Measurement of Large Aperture Long Focus Off‑Axis Paraboloid Mirror Based on Computer Generated Hologram

Chen Hu; Chaoyang Wei; Songlin Wan; Guochang Jiang; Haojin Gu; Jianda Shao

doi:10.3788/CJL230567

Journals >Chinese Journal of Lasers >Volume 50 >Issue 23 >Page 2304002 > Article

Chinese Journal of Lasers
Vol. 50, Issue 23, 2304002 (2023)

Measurement of Large Aperture Long Focus Off‑Axis Paraboloid Mirror Based on Computer Generated Hologram

Chen Hu^1、3, Chaoyang Wei^1、3、*, Songlin Wan¹, Guochang Jiang¹, Haojin Gu¹, and Jianda Shao^{1、2、3、**}

Author Affiliations

¹Precision Optical Manufacturing and Testing Center, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China

²Key Laboratory for High Power Laser Material, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences Shanghai201800, China

³Center of Material Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China

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DOI: 10.3788/CJL230567 Cite this Article Set citation alerts

Chen Hu, Chaoyang Wei, Songlin Wan, Guochang Jiang, Haojin Gu, Jianda Shao. Measurement of Large Aperture Long Focus Off‑Axis Paraboloid Mirror Based on Computer Generated Hologram[J]. Chinese Journal of Lasers, 2023, 50(23): 2304002 Copy Citation Text

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$CGH for null test. (a) Diffractive sections on CGH; (b) physical map of CGH$

Fig. 1. CGH for null test. (a) Diffractive sections on CGH; (b) physical map of CGH

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Fig. 2. Optical path of testing off-axis paraboloid mirror with CGH. (a) Schematic diagram of optical path; (b) photograph of optical path

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Fig. 3. Comparison of results from different measurement methods. (a) Surface map measured by CMM (2 mm interpolation for data with scanning step of 10 mm); (b) surface map measured by interferometer

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Fig. 4. Transmitted wavefront error of the CGH substrate over the clear aperture

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Fig. 5. Transmitted wavefront error of beam expanding system. (a) Theoretical transmitted wavefront error (spherical aberration); (b) transmitted wavefront error over the clear aperture after polishing(after removing power)

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Fig. 6. Figure error of Φ800 mm fold-mirror in measuring optical path. (a) Figure error (90% clear aperture); (b) figure error of effective measurement area

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Fig. 7. Positioning error of Φ800 mm fold-mirror. (a) Translation (5 mm, 5 mm); (b) rotation 0.5°

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Fig. 8. System error of measuring optical path

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Fig. 9. Flow chart of distortion correction

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Fig. 10. Distortion correction error

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Fig. 11. Iterative polishing results. (a) Surface map before distortion correction; (b) surface map after distortion correction; (c) 1650 mm×1120 mm off-axis paraboloid mirror

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Optical parameter	Value	Note
Aperture	1650 mm×1120 mm
Material	Glass ceramics
Vertex radius of curvature	2.4×10⁴ mm
Off-axis distance	2000 mm	Distance from the parent vertex
Conic constant	-1	Parabola
Aspheric departure	118 μm	Astigmatic peak-to-valley departure
Measure method	Null test with standard plane mirror

Table 1. Optical design prescription of OAP mirror

Specification	Value
Description	Vibration insensitive dynamic Twyman-Green interferometer
Acquisition mode	Instantaneous phase shifting with pixelated phase sensor
Beam diameter	9 mm collimated FWHM
Focus range /mm	±12.5
Minimum exposure /μs	30
RMS repeatability	<0.001λ
RMS precision	<0.002λ

Table 2. Main specifications of PhaseCam 6000

Surface	Radius /mm	Thickness /mm	Glass	Semi-diameter /mm	Conic constant
OBJ	INF	INF		60.00
1	260.20	20.00	SILICA	60.00
2	INF	603.86		60.00	-0.636
3	50.60		N-BK7	12.70
4	-50.60			12.70
IMA		INF		4.36

Table 3. Optical design parameters of beam expander

Design and fabrication contributor		Figure error RMS
	Design residual	0.1
	Wavelength uncertainty of 0.002 nm	0.1
	Encoding error	0.5
	Patterning error（10 nm RMS in one direction）	0
	Etching uniformity error	0
	Substrate thickness	0
	Substrate wedge（1.5 µrad）	0
	Substrate index error of 0.0001	0
	CGH substrate deformation error / design（the same deformation on both faces，that is not seen in the transmission measurement）. Assumes 1 μm sag over 140 mm diameter	0
	Total RSS	0.5

Table 4. CGH design and fabrication error budget

Measuring component contributor	Figure error RMS /nm
Total RSS	<5.4
Interferometer	<1.2
Beam expanding system（remove after calibration）	<0.7
CGH（remove after calibration）	0.5
Flod mirror（5° reflecting angle，remove after calibration）	<5.2

Table 5. Measurement error budget

No.	Marked points /mm				Deviation /mm
No.	u_mir	v_mir	u_CCD	v_CCD	u_err	v_err	ρ_err
1	0	0	652.12	600.52	0.00	0.39	0.39
2	0	-510	645.63	365.70	0.58	0.64	0.86
3	0	510	647.73	835.50	0.78	-0.11	0.78
4	775	0	196.70	603.01	1.82	-0.37	1.86
5	775	0	1036.20	598.19	1.08	1.64	1.96
6	775	510	1034.30	821.00	0.84	0.64	1.05
7	775	-510	1033.10	376.40	-1.07	0.39	1.14
8	775	-510	189.80	350.00	-0.23	-0.57	0.62
9	775	510	192.60	856.10	-0.94	-0.27	0.98
Max deviation					1.82	1.64	1.96
RMS					0.95	0.69	1.18

Table 6. Position deviation of marked points

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