	US 12,241,739 B1
	Bidirectional Littrow two-degree-of-freedom grating interference measurement device based on double gratings
Wenhao Li, Changchun (CN); Wenyuan Zhou, Changchun (CN); Zhaowu Liu, Changchun (CN); Yujia Sun, Changchun (CN); and Lin Liu, Changchun (CN)
Assigned to Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun (CN)
Filed by Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences, Changchun (CN)
Filed on Sep. 25, 2024, as Appl. No. 18/896,369.
Claims priority of application No. 202311681756.2 (CN), filed on Dec. 8, 2023.
Int. Cl. G01B 9/02015 (2022.01); G01B 9/02 (2022.01); G01B 9/02001 (2022.01); G01B 11/02 (2006.01)

CPC G01B 9/02015 (2013.01) [G01B 9/02007 (2013.01); G01B 9/02045 (2013.01); G01B 11/02 (2013.01); G01B 2290/30 (2013.01); G01B 2290/70 (2013.01)]

4 Claims

1. A bidirectional Littrow two-degree-of-freedom grating interference measurement device based on double gratings, comprising a light source, a transmission two-dimensional grating, a reflection two-dimensional grating, an X-direction quarter-wave plate, a Y-direction quarter-wave plate, a first optical system, a second optical system, a third optical system, and a fourth optical system, wherein

the light source is a dual-frequency laser configured to generate X-direction measurement laser beams with frequencies f1 and f2 respectively that have mutually perpendicular polarization states and Y-direction measurement laser beams with frequencies f1 and f2 respectively that have mutually perpendicular polarization states;

+1^storder diffracted light obtained by vertically injecting the X-direction measurement laser beam into the transmission two-dimensional grating passes through the X-direction quarter-wave plate and is incident on the reflection two-dimensional grating at a Littrow angle to obtain new +1^storder diffracted light, and the new +1^storder diffracted light passes through the X-direction quarter-wave plate and returns to the transmission two-dimensional grating in a direction of the +1^storder diffracted light to obtain 0^thorder diffracted light and −2^ndorder diffracted light, so that horizontal polarization light having the frequency f1 in the 0^thorder diffracted light and the −2nd order diffracted light generated by the new +1^storder diffracted light is converted into vertical polarization light, and vertical polarization light having the frequency f2 in the 0^thorder diffracted light and the −2^ndorder diffracted light generated by the new +1^storder diffracted light is converted into horizontal polarization light;

−1^storder diffracted light obtained by vertically injecting the X-direction measurement laser beam into the transmission two-dimensional grating is incident on the reflection two-dimensional grating at a Littrow angle to obtain new −1^storder diffracted light, and the new −1^storder diffracted light returns to the transmission two-dimensional grating in a direction of the −1^storder diffracted light to obtain 0^thorder diffracted light and −2^ndorder diffracted light after diffraction by the transmission two-dimensional grating;

the first optical system is configured to filter out a stable interference signal of a horizontal component in the −2^ndorder diffracted light generated by the new +1^storder diffracted light and the 0^thorder diffracted light generated by the new −1^storder diffracted light, so that diffracted light of a vertical component having the frequency f2 and diffracted light of the vertical component having the frequency f₁form a stable interference;

the second optical system is configured to filter out a stable interference signal of a vertical component in the −2^ndorder diffracted light generated by the new −1^storder diffracted light and the 0^thorder diffracted light generated by the new +1^storder diffracted light, so that diffracted light of a horizontal component having the frequency f₂and diffracted light of the horizontal component having the frequency f₁form a stable interference; and

a stable interference signal obtained in the first optical system and a stable interference signal obtained in the second optical system are processed by a photodetector to obtain a displacement change of the reflection two-dimensional grating in the X direction.