fabrication report lsst m1 null lens certifier cgh

LSST M1 Null Lens Certifier CGH

Substrate M1C-01

Fabrication report

2011

Contents 1. Fabrication report ................................................................................................................. 3

1.1 Hologram composition ......................................................................................................... 3

1.2 Writing conditions and displacement errors ..................................................................... 4

1.3 Center errors ......................................................................................................................... 4

1.4 Independent certification of the writing process .............................................................. 5

1.5 Trajectory of rotation ............................................................................................................ 7

1.6 Summary of fabrication errors ............................................................................................ 8

Author: Jean-Michel Asfour Created: 03/11/2021 14:11:00 Version: 03/11/2021 14:11:00 Fabrication report LSST M1 Null Lens Certifier CGH.doc / 8

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1. Fabrication report

1.1 Hologram composition

Table 1. Hologram composition Radial positions

Rings for centering-test Rmin, Rmax, µm 100 Hologram structure, Rmin, Rmax, mm Data filename:

1 – 19.5 20 – 110 LSST_M1CF70_frgpos+ LSST_M1C70_frgpos

Caption: M1 Null Lens Certifier CGH. Substrate M1C-01. CLWS-300IAE - 2011

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Fig. 1 Photo of the fabricated hologram.


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1.2 Writing conditions and displacement errors

Table 2. Writing condition. Temperature 22.6±0.05 Co

Air pressure 1010 mbar

The laser writing beam displacement error across the hologram radius is less than < 50 nm (P-V) and 10 nm rms.

1.3 Center errors

The coordinates of the on-axis hologram center (origin of coordinate) are measured before, during and then after finishing the hologram patterning. The measured data of the coordinate errors (error of origin of polar coordinate) in the time of M1 Null Lens Certifier CGH patterning is given in Table 3. The coordinate error er corresponds to a certain pattern distortion at a given radius r. Table. 3 #/# Coordinate,

r [μm] Coordinate error, �r [μm]

Spacing, S [μm]

Wavefront error [�]

Trajectory error, Esp/S

1 109995.7 -0.003 4.594 -0.00065 0.00479 2 107999.5 -0.007 4.594 -0.00152 0.00479 3 104998.5 -0.015 4.64 -0.00323 0.00474 4 101999.3 -0.025 4.672 -0.00535 0.00471 5 98999.91 -0.032 4.718 -0.00678 0.00466 6 95999.13 -0.006 4.75 -0.00126 0.00463 7 92996.99 0.007 4.812 0.00145 0.00457 8 89999.02 0.011 4.844 0.00227 0.00454 9 86999.78 0.014 4.906 0.00285 0.00448 10 83998.47 0.002 4.968 0.00040 0.00443 11 80999.26 -0.005 5 -0.00100 0.00440 12 77999.82 -0.025 5.078 -0.00492 0.00433 13 74998.78 -0.009 5.126 -0.00176 0.00429 14 71999.97 0 5.188 0.00000 0.00424 15 68999.53 0.005 5.266 0.00095 0.00418 16 65998.76 -0.002 5.344 -0.00037 0.00412 17 62997.59 0.009 5.406 0.00166 0.00407 18 59996.33 0.012 5.484 0.00219 0.00401 19 56999.05 0.01 5.57 0.00180 0.00395 20 53998.63 0.013 5.672 0.00229 0.00388 21 50998.82 0.021 5.774 0.00364 0.00381 22 47997.62 0.01 5.876 0.00170 0.00374 23 44998.62 -0.007 5.992 -0.00117 0.00367 24 41999.38 -0.005 6.11 -0.00082 0.00360 25 38996.9 0.003 6.25 0.00048 0.00352 26 35999.87 0.031 6.398 0.00485 0.00344 27 32999.71 0.018 6.57 0.00274 0.00335 28 29996.71 -0.002 6.758 -0.00030 0.00326 29 26999.5 0.019 6.968 0.00273 0.00316 30 23999.83 0.006 7.208 0.00083 0.00305 31 20995.61 -0.002 7.504 -0.00027 0.00293 32 17999.86 -0.004 5.188 -0.00077 0.00424


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33 14999.45 0.004 5.47 0.00073 0.00402 34 11999.75 0.018 5.832 0.00309 0.00377 35 8999.93 0.005 6.306 0.00079 0.00349 36 5995.63 0.001 7.014 0.00014 0.00314 37 2995.43 0.002 8.26 0.00024 0.00266 38 1007.15 -0.012 1006.652 -0.00001 0.00002

RMS

0.01 0.003 0.004

Fig. 2 Wavefront errors of the M1 Null Lens Certifier CGH.

Thus, the peak coordinate error between start and end of the hologram writing is below er < 63 nm. The

wavefront errors produced by the CGH pattern distortion can be calculated to

Wr=l×er/S

where er is the CGH pattern coordinate error and S is the localized CGH pattern spacing. Wavefront errors of

the hologram are presented in Fig. 2.

1.4 Independent certification of the writing process

In order to certificate the diffractive pattern so called fiducial marks are used. These marks are written directly before the writing process of the diffractive pattern. Every mark consists of three small lines on an

area of approx. ~30 x 30 µm. The time of writing of these marks is typically within ten to twenty seconds.

During this time the writing the system is highly stable and positioning errors can be neglected. The marks are written along different radius as shown in Fig. 3 forming a ruler. The marks are placed every 3 mm along the radius. Microphotographs of all marks along the ruler are shown in Fig.4.

-0.04

-0.02

0.00

0.02

0.04

0 10 20 30 40 50 60 70 80 90 100 110

Coordinate, mm

Wav

efro

nt e

rror

, wav

es

Substrate

Hologram pattern

Ruler marks (Scale division is 3 mm)


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Fig. 3 Ruler location. The results of the measured displacements taken from the microphotographs are presented in Table 4. The writing errors are within the desired accuracy of 0.1 µm. Table. 4.

Radius, mm 3 12 24 36 48 60 72 84 96 108

Error*, um <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1

• The accuracy of the measurements is about 0.1 µm (rms). •

r=3mm

r=12mm

r=24mm

r=36mm

r=48mm r=60mm


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r=72mm r=84mm

r=96mm

r=108mm

Fig.4 Microphotographs of the fiducial marks of the M1 Null Lens Certifier CGH.

1.5 Trajectory of rotation

The trajectory of the spindle rotation was measured before the writing process. The measured deviation of the trajectory of the spinning table rotation from an ideal circle is shown in

Fig. 5. The deviation of the trajectory of rotation - and hence the shape of the hologram zones - is less than

± 22 nm.


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Fig. 5 Trajectory of the spindle rotation. The deviations are below ±0.022 µm (0.004 µm rms). The

uncertainty of the measurement is ~ 0.01 µm.

1.6 Summary of fabrication errors

Table 5. Error summary for M1 Null Lens Certifier CGH fabrication

Error term (Manufacturing errors for main hologram)

Value PV [µm]

Value RMS [µm]

WFE (λ) PV

WFE(λ) RMS

Origin of coordinates 0.063 0.01 0.012 0.003 Trajectory of rotation 0.002 0.004

Diffractive efficiency variation along hologram

RSS [λ] 0.005 RSS [nm] 4 Dr. Alexander Poleshchuk

fabrication report lsst m1 null lens certifier cgh

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