METHOD FOR SIMULTANEOUSLY MEASURING MULTI DOF GEs BY LASER AND SYSTEM THEREFOR

A system for simultaneously measuring multiple DOF GEs by a laser, wherein the system comprises a measuring unit and a target mirror unit;

• the measuring unit comprising a laser emitting module, a polarizing beam splitter, a fixed reflector, a first λ/4 wave plate, a second λ/4 wave plate, a first polarizer, a first photodetector, an interference length measuring module, and a two-dimensional angle measuring module;
• the target mirror unit comprises a beam splitter and a reflector;
• the laser emitting module is used to generate an emitting light L1;
• the polarizing beam splitter is used for 1) “beam splitting” which comprises splitting the emitting light L1 into a measuring light L11 and a reference light L12;
• the measuring light L11 is incident on the target mirror unit, is transmitted by the beam splitter of the target mirror unit, and is reflected back by the reflector as a light L111;
• the light L111 carries a 3DOF LGE signal back to the measuring unit as a linear GE measuring light;
• the reference light L12 only propagates inside the measurement unit;
• 2) “beam combining” which comprises transmitting or reflecting the reference light L12 that passes by the polarizing beam splitter again and the measuring light L111 that is reflected back 180° toward its original direction by the target mirror unit according to its polarizing status, so that above two beams are superposed together in a spatial position, so as to form a combined light L3;
• and 3) “beam separating” which separates the light L112 reflected by the beam splitter in the target mirror unit from the measuring light L11 as a two-dimensional angle measuring light, and the light L112 is transmitted or reflected by the polarizing beam splitter according to its polarizing state;
• the fixed reflector is used for reflecting backward the reference light L12 propagating only within the measuring unit to return the reference light L12 to the polarizing beam splitter;
• the first λ/4 wave plate is used to change a polarizing direction of the reference light L12, so that when the reference light L12 passes by the polarizing beam splitter again, its transmitting or reflecting status is switched, that is, the reference light L12 is reflected at the first pass, but is transmitted at the second pass;
• or is transmitted at the first pass, but is reflected at the second pass;
• the second λ/4 wave plate is used to change polarizing directions of the LGE measuring light L111 and a two-dimensional angle measuring light L112, so that when the LGE measuring light L111 and the two-dimensional angle measuring light L112 pass by the polarizing beam splitter again, their transmitting status or reflecting status is switched;
• the first polarizer is arranged between the polarizing beam splitter and the first photodetector;
• as a light transmitting axial direction of the first polarizer is adjusted, the combined light L3 interferes after passing through the first polarizer;
• the first photodetector is used to receive a superimposed light beam L3 including the reference light L12 and the measuring light L111, so as to simultaneously measure LGEs along X, Y and Z axes;
• specifically:
• 1) according to a spot offset of the LGE measuring light L111 on the first photodetector, calculating a relative straightness error between the target mirror unit and the measuring unit along Y axis or Z axis;
• and 2) cooperating with the interference length measuring module to measure a relative position error between the target mirror unit and the measuring unit along X-axis;
• the two-dimensional angle measuring module includes a focusing lens or lens group, and a second photodetector;
• the focusing lens or lens group is used to focus the two-dimensional angle measuring light L112 on the second photodetector;
• and the two-dimensional relative angle error between the target mirror unit and the measuring unit resulted from rotating about Y-axis and Z-axis is calculated according to a spot offset on the second photodetector;
• the beam splitter in the target mirror unit is used to split the measuring light L11, in which a transmitted light L111 is reflected back by the reflector in the target mirror unit and returns to the measuring unit with straightness and positioning error information;
• while a reflected light L112 carries the two-dimensional angle information back to the measuring unit;
• and
• the reflector in the target mirror unit is used to reflect the measuring light L111 back 180° toward its original direction and return the measuring light L111 to the polarizing beam splitter, so as to realize:
• 1) changing a spatial position of the measuring light L111 along Y-axis and/or Y-axis, its spatial offset is twice the relative displacement between the reflector in the target mirror unit and the measuring unit along Y axis and/or Z-axis;
• and 2) changing an optical path and frequency of the measuring light L111, and a drift of the optical path and frequency is proportional to a relative displacement between the reflector in the target mirror unit and the measuring unit along X-axis.