Compact tri-band infrared afocal telescope
An optical system includes an external common entrance pupil, a front multispectral objective lens group configured to receive and direct electromagnetic radiation in the multispectral infrared wavelengths, and a first beamsplitter configured to receive electromagnetic radiation from the front objective lens group. The first beamsplitter further is configured to reflect electromagnetic radiation in the short wave infrared (SWIR) wavelength and the middle wave infrared (MWIR) wavelength and to transmit electromagnetic radiation in the long wave infrared (LWIR) wavelength. The optical system further includes a second beamsplitter configured to receive electromagnetic radiation from the first beamsplitter. The second beamsplitter further is configured to reflect electromagnetic radiation in the SWIR wavelength and to transmit electromagnet radiation in the MWIR wavelength. The optical assembly further includes a spectral hybrid optics groups configured to direct spectrum beams in the LWIR wavelength band, the MWIR wavelength band and the SWIR wavelength.
1 . An optical system comprising:
an external common entrance pupil;
a front multispectral objective lens group configured to receive and direct electromagnetic radiation in multispectral infrared wavelengths;
a first beamsplitter configured to receive the electromagnetic radiation from the front multispectral objective lens group, the first beamsplitter further configured to reflect electromagnetic radiation in a short wave infrared (SWIR) wavelength band and a middle wave infrared (MWIR) wavelength band and to transmit electromagnetic radiation in a long wave infrared (LWIR) wavelength band;
a second beamsplitter configured to receive the electromagnetic radiation in the SWIR wavelength band and the MWIR wavelength band from the first beamsplitter, the second beamsplitter further configured to reflect the electromagnetic radiation in the SWIR wavelength band and to transmit the electromagnetic radiation in the MWIR wavelength band; and
a spectral hybrid optics group configured to direct spectrum beams in the LWIR wavelength band, the MWIR wavelength band, and the SWIR wavelength band.
2 . The optical system of claim 1 , wherein the front multispectral objective lens group is configured to produce a positive refractive power and includes a first lens, a second lens, and a third lens.
3 . The optical system of claim 2 , wherein the first lens has a non-spherical surface and a spherical surface, the second lens has spherical surfaces, and the third lens has a spherical surface and a non-spherical surface.
4 . The optical system of claim 2 , wherein the first lens is fabricated from ZnSMS, the second lens is fabricated from BaF 2 , and the third lens is fabricated from IRG-24.
5 . The optical system of claim 2 , wherein the spectral hybrid optics group includes a fourth lens, a fifth lens, and a sixth lens.
6 . The optical system of claim 5 , wherein each of the fourth lens, the fifth lens, and the sixth lens includes a positive meniscus lens having a hybrid optical surface.
7 . The optical system of claim 5 , wherein the fourth lens is fabricated from Ge, the fifth lens is fabricated from Si, and the sixth lens is fabricated from CaF 2 .
8 . The optical system of claim 1 , wherein the first beamsplitter is fabricated from Ge.
9 . The optical system of claim 1 , wherein the first beamsplitter includes a plate beamsplitter with a wedge of 20 arcmin.
10 . The optical system of claim 1 , wherein the second beamsplitter is fabricated from ZnSMS.
11 . The optical system of claim 1 , wherein the second beamsplitter includes a plate beamsplitter with a wedge of 21 arcmin.
12 . The optical system of claim 1 , further comprising:
a first folding mirror configured to reflect the spectrum beam in the LWIR wavelength band to a first lens of the spectral hybrid optics group.
13 . The optical system of claim 12 , further comprising:
a second folding mirror configured to reflect the spectrum beam in the MWIR wavelength band to a second lens of the spectral hybrid optics group.
14 . The optical system of claim 13 , wherein the second beamsplitter is configured to reflect the spectrum beam in the SWIR wavelength band to a third lens of the spectral hybrid optics group.
15 . The optical system of claim 1 , further comprising:
a multispectral window configured to direct electromagnetic radiation from the external common entrance pupil to the front multispectral objective lens group.
16 . The optical system of claim 1 , wherein the spectral hybrid optics group includes:
a first lens configured to direct the spectrum beam in the LWIR wavelength band to an LWIR exit pupil;
a second lens configured to direct the spectrum beam in the MWIR wavelength band to an MWIR exit pupil; and
a third lens configured to direct the spectrum beam in the SWIR wavelength band to an SWIR exit pupil.
17 . The optical system of claim 16 , wherein each of the first lens, the second lens, and the third lens includes a positive meniscus lens having a hybrid optical surface.
18 . The optical system of claim 16 , wherein the first lens is fabricated from Ge, the second lens is fabricated from Si, and the third lens is fabricated from CaF 2 .
19 . The optical system of claim 1 , wherein the optical system when folded achieves a volume of 12 inches by 12 inches by 6 inches for an afocal telescope having a 4-inch diameter entrance pupil and a magnification of 4×/4×/3.2×.