Progress on the fabrication of the DESI corrector optics

ABSTRACT The Dark Energy Spectroscopic Instrument (DESI) is under construction to measure the expansion history of the Unive rse using the Baryon Acoustic Oscillation technique. The spectra of 40 million galaxies over 14000 sq uare deg rees will be measured during the life of the experiment. A new prime focus corrector for the Kitt Peak National Observatory Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers in turn feed ten broad- band spectrographs. We will describe the status of the DESI corrector optics, a series of 0.8 to 1.1 -meter fused silica and borosilicate lenses currently being fabricated t o demanding requirements. We will describe the specs for lenses that are finished or underway, including surface figure, homogeneity, and other parameters; the current schedule for lens production; and a comparison against DESI corrector requirements . Ke ywords: DESI, dark energy, Mayall, prime focus, corrector, lens, meter -class 1. INTRODUCTION