NIRCAM PUPIL IMAGING LENS MECHANISM AND OPTICAL DESIGN
Charles S. Clark and Thomas Jamieson Lockheed Martin Advanced Technology Center
The Near Infrared Camera (NIRCam) instrument for NASA’s James Webb Space telescope (JWST) is one of four science instruments to be installed into the integrated science instrument module (ISIM) on JWST for the purpose of conducting scientific observations over a five year mission lifetime. NIRCam is required to operate at 37 Kelvin to produce high resolution images in two-wave bands ranging from 0.6 to5 microns. A relatively recent requirement for the NIRCam instrument is to provide a means of imaging the primary mirror for ground testing, instrument commissioning, and diagnostics throughout the mission.
This paper discusses the development of the pupil imaging lens (PIL) assembly. In addition to detailing the driving requirements, this paper briefly covers the mechanism design and delves more deeply into the engineering of the optical design.
Keywords: PIL, pupil imaging lens, mechanism, cryogenic mechanism, near infrared camera, NIRCam, James Webb, JWST
PIL assembly overview
The pupil imaging lens (PIL) assembly is one component within the NIRCam instrument, which is the primary imaging instrument on the James Webb Space Telescope. The main purpose of the PIL assembly is to form an image of the eighteen primary mirror segments of the JWST Telescope onto the NIRCam focal plane arrays (FPAs). NIRCam is the only instrument on the JWST observatory with wave front sensing (WFS) capability, and will use the PIL in conjunction with the WFS measurements. Furthermore, because wavefront sensing is performed around the 2 micron wavelength, the PIL optics were designated to be deployed within the NIRCam shortwave beam between the two fold mirrors and just before the FPA. The location of the PIL is shown in Figure 1. The actual mirror image is directed onto one of the four single chip arrays (SCAs) that populate a shortwave FPA. Operationally, the PIL assembly will introduce the pupil imaging lens into the shortwave beam of the NIRCam instrument several times during commissioning and on monthly intervals throughout the mission life.