Stress measurement method and system for optical materials

Patent metadata

Field	Value
Publication number	US-10067012-B2
Application number	US-201715618145-A
Country	US
Kind code	B2
Filing date	Jun 9, 2017
Priority date	Dec 9, 2016
Publication date	Sep 4, 2018
Grant date	Sep 4, 2018

Abstract

A stress measurement method is provided of the present disclosure. The stress measurement method includes an image capturing procedure, a phase shift calculation procedure, an isochromatic intensifying procedure and a transformation procedure. The image capturing procedure is used to capture four light intensity images with four different phase angles of a sample. The phase shift calculation procedure is used to obtain an isochromatic retardation of the sample when the four light intensity images have sufficient light intensity values. The isochromatic intensifying procedure is used to calculate two enhanced light intensity values, the background of intensified isochromatic light intensity value and the amplitude of intensified isochromatic light intensity value to obtain an isochromatic retardation when the sample is in a low stress condition. The transformation procedure is used to transform the isochromatic retardation to a stress value of the sample.

First claim

What is claimed is:

1. A stress measurement method for a sample whose optical material has a transmission property, the stress measurement method comprising:
an image capturing procedure to capture four light intensity images with four different phase angles of the sample;
a phase shift calculation procedure to obtain an isochromatic retardation of the sample by calculating light intensity values of the four light intensity images when the four light intensity images have sufficient light intensity values;
an isochromatic intensifying procedure to capture two intensified isochromatic light intensity images and obtain two enhanced light intensity values, a background of intensified isochromatic light intensity value and an amplitude of intensified isochromatic light intensity value when the sample is in a low stress condition so that a light intensity value of any one of the four light intensity images is insufficient, and then calculate the two enhanced light intensity values, the background of intensified isochromatic light intensity value and the amplitude of intensified isochromatic light intensity value to obtain the isochromatic retardation; and
a transformation procedure to transform the isochromatic retardation to a stress value of the sample.

2. The stress measurement method of claim 1 , wherein in the phase shift calculation procedure, the isochromatic retardation of the sample is δ, a principal stress angle of the sample is θ, the amplitude of light intensity is I a , the background of light intensity is I b , the phase shift calculation procedure is used to obtain two light intensity values with sin 2 (δ/2) and cos 2 (δ/2) as well as without θ by simultaneously calculating four light intensity values I 1 , I 2 , I 3 and I 4 , then obtain the isochromatic retardation δ by simultaneously calculating the two light intensity values and obtain the principal stress angle θ by simultaneously calculating four light intensity values I 1 , I 2 , I 3 and I 4 through the following relationships:

(

I
4

-

I
2

)

2

+

(

I
1

-

I
3

)

2

=

I
a

⁢

sin
2

⁢

δ
2

;

I
1

+

I
3

-

I
4

-

I
2

=

I
a

⁢

cos
2

⁢

δ
2

;

δ
=

2
⁢

⁢

tan

-
1

⁢

(

I
4

-

I
2

)

2

+

(

I
1

-

I
3

)

2

I
1

+

I
3

-

I
4

-

I
2

;

and

θ
=

1
4

⁢

tan

2
⁢
π

-
1

⁡

(

I
1

-

Assignees

• Univ Nat Tsing Hua

Inventors

• Wang Wei-Chung
• Sung Po-Chi
• Lu zheng-yong
• Yeh Yu-Liang
• Chen Po-Yu

Classifications

• G03F1/32

  Attenuating PSM [att-PSM], e.g. halftone PSM or PSM having semi-transparent phase shift portion,; Preparation thereof · CPC title

• G01L5/0047

  measuring forces due to residual stresses · CPC title

• G01L1/24 Primary

  by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis {using infrared, visible light, ultraviolet} · CPC title

• G01L1/241 Primary

  by photoelastic stress analysis · CPC title

• G03F1/82

  Auxiliary processes, e.g. cleaning or inspecting · CPC title