**2.3 Astronomy telescope science requires nano-accuracy optics in large scale**

In order to improve the resolution of astronomical telescopes, the desired tendency is to enlarge the aperture of the telescope and achieve the diffraction limited image by use of

Control of surface slope error is especially important in the fabrication of far off-axis aspheres used in grazing incidence x-ray applications. Incoherent x-rays act much like bullets in reflecting off of aspheric surfaces. Slight deviations in surface slope, on the order of fractions of a micro-radian, are sufficient to reduce the quality of the focal spot in long synchrotron beam lines. The stringent requirements for these precision optical components have stimulated research into new measurement methods for spheres and aspheres, and new sophisticated optical measurement instruments are rapidly evolving. A specially designed nano-accuracy profiler for synchrotron optics is urgently needed. It should be also

able to measure mid-spatial frequencies and be able to test strongly curved surfaces.

metrology instrumentation from the micro-accuracy level to the nano-accuracy level.

Since the early 1980s, when the first and second-generation synchrotron light sources came on-line, the requirement for RMS slope error tolerance of SR optics has dropped from 5 μrad to 100 nrad as the desired focal spot size at the beam line end-station has gone from 10µm to 1 nm (Table 1). These continual machine improvements have driven the development of the

Years Slope error requirement Spot size 1980s 5 μrad 10 μm 1990s 1 μrad 1 μm 2011 for NSLS II 100 **nrad 1 nm**

X-ray free electron lasers (XFEL) and EUV lithography require a variety precise of optics with nano-radian accuracy as well. For example, "elliptical mirror with 0.21 μrad rms accuracy is required for XFEL oscillator" (Kim, K., 2009) and "0.1 μrad accuracy mirror is required for FEL focusing" (Assoufid, L. et al.; Minura et al., 2008). In the case of extreme ultra violet lithography (EUVL) "Neither the figure errors nor the roughness of mirrors for

In order to improve the resolution of astronomical telescopes, the desired tendency is to enlarge the aperture of the telescope and achieve the diffraction limited image by use of

**2.3 Astronomy telescope science requires nano-accuracy optics in large scale** 

Fig. 1. K-B elliptical mirrors for nanometer spot focusing

Table 1. The requirements of slope error and spot size

**2.2 X-ray free electron lasers (XFEL) and EUVL Lithography** 

the imaging system must exceed a few angstroms" (Soufli, R., 2011).

perfect optics. This leads to the application of optics with nano-accuracy. This is the new challenge to manufacturing and metrology. Following quoted contents is the clear examples for describing these demands.

"The NASA Science Missions Directorate seeks technology for nano-accuracy metrology on NASA SBIR AND STTR 2011 Program Solicitations. Following are some requirements for telescopes: "Metrology instruments should have 10 nm or better surface height resolution and span at least 3 orders of magnitude in lateral spatial frequency for Optics Manufacturing and Metrology of Telescope Optical Surfaces" and "In situ metrology systems that can measure optics and provide feedback to figuring/polishing instruments without removing the part from the spindle". "NASA is preparing potential future space telescopes, which have very specific mirror technology needs. UV/optical telescopes require 1 to 3 meter class mirrors with < 5 nm rms surface figures. IR telescopes (such as SAFIR/CALISTO) require 2 to 3 to 8 meter class mirrors with cryo-deformations < 100 nm rms. X-ray telescopes (such as GenX) require 1 to 2 meter long grazing incidence segments with angular resolution < 5 arc-sec down to 0.1 arc-sec and surface micro-roughness < 0.5 nm rms." (NASA NASA SBIR and STTR 2011 Program Solicitations)
