Glasses for the correction of chromatic and thermal optical aberations for lenses transmitting in the near, mid, and far-infrared spectrums

Abstract

The invention relates to chalcogenide glass compositions for use in a lens system to balance thermal effects and chromatic effects and thereby provide an achromatic and athermal optical element that efficiently maintains achromatic performance across a broad temperature range. The glass composition is based on sulfur compounded with germanium, arsenic and/or gallium, and may further comprise halides of, for example, silver, zinc, or alkali metals. Alternatively, is based on selenium compounded with gallium, and preferably germanium, and contains chlorides and/or bromides of, for example, zinc, lead or alkali metals.

Claims

1. In a night vision device comprising an infrared optical element, an image enhancer or intensifier, and a phosphor or fluorescent display, the improvement wherein said infrared optical element comprises a lens made from a chalcogenide glass composition consisting essentially of (based on mol % of total moles): TABLE-US-00013 Component Mole % S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 0.00-5.00 (added in the form of R.sup.1Hal) wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and wherein a portion of the gallium can be replaced by indium.

2. A night vision device according to claim 1, wherein said composition contains 5.00-7.00 mol % Ga.

3. A night vision device according to claim 1, wherein a portion of the gallium is replaced by indium in said composition.

4. A night vision device according to claim 1, wherein said composition contains 23.00-25.00 mol % Ge.

5. A night vision device according to claim 1, wherein said composition does not contain arsenic.

6. A night vision device according to claim 1, wherein said composition consists of (based on mol % of total moles): TABLE-US-00014 S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 0.00-5.00 (added in the form of R.sup.1Hal) wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and a portion of the gallium can be replaced by indium.

7. In an infrared or thermal imaging system comprising an infrared optical element, a plurality of thermal sensors for detecting the infrared light and converting it into electrical signals, and a signal-processing unit for converting the electrical signals into a visual image, the improvement wherein said infrared optical element comprises a lens made from a chalcogenide glass composition consisting essentially of (based on mol % of total moles): TABLE-US-00015 Component Mole % S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 0.00-5.00 (added in the form of R.sup.1Hal) wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and wherein a portion of the gallium can be replaced by indium.

8. An infrared or thermal imaging system according to claim 7, wherein said composition contains 5.00-7.00 mol % Ga.

9. An infrared or thermal imaging system according to claim 7, wherein a portion of the gallium is replaced by indium in said composition.

10. An infrared or thermal imaging system according to claim 7, wherein said composition contains 23.00-25.00 mol % Ge.

11. An infrared or thermal imaging system according to claim 7, wherein said composition does not contain arsenic.

12. An infrared or thermal imaging system according to claim 7, wherein said composition consists of (based on mol % of total moles): TABLE-US-00016 S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 (added in the form of R.sup.1Hal) 0.00-5.00 wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and a portion of the gallium can be replaced by indium.

13. A doublet lens comprising an infrared lens paired with a corrective lens wherein said infrared lens is made of ZnSe, ZnS, Ge, GaAs, BaF.sub.2, or chalcogenide glass, and said corrective lens is made from a chalcogenide glass composition consisting essentially of (based on mol % of total moles): TABLE-US-00017 Component Mole % S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 0.00-5.00 (added in the form of R.sup.1Hal) wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and wherein a portion of the gallium can be replaced by indium.

14. A doublet lens according to claim 13, wherein said composition contains 5.00-7.00 mol % Ga.

15. A doublet lens according to claim 13, wherein a portion of the gallium is replaced by indium in said composition.

16. A doublet lens according to claim 13, wherein said composition contains 23.00-25.00 mol % Ge.

17. A doublet lens according to claim 13, wherein said composition does not contain arsenic.

18. A doublet lens according to claim 13, wherein said composition consists of (based on mol % of total moles): TABLE-US-00018 S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 (added in the form of R.sup.1Hal) 0.00-5.00 wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and a portion of the gallium can be replaced by indium.

19. An infrared lens system comprising a first infrared lens and a focal corrector doublet lens comprising a pair of corrective lenses, wherein said first infrared lens is made of ZnSe, ZnS, Ge, GaAs, BaF.sub.2, or chalcogenide glass, one of said pair of corrective lenses has a positive power and the other has a negative power, and at least one of said pair of corrective lens is made from a chalcogenide glass composition consisting essentially of (based on mol % of total moles): TABLE-US-00019 Component Mole % S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 0.00-5.00 (added in the form of R.sup.1Hal) wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and wherein a portion of the gallium can be replaced by indium.

20. An infrared lens system according to claim 19, wherein said composition contains 5.00-7.00 mol % Ga.

21. An infrared lens system according to claim 19, wherein a portion of the gallium is replaced by indium in said composition.

22. An infrared lens system according to claim 19, wherein said composition contains 23.00-25.00 mol % Ge.

23. An infrared lens system according to claim 19, wherein said composition does not contain arsenic.

24. An infrared lens system according to claim 19, wherein said composition consists of (based on mol % of total moles): TABLE-US-00020 S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 (added in the form of R.sup.1Hal) 0.00-5.00 wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and a portion of the gallium can be replaced by indium.

25. A chalcogenide glass comprising (based on mol % of total moles): TABLE-US-00021 Component Mole % S 58.00-90.00 Ga 0-25.00 As 0-40.0 Ge 0-35.00 R.sup.1 0-7.25 (added in the form of R.sup.1Hal) R.sup.2 0-13.5 (added in the form of R.sup.2Hal) M.sup.1 0-5 (added in the form of M.sup.1Hal.sub.2) M.sup.2 0-7.25 (added in the form of M.sup.2Hal.sub.2) Ln 0-4 (added in the form of LnHal.sub.3) Sum of Ga, As, and Ge 10.00-42.00 Sum of R.sup.1, R.sup.2, M.sup.1, M.sup.2, and Ln 0-16.00 Sum of Hal 0-16.00 wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, R.sup.2=Ag and/or Cu, M.sup.1=Mg, Ca, Sr, and/or Ba, M.sup.2=Zn, Cd, Hg, and/or Pb, and Ln=La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Ty, Lu, Y, and Sc; wherein a portion of the gallium can be replaced by indium, and wherein a portion of the arsenic can be replaced by antimony.

26. In a night vision device comprising an infrared optical element, an image enhancer or intensifier, and a phosphor or fluorescent display, the improvement wherein said infrared optical element comprises a lens made from a chalcogenide glass composition according to claim 25.

27. In an infrared or thermal imaging system comprising an infrared optical element, a plurality of thermal sensors for detecting the infrared light and converting it into electrical signals, and a signal-processing unit for converting the electrical signals into a visual image, the improvement wherein said infrared optical element comprises a lens made from a chalcogenide glass composition according to claim 25.

28. A doublet lens comprising an infrared lens paired with a corrective lens wherein said infrared lens is made of ZnSe, ZnS, Ge, GaAs, BaF.sub.2, or chalcogenide glass, and said corrective lens is made from a chalcogenide glass composition according to claim 25.

29. An infrared lens system comprising a first infrared lens and a focal corrector doublet lens comprising a pair of corrective lenses, wherein said first infrared lens is made of ZnSe, ZnS, Ge, GaAs, BaF.sub.2, or chalcogenide glass, one of said pair of corrective lenses has a positive power and the other has a negative power, and at least one of said pair of corrective lens is made from a chalcogenide glass composition according to claim 25.

30. In a night vision device comprising an infrared optical element, an image enhancer or intensifier, and a phosphor or fluorescent display, the improvement wherein said infrared optical element comprises a lens made from A chalcogenide glass composition that transmits near-, mid-, and/or far-infrared light comprising sulfur compounded with germanium, arsenic and/or gallium, wherein all or a portion of gallium can be replaced by indium, and said composition optionally contains halides of silver, copper (Cu.sup.+1), cadmium, zinc, lead (Pb.sup.+2), alkali metals, alkaline earth metals, or rare earth metals, wherein the total of the combined Ga and In content of said composition (based on mol % of total moles) 6.00-15.00 mol %, and the amount of Ge in said composition is 10.00-20.00 mol %.

31. In an infrared or thermal imaging system comprising an infrared optical element, a plurality of thermal sensors for detecting the infrared light and converting it into electrical signals, and a signal-processing unit for converting the electrical signals into a visual image, the improvement wherein said infrared optical element comprises a lens made from a chalcogenide glass composition that transmits near-, mid-, and/or far infrared light comprising sulfur compounded with germanium, arsenic and/or gallium, wherein all or a portion of gallium can be replaced by indium, and said composition optionally contains halides of silver, copper (Cu.sup.+1), cadmium, zinc, lead (Pb.sup.+2), alkali metals, alkaline earth metals, or rare earth metals, wherein the total of the combined Ga and In content of said composition (based on mol % of total moles) 6.00-15.00 mol %, and the amount of Ge in said composition is 10.00-20.00 mol %.

32. A doublet lens comprising an infrared lens paired with a corrective lens wherein said infrared lens is made of ZnSe, ZnS, Ge, GaAs, BaF.sub.2, or chalcogenide glass, and said corrective lens is made from a chalcogenide glass composition that transmits near-, mid-, and/or far infrared light comprising sulfur compounded with germanium, arsenic and/or gallium, wherein all or a portion of gallium can be replaced by indium, and said composition optionally contains halides of silver, copper (Cu.sup.+1), cadmium, zinc, lead (Pb.sup.+2), alkali metals, alkaline earth metals, or rare earth metals, wherein the total of the combined Ga and In content of said composition (based on mol % of total moles) 6.00-15.00 mol %, and the amount of Ge in said composition is 10.00-20.00 mol %.

33. An infrared lens system comprising a first infrared lens and a focal corrector doublet lens comprising a pair of corrective lenses, wherein said first infrared lens is made of ZnSe, ZnS, Ge, GaAs, BaF.sub.2, or chalcogenide glass, one of said pair of corrective lenses has a positive power and the other has a negative power, and at least one of said pair of corrective lens is made from a chalcogenide glass composition that transmits near-, mid-, and/or far infrared light comprising sulfur compounded with germanium, arsenic and/or gallium, wherein all or a portion of gallium can be replaced by indium, and said composition optionally contains halides of silver, copper (Cu.sup.+1), cadmium, zinc, lead (Pb.sup.+2), alkali metals, alkaline earth metals, or rare earth metals, wherein the total of the combined Ga and In content of said composition (based on mol % of total moles) 6.00-15.00 mol %, and the amount of Ge in said composition is 10.00-20.00 mol %.

34. A chalcogenide glass composition consisting essentially of (based on mol % of total moles): TABLE-US-00022 Component Mole % S 70.00-75.00 Ga 5.00-10.00 Ge 20.00-25.00 R.sup.1 0.00-5.00 (added in the form of R.sup.1Hal) wherein Hal=fluoride, chloride, bromide, and/or iodide, R.sup.1=Li, Na, K, Rb, and/or Cs, and wherein a portion of the gallium is replaced by indium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein:

(2) FIG. 1 illustrates a doublet lens system containing a corrective lens in accordance with the invention; and

(3) FIG. 2 illustrates a triplet lens system containing a corrective lens made from two glasses in accordance with the invention.

(4) As described above, optical materials for IR wavelengths suffer from thermally-induced changes in focal length in lenses due to thermal expansion and dn/dT. In an achromatic doublet lens, the dispersions combine to provide equal powers at 2 wavelengths. To athermalize a lens (i.e., to reduce thermal effects), the coefficient of thermal expansion (CTE) and dn/dT need to be balanced. Therefore, using the following equations:

(5) $\left(CTE\right)=\frac{I}{L}\frac{\mathrm{DL}}{\left(\mathrm{DT}\right)},=\frac{\mathrm{dn}}{\mathrm{dt}},\mathrm{and}$$=\frac{}{n-1}-\left(\mathrm{thermal}\mathrm{change}\mathrm{in}\mathrm{focal}\mathrm{power}\right),$
one can estimate the requirements for achieving an athermal and achromatic system.

(6) For a doublet lens, the power, K, is equal to the powers of the individual lens, i.e., K.sub.1+K.sub.2=K (doublet). For an achromatic lens, K.sub.1/V.sub.1+K.sub.2/V.sub.2=0 (i.e., K.sub.2=K.sub.1V.sub.2/V.sub.1) V represents the Abbe No. For athermalization, K.sub.1.sub.1+K.sub.2.sub.2=K.sub.h, where .sub.h is the thermal expansion coefficient of the housing material (i.e., the housing holding the lens). Combining the equations results in .sub.2=[V.sub.1(.sub.h.sub.1)/V.sub.2]+.sub.h. Thus, the corrective lens of the doublet preferably satisfies this criterion.

(7) FIG. 1 illustrates a doublet lens wherein an infrared lens 1 is paired with a corrective lens 2 made a chalcogenide glass composition according to the invention. The IR lens 1 and corrective lens 2 are preferably fused together, although they can also be separated by a small air space. Lens 1 can be made from any of the commonly used material for IR lenses, for example, ZnSe, ZnS, Ge, GaAs, BaF.sub.2, and chalcogenide glasses, preferably ZnSe or ZnS. Preferably, a ZnSe IR lens is paired with a corrective lens made from a selenium based glass composition according to the invention, as these glasses will have similar transmission properties. For similar reasons, a ZnS IR lens is preferably paired with a corrective lens made form a sulfur based glass composition according to the invention.

(8) As shown in FIG. 1, light passing through the IR lens 1 is subjected to dispersion due to the variance in refractive index, which causes the focal length to be shorter at shorter wavelengths. This light then passes through corrective lens 2 which corrects the light transmission by preferentially increasing the focal length relative to that created by the first lens at shorter wavelengths, thereby counteracting the effects of the first lens.

(9) FIG. 2 illustrates another embodiment according to the invention wherein a pair of lenses may be added to the system in order to leave the focal length at a single wavelength unaffected but to change either the dispersive or thermal behavior of the system in order to counteract the effects of the main focusing element. This is most efficacious in correcting problems in existing systems. For instance, thermal defocus in Germanium-based optical systems may be corrected by inserting a lens pair with an infinite focal length at room temperature, but which becomes negative at elevated temperatures or positive at decreased temperatures, thereby correcting the errors introduced by the germanium element.

(10) Thus, an existing lens may be corrected using two lenses (one positive and one negative) which give a total power of 0 (afocal) at the center wavelength, but which have different V and to correct deficiencies of the primary lens without change overall focal length. Thus, the powers of the two corrective lenses are to cancel each other out, i.e., K.sub.1+K.sub.2+K.sub.3=K.sub.1 when K.sub.2=K.sub.3 (K.sub.1 is the power of the existing lens and K.sub.2 and K.sub.3 are the powers of the doublet lens). Going through the process of achromatizing and althermalizing using the equations described above, the 2 glasses of the doublet lens preferably satisfy the following (with a preference for small K.sub.2): [V.sub.2V.sub.3/V.sub.1(V.sub.3V.sub.2)=(.sub.h.sub.1)/(.sub.2..sub.3).

(11) Thus, in FIG. 2 an infrared lens 1 is used in combination with a doublet lens containing lens elements 2 and lens 3, one having a negative power and the other having a positive power. The negative power lens element should have higher dispersion (smaller V) and higher than positive lens element. Lens 2 and lens 3 are preferably fused. Lens 1 can be made from any of the commonly used material for IR lenses, for example, ZnSe, ZnS, Ge, GaAs, BaF.sub.2, and known chalcogenide glasses, preferably ZnSe or ZnS. At least one of lens 2 and lens is made from a chalcogenide glass composition according to the invention. The other lens can be made from a chalcogenide glass composition according to the invention or from any of the commonly used material for IR lenses, such as ZnSe, ZnS, Ge, GaAs, BaF.sub.2, and known chalcogenide glasses. For example, lens 1 can be of ZnS, lens 2 can be from a chalcogenide glass composition according to the invention, and lens 3 can be made of ZnSe.

EXAMPLES

(12) The glasses of this invention can be fully conventionally prepared by mixing the appropriate amounts of each constituent to form a batch composition which is then charged into a fused silica ampoule and melted by radiative heating, e.g., from 600 C. to as much as 1050 C., depending on the chosen composition typically 2 to 4 hours, again depending on composition and melt viscosity while rocking the melt in order to cause agitation and increase homogeneity. The glass within its ampoule is then typically removed from the furnace and allowed to cool by convection in room temperature air to a temperature near its glass transition temperature. The ampoule and glass sample are then placed into a heated oven at the glass transition temperature plus about 20 C. for about 2 hours followed by cooling at about 30 C./hour. These procedures are followed in the examples below.

(13) As noted above, the examples of this application are melted in a fused silica ampoule. It is well known that chalcogenide compounds, particularly those of S with Ge or Ga possess high vapor pressures near the melt temperature. The pressure evolved during melting may exceed the burst pressure of the silica vessel, leading to rupture of the ampoule. Also, the thermal expansion of these glasses is relatively large compared to that of the ampoule. Under the conditions of wetting of the glass to the interior of the ampoule, the stress induced during quenching may cause a rupture ampoule and/or glass ingot within. The temperatures and heating rates during the melting and quenching operations must therefore be chosen judiciously in order to prevent rupture, depending on the design of the ampoule and dimensions and composition of the glass ingot. The need to control these factors while still providing sufficiently high melting temperatures and cooling rates while quenching combine to limit the dimensions of the ampoule and glass sample which may be prepared.

(14) Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

(15) Tables 1A, 1B, 1C, 1D, 1E, and 1F list examples of the glass composition according to the invention. Tables 1A-1D list examples of the sulfur based glass composition and Tables 1E and 1F lists examples of the selenium based glass composition.

(16) TABLE-US-00007 TABLE 1A Examples of Sulfur Based Glass Compositions (mol %) According to the Invention Component Content (mol %) 1 2 3 4 5 6 7 S 60 60 60 65 58 65 70 Ge 5 10 10 20 25 23 Ga As 40 35 30 25 12 10 7 Total 100 100 100 100 100 100 100

(17) TABLE-US-00008 TABLE 1B Further Examples of Sulfur Based Glass Compositions (mol %) According to the Invention Component Content Examples (mol %) 8 9 10 11 S 70 70 75 70 Ge 25 20 20 23 Ga 5 10 5 7 As Total 100 100 100 100

(18) TABLE-US-00009 TABLE 1C Examples of Selenium Based Glass Compositions (mol %) According to the Invention Component Content Examples (mol %) 12 13 14 15 16 17 18 19 Se 37 37 52.5 54.2 55.6 52.5 54.2 55.6 Ga 21 21 9.5 8.3 7.4 9.5 8.3 7.4 Ge 19 20.9 22.2 19 20.9 22.2 Br 21 9.5 8.3 7.4 Cl 21 9.5 8.3 7.4 Cs, Na, 21 21 9.5 8.3 7.4 9.5 8.3 7.4 K, Ag (Cs) (Cs) (Na) (Na) (Na) (Na) (Na) (Na) Total 100 100 100 100 100 100 100 100

(19) TABLE-US-00010 TABLE 1D Examples of Selenium Based Glass Compositions (mol %) According to the Invention Component Content Examples (mol %) 20 21 22 23 24 25 26 27 Se 37 37 52.5 54.2 55.6 52.5 54.2 55.6 Ga 21 21 9.5 8.3 7.4 9.5 8.3 7.4 Ge 19 20.9 22.2 19 20.9 22.2 Br 21 9.5 8.3 7.4 Cl 21 9.5 8.3 7.4 Cs, Na, 21 21 9.5 8.3 7.4 9.5 8.3 7.4 K, Ag (Ag) (Ag) (K) (K) (K) (K) (K) (K) Total 100 100 100 100 100 100 100 100

(20) TABLE-US-00011 TABLE 1E Further Examples of Selenium Based Glass Compositions (mol %) According to the Invention Component Content Examples (mol %) 28 29 30 31 32 33 Se 55 65.5 57.7 55 65.5 57.7 Ga 10 8.7 7.7 10 8.7 7.7 Ge 20 21.8 23 20 21.8 Br 10 8.7 7.7 Cl 10 8.7 7.7 Zn 5 4.3 3.9 5 4.3 3.9 Total 100 100 100 100 100 100

(21) TABLE-US-00012 TABLE 1F Further Examples of Selenium Based Glass Compositions (mol %) According to the Invention Component Content Examples (mol %) 34 35 36 37 38 39 Se 55 65.5 57.7 55 65.5 57.7 Ga 10 8.7 7.7 10 8.7 7.7 Ge 20 21.8 23 20 21.8 Br 10 8.7 7.7 Cl 10 8.7 7.7 Pb 5 4.3 3.9 5 4.3 3.9 Total 100 100 100 100 100 100

(22) The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

(23) From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

(24) The entire disclosure[s] of all applications, patents and publications, cited herein, are incorporated by reference herein.