Far infrared band optical thin film, preparation method thereof and optical element

Abstract

The invention discloses a far-infrared band optical thin film, a preparation method thereof and an optical element, and relates to a far-infrared band optical thin film technology, the far-infrared band optical thin film comprises a substrate, a front band-pass film system and a back cut-off film system; wherein the front band-pass film system is located on one side of the substrate, and the back cut-off film system is located on the other side of the substrate; the far infrared band optical thin film is prepared by alternately depositing lead telluride serving as a high-refractive-index thin film material and cadmium telluride serving as a low-refractive-index thin film material. The far infrared band optical thin film can cut off the band with the wavelength smaller than 4 microns, and the average transmittance is 0.23%; anti-reflection is carried out at the wave band of 5-50 microns; the moisture-resistant performance is excellent.

Description

Technical Field

[0001] The present invention relates to far-infrared band optical film technology, and in particular to a far-infrared band optical film, a preparation method thereof, and an optical element. Background Art

[0002] With the rapid development of modern science and technology, the application of far-infrared spectroscopy is expanding, encompassing a wide range of fields, including infrared astronomical observations, atmospheric environmental monitoring, and far-infrared target identification. However, current research in both science and industry focuses primarily on the mid-wave infrared (3-8μm) and long-wave infrared (8-14μm) bands, as these bands lie within the atmospheric window and have a wide range of practical applications. In contrast, the far-infrared band of 16-50μm has been less studied, but it also holds important application value in areas such as infrared astronomical observations and Earth radiation budget research.

[0003] Infrared astronomy is the technique of observing celestial objects using infrared electromagnetic waves (typically wavelengths between 0.75µm and 1000µm). Because many celestial objects emit peak radiation in the infrared, infrared observations can reveal cosmic information that is inaccessible to visible light, playing a vital role in star formation, galaxy evolution, cosmic dust distribution, and exoplanet research. The JWST space telescope, slated for launch in late 2021, will cover the far-infrared wavelength range of 0.6-28µm. Future deep space exploration will inevitably expand the spectral range to 50µm and beyond to capture targets farther away and at lower temperatures.

[0004] In the fields of astronomical observation and space science, the application of far-infrared optical thin film windows in the 5-50μm band has multiple implications. This band is a key window for studying the chemical characteristics of low-temperature matter and molecules in the universe. Cold matter, such as interstellar dust, cold molecular clouds (such as CO and H₂O molecular clouds), and protoplanetary disks, lack sufficient visible light radiation and primarily release energy through far-infrared thermal radiation (their blackbody emission peaks in this band). For example, the dust in protoplanetary disks has a temperature of approximately 20-100K, and its radiation is concentrated in the 20-200μm band, making it a core data source for studying the early stages of planet formation. Furthermore, the rotational-vibrational bands and electronic transition lines of many important molecules typically lie in the range of 2μm to tens of microns. For early or very early cosmic objects, their radiation is often shifted to the infrared or even mid- and far-infrared bands due to the cosmic redshift effect. Therefore, when detecting low-temperature, long-distance objects, reducing noise interference from light in other bands is crucial for obtaining accurate detection signals. Optical windows are key components in this process. Optical thin film windows combined with high-sensitivity detectors (such as superconducting nanowire single-photon detectors) can enhance the imaging capabilities of such faint celestial bodies.

[0005] In the field of environmental and meteorological monitoring, optical thin film windows with a far-infrared transmission band of 5-50μm can be used for trace gas detection. Ozone (O3) exhibits rotational vibration lines at 16-20μm, which can be used for stratospheric ozone layer monitoring. Nitrogen oxides (NOx) have characteristic absorption spectra at 20-30μm in industrial emissions. This window, combined with Fourier transform infrared spectroscopy (FTIR), can monitor pollution sources in real time.

[0006] In the field of far-infrared window materials, various technical proposals have been developed in China. Some studies have used organic materials such as polyethylene and plastics as window materials for infrared detectors in the 15-50μm band. These materials have good mechanical impact resistance, but they lack effective spectral response below 15μm. Furthermore, plastic polymers have limited aerospace applications due to their poor temperature resistance. Furthermore, research in China has used lead telluride (PbTe) and zinc selenide (ZnSe) as high- and low-refractive-index thin film materials, fabricated on a CVD diamond substrate for far-infrared filters. These filters exhibit excellent environmental stability. However, due to the strong absorption of ZnSe in the 45-50μm range, transmittance in this band is limited. Research has also been conducted on far-infrared optical thin film windows with mid-wavelength infrared cutoff, using lead telluride (PbTe) and cesium iodide (CsI) as high- and low-refractive-index thin film materials. This type of film has high spectral transmittance in the far-infrared band, but CsI is easily deliquescent due to its water solubility and poor spatial adaptability, which limits its application in harsh environments. Summary of the Invention

[0007] In order to solve the above technical problems, the present invention provides a far-infrared band optical film, which is achieved by coating a multilayer film on a substrate to achieve transmission of the far-infrared band of 5-50 microns and cutoff of the 4 micron front band, and has good moisture resistance.

[0008] A further technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned far-infrared optical film.

[0009] The present invention also provides an optical element comprising the far-infrared band optical film.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A far-infrared optical film, comprising a substrate, a front bandpass film system and a rear cutoff film system; wherein the front bandpass film system is located on one side of the substrate, and the rear cutoff film system is located on the other side of the substrate;

[0012] The far-infrared band optical film is prepared by alternately depositing lead telluride as a high-refractive-index film material and cadmium telluride as a low-refractive-index film material.

[0013] The front bandpass film is composed of lead telluride film layers and cadmium telluride film layers deposited alternately, wherein the first lead telluride film layer is deposited on the substrate.

[0014] Preferably, the film structure of the front bandpass film system is:

[0015] Base / 0.542H (1L 1H) 6 1.147L 0.735H 1.474L 0.344H 3.432L / air;

[0016] Where H represents a lead telluride film layer with an optical thickness of λ0 / 4, L represents a cadmium telluride film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, which is 3.1 microns, and the numbers before H and L are the λ0 / 4 optical thickness proportional coefficient multipliers.

[0017] Preferably, the reverse cutoff film is composed of lead telluride film layers and cadmium telluride film layers deposited alternately, wherein the first lead telluride film layer is deposited on the substrate.

[0018] Preferably, the film system structure of the reverse cutoff film system is:

[0019] Base / 0.306H (0.674L 0.564H) 6 0.773L 0.415H 0.994L 0.194H 3.313L / air;

[0020] Where H represents a lead telluride film layer with an optical thickness of λ0 / 4, L represents a cadmium telluride film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, which is 3.1 microns, and the numbers before H and L are the λ0 / 4 optical thickness ratio coefficients.

[0021] An optical element comprises the above-mentioned far-infrared band optical film.

[0022] The method for preparing the above-mentioned far-infrared optical film comprises the following steps:

[0023] Cleaning the substrate to be plated;

[0024] Using an alternating deposition process, a lead telluride film layer and a cadmium telluride film layer of preset thickness are sequentially deposited on the front surface of the cleaned substrate to obtain a front bandpass film system;

[0025] By adopting an alternating deposition process, a lead telluride film layer and a cadmium telluride film layer of preset thickness are sequentially deposited on the reverse side of the cleaned substrate to obtain a reverse side cutoff film system.

[0026] The deposition rate of the lead telluride film layer is 1.2-1.5 nm / s, and the deposition rate of the cadmium telluride film layer is 1.8-2.2 nm / s.

[0027] In the alternating deposition process, the film deposition vacuum is 1-2×10 -3 Pa, and the deposition temperature of the substrate was controlled at 200±2℃.

[0028] The cleaning process adopts ion source assisted bombardment cleaning, the anode voltage of the ion source is 180 volts, the cathode current is 4 amperes, and the bombardment lasts 8 to 10 minutes.

[0029] The beneficial effects of the present invention are as follows:

[0030] (1) The far-infrared optical film of the present invention can achieve cutoff of wavelengths less than 4 μm, with an average transmittance of 0.23%; and can enhance transmittance in the 5-50 μm band.

[0031] (2) The far-infrared optical film of the present invention has excellent moisture resistance.

[0032] (3) The far-infrared optical film of the present invention has stable performance and can be applied to the fields of infrared astronomical observation, earth radiation detection, far-infrared target identification and deep space exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic structural diagram of the far-infrared band optical film of the present invention.

[0034] Figure 2 This is the spectral transmittance curve of the far-infrared band optical film of the present invention.

[0035] Figure 3 This is a comparison diagram of the spectral transmittance curves of the far-infrared band optical film of the present invention before and after the humidity test.

[0036] The figures are marked as follows: 1-front bandpass film system; 2-substrate; 3-rear cutoff film system. DETAILED DESCRIPTION

[0037] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0038] The present invention provides a far-infrared optical film with an anti-reflection spectrum range of 5-50 μm and a cutoff spectrum range of 0-4 μm. PbTe and CdTe are selected as high-refractive-index and low-refractive-index film materials, wherein PbTe is a high-refractive-index film material and CdTe is a low-refractive-index film material.

[0039] The far-infrared optical thin film system (front bandpass film system 1) and the back cutoff film system (rear cutoff film system 3) of the present invention both employ a multi-layer, irregular film structure. Deposition of the film system utilizes a complementary monitoring method of quartz crystal monitoring and direct optical monitoring to control film thickness deposition errors and achieve results close to the designed value.

[0040] For details, see Figure 1 A far-infrared optical film comprises a substrate 2, a front bandpass film system 1, and a rear cutoff film system 3; the front bandpass film system 1 is located on one side of the substrate 2, and the rear cutoff film system 3 is located on the other side of the substrate 2. The far-infrared optical film of this embodiment is prepared by alternately depositing lead telluride (PbTe) as a high-refractive-index thin film material and cadmium telluride (CdTe) as a low-refractive-index thin film material.

[0041] Specifically, the front bandpass film system 1 is composed of alternately deposited lead telluride film layers and cadmium telluride film layers, wherein the first lead telluride film layer is deposited on the substrate 2 , and the outermost cadmium telluride film layer is in contact with air.

[0042] More preferably, the film structure of the front bandpass film system 1 is:

[0043] Base / 0.542H (1L 1H) 6 1.147L 0.735H 1.474L 0.344H 3.432L / air;

[0044] Where H represents a lead telluride film layer with an optical thickness of λ0 / 4, L represents a cadmium telluride film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, which is 3.1 microns, and the numbers before H and L are the λ0 / 4 optical thickness proportional coefficient multipliers.

[0045] Similarly, the reverse-side cutoff film system 3 is composed of alternately deposited lead telluride film layers and cadmium telluride film layers, wherein the first lead telluride film layer is deposited on the substrate 2 , and the outermost cadmium telluride film layer is in contact with air.

[0046] More preferably, the film structure of the reverse cutoff film system 3 is:

[0047] Base / 0.306H (0.674L 0.564H) 6 0.773L 0.415H 0.994L 0.194H 3.313L / air;

[0048] Where H represents a lead telluride film layer with an optical thickness of λ0 / 4, L represents a cadmium telluride film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, which is 3.1 microns, and the numbers before H and L are the λ0 / 4 optical thickness ratio coefficients.

[0049] The present invention also provides an optical element, which includes the above-mentioned far-infrared band optical film.

[0050] The method for preparing the above-mentioned far-infrared optical film comprises the following steps:

[0051] The substrate to be plated is cleaned; the substrate in this embodiment is a diamond substrate.

[0052] Using an alternating deposition process, a lead telluride film layer and a cadmium telluride film layer of preset thickness are sequentially deposited on the front surface of the cleaned substrate 2 to obtain a front bandpass film system 1;

[0053] By adopting an alternating deposition process, a lead telluride film layer and a cadmium telluride film layer of preset thickness are sequentially deposited on the reverse side of the cleaned substrate 2 to obtain a reverse side cutoff film system 3 .

[0054] Preferably, the deposition rate of the lead telluride film layer is 1.2-1.5 nm / s, and the deposition rate of the cadmium telluride film layer is 1.8-2.2 nm / s.

[0055] Preferably, in the alternating deposition process, the film deposition vacuum is 1-2×10 -3 Pa, and the deposition temperature of the substrate was controlled at 200±2℃.

[0056] Preferably, the cleaning process adopts ion source assisted bombardment cleaning, the anode voltage of the ion source is 180 volts, the cathode current is 4 amperes, and the bombardment lasts for 8-10 minutes.

[0057] Preferably, the cleaning treatment of the substrate to be plated comprises the following steps: ultrasonic cleaning for 10 minutes in an alcohol-ether mixed solution (volume ratio 1:1), and then wiping and cleaning with a dust-free cloth specially used for optical sheets.

[0058] Figure 2 is the spectral transmittance curve of the far infrared band optical film of the present invention. Figure 2 It can be seen that the far-infrared optical film of the present invention has an average transmittance of less than 0.23% in the 0-4 micron band, an average transmittance of greater than 58.90% in the 5-50 micron band, and a maximum transmittance of 81.47%.

[0059] Figure 3 The figure is a comparison of the spectral transmittance curves of the far-infrared optical film of the present invention before and after the humidity test. Figure 3As can be seen, after being placed in a humidity environment exceeding 90% for 24 hours, the far-infrared optical film of the present invention maintained good surface quality and showed no significant change in transmittance. Therefore, the far-infrared optical film of the present invention exhibits excellent moisture resistance.

[0060] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0061] Any portions not described in detail in this specification are known in the art. The above embodiments are provided for illustrative purposes only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications that do not depart from the spirit and principles of the present invention are intended to be encompassed within the scope of the present invention.

Claims

1. A far-infrared optical film, characterized in that: The far-infrared optical film comprises a substrate, a front bandpass film system and a rear cutoff film system; wherein the front bandpass film system is located on one side of the substrate, and the rear cutoff film system is located on the other side of the substrate; The far-infrared band optical film is prepared by alternately depositing lead telluride as a high-refractive-index film material and cadmium telluride as a low-refractive-index film material.

2. The far-infrared optical film according to claim 1, characterized in that: The front bandpass film is composed of lead telluride film layers and cadmium telluride film layers deposited alternately, wherein the first lead telluride film layer is deposited on the substrate.

3. The far-infrared optical film according to claim 2, characterized in that: The film structure of the front bandpass film system is: Base / 0.542H (1L 1H) 6 1.147L 0.735H 1.474L 0.344H 3.432L / air; Where H represents a lead telluride film layer with an optical thickness of λ0 / 4, L represents a cadmium telluride film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, which is 3.1 microns, and the numbers before H and L are the λ0 / 4 optical thickness proportional coefficient multipliers.

4. The far-infrared optical film according to claim 1, wherein: The reverse-side cutoff film is composed of lead telluride film layers and cadmium telluride film layers deposited alternately, wherein the first lead telluride film layer is deposited on the substrate.

5. The far-infrared optical film according to claim 4, characterized in that: The film system structure of the reverse cutoff film system is: Base / 0.306H (0.674L 0.564H) 6 0.773L 0.415H 0.994L 0.194H 3.313L / air; Where H represents a lead telluride film layer with an optical thickness of λ0 / 4, L represents a cadmium telluride film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, which is 3.1 microns, and the numbers before H and L are the λ0 / 4 optical thickness ratio coefficients.

6. An optical element, characterized in that: The far-infrared optical film comprises the far-infrared band optical film according to any one of claims 1 to 5.

7. The method for preparing a far-infrared optical film according to any one of claims 1 to 5, characterized in that: The steps include: Cleaning the substrate to be plated; Using an alternating deposition process, a lead telluride film layer and a cadmium telluride film layer of preset thickness are sequentially deposited on the front surface of the cleaned substrate to obtain a front bandpass film system; By adopting an alternating deposition process, a lead telluride film layer and a cadmium telluride film layer of preset thickness are sequentially deposited on the reverse side of the cleaned substrate to obtain a reverse side cutoff film system.

8. The method for preparing a far-infrared optical film according to claim 7, wherein: The deposition rate of the lead telluride film layer is 1.2-1.5 nm / s, and the deposition rate of the cadmium telluride film layer is 1.8-2.2 nm / s.

9. The method for preparing a far-infrared optical film according to claim 7, wherein: In the alternating deposition process, the film deposition vacuum is 1-2×10 -3 Pa, and the deposition temperature of the substrate was controlled at 200±2℃.

10. The method for preparing a far-infrared optical film according to claim 7, wherein: The cleaning process adopts ion source assisted bombardment cleaning, the anode voltage of the ion source is 180 volts, the cathode current is 4 amperes, and the bombardment lasts 8 to 10 minutes.

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