Flexure compensation simulation tool for TMT-WFOS spectrograph

Abstract

The Wide Field Optical Spectrograph (WFOS) is one of the first-light instruments of Thirty Meter Telescope. It is a medium resolution, multi object, wide field optical spectrograph. Since 2005 the conceptual design of the instrument has focused on a slit-mask based, grating exchange design that will be mounted at the Nasmyth focus of TMT. Based on the experience with ESI, MOSFIRE and DEIMOS for Keck we know flexure related image motion will be a major problem with such a spectrograph and a compensation system is required to mitigate these effects.We have developed a Flexure Compensation and Simulation (FCS) tool for TMT-WFOS that provides an interface to accurately simulate the effects of instrument flexure at the WFOS detector plane (e.g image shifts) using perturbation of key optical elements and also derive corrective motions to compensate the image shifts caused by instrument flexure. We are currently using the tool to do mote-carlo simulations to validate the optical design of a slit-mask concept we call Xchange-WFOS, and to optimize the flexure compensation strategy. We intend to use the tool later in the design process to predict the actual flexure by replacing the randomized inputs with the signed displacement and rotations of each element predicted by global Finite Element Analysis (FEA) model on the instrument.

Lightweight cylindrical composite shell structures to support optical instruments in extremely large telescopes: A case study

“…The development of active compensation technology could effectively compensate for image drift caused by structural deformation and ensure stable performance of the instrument. When the maximum deformation of WFOS is on the order of 1 mm, the active compensation system of WFOS could meet the deformation requirements of the optical system well, which has been proved by Surya et al 26 Therefore, the design requires that the maximum deformation of the WFOS supporting structure should be less than 1 mm, and the mass of the main structure should be less than 3000 kg. The working frequency of the TMT machine is 2 Hz.…”