Pierre Morin

First light adaptive optics systems and components for the Thirty Meter Telescope

Adaptive optics (AO) is essential for many elements of the science case for the Thirty Meter Telescope (TMT). The initial requirements for the observatorys facility AO system include diffraction-limited performance in the near IR, with 50 per cent sky coverage at the galactic pole. Point spread function uniformity and stability over a 30 arc sec field-ofview are also required for precision photometry and astrometry. These capabilities will be achieved via an order 60×60 multi-conjugate AO system (NFIRAOS) with two deformable mirrors, six laser guide star wavefront sensors, and three low-order, IR, natural guide star wavefront sensors within each client instrument. The associated laser guide star facility (LGSF) will employ 150W of laser power at a wavelength of 589 nm to generate the six laser guide stars. We provide an update on the progress in designing, modeling, and validating these systems and their components over the last two years. This includes work on the layouts and detailed designs of NFIRAOS and the LGSF; fabrication and test of a full-scale prototype tip/tilt stage (TTS); Conceptual Designs Studies for the real time controller (RTC) hardware and algorithms; fabrication and test of the detectors for the laser- and natural-guide star wavefront sensors; AO system modeling and performance optimization; lab tests of wavefront sensing algorithms for use with elongated laser guide stars; and high resolution LIDAR measurements of the mesospheric sodium layer. Further details may be found in specific papers on each of these topics.

The field stabilization and adaptive optics mirrors for the European Extremaly Large Telescope

A 42 meters telescope does require adaptive optics to provide few milli arcseconds resolution images. In the current design of the E-ELT, M4 provides adaptive correction while M5 is the field stabilization mirror. Both mirrors have an essential role in the E-ELT telescope strategy since they do not only correct for atmospheric turbulence but have also to cancel part of telescope wind shaking and static aberrations. Both mirrors specifications have been defined to avoid requesting over constrained requirements in term of stroke, speed and guide stars magnitude. Technical specifications and technological issues are discussed in this article. Critical aspects and roadmap to assess the feasibility of such mirrors are outlined.

Demonstration prototype and breadboards of the piezo stack M4 adaptive unit of the E-ELT

In order to mitigate the risks of development of the M4 adaptive mirror for the E-ELT, CILAS has proposed to build a demonstration prototype and breadboards dedicated to this project. The objectives of the demonstration prototype concern the manufacturing issues such as mass assembly, integration, control and polishing but also the check the global dynamical and thermal behaviour of the mirror. The local behaviour of the mirror (polishing quality, influence function, print through...) is studied through a breadboard that can be considered as a piece of the final mirror. We propose in this paper to present our breadboard strategy, to define and present our mock-up and to comment the main results and lessons learned.

Recent results and future DMs for astronomy and for space applications at CILAS

We present recent experimental results obtained with CILAS deformable mirrors (DMs) or demonstration prototypes in solar and night-time astronomy (with ground-based telescopes) as well as observation of the Earth (with space telescopes). These important results have been reached thanks to CILAS technology range composed of monomorph and piezostack deformable mirrors, drivers and optical coatings. For instance, the monomorph technology, due to a simple architecture can offer a very good reliability for space applications. It can be used for closed or open loop correction of the primary mirror deformation (thermal and polishing aberrations, absence of gravity). It can also allow a real-time correction of wavefront aberrations introduced by the atmosphere up to relatively high spatial and temporal frequencies for ground-based telescopes. The piezostack technology is useful for very high order correction at high frequency and under relatively low operational temperature (down to -30°C), which is required for future Extremely Large Telescopes (ELTs). This wide range of applications is exposed through recent examples of DMs performances in operation and results obtained with breadboards, allowing promising DMs for future needs.

Last progress concerning the design of the piezo stack M4 adaptive unit of the E-ELT

CILAS proposes a M4 adaptive mirror (M4AM) that corrects the atmospheric turbulence at high frequencies and residual tip-tilt and defocus due to telescope vibrations by using piezostack actuators. The design presents a matrix of 7217 actuators (triangular geometry, spacing equal to 29 mm) leading to a fitting error reaching the goal. The mirror is held by a positioning system which ensures all movements of the mirror at low frequency and selects the focus (Nasmyth A or B) using a hexapod concept. This subsystem is fixed rigidly to the mounting system and permits mirror displacements. The M4 control system (M4CS) ensures the connection between the telescope control/monitoring system and the M4 unit - positioning system (M4PS) and piezostack actuators of the M4AM in particular. This subsystem is composed of electronic boards, mechanical support fixed to the mounting structure and the thermal hardware. With piezostack actuators, most of the thermal load is minimized and dissipated in the electronic boards and not in the adaptive mirror. The mounting structure (M4MS) is the mechanical interface with the telescope (and the ARU in particular) and ensures the integrity and stability of M4 unit subsystems. M4 positioning system and mounting structure are subcontracted to AMOS company.

Developments of piezo deformable mirrors

We present recent developments on deformable mirrors (DM) for astronomy with ground-based telescopes. A new generation of actuators with high reliability and high performances has been developed for Stack Array Mirrors. These actuators are suitable for a large range of DMs, including future needs for Extremely Large Telescopes. Design and modelling of large DMs for Thirty Meter Telescope and European Extremely Large Telescope are presented. The Monomorph mirrors combines simplicity and efficiency to correct the wavefront deformation. Astronomical telescopes can benefit of the developments performed on this Monomorph technology for high power laser chains and for spaceborn instrumentation.

Laser source for DIRCM at CILAS

We report on the development and characteristics of infrared solid state laser as compact and robust light sources for Directed Infrared Countermeasures (DIRCM). DIRCM against infrared missile seekers requires wavelength tunable laser sources. When adding an optical parametric oscillator to a pump laser source, it is possible to cover the 2-5 μm wavelength transmission windows. For more than five years, CILAS has developed critical technologies for the development of a laser source adapted for DIRCM application. This includes: The choice of the crystals, the optical coatings in band II, the thermal management and an optimized oscillator configuration insensitive to repetition rate variation in a wide range. The scope of this presentation is to recall performances of the technologies developed and to present the technical base line of our laser concept. This work is supported by the French MOD (DGA).

Prototyping of large deformable mirrors for TMT: test results

Stack Array Mirrors (SAM) technology offers high order correction, with up to several thousands of actuators, controllable at high frequency, up to several kHz. A new generation of piezo-electric actuators with high reliability has been developed during the last years. This technology is well-adapted for large deformable mirrors (DMs) with thousands of actuators for future needs for Extremely Large Telescopes. We present the design and the modelling of the two large DMs for NFIRAOS, the multi-conjugate adaptive optics system of the Thirty Meter Telescope (TMT): DM0 which shows 3125 actuators and DM11 which shows 4548 actuators. A DM prototype with 616 actuators has been manufactured to validate the manufacturing steps and the specifications of the future large DMs, including their behavior at both ambient and low temperature (-30°C). The prototype includes the new generation of piezo actuators with improved reliability thanks to an optimization of the fabrication processes. Experimental results of accelerated ageing tests and mechanical fatigue are presented. After complete assembly, the prototype is qualified in a specific cool chamber with interferometric measurements. The results are the following: operational stroke higher than 10 μm PV at both ambient and -30°C with uniformity better than 5%, overall non-linearity lower than 5%, resonance frequency of the actuators higher than 10 kHz. Based on the measurements done on the overall temperature range (+20°C to -30°C), the best flat is lower than the goal specification of 10 nm RMS mechanical. An enhanced protected silver coating done by magnetron sputtering allows a high level of reflectivity especially in the near infrared range and long-life durability.

MILDA: mid-infrared laser source for DIRCM application

We report on the development and characteristics of infrared solid state laser as compact and robust light sources for Directed Infrared Countermeasures (DIRCM). DIRCM against infrared missile seekers requires wavelength tunable laser sources. When adding an optical parametric oscillator (OPO) to a pump laser source, it is possible to cover the 2-5 μm wavelength transmission windows. After a risk reduction phase of five years, CILAS has designed a solid state laser source (SSLS) adapted for DIRCM jamming and has delivered a prototype to DGA-MI for testing and evaluation. The purpose of this paper is to recall the requirements of such a laser source, to present the main design trade-off and the testing experiments. This work is supported by the French MoD (DGA).