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					GEMINI NEAR INFRARED SPECTROGRAPH INTEGRAL FIELD UNIT DOCUMENTATION
FOR THE

CRITICAL DESIGN REVIEW (23 May, 2000; at the University of Durham) 17 May, 2000

Compiled by: C.M. Dubbeldam, Senior Mechanical Engineer, for the GNIRS Project Team

Reviewed by: J.R. Allington-Smith, Work Package Scientist

Approved by: D.J. Robertson, Work Package Manager

University of Durham

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GNIRS IFU CDR DOCUMENTATION

EXECUTIVE SUMMARY

The Gemini Near InfraRed Spectrograph (GNIRS) currently under development at NOAO and scheduled for delivery in the summer of 2002, will include a powerful and innovative Integral Field Spectroscopy (IFS) capability. The design, integration and test of the GNIRS Integral Field Unit (IFU) are the responsibility of the University of Durham’s Astronomical Instrumentation Group. Its design is based on the Advanced Image Slicer concept developed as a result of research conducted under the auspices of the Durham Instrumentation R&D Program. A slicer-based system has many advantages over fibre-based designs, especially for cryogenic instruments such as GNIRS. The GNIRS IFU consists of two fully independent, self-contained modules offering different spatial resolution and field size. Both modules are mounted inside the GNIRS slit slide mechanism. This slide mechanism is employed to select the required spectroscopy mode by sliding the respective module into the instrument’s optical path. The High Resolution (HR) mode, which provides a field of view of 1.0”  1.5” with a sampling resolution of 0.04” over 972 spatial elements and a spectrum length of 1024 pixels, is optimised for use with fully adaptively corrected images, while the Low Resolution (LR) mode provides a larger field of view of 3.2”  4.4” with a sampling resolution of 0.15” over 625 spatial elements and a spectrum length of 1024 pixels, will be used with tip-tilt corrected images. They will be used in conjunction with the long and short cameras respectively. The instrument will be able to change remotely between the conventional aperture spectroscopy (AS) mode, in which light enters the spectrograph main optics via a slit, and each of the IFS modes. Location of the IFU modules at the telescope focal plane inside the slit slide mechanism allows for a rapid changeover of observing mode by simply inserting or withdrawing the appropriate module from the beam.

Summary of GNIRS IFU System Parameters MODE Low Resolution Spatial Sampling Magnification (Parallel  Perpendicular to Slice) Number of Slices Field of View Number of Spatial Elements Spectrum Length Slice Dimensions GNIRS Camera Employed 0.15”  0.15” 1.0  2.0 21 3.15”  4.46” 625 1024 pixels 7.4  0.5 mm
2

High Resolution 0.04”  0.04” 1.25  2.5 26 1.04”  1.50” 972 1024 pixels 9.4  0.5 mm
2

Short Camera

Long Camera

A crucial feature of the IFU’s optical design is the excellent image quality, which has been optimised to take full advantage of the outstanding images provided by the Gemini telescopes. The mechanical design ensures that all optical components remain accurately aligned and that the IFU’s performance remains predictable and maintainable under all environmental conditions. These challenging goals have been achieved in a module, which is sufficiently compact to be easily accommodated inside the GNIRS instrument’s slit slide mechanism.

University of Durham

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TABLE OF CONTENTS

EXECUTIVE SUMMARY ........................................................................................................................ 2 1. INTRODUCTION................................................................................................................................ 4 2. CDR DOCUMENTATION .................................................................................................................. 4

The following documents form an integral part of the CDR Documentation:

1. FUNCTIONAL AND PERFORMANCE REQUIREMENTS DOCUMENT 2. OPERATIONAL CONCEPTS DEFINITION DOCUMENT 3. INTERFACE CONTROL DOCUMENT 4. DESIGN REPORT 5. ASSEMBLY, INTEGRATION AND TEST PLAN 6. MANAGEMENT PLAN

University of Durham

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GNIRS IFU CDR DOCUMENTATION

DOCUMENTATION FOR THE GNIRS IFU CRITICAL DESIGN REVIEW

1. INTRODUCTION The Gemini Near InfraRed Spectrograph (GNIRS) currently under development at NOAO and scheduled for delivery in the summer of 2002, is one of the initial phase instruments for Gemini. In its baseline form it provides a powerful capability for low to medium resolution spectroscopy over the 1 to 5 m wavelength range with two different cameras giving image scales of 0.05 and 0.15 arcsec per pixel. With the addition of the Integral Field Unit (IFU), it will gain a powerful and innovative integral field spectroscopic capability. The design, integration and test of the GNIRS IFU are the responsibility of the University of Durham’s Astronomical Instrumentation Group. Its design is based on the Advanced Image Slicer concept developed as a result of research conducted under the auspices of the Durham Instrumentation R&D Program. A slicer-based system has many advantages over fibrebased designs, especially for cryogenic instruments such as GNIRS. The contract to build GNIRS has been awarded to the National Optical Astronomy Observatories (NOAO) of the USA. This was before the requirement for an Integral Field Spectroscopy (IFS) mode had been clearly defined. The priority for the inclusion of an IFS mode in GNIRS was subsequently identified by the Gemini Project. Building on the development of the Advanced Image Slicer carried out at the University of Durham’s Astronomical Instrumentation Group (AIG), the Gemini Project asked Durham to propose an IFU design for GNIRS. As a result of this work the AIG have been awarded a Gemini Work Package (through the UK Gemini Project Office - UKGPO) to design and build an IFU for the GNIRS. The project has now progressed to its Critical Design Review (CDR); the information presented in the CDR documentation will give a detailed description of the proposed optical, mechanical and thermal design of the IFU, and will enable the CDR Review Board to fully evaluate the current status of the program. At this review, we present details of the Low Resolution (LR) Mode only. Additional work is required to develop the design of the High Resolution (HR) Mode; this work will be completed after this CDR. This will give Durham the opportunity to apply to the HR Module the experience gained during the design and production of the LR Module. In our project plan we have included provisions for a further review of the HR Mode.

2. CDR DOCUMENTATION The following documents form an integral part of the CDR Documentation: 1. Functional and Performance Requirements Document (FPRD) 2. Operational Concepts Definition Document (OCDD) 3. Interface Control Document (ICD) 4. Design Report 5. Assembly, Integration and Test (AIT) Plan 6. Management Plan The IFU’s system-level functional and performance requirements are specified in the FPRD. Operational issues, such the generic observation procedure, system calibration, data reduction, etc. are discussed in the OCDD. All interfaces (mechanical, electrical, thermal, optical, etc.) with the GNIRS instrument are controlled by the ICD. A detailed description of the IFU’s optical, mechanical and thermal design is presented in the Design Report. The optical design section includes the specification (prescription data) of all optical surfaces, and the results from the performance analysis (image quality, throughput, etc.), diffraction analysis and tolerance analysis. Note that completion of the stray light analysis has been postponed until after this CDR. The mechanical design section includes the analysis of the tolerances produced by the tolerance analysis of the optical design, the structural analysis using finite element models, and a discussion of the thermal aspects of the design. The design report will also include detailed manufacturing and assembly drawings. The AIT plan presents an overview of the integration and test strategy, and gives a specification of the applicable

University of Durham

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test requirements and essential test equipment. The management plan presents an overview of the project organisation (including details of key management, scientific and technical personnel), a discussion of the quality control issues and a detailed project plan (schedule) and cost breakdown. An introduction to the principles or Integral Field Spectroscopy and a review of the current state of the technology is given in the following paper by Dubbeldam et al.: “An Integral Field Unit for the Gemini Near InfraRed Spectrograph”, SPIE Proceedings, Vol. 4008-136, 2000.

University of Durham

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