High-Precision Transmission-Wavefront-Processing Technology of Large Aperture Ti∶sapphire Crystal at Full Spatial Frequency

Fig. 2. Phenomenon that interference fringes cannot be resolved due to birefringence produced by detection light transmitted from crystal. (a) Interference fringe; (b) transmission wavefront

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Fig. 3. Schematic of using Ti∶sapphire crystal

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Fig. 4. Schematic of orthogonal polarization detecting system

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Fig. 5. Two sides of surface accuracy after rough polishing by single-spindle machine. (a) Surface accuracy of side S1 after rough polishing; (b) surface accuracy of side S2 after rough polishing

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Fig. 6. Polishing results of copper pad. (a) Copper pad after polishing; (b) surface of copper pad

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Fig. 7. Measurement results of transmission wavefront of sample after rough polishing by single-spindle machine

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Fig. 8. Measurement results of surface roughness of sample. (a) Surface roughness of sample after rough polishing; (b) surface roughness of sample after fine polishing

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Fig. 9. Surface roughness of Ti∶sapphire crystal

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Fig. 10. Results of fine polishing by small grinding head. (a) Transmission wavefront of sample after fine polishing by small grinding head; (b) power spectral density at mid-spatial frequency (spatial period is 2.5-33 mm)

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Fig. 11. Schematic of smoothing process

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Fig. 12. Results of smoothing. (a) Transmission wavefront of Ti∶sapphire sample after smoothing; (b) power spectral density after smoothing (spatial period is 2.5-33 mm)

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Table 1. Experimental parameters of grinding and polishing of single-spindle machine

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Table 1. Experimental parameters of grinding and polishing of single-spindle machine

Proces	Abrasives	Abrasive disc(Ф120 mm)	Diametersize /μm	Time /min	Speed /(r·min^-1)	Force /N
Grinding	Diamondpowder	Iron plate	20.0	30	35	10
	Diamondpowder	Aluminumplate	10.0	40	35	5
Rough polishing	Diamondpowder	Resincopper plate	2.0	120	30	5
Fine polishing	Diamondpowder	Polyurethaneplate	2.0	120	25	2.5
	Silica sol	Resincopper plate	0.1	20	25	2.5

Table 2. Experimental parameters of small-grinding-head polishing

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Table 2. Experimental parameters of small-grinding-head polishing

Process	Lapping andpolishing plate	Abrasives	Diametersize /μm	Time /min	Pressure /Pa	Revolution /(r·min^-1)	Rotation /(r·min^-1)
Roughpolishing	Resincopper plate	Diamondpowder	2.0	970	10000	50	100
Finepolishing	Polyurethaneplate	Diamondpowder	2.0	770	5000	40	90
Super smooth	Resincopper plate	Silica sol	0.1	60	5000	0	125

Table 3. Orthogonal experimental factors and horizontal distribution table

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Table 3. Orthogonal experimental factors and horizontal distribution table

Factor	Polishing plate(A)	Pressure (B) /Pa	Rotational speed (C) /(r·min^-1)	Silica sol concentration (D)
Level 1	Resin copper plate	5000	100	1∶1
Level 2	Pitch lap	6000	125	2∶1
Level 3	Polyurethaneplate	8000	150	4∶1

Table 4. Orthogonal experimental scheme and results
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Table 4. Orthogonal experimental scheme and results
Serialnumber A B C D RMS /nm Defect rate(10^-3 mm^-1)
1 1 1 1 1 0.380 1.6
2 1 2 2 2 0.401 2.2
3 1 3 3 3 0.525 2.4
4 2 1 2 3 0.812 1.6
5 2 2 3 1 0.717 1.8
6 2 3 1 2 0.977 2.0
7 3 1 3 2 0.995 1.8
8 3 2 1 3 1.117 2.6
9 3 3 2 1 1.000 2.8

Table 5. Results of range analysis
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Table 5. Results of range analysis
Factor A B C D
RMS 0.427 0.105 0.087 0.119
Defect rate 0.47 0.64 0.13 0.13

Table 6. Calculation results of grey relational analysis degree

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Table 6. Calculation results of grey relational analysis degree

Factor	Level	Greyrelationalcoefficient		Greyrelationaldegree
Factor	Level		RMS	Defect
	1	0.919	0.7	0.81
A	2	0.554	0.836	0.695
	3	0.458	0.573	0.516
	1	0.679	0.938	0.809
B	2	0.671	0.63	0.651
	3	0.581	0.541	0.561
	1	0.637	0.723	0.68
C	2	0.665	0.696	0.681
	3	0.629	0.71	0.67
	1	0.697	0.748	0.723
D	2	0.64	0.703	0.672
	3	0.594	0.658	0.626

Table 7. Smoothing parameters of small grinding head

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Table 7. Smoothing parameters of small grinding head

Parameter	Content
Polishing plate	Resincopper plate
Abrasives	Silica sol
Diameter size /μm	0.1
Pressure /Pa	5000
Rotating speed of smoothing plate /(r·min^-1)	42
Rotation speed of C-spindle /(r·min^-1)	33
Moving range /mm	-30 to 30
Moving speed /(mm·min^-1)	273
Time /min	7.3

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Jin shouping, Fu Yuegang, Jin Yuhao, Hao Zhixu. High-Precision Transmission-Wavefront-Processing Technology of Large Aperture Ti∶sapphire Crystal at Full Spatial Frequency[J]. Chinese Journal of Lasers, 2019, 46(9): 903002

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