High-resolution optical modeling of the Thirty Meter Telescope for systematic performance trades

Abstract

We consider high-resolution optical modeling of the Thirty Meter Telescope for the purpose of error budget and instrumentation trades utilizing the Modeling and Analysis for Controlled Optical Systems tool. Using this ray-trace and diffraction model we have simulated the TMT optical errors related to multiple effects including segment alignment and phasing, segment surface figures, temperature, and gravity. We have then modeled the effects of each TMT optical error in terms of the Point Source Sensitivity (a multiplicative image plane metric) for a seeing limited case and an adaptive optics corrected case (for the NFIRAOS). This modeling provides the information necessary to rapidly conduct design trades with respect to the planned telescope instrumentation and to optimize the telescope error budget.

Analysis of normalized point source sensitivity as a performance metric for large telescopes

“…The TMT primary errors include segment figuring residual, segment thermal distortion, segment support print-through, segment in-plane residual, M1 segment out-of-plane residual, and M1 segment dynamic displacement residual. We have described these errors in detail in our previous studies [3].…”

“…The TMT pupil we consider includes 492 hexagonal segments with segment gaps, the secondary mirror obscuration, and no support obscuration [3]. The α values for the two pupil maps are similar except that the α values for the TMT pupil become smaller than those of the ideal circular pupil when the azimuthal mode is small.…”

“…In addition, it is desirable to predict or estimate overall performance of the telescope when aberrations from multiple error sources are combined. This estimation feature of a metric is especially important when designing and budgeting errors for a large telescope such as TMT, since its design and modeling tasks are highly distributed to multiple optical designers, vendors, and manufacturers [3].…”

Estimation of normalized point-source sensitivity of segment surface specifications for extremely large telescopes

“…Figure 9(c) shows that the WH correction has no impact on the high residual surfaces in terms of PSSN if LOZs of 15 or more are removed. The PSSN differences below 10 −4 is difficult to resolve due to the numerical precision of PSSN computation [2].…”

“…The PSSN is a recently developed performance metric that has been adopted for the Thirty Meter Telescope (TMT) and European Extremely Large Telescope for their error budgeting and performance evaluation [1][2][3][4]. This metric is directly related to the photometric error of background-limited observations so that it accurately represents the efficiency loss of science due to increased telescope observing time [5,6].…”