By Thomas Guengerich
SOCORRO, N.M., July 24, 2008 – New Mexico Tech took center stage at an international conference for optical engineering in Marseilles, France, in late June.
Right: from left are Carlo Flebus, Pierre Gloesener, Colby Jurgenson, Michelle Creech-Eakman and Jean-Pierre Chisogne. MRO Interferometer Project Scientist Michelle Creech-Eakman led the New Mexico Tech contingent at the SPIE conference in Marseille. In photo, she and Tech instrument specialist Colby Jurgenson visit with three representatives of AMOS, the Belgian firm that is building the telescope mounts.
Magdalena Ridge Observatory’s interferometry team presented several posters and papers, including an invited talk by project scientist Michelle Creech-Eakman. The MRO team also included talks by Tech students and researchers, Cambridge scientists and the Belgian company building the telescopes.
“It’s always exciting to go to these conferences,” said Creech-Eakman. “We always learn a lot about what everybody else is doing. The interferometry community is rather small. There’s probably no more than 250 people working in the area, so it’s good to get together and build consortia.”
An interferometer is an instrument that uses an array of telescopes to simulate a much larger telescope. The New Mexico Tech interferometer will use six 1.4-meter telescopes to mimic the capabilities of a telescope that is up to 340 meters in diameter. The concept was first proposed more than 100 years ago, but only in the past 20 years has the computer technology caught up with the theories. The main trick is to combine the beams collected at multiple telescopes to create a coherent and reliable image.
Stellar interferometry combines light from multiple telescopes to form “interference fringes.” A complex optical system with multiple light reflections from the light-collecting surfaces to the detectors measures these fringes. Beams from the six telescopes will be combined in a 190-meter long facility that includes more than 10 kilometers of aluminum pipe, carrying the signals.
The Magdalena Ridge Observatory Interferometer, or MROI, has one main goal – producing very-high-resolution images of faint astronomical targets, Creech-Eakman said. Ultimately, the facility will produce images with resolution 100 times greater than the Hubble Space Telescope.
Magdalena Ridge Observatory facility will employ a variety of new technologies that are revolutionizing interferometry. Tech and Cambridge scientists unveiled several of their breakthroughs in late June.
The Society for Optical Engineering, known by its French acronym of SPIE, hosted more than 2,000 scientists at the conference “Astronomical Instrumentation: Synergies between Ground and Space” from June 23 to 28. The MRO crew participated in the sub-conference on Optical and Infrared Interferometry.
Creech-Eakman presented an updated on the Magdalena Ridge Observatory Interferometer called “Progress Towards First Light.”
“It’s like a stake in the ground,” she said. “It’s an opportunity for us to give updates and show our progress.”
Several other Tech students, researchers and faculty members attended the conference to present talks and posters. Instrumentation specialist Dr. Colby Jurgenson spoke about the development of the fringe tracking beam combiner and spectrographs.
Alisa Shtromberg shows off her poster to her Cambridge colleagues (from left) John Young, Chris Haniff and David Buscher.
Alisa Shtromberg presented her work on designing an automated alignment system. Dr. Eric Bakker presented a poster on cost-estimates for large-scale projects. Block presented her work on custom coatings for optics on the fringe tracker. Fernando Santoro, who was unable to attend, presented a poster on the mechanical and optical design of the interferometer. Electrical engineering professor Dr. Anders Jorgensen gave a talk and presented a poster on fringe-tracking algorithms.
Jurgenson came to New Mexico Tech as a post-doctoral researcher and is now a permanent staff member at the interferometer as the instrument scientist. He presented a talk about a new instrument he is designing to combine light beams from the telescopes.
“We are designing and building this instrument in-house,” Jurgenson said. “It will go on the back end of the interferometer.”
Creech-Eakman said Jurgenson’s instrument is at the heart of the interferometer.
“If we didn’t have to contend with the atmosphere, the process would be straight-forward. We’d lock in on an object and we’d be done,” she said. “But the atmosphere distorts the light, so we have to move the delay lines to catch up with the distortions. Colby’s fringe-tracker has to move fast to catch up.”
He was especially pleased to hear scientists from other interferometry observatories show interest in his development.
“Certain parties were interested in applying what we’re doing on their projects,” he said. “That’s the best sort of feedback.”
Shtromberg, who is an interferometer lab technician, presented her research for an automated alignment system. The 2005 Tech graduate has designed a system of mirrors that is intended to eliminate optical errors.
“It’s a very tough problem to fix,” she said. “No one has been able to achieve it in an automated sense before now. Previous interferometers had not even planned for an alignment system before construction. We have the advantage of integrating into the system as we build it.”
Shtromberg’s presentation represented the official international unveiling of her design.
“There was a lot of interest,” she said. “There are a few people who will be keeping an eye on me and how I progress … so no pressure.”
Shtromberg apparently has enjoyed her work with the MRO. She is beginning a master’s program at Tech in August in physics with an emphasis in instrumentation.
Erica Block and Colby Jurgenson stop for a photo at Blockâ€™s poster she presented at the SPIE conference in Marseilles.
Erica Block is a rising senior in the physics department who is on the interferometer staff. She presented a poster explaining her research to develop three different custom coatings for the optics – one for the interferometer and two for the beam-splitters.
Block developed a 14-layer coating composed of strontium titanate, niobium oxide and magnesium flouride. She developed two other coatings for the beam-splitters, one of eight layers and one of nine layers.
“We want to minimize the number of layers because … if you apply too many coatings, the substrate tends to bend and gives you distortion,” Block said. “But we also want to maximize the performance of the coatings.”
She said the feedback was overwhelmingly positive. Numerous people were impressed with the performance of Block’s coatings, including an Italian group that expressed interest in purchasing her design.
Overall, Creech-Eakman felt that the breadth and detail of the work happening in Socorro shows the pioneering nature of the Magdalena Ridge Observatory.
“When you look at all our sub-projects, our interferometer seems unique compared to others,” Creech-Eakman said. “It always makes you feel good when people are interested in your design, but it also shows how important it is for the pieces to fit together.”
The interferometer atop Magdalena Ridge is expected to see first light – or, in this case, “first fringes” – in late 2009 or early 2010. Tech and builders Advanced Mechanical and Optical Systems, or AMOS, of Liège, Belgium, are finalizing the contract to complete the first phase of the telescopes.
Dr. Eric Bakker, interferometer project manager, said the SPIE conference is “the big one.”
“It’s a great place to hear the latest information about what’s going on around the world,” Bakker said.
He gave two presentations – one a history of the MRO and the other a glimpse into the future of astronomy instrumentation.
“The next generation will be a kilometer-based interferometer,” he said. “Our telescopes are 1.4 meters. The next generation will be 4 to 8 meters.”
Bakker presented a cost-study, estimating that the next configuration will more closely resemble the VLA, is about 20 years away and will cost $2.5 billion.
“These are expensive toys,” he said.
Bakker predicts that the current advances in telescope optics involve building mirrors that are 30 to 40 meters wide. Bakker said there are three projects underway to build these large scopes. That represents the practical limit of single-mirror telescopes, he said.
“Those are all billion dollar projects,” he said. “Once they have first light about 10 years from now in 2017, then the astronomy community will push for the next step, which will be a kilometer-based interferometer.”
Dave Buscher, a Cambridge scientist, presented two talks – "Polarization fidelity in an optical interferometer" and “Fringe-tracking and spatial filtering: phase jumps and dropouts.”
Chris Haniff, a Cambridge scientist working in Socorro, spoke on "The long-stroke MROI vacuum delay lines from concept to production."
Fabien Baron of Cambridge talked about "A high-sensitivity near-infrared science combiner for MROI" and presented a poster titled "Image reconstruction at Cambridge University."
Martin Fisher of Cambridge spoke about "Innovative mechatronics for the MROI delay lines."
Currently only eight operating optical/infrared interferometers exist in the world, with only three facilities using large apertures and having dedicated science missions. The Magdalena Ridge Observatory will be the fourth "facility-class" interferometer, Creech-Eakman said, but is the only one committed to a model-independent imaging program.
“Most interferometers weren’t built with such a systems approach,” Creech-Eakman said. “Chris Haniff and Dave Buscher – our system architects – have taken an overall systems approach from the beginning. It’s like we’re putting together a puzzle that fits together very nicely.”
Haniff and Buscher, both of Cambridge, are like orchestra conductors bringing together an incredibly complex project.
“They’ve paid attention to every minute detail,” Creech-Eakman said. “It’s exciting to see it all come together.”