Spectral device and confocal scanning microscope provided with spectral device

1. A method for guiding light in a spectral device, wherein the spectral device comprises: a diffraction element which disperses light for each wavelength; an optical condensing system which condenses diffracted light of a specific order generated by diffraction in the diffraction element, the diffracted light of the specific order including first diffracted light of the specific order and second diffracted light of the specific order; a photo-detector which is arranged at a condensing position where the diffracted light of the specific order is condensed by the optical condensing system; a first deflection device which is arranged to invert a direction of travel of second light which is zeroth-order diffracted light generated by diffraction of first light which has entered the diffraction element as a parallel luminous flux, and to lead the second light into the diffraction element, whereby the second diffracted light of the specific order is generated by diffraction of the second light in the diffraction element; and a second deflection device which is arranged to invert a direction of travel of the second diffracted light of the specific order generated by the diffraction of the second light which has entered the diffraction element so as to be in a same direction as the first diffracted light of the specific order which is generated by the diffraction of the first light, and to slightly translate in parallel the second diffracted light of the specific order, so as to lead the second diffracted light of the specific order into the optical condensing system without re-entering the diffraction element;

wherein the method comprises:

diffracting, with the diffraction element, the first light which enters the diffraction element as a parallel luminous flux, to (i) generate the first diffracted light of the specific order and lead the first diffracted light to the optical condensing system to be condensed by the optical condensing system and received by the photo-detector at the condensing position, and (ii) generate the second light which is the zeroth-order diffracted light, and lead the second light to the first deflection device;

inverting, with the first deflection device, a direction of travel of the second light, to lead the second light into the diffraction element;

diffracting, with the diffraction element, the second light which entered the diffraction element, to generate the second diffracted light of the specific order, and to lead the second diffracted light of the specific order to the second deflection device;

inverting, with the second deflection device, a direction of travel of the second diffracted light of the specific order so as to be in a same direction as the first diffracted light of the specific order, and slightly translating in parallel the second diffracted light of the specific order, with the second deflection device, so as to lead the second diffracted light of the specific order into the optical condensing system without re-entering the diffraction element, wherein the second diffracted light of the specific order is condensed by the optical condensing system and received by the photo-detector at the condensing position.

2. The method according to claim 1 , wherein the diffraction element is arranged as freely rotatable to change an angle of incidence of the first light.

3. The method according to claim 2 , wherein the diffraction element is a transmissive diffraction grating.

4. The method according to claim 3 , wherein:

the first deflection device and the second deflection device are arranged opposite each other with the diffraction element interposed between the devices; and

the inverting with the first deflection device comprises inverting the direction of travel of the second light and leading the second light into the diffraction element from a surface different from a surface of incidence of the first light.

5. The method according to claim 3 , wherein the diffraction element is a transmissive volume phase holographic grating.

6. The method according to claim 3 , wherein the second deflection device comprises:

a second optical condensing system having a front focal position at a position where the first light enters the diffraction element; and

a reflective member arranged at a back focal position of the second optical condensing system,

wherein the inverting with the second deflection device comprises:

condensing, with the second optical condensing system, the second diffracted light of the specific order to thereby lead the second diffracted light to the reflective member; and

reflecting, with the reflective member, the second diffracted light of the specific order.

7. The method according to claim 2 , wherein the diffraction element is a reflective diffraction grating.

8. The method according to claim 7 , wherein the second deflection device comprises:

an inversion member which is arranged to invert the direction of travel of the second diffracted light of the specific order generated by diffraction of the second light;

and

a reflective member which is arranged to reflect the second diffracted light of the specific order whose direction of travel is inverted by the inversion member, the reflective member being arranged near the diffraction element;

wherein the inverting with the second deflection device comprises:

inverting, with the inversion member, the direction of travel of the second diffracted light of the specific order to lead the second diffracted light of the specific order to the reflective member; and

reflecting, with the reflective member, the second diffracted light of the specific order.

9. The method according to claim 7 , wherein the second deflection device comprises:

a second optical condensing system having a front focal position at a position where the first light enters the diffraction element;

a first reflective member arranged at a back focal position of the second optical condensing system; and

a second reflective member which is arranged to reflect the second diffracted light of the specific order whose direction of travel has been inverted by the second optical condensing system and the reflective member, the second reflective member being arranged near the diffraction element,

wherein the inverting with the second deflection device comprises:

condensing, with the second optical condensing system, the second diffracted light of the specific order to thereby lead the second diffracted light to the first reflective member;

reflecting, with the first reflective member, the second diffracted light to lead the second refractive light to the second optical condensing system;

condensing the second diffracted light with the second optical condensing system to thereby lead the second diffracted light to the second reflective member; and

reflecting, with the second reflective member, the second diffracted light.

10. The method according to claim 7 , wherein:

the first deflection device is a reflective member which is arranged to rotate with a rotation of the diffraction element, and to travel by rotating about a rotation axis of the diffraction element two times a rotation angle of the diffraction element, and

the second deflection device is arranged to rotate with a rotation of the diffraction element, and to travel by rotating about the rotation axis of the diffraction element at a same rotation angle as the diffraction element.

11. The method according to claim 1 , further comprising a third deflection device which is arranged to invert a direction of travel of third light which is zeroth-order diffracted light generated by diffraction of the second light, and to lead the third light into the diffraction element,

wherein the method further comprises inverting, with the third deflection device, the direction of travel of the third light, to lead the third light into the diffraction element.

12. The method according to claim 1 , wherein the photo-detector comprises a plurality of detection elements which detect diffracted light of the specific order having different wavelength bands.

13. The method according to claim 1 , wherein the second deflection device comprises a corner cube, and the inverting with the second deflection device comprises inverting the direction of travel of the second diffracted light and slightly translating in parallel the second diffracted light with the corner cube.