. Detailed analysis of micromirror throughputs has also been studied for a whole set of tests, and shows a rather low variation and no impact of the space environment. We have also developed a bench for MOS demonstration using MOEMS devices. DMD chip has been successfully tested revealing good contrast values as well as good functionality for applying any mask pattern, demonstrating its full ability for space instrumentation, especially in multi-object spectroscopy applications.

Interferometric characterization of MOEMS devices in cryogenic environment for astronomical instrumentation

Next generation of infra-red astronomical instrumentation for space telescopes as well as ground-based extremely large telescopes requires MOEMS devices with remote control capability and cryogenic operation, including programmable multi-slit masks for multi-object spectroscopy (MOS). For the complete testing of these devices, we have developed in parallel and coupled a high-resolution Twyman-Green interferometer and a cryogenic-chamber for full surface and operation characterization. The interferometer exhibits a nanometer accuracy by using phase-shifting technique and low-coherence source. The cryogenic-chamber has a pressure as low as 10e-6 mbar and is able to cool down to 60K. Specific interfaces minimizing stresses for vacuum and cryo have been set. Within the framework of the European program on Smart Focal Planes, micro-mirrors have been selected for generating MOEMS-based slit masks. A first 5×5 micro-mirror array (MMA) with 100×200μm2 mirrors was successfully fabricated using a combination of bulk and surface silicon micromachining. They show a mechanical tilting angle of 20° at a driving voltage below 100V, with excellent surface quality and uniform tilt-angle. The mirrors could be successfully actuated before, during and after cryogenic cooling. The surface quality of the gold coated micro-mirrors at room temperature and below 100K, when they are actuated, shows a slight increase of the deformation from 35nm peak-to-valley to 50nm peak-to-valley, due to CTE mismatch between silicon and gold layer. This small deformation is still well within the requirement for MOS application.

Space evaluation of 2048×1080 mirrors DMD chip for ESA's EUCLID Mission

Next-generation infrared astronomical instrumentation for ground-based and space telescopes could be based on MOEMS programmable slit masks for multi-object spectroscopy (MOS). This astronomical technique is used extensively to investigate the formation and evolution of galaxies. We are engaged in an ESA study for a technical assessment of using a DMD from Texas Instruments for space applications (for example in ESA EUCLID mission). The DMD features 2048×1080 mirrors on a 13.68μm pitch, where each mirror can be independently switched between an ON (+12°) position and an OFF (-12°) position. For MOS applications in space, the device should work in vacuum, at low temperature, and each MOS exposure would last for typically 1500s with micromirrors held in a static state (either ON or OFF). A specific thermal/vacuum test chamber has been developed for test conditions down to -40°C at 10-5 mbar vacuum. Imaging capability for resolving each micromirror has also been developed for determining degradation in any single mirror. Our first tests reveal that the DMD remains fully operational at -40°C and in vacuum. A 1038 hours life test in space conditions, Total Ionizing Dose radiation, thermal cycling and vibrations/shocks have also been successfully completed. These results do not reveal any concerns regarding the ability of the DMD to meet environmental space requirements. We have also developed a bench for MOS demonstration using MOEMS devices. DMD chip has been successfully tested revealing good contrast values as well as good functionality for applying any mask pattern, demonstrating its full ability for space instrumentation, especially in multi-object spectroscopy applications.

Manufacturing and integration of the IRDIS dual imaging camera and spectrograph for SPHERE

SPHERE is a planet hunting instrument for the VLT 8m telescope in Chile whose prime objective is the discovery and characterization of young Jupiter-sized planets outside of the solar system. It is a complex instrument, consisting of an extreme Adaptive Optics System (SAXO), various coronagraphs, an infrared differential imaging camera (IRDIS), an infrared integral field spectrograph (IFS) and a visible differential polarimeter (ZIMPOL). The performance of the IRDIS camera is directly related to various wavefront error budgets of the instrument, in particular the differential aberrations occurring after separation of the two image beams. We report on the ongoing integration and testing activities in terms of optical, mechanical, and cryo-vacuum instrument parts. In particular, we show results of component level tests of the optics and indicate expected overall performance in comparison with design-level budgets. We also describe the plans for instrumental performance and science testing of the instrument, foreseen to be conducted during coming months.

DMD chip space evaluation for ESA's EUCLID mission

The EUCLID mission from the European Space Agency (ESA) will study the dark universe by characterizing a very high number of galaxies in shape and in spectrum. The high precision spectra measurements could be obtained via multi-object spectroscopy (MOS) using Digital Micromirror Devices (DMD). These devices would act as object selection reconfigurable masks. ESA has engaged with Visitech and LAM in a technical assessment of the DMD from Texas Instruments that features a 2048 x 1080 mirrors and a 13.68μm pixel pitch for space applications. For EUCLID, the device should work in vacuum, at low temperature, and each MOS exposure lasts 1500s with micromirrors held in a static state (either ON or OFF) during that duration. A specific thermal / vacuum test chamber has been developed for test conditions down to -40°C at 10-5 mbar vacuum. Imaging capability for resolving each micromirror has also been developed for determining any single mirror failure. Dedicated electronics and software permit to hold any pattern on the device for a duration as long as 1500s. Our first tests reveal that the DMD remains fully operational at -40°C. A 1038 hours life test, in EUCLID conditions (temperature and vacuum) has been successfully completed. Total Ionizing Dose (TID) radiation tests have been completed, establishing between 10 and 15 Krads, the level of TID that the DMD can tolerate; at mission level, this limitation could most likely be overcome by a proper shielding of the device. Finally, thermal cycling, vibration tests and MOS-like tests are under way.

SUBARU prime focus spectrograph integration and performance at LAM

The Prime Focus Spectrograph (PFS) of the Subaru Measurement of Images and Redshifts (SuMIRe) project for Subaru telescope includes four identical spectrograph modules fed by 600 fibers each. This paper presents the integration, alignment and test procedures for the first spectrograph module composed by an optical entrance unit that creates a collimated beam and distributes the light to three channels, two visible and one near infrared. In particular, we present the performance of the single Red channel module. Firstly, we report on the measured optical performance: optical quality and ghost analysis. We also report on the thermal performance of the visible camera cryostat. Finally, we describe the software used to control and monitor the instrument.

Operation of a MOEMS Deformable Mirror in Cryo: Challenges and Results

Micro-opto-electro-mechanical systems (MOEMS) Deformable Mirrors (DM) are key components for next generation optical instruments implementing innovative adaptive optics systems, both in existing telescopes and in the future ELTs. Characterizing these components well is critical for next generation instruments. This is done by interferometry, including surface quality measurement in static and dynamical modes, at ambient and in vacuum/cryo. We use a compact cryo-vacuum chamber designed for reaching 10–6 mbar and 160 K in front of our custom Michelson interferometer, which is able to measure performance of the DM at actuator/segment level and at the entire mirror level, with a lateral resolution of 2 µm and a sub-nanometer z-resolution. We tested the PTT 111 DM from Iris AO: an array of single crystalline silicon hexagonal mirrors with a pitch of 606 µm, able to move in tip, tilt, and piston (stroke 5–7 µm, tilt ±5 mrad). The device could be operated successfully from ambient to 160 K. An additional, mainly focus-like, 500 nm deformation of the entire mirror is measured at 160 K; we were able to recover the best flat in cryo by correcting the focus and local tip-tilts on all segments, reaching 12 nm rms. Finally, the goal of these studies is to test DMs in cryo and vacuum conditions as well as to improve their architecture for stable operation in harsh environments.

Cryo micro-deformable mirrors for next generation AO systems

MOEMS Deformable Mirrors (DM) are key components for next generation optical instruments implementing innovative adaptive optics systems, both in existing telescopes and in the future ELTs. Characterizing these components well is critical for next generation instruments. This is done by interferometry, including surface quality measurement in static and dynamical modes, at ambient and in vacuum/cryo. We use a compact cryo-vacuum chamber designed for reaching 10–6 mbar and 160 K in front of our custom Michelson interferometer, which is able to measure performance of the DM at actuator/segment level and at the entire mirror level, with a lateral resolution of 2 μm and a sub-nanometer z-resolution. We tested the PTT 111 DM from Iris AO: an array of single crystalline silicon hexagonal mirrors with a pitch of 606 μm, able to move in tip, tilt, and piston (stroke 5–7 μm, tilt +/− 5 mrad). The device could be operated successfully from ambient to 160 K. At room temperature, we developed an improved best flat procedure and obtained a mirror surface deformation, as low as 10 nm RMS. An additional, 500 nm deformation of the entire mirror is measured at 160K; by analyzing at all spatial scales our measurements, we are able to discriminate the different effects at packaging, actuator and mirror segment level. We developed a strategy of weighted addition of the consecutive measurement residual errors to be applied to each actuator; in a single measurement step, we were able to recover the cryo best flat by correcting the focus and local tip-tilts on all segments, reaching a mirror surface deformation as low as 12 nm RMS at 160K. Finally, the goal of these studies is to test DMs in cryo and vacuum conditions as well as to improve their architecture for stable operation in a harsh environment. They are foreseen in a wide variety of applications, from astronomy as presented in this paper, but also in microscopy and in laser beam shaping.

Cryogenic testing of MOEMS deformable mirror for future optical instrumentation

An Iris AO MOEMS deformable mirror has been successfully operated and tested at 160K. Surface deformation at room temperature and in cryo has been measured and DM architecture contributions analyzed.

MOEMS deformable mirror testing in cryo for future optical instrumentation

MOEMS Deformable Mirrors (DM) are key components for next generation optical instruments implementing innovative adaptive optics systems, in existing telescopes as well as in the future ELTs. Due to the wide variety of applications, these DMs must perform at room temperature as well as in cryogenic and vacuum environment. Ideally, the MOEMS-DMs must be designed to operate in such environment. This is unfortunately usually not the case. We will present some major rules for designing / operating DMs in cryo and vacuum. Next step is to characterize with high accuracy the different DM candidates. We chose to use interferometry for the full characterization of these devices, including surface quality measurement in static and dynamical modes, at ambient and in vacuum/cryo. Thanks to our previous set-up developments, we are placing a compact cryo-vacuum chamber designed for reaching 10-6 mbar and 160K, in front of our custom Michelson interferometer, able to measure performances of the DM at actuator/segment level as well as whole mirror level, with a lateral resolution of 2μm and a sub-nanometric zresolution. Using this interferometric bench, we tested the PTT 111 DM from Iris AO: this unique and robust design uses an array of single crystalline silicon hexagonal mirrors with a pitch of 606μm, able to move in tip, tilt and piston with strokes from 5 to 7μm, and tilt angle in the range of +/- 5mrad. They exhibit typically an open-loop flat surface figure as good as < 20nm rms. A specific mount including electronic and opto-mechanical interfaces has been designed for fitting in the test chamber. Segment deformation, mirror shaping, open-loop operation are tested at room and cryo temperature and results are compared. The device could be operated successfully at 160K. An additional, mainly focus-like, 500 nm deformation is measured at 160K; we were able to recover the best flat in cryo by correcting the focus and local tip-tilts on some segments. Tests on DM with different mirror thicknesses (25μm and 50μm) and different coatings (silver and gold) are currently under way. Finally, the goal of these studies is to test DMs in cryo and vacuum conditions as well as to improve their architecture for staying efficient in harsh environment.