Precise Prediction of Optical Performance for Near Infrared Instrument Using Adaptive Fitting Line

Abstract

Infrared optical systems are operated at low temperature and vacuum (LT-V) condition, whereas the assembly and alignment are performed at room temperature and non-vacuum (RT-NV) condition. The differences in temperature and pressure between assembly/alignment environments and operation environment change the physical characteristics of optical and opto-mechanical parts (e.g., thickness, height, length, curvature, and refractive index), and the resultant optical performance changes accordingly. In this study, using input relay optics (IO), among the components of the Immersion GRating INfrared Spectrograph (IGRINS) which is an infrared spectrograph, a simulation based on the physical information of this optical system and an actual experiment were performed; and optical performances in the RT-NV, RT-V, and LT-V environments were predicted with an accuracy of 0.014±0.007 λ rms WFE, by developing an adaptive fitting line. The developed adaptive fitting line can quantitatively control assembly and alignment processes below λ/70 rms WFE. Therefore, it is expected that the subsequent processes of assembly, alignment, and performance analysis could not be repeated.

Keywords

• instrument: infrared spectrograph 1. INTRODUCTION Infrared optical systems are operated at low temperature and vacuum (LT-V) condition to minimize thermal noise. In general
• the manufacture
• assembly
• and alignment of optical systems are performed at room temperature and non-vacuum (RT-NV) condition. If the temperature and pressure conditions alter
• the physical changes of optical and opto-mechanical parts occur (Kaneda et al. 2005
• Leviton et al. 2005)
• and this drives the optical performance variation. For visible light optical systems that are operated at RT-NV condition
• the tasks of alignment and performance measurement after measurement are also performed at RT-NV condition
• and thus the alignment process is intuitive (Kim et al. 2005
• Liu et al. 2005
• Kim et al. 2007
• Kim et al. 2009). However
• for infrared optical systems that are operated at LT-V condition
• assembly is performed at RT-
• wavefront error prediction and no adjustment philosophy
• instrument: infrared spectrograph