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Thirty Meter Telescope

Interview with Corinne Boyer

Corinne Boyer is a Senior Adaptive Optics Software Engineer for the Thirty Meter Telescope project. She spoke recently with Warren Skidmore to discuss the integral role that adaptive optics (AO) technology will play in the scientific productivity of the TMT.

Q. What educational and career path did you follow up until you started working in the field of adaptive optics?

I completed my engineering school and master degrees in servo control in 1986 with an internship at a research laboratory in France called "Les Laboratoires de Marcoussis." The subject of my internship was to implement the servo transfer function of an astronomical AO system, and to optimize the transfer function based on the AO parameters, such as the number of actuators and the influence diameter. At the end of my six-month internship, my director of study and I published in a paper on the results in Applied Optics, which is still used as a reference. Since this time, I have worked in the field of AO.

Q. What motivated you to take up a career in adaptive optics?

I really loved the subject of my internship and believed that we could build such an AO system for astronomy. And when it was proposed to me to join such a team, I did not hesitate. The plan was to build an AO system for the 3.6-meter telescope of the European Southern Observatory (ESO), the first AO system for astronomy, which we did.

Q. Which projects have you been involved with that are relevant to your role with TMT?

All the AO projects I have been involved with are directly relevant with the TMT AO projects; in particular the most recent projects like the Gemini South multi-conjugate AO system and the Gemini Laser Guide Star Facility. My participation in the first light and commissioning of the Gemini telescope is also very useful in helping my understanding on how works a big telescope and how it interacts with AO

Q. Why is AO so important for ground based telescopes and especially for TMT?

The main purpose of AO is to compensate for natural atmospheric turbulence in order to approach the theoretical diffraction limit, which for a particular telescope and a particular instrument depends on the wavelength of the incoming light and the diameter of the telescope. Roughly speaking, AO will improve the resolution of TMT by a factor of about 60 for many types of observations.

It is important to equip TMT with full AO correction capabilities in order to scientifically exploit the full power of TMT’s spatial resolution. Using AO for TMT will allow to achieve resolution of the order of milli-arcseconds, and as a consequence will allow scientists and astronomers to answer the most challenging questions in astronomy and astrophysics.

Q. What areas of science will benefit through the use of AO on TMT?

At least six of the eight scientific instruments planned for TMT will rely upon adaptive optics for their observations of planets, stars, and distant galaxies. Some of these observations include direct detection and spectroscopy of extrasolar planets, studies of star and planet formation, the birth and evolution of stellar populations, assembly of galaxies and characterization of the intergalactic medium in the early universe, and our own Galactic Center.

Q. What are the most cutting edge AO systems in operation today, and how do these differ from the systems planned for TMT?

The AO systems currently in operation at telescopes use natural guide stars and, very recently, single laser guide star systems (such as Lick, Keck, Palomar, Gemini, and the VLT). These telescopes are now planning their next generation of AO systems using multiple guide stars, multi-conjugate AO (MCAO) and "extreme" AO.

One of the most mature projects to my knowledge is the Gemini MCAO system that will be integrated and tested in 2007, and hopefully become operational in 2008. A MCAO system is a further development of the original AO concept. It consists of correcting the turbulence in three dimensions with more than one deformable mirror (DM). Each DM is optically conjugated to a certain distance from the telescope. The benefit of MCAO is an increase in the size of the compensated field of view.

TMT is building several different AO systems, each of which will be an evolution of the systems currently in operation or under development. Four of the five AO systems will require multiple laser guide stars. Additionally, the TMT AO systems will require higher-order wavefront sensors, higher-order deformable mirrors with higher stroke and, of course, more computing power and more powerful lasers.

Q. What particular challenges are facing the TMT AO system and how are they being attacked?

TMT has funded a study at CILAS to demonstrate the feasibility of the high-order, high-stroke, low-temperature deformable mirror needed for the first generation of TMT AO systems. [Note: for more details, see this Project Manager’s Corner.]

The UC Santa Cruz Center for Adaptive Optics is also supporting work to develop high-order Micro-Electro-Mechanical Systems (MEMS) that will be used by the TMT.

In the area of more powerful lasers, the U.S. Air Force Starfire Optical Range has recently successfully demonstrated on the sky a 50-watt continuous wave laser. Lockheed Martin Coherent Technologies is currently developing a similarly powerful laser for the Gemini MCAO system.

Pulsed-sodium lasers to defeat the elongation of the laser guide star spot via dynamic refocusing are being studied at the Lawrence Livermore National Laboratory and at Lockheed Martin via the NSF’s Adaptive Optics Development Program. MIT Lincoln Laboratory is working on demonstrating a low noise, polar coordinate CCD array optimized for helping the wavefront sensor with this task, also supported by that NSF program

To achieve our high sky-coverage requirements, we will need to sense very faint natural guide stars for tip-tilt correction within the laser guide AO systems. ESO and Gemini are planning to develop low noise, high speed infrared detectors for this application.

Q. What are the biggest technical challenges in building the AO system for TMT?

Even though we have obtained encouraging results toward demonstrating the feasibility of some of the needed AO components, I still believe that some of them are very challenging, such as the Real Time Controller, the advanced algorithms required to process all the incoming information, the pulsed lasers and the MEMS.

Q. Could you outline the new or advanced features, services and capabilities that the planned suite of AO facilities will provide for astronomers?

Multi-conjugate AO (MCAO) will provide near diffraction limited performances in the near infrared over a 30-arcsecond field of view. This is roughly four times larger than "conventional" AO systems. Up to eight laser guide stars in four separate constellations will be generated by the TMT using three 50-watt lasers.

Mid-infrared AO will be implemented by a separate multiple LGS AO system. The requirements on this system are different from MCAO because the necessary order of correction is reduced and the number of warm surfaces must be minimized to limit emissivity.

Ground layer AO (GLAO) will be used in conjunction with at least two instruments. The purpose of GLAO will be to correct for low-altitude atmospheric turbulence over a very wide field of view. This system is expected to “enhance” atmospheric seeing, thereby reducing the integration times and improving observing efficiency. Farther in the future, extreme AO (ExAO) will be done within the TMT Planet Formation Imager. [Note: see story on PFI here in this Newsletter.]

Q. What is the schedule for the construction of TMT? When will we see the first observations with AO?

At the present, the TMT MCAO system (called NFIRAOS) and the IRIS instrument will be commissioned with the laser guide star facility of the telescope as soon as it is operational circa 2015 (with all of the mirror segments phased). Early science operations with this AO system could happen no later than three to six months after that.

Q. In the end, what fascinates you about being involved in the building of TMT and why?

All of the engineering issues that TMT scientists and engineers have to solve to help the telescope become a reality make it a very inspiring daily challenge.

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