Patent ID: 11940349
Assignee: TSINGHUA UNIVERSITY
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 8:
9. The plane grating calibration system of claim 7, wherein, in the grating calibration process, the X-direction interferometer and the Y-direction interferometer respectively obtain the displacements of the workpiece stage in X and Y directions in real time, and input them into the controller, and then the controller performs process according to the following formula:

xe=[cos α(xr−x)+sin α(yr−y)]

wherein xe represents a phase shift of the beam after diffracted by the plane grating caused by a motion error of the workpiece stage, a represents a deflection angle of the grating line in the coordinate system of the workpiece stage, xr represents a reference ideal displacement of the workpiece stage in the x-axis direction in the coordinate system, yr represents a reference ideal displacement of the workpiece stage in the y-axis direction in the coordinate system, x represents an actually measured displacement in the x-axis direction of the interferometer, and y represents an actually measured displacement in the y-axis direction of the interferometer,
wherein a total phase shift of the beam after diffracted by the plane grating is obtained as below:

xfle=xm−xe,

wherein xfle represents a total phase shift of the beam after diffracted by the plane grating, and
wherein the controller generates a control command according to a result of preceding process and transmits the control command to the phase modulator, and the phase modulator modulates the laser beam according to the control command to correct an error in the calibration of the plane grating.