Researching | Measurement for far-field focal spot of high power laser based on the diffraction inversion of sidelobe beam

Journals >Optics and Precision Engineering >Volume 30 >Issue 4 >Page 380 > Article

Optics and Precision Engineering
Vol. 30, Issue 4, 380 (2022)

Measurement for far-field focal spot of high power laser based on the diffraction inversion of sidelobe beam

Zhengzhou WANG^*, Li WANG, Jitong WEI, Wei WANG..., Gang LI, Dongchi YI and Yajun WANG|Show fewer author(s)

Author Affiliations

Xi’an Institute of Optics and Precision Mechanics， Chinese Academy of Sciences， Xi'an710119， China

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DOI: 10.37188/OPE.20223004.0380 Cite this Article

Zhengzhou WANG, Li WANG, Jitong WEI, Wei WANG, Gang LI, Dongchi YI, Yajun WANG. Measurement for far-field focal spot of high power laser based on the diffraction inversion of sidelobe beam[J]. Optics and Precision Engineering, 2022, 30(4): 380 Copy Citation Text

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$Optical design for far-field focal spot measurement using schlieren method based on diffraction inversion of sidelobe beam$

Fig. 1. Optical design for far-field focal spot measurement using schlieren method based on diffraction inversion of sidelobe beam

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Schematic diagram of different area of far-field focal reconstruction

Fig. 2. Schematic diagram of different area of far-field focal reconstruction

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Fig. 3. Flow chart of data processing

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Fig. 4. Generated experimental data of far field focal spot obtained by simulated parameters

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Fig. 5. Original image

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Fig. 6. Preprocessing result of mainlobe and sidelobe beam of focal spot image

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$Diffraction image of sidelobe beam z=200 mm$

Fig. 7. Diffraction image of sidelobe beam z=200 mm

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Fig. 8. Images of adding random noise

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Fig. 9. Denoising result of add noise images

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$Denoising image of sidelobe beam diffraction inversion z=200 mm$

Fig. 10. Denoising image of sidelobe beam diffraction inversion z=200 mm

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Fig. 11. Intensity distribution reconstructed result of far-field focal spot

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$Simulated data processing flow of sidelobe beam diffraction inversion$

Fig. 12. Simulated data processing flow of sidelobe beam diffraction inversion

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$Sidelobe beam diffraction inversion results in simulated error environment$

Fig. 13. Sidelobe beam diffraction inversion results in simulated error environment

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$Inverse curve of sidelobe diffraction beam with different distance error （y=256）$

Fig. 14. Inverse curve of sidelobe diffraction beam with different distance error （y=256）

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$Analysis the influence of phase error on diffraction inversion of sidelobe beam$

Fig. 15. Analysis the influence of phase error on diffraction inversion of sidelobe beam

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$Effect of phase measurement error on diffraction inversion of sidelobe beam$

Fig. 16. Effect of phase measurement error on diffraction inversion of sidelobe beam

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$Denoise effect of improve DnCNN algorithm on sidelobe diffraction beam addnoise image$

Fig. 17. Denoise effect of improve DnCNN algorithm on sidelobe diffraction beam addnoise image

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$Comparison of sidelobe diffraction image of denoising effect （y=256）$

Fig. 18. Comparison of sidelobe diffraction image of denoising effect （y=256）

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$Comparison between no diffraction and denoise and addnoise inverse curve of sidelobe diffraction laser beam （δ=25）$

Fig. 19. Comparison between no diffraction and denoise and addnoise inverse curve of sidelobe diffraction laser beam （δ=25）

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$Inverse curve of denoise sidelobe diffraction beam when noise MSE is different （y=256）$

Fig. 20. Inverse curve of denoise sidelobe diffraction beam when noise MSE is different （y=256）

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Fig. 21. Reconstructed accuracy analysis of far-field focal spot

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Fig. 22. Comparison of logarithm transform result of intensity distribution between original and reconstructed horizontal curve（y=256） of far-field focal spot

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No.	Parameter	Name	Value	Unit
1	lmda	Wavelength	6.350 0×10^-4	mm
2	a	Radius of the sphere	0.5	mm
3	f	Focal length of telecentric lens	100	mm
4	Am	Magnification	1	mm
5	pixel	Pixel size	0.005 6	mm

Table 1. Simulated experimental parameters of far-field focal spot to obtain intensity distribution

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Error name	Unit	Symbol	Theoretical value	Error value
Transmission distance error	mm	z	200	2
Average phase error of sidelobe beam	degree	$ϕ$	0	10
Noise mean square error		$σ$	0	25
Radius error of schlieren sphere	mm	d	0.4480	0.056

Table 2. Error statistics of sidelobe beam diffraction inversion experiment

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Beam		Org. Max （y=256）	Merge Max （y=256）	Error of log10 curve	Error of gray curve	Dynamic range
Beam		Org. Max （y=256）	Merge Max （y=256）	Error of log10 curve	Error of gray curve	Used	Org. Image	Merge Image	Error
Mainlobe		$C_{m a x}^{}$ =5.8554	$M_{m a x}^{}$ =5.8481	-0.0073	11875	Yes	1 286.3	1 328.9	3.22%
Side- lobe	Peak 1	$S_{m a x}^{1}$ =4.091	$M_{m a x}^{1}$ =3.904	0.1870	4314	No
	Peak 2	$S_{m a x}^{2}$ =3.474	$M_{m a x}^{2}$ =3.184	0.2900	1452	No
	Peak 3	$S_{m a x}^{3}$ =3.06	$M_{m a x}^{3}$ =3.056	0.0040	11	No
	Peak 4	$S_{m a x}^{4}$ =2.746	$M_{m a x}^{4}$ =2.725	0.0210	26	Yes

Table 3. Comparison of dynamic range ratio errors between original and reconstructed far-field focal spot

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Zhengzhou WANG, Li WANG, Jitong WEI, Wei WANG, Gang LI, Dongchi YI, Yajun WANG. Measurement for far-field focal spot of high power laser based on the diffraction inversion of sidelobe beam[J]. Optics and Precision Engineering, 2022, 30(4): 380

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