Spectroscopic measurement device having diffraction grating at conjugate plane of relay lens

1. A spectroscopic measurement device, comprising:

a) a dividing optical system that divides a measurement beam emitted from each of a plurality of measurement points located within a measurement area of an object to be measured, into a first measurement beam and a second measurement beam, wherein the dividing optical system comprises:

an objective lens, and

a phase shifter that provides a continuous distribution of an optical path length difference between the first measurement beam and the second measurement beam

b) an imaging lens that converges the first measurement beam and the second measurement beam to interfere with each other;

c) a detector, including a plurality of pixels, that detects intensity distribution of the interference lights corresponding to the continuous distribution of the optical path length;

d) at least one computer processor programmed with instructions to: (i) acquire an interferogram of the measurement point of the object to be measured based on the light intensity distribution of the interference light detected by the detector, and (ii) compute a Fourier-transform of the interferogram of the object to be measured to obtain a spectrum;

f) a relay lens located between the object to be measured and the objective lens, the relay lens having a conjugate plane shared with the objective lens; and

g) a diffraction grating, located on the conjugate plane, that provides a spatially periodic modulation to the measurement beams emitted from the plurality of measurement points.

2. The spectroscopic measurement device according to claim 1 , wherein:

the phase shifter is a reflective phase shifter having a fixed reflection unit, and a movable reflection unit which is arranged next to the fixed reflection unit and which is movable in a direction of an optical axis,

a reflecting plane of the fixed reflection unit is a first optical member and a reflecting plane of the movable reflection unit is a second optical member;

the reflecting plane of the fixed reflection unit and the reflecting plane of the movable reflection unit reflect the measurement beam through the objective lens respectively;

the imaging lens receives the measurement beam reflected by the fixed reflection unit as the first measurement beam and the measurement beam reflected by the movable reflection unit as the second measurement beam, and produces an interference light by guiding the two measurement beams to a same point, wherein

the at least one computer processor is further programmed to: acquire an interferogram of the two measurement beams based on a change in the light intensity of the interference light detected by the interference light detector, by moving the movable reflection unit.

3. The spectroscopic measurement device according to claim 1 , wherein:

the phase shifter is a transmissive phase shifter having a first transmissive part having an entrance face and an exit face parallel to each other and a second transmissive part located next to the first transmissive part having an entrance face and an exit face one of which is sloped relative to the other, with either the entrance face or the exit face of the second transmissive part lying on a same plane as either the entrance face or the exit face of the first transmissive part;

the objective lens collimates the measurement beam and causes the collimated beam to enter the first transmissive part and the second transmissive part;

the imaging lens is a cylindrical lens that has an axis parallel to a line of intersection of the entrance face of the first transmissive part and a boundary surface between the first transmissive part and the second transmissive part, for receiving the measurement beam transmitted through the first transmissive part as the first measurement beam and the measurement beam transmitted through the second transmissive part as the second measurement beam;

the detector, including a plurality of pixels, detects an intensity distribution of an interference light produced from the first measurement beam and the second measurement beam entering the cylindrical lens; and

the at least one computer processor is further programmed to:

acquire an interferogram of the measurement points of the object to be measured based on the intensity distribution of the interference light detected by the detector, and

compute the Fourier-transform of the interferogram to obtain a spectrum.

4. The spectroscopic measurement device according to claim 3 , further comprising a tubular case for containing the objective lens, the transmissive phase shifter, the cylindrical lens and the detector in a linearly arranged form, the tubular case having a window formed at an end portion where the objective lens is located, and the window forming an entrance for a measurement beam emitted from a measurement point of the object to be measured.

5. The spectroscopic measurement device according to claim 4 , comprising an inner case for containing the transmissive phase shifter and the cylindrical lens, the inner case fitted in the tubular case in a rotatable manner.

6. The spectroscopic measurement device according to claim 5 , further comprising a drive mechanism that rotates the inner case.

7. The spectroscopic measurement device according to claim 4 , wherein the objective lens is fitted in the tubular case in such a manner as to move along an optical axis.

8. The spectroscopic measurement device according to claim 1 , wherein the diffraction grating is an amplitude-type diffraction grating.

9. The spectroscopic measurement device according to claim 5 , wherein the objective lens is fitted in the tubular case in such a manner as to be capable of moving along an optical axis.

10. The spectroscopic measurement device according to claim 6 , wherein the objective lens is fitted in the tubular case in such a manner as to be capable of moving along an optical axis.

11. The spectroscopic measurement device according to claim 2 , wherein the diffraction grating is an amplitude-type diffraction grating.

12. The spectroscopic measurement device according to claim 3 , wherein the diffraction grating is an amplitude-type diffraction grating.

13. The spectroscopic measurement device according to claim 4 , wherein the diffraction grating is an amplitude-type diffraction grating.

14. The spectroscopic measurement device according to claim 5 , wherein the diffraction grating is an amplitude-type diffraction grating.

15. The spectroscopic measurement device according to claim 6 , wherein the diffraction grating is an amplitude-type diffraction grating.

16. The spectroscopic measurement device according to claim 7 , wherein the diffraction grating is an amplitude-type diffraction grating.