IR microscope with image field curvature compensation, in particular with additional illumination optimization
An IR microscope ( 1 ) is constituted such that, in an optical viewing mode in a beam path of visible light (VIS-R, VIS-T), a first intermediate focus (ZW 1 ) is imaged onto a flat detector surface ( 15 a ) of a camera. The IR microscope ( 1 ) is constituted such that, in the beam path of the visible light (VIS-R, VIS-T), the first intermediate focus (ZW 1 ) is imaged onto a second intermediate focus (ZW 2 ), and, in the second intermediate focus (ZW 2 ), a Mangin mirror ( 11 ) is disposed that corrects a field curvature of the Cassegrain objective ( 4 ). The invention provides an IR microscope in which the field curvature generated by the Cassegrain objective is corrected in a simple manner in the optical viewing mode when detection is performed using a flat detector and without restricting the spectral range of the IR microscope.
1. An infrared (=IR) microscope, the microscope comprising;
elements defining a beam path for visible light;
elements defining a beam path for IR light;
a first intermediate focus;
a Cassegrain objective having a sample position, said Cassegrain objective imaging the sample position onto said first intermediate focus, wherein said beam paths for visible and for IR light are coextensive in a region of the sample position;
an IR detector, wherein the IR microscope is constituted such that, at least in an IR viewing mode, IR light is directed from said first intermediate focus to said IR detector;
a second intermediate focus, wherein the IR microscope is constituted such that, in the beam path for visible light, said first intermediate focus is imaged onto said second intermediate focus;
a Mangin mirror disposed at said second intermediate focus, said Mangin mirror being structured to correct a field curvature of said Cassegrain objective; and
a flat viewing surface disposed downstream of said Mangin mirror, wherein, at least in an optical viewing mode and in the beam path for visible light, said first intermediate focus is imaged onto said flat viewing surface, wherein a curvature radius R 1 of a front surface of said Mangin mirror, a curvature radius R 2 of a reflective rear surface of said Mangin mirror, a refractive index n of a refractive material between said front and said rear surfaces of said Mangin mirror and a thickness t of said Mangin mirror are chosen such that not only said field curvature is corrected but an image field on said flat viewing surface is also free of vignetting.
2. The IR microscope of claim 1 , wherein said flat viewing surface is a detector surface of a camera.
3. The IR microscope of claim 1 , wherein, in the beam path for visible light, said Mangin mirror images an exit pupil of an optical system in front of said Mangin mirror onto an entrance pupil of an optical system behind said Mangin mirror.
4. The IR microscope of claim 3 , wherein said optical system in front of said Mangin mirror is an Offner objective and said optical system behind of said Mangin mirror is an achromatic lens.
5. The IR microscope of claim 1 , wherein a<n/(n−1) applies, where a=R 2 /R 1 .
6. The IR microscope of claim 1 , wherein said curvature radius R 1 of a front surface of the Mangin mirror, said curvature radius R 2 of a reflective rear surface of the Mangin mirror and said refractive index n of said refractive material between said front and rear surfaces of said Mangin mirror are chosen such that a Petzval radius R Petzval of said Mangin mirror is at least essentially diametrically opposed with respect to a Petzval radius R Petzval VIS in the beam path for visible light, including said Cassegrain objective and without said Mangin mirror,
where R Petzval =+na|R 1 |/[2a(n−1)+2]
and a=R 2 /R 1 ,
wherein said Cassegrain objective introduces a Petzval radius R Petzval Obj of −f Obj into said Petzval radius R Petzval VIS in the beam path for visible light, f Obj being a focal distance of said Cassegrain objective.
7. The IR microscope of claim 1 , wherein 0.5*f Obj ≦|R 1 |≦2*f Obj applies, where f Obj is a focal distance of said Cassegrain objective and R 1 is a curvature radius of a front surface of said Mangin mirror.
8. The IR microscope of claim 1 , wherein an Offner objective is disposed in the beam path for visible light between said first intermediate focus and said second intermediate focus.
9. The IR microscope of claim 1 , wherein a beam splitter is provided in the beam path for visible light to split incident and reflected light at said Mangin mirror.
10. The IR microscope of claim 1 , wherein the IR microscope is constituted for operation with reflection and/or transmission.
11. The IR microscope of claim 1 , further comprising an interferometer that is integrated into a housing of the IR microscope.
12. The IR microscope of claim 1 , further comprising a lens system to image said second intermediate focus onto said flat viewing surface.
13. The IR microscope of claim 12 , wherein said lens system comprises two achromatic lenses.
14. The IR microscope of claim 1 , further comprising a variable aperture for IR light disposed at said first intermediate focus.