The Giant Magellan Telescope laser tomography adaptive optics system

The Giant Magellan Telescope adaptive optics system will be an integral part of the telescope, providing laser guide star generation, wavefront sensing, and wavefront correction to most of the currently envisioned instruments. The system will provide three observing modes: Natural Guidestar AO (NGSAO), Laser Tomography AO (LTAO), and Ground Layer AO (GLAO).All observing modes will use the telescope's segmented adaptive secondary mirror to deliver a corrected beam directly to the instruments. High-order wavefront sensing for the NGSAO and LTAO modes is provided by a set of wavefront sensors replicated for each instrument and fed by visible light reflected off the cryostat window. An infrared natural guidestar wavefront sensor with open-loop AO correction is also required to sense tip-tilt, focus, segment piston, and dynamic calibration errors in the LTAO mode. GLAO mode wavefront sensing is provided by laser guidestars over a ~5 arcminute field of view, and natural guidestars over wider fields. A laser guidestar facility will project 120 W of 589 nm laser light in 6 beacons from the periphery of the primary mirror. An off-axis phasing camera and primary and secondary mirror metrology systems will ensure that the telescope optics remain phased. We describe the system requirements, overall architecture, and innovative solutions found to the challenges presented by high-order AO on a segmented extremely large telescope. Further details may be found in specific papers on each of the observing modes and major subsystems.

Section: Laser Guidestar Facilitymentioning

confidence: 99%

“…Thus the atmospheric segment piston remains uncorrected, contributing ~110 nm RMS to the wavefront error budget [7]. Tomography error is the other dominant contributor, also approximately 110 nm RMS [8].…”

Section: Error Budgetsmentioning

confidence: 99%

The Giant Magellan Telescope adaptive optics program

Bouchez¹,

Acton²,

Agapito³

et al. 2012

“…MultiConjugate Adaptive Optics (MCAO) with several sodium LGS has been the tendency of the next generation telescopes. For example, both GMT and TMT will initially include six lasers to meet the demand of MCAO systems in the purpose of diffraction-limited capacity [7,8] . Compared with cw lasers, long pulsed sodium lasers are preferable because they allow for Rayleigh blanking and fratricide avoidance in multiple LGS systems [9] .…”

Section: Introductionmentioning

confidence: 99%

Experimental demonstration of brighter sodium resonant scattering with 1.7 GHz sideband repumping for long pulse laser

Zhang

Wang

et al. 2014

Adaptive Optics (AO) based on artificial beacons is the key to achieve high resolution images from large ground-based telescopes. Long pulsed lasers are preferable to create sodium laser guide stars (LGS) as they allow for Rayleigh blanking. However, these lasers may increase the effective light intensity irradiated at the sodium layer, which may lead to transition saturation, and then decline the normalized return flux efficiency. The return flux might be boosted by optical repumping, which could make full use of the advantages of optical pumping without trapping the atoms to the F=1 ground state. In this paper, we study the optical repumping effect by using a small scale long pulsed sodium laser developed in Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences, whose pulse format may be pretty suitable for large telescopes. An electro-optic phase modulator is used to produce 1.713 GHz sidebands from the D 2a center wavelength with the fraction of 20%. As for a vacuum sodium cell at the temperature of 40 ℃, when the effective laser intensity increases from 4.53 × 10 2 W/m 2 to 6.99 × 10 5 W/ m 2 , resonant fluorescence with and without repumping is measured. The result illustrates that the resonant scattering brightness with repumping can be as over 3 times as without it when the light intensity changes between 4.53×10 2 W/m 2 to 5 ×10 4 W/ m 2 . The saturated phenomenon is also observed. This gives direct evidence that repumping could improve the performance of sodium laser guide stars based on TIPC long pulsed lasers. To our knowledge, this is the first experimental demonstration of the repumping effect with the TIPC type long pulsed laser in laboratory.

“…More examples of bottom-up analysis for the GMT AO System are shown in Conan [8], van Dam [10], and Esposito [11].…”

Section: Worked Example -Ltao Atmospheric Fitting Errormentioning

confidence: 99%

“…More about GMT AO System trade studies are described in Conan [8], Hinz [9], van Dam [10] and Esposito [11].…”

Section: Trades In Subsystem Requirementsmentioning

confidence: 99%

GMT AO system requirements and error budgets in the preliminary design phase

Trancho¹,

Espeland

Bouchez³

et al. 2012

Self Cite

Error budgets are an indispensable tool for assuring that project requirements can be and are being met. An error budget will typically include terms associated with subsystems which are being designed by different teams of engineers, and fabricated by different vendors. It is a useful tool at all levels of design since it provides a means to negotiate design trades in the broadest possible context. Error budgeting is in many ways fundamental to the mission of systems engineering and of course to the overall project success.In this paper we will describe the GMT Adaptive Optics System flow down requirements and their integration with their wavefront error budgets. We will focus on the GMT Adaptive Optics wavefront error budgets for the following observing modes: Natural Guide Star Adaptive, Laser Tomography Adaptive Optics and Ground Layer Adaptive Optics. Finally, a description of the error budgets and the close link between the error budgets and other parameter such as sky coverage, zenith angle, etc., will be discussed in this paper.