6.5  m telescope for multi-object spectroscopy over a 3° field of view

Area of Science:

• Astronomy
• Optical Engineering

Background:

• Multi-object spectroscopy using optical fibers is crucial for astronomical research.
• The Dark Energy Spectroscopic Instrument (DESI) is the current leading instrument for this technique.

Purpose of the Study:

• To present an optical design for a new telescope with enhanced capabilities for multi-object spectroscopy.
• To achieve a significantly larger etendue compared to existing instruments like DESI.

Main Methods:

• Designed a two-mirror telescope system with a 6.5 m primary mirror and a 3.0° field of view.
• Incorporated a wide-field corrector with a 1.56 m diameter gull-wing lens.
• Detailed polishing and testing methods for the large lens.

Main Results:

• The proposed telescope design offers an etendue 2.6 times greater than DESI.
• Achieved an image quality of 0.53 arcsec diameter for 80% encircled energy, suitable for fiber matching at f/3.7.
• Outlined a scalable design that could be adapted for an 8.4 m primary mirror, yielding a 4.3-fold etendue advantage.

Conclusions:

• The presented optical design enables a significant advancement in multi-object spectroscopy capabilities.
• The design is feasible with current and near-future optical manufacturing techniques.
• The proposed telescope architecture provides a pathway to substantially increase astronomical survey efficiency.