Design Method for Near‑Field Equivalent Far‑Field Laser Spot

Fig. 5. Comparison of laser spot patterns between ZEMAX physical optics simulation and actual measurement. (a) Simulated laser spot on image plane; (b) experimentally observed laser spot at image plane; (c) simulated laser spot at 5 m behind image plane; (d) experimentally observed laser spot at 5 m behind image plane

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Table 1. Design parameters of equivalent far-field optical path system

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Table 1. Design parameters of equivalent far-field optical path system

$L$	$l_{1}$	$l_{2}$	$l_{3}$	$l$	$F_{1}$	$F_{2}$	$R (l)$	$ω (l)$	$R (L)$	$ω (L)$
200	0.1	0.635	0.754	2.2240	0.6	0.035	636	0.0121	636	0.0121
1000	0.1	1.035	1.2972	3.5672	1.0	0.035	1087	0.0353	1087	0.0353
3000	0.1	1.535	1.7049	4.9749	1.5	0.035	3029	0.1021	3029	0.1021
5000	0.1	2.035	1.6024	5.8724	2.0	0.035	5017	0.1696	5017	0.1696
10000	0.1	2.035	3.1337	7.4037	2.0	0.035	10000	0.3388	10000	0.3388

Table 2. Error analysis of equivalent far-field optical path system

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Table 2. Error analysis of equivalent far-field optical path system

$L$ /m	$l_{1}$ /m	$l_{2}$ /m	$l_{3}$ /m	$l_{4}$ /m	$l_{5}$ /m	$F_{1}$ /m	$F_{2}$ /m	Error term	Error/m	$Δ R (l)$ /%	$Δ ω (l)$ /%
3000	0.2	5.05	0.401	5.05	0.2	0.05	5	$Δ l_{1}$	0.001	<1.0	<1.0
3000	0.2	5.05	0.401	5.05	0.2	0.05	5	$Δ l_{2}$	0.001	<1.0	<1.0
3000	0.2	5.05	0.401	5.05	0.2	0.05	5	$Δ l_{3}$	0.001	<1.0	<1.0
3000	0.2	5.05	0.401	5.05	0.2	0.05	5	$Δ l_{4}$	0.001	13.8	<1.0
3000	0.2	5.05	0.401	5.05	0.2	0.05	5	$Δ l_{5}$	0.001	<1.0	<1.0
3000	0.2	10.10	0.502	10.10	0.2	0.10	10	$Δ l_{1}$	0.002	<1.0	<1.0
3000	0.2	10.10	0.502	10.10	0.2	0.10	10	$Δ l_{2}$	0.002	<1.0	<1.0
3000	0.2	10.10	0.502	10.10	0.2	0.10	10	$Δ l_{3}$	0.002	<1.0	<1.0
3000	0.2	10.10	0.502	10.10	0.2	0.10	10	$Δ l_{4}$	0.002	6.5	<1.0
3000	0.2	10.10	0.502	10.10	0.2	0.10	10	$Δ l_{5}$	0.002	<1.0	<1.0

Table 3. Lens element parameters

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Table 3. Lens element parameters

Parameter	Long-focus lens with $F_{1}$	Short-focus lens with $F_{2}$	Short-focus lens with $F_{3}$	Long-focus lens with $F_{4}$
Material	H-K9L	H-K9L	H-K9L	H-K9L
Refractive index n @ 532 nm	1.5195	1.5195	1.5195	1.5195
Lens type	Plano-convex	Convex-plano	Plano-convex	Convex-plano
Curvature radius R /mm	258.398	38.761	77.520	516.797
Focal length @ 587.6 nm	500 mm±1%	75 mm±1%	150 mm±1%	1000 mm±1%
Focal power （n-1） /R	2.0105 /m	13.4026 /m	6.7015 /m	1.0052 /m
Center thickness /mm	3.5	5	4	3.5
Aperture diameter /mm	25.4	25.4	25.4	25.4

Table 4. Design of actual optical path system parameters
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Table 4. Design of actual optical path system parameters
$L$ $l_{1}$ $l_{2}$ $l_{3}$ $l_{4}$ $l_{5}$ $ω (l)$ $R (l)$
100 0.3 0.5720 2.4874 1.1440 0.0121 0.0452 100.01
150 0.3 0.5720 3.6124 1.1440 0.0353 0.0677 150.01
222 0.3 0.5720 5.2326 1.1440 0.1021 0.1003 222.02
250 0.3 0.5720 6.9877 1.1440 0.1696 0.1355 250.02

Table 5. Similarity analysis of near-field and far-field laser interference imaging
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Table 5. Similarity analysis of near-field and far-field laser interference imaging
Metric Figs.4（a） and （e） Figs.4 （b） and （f） Figs.4 （c） and （g） Figs.4 （d） and （h）
MSE 0.02 0.01 0.02 0.01
PSNR /dB 17.74 18.56 17.28 22.40
SSIM 0.60 0.58 0.33 0.12
VGG-16 0.47 0.58 0.64 0.71

Table 6. Parameters of paraxial Gaussian beam at image plane and 5 m behind image plane

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Table 6. Parameters of paraxial Gaussian beam at image plane and 5 m behind image plane

Surface

Size /mm

Beam

waist /mm

Transmission

distance /mm

Wavefront curvature

radius /mm

Divergence

angle /rad

Rayleigh

range /mm

At image plane

1.00233×10²

3.69781×10^-1

2.18872×10⁵

2.18875×10⁵

4.57949×10^-4

8.07472×10²

At 5 m behind image plane

1.02523×10²

3.69781×10^-1

2.23872×10⁵

2.23875×10⁵

4.57949×10^-4

8.07472×10²

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Chenglong Jiang, Yanbin Wang, Xuanfeng Zhou, Wenjian Xiao, Yun Ye. Design Method for Near‑Field Equivalent Far‑Field Laser Spot[J]. Chinese Journal of Lasers, 2025, 52(17): 1701006

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