Broadband infrared polarization device based on mercurous halide crystal and preparation method and application thereof

Abstract

The invention provides a broadband infrared polarization device based on a mercurous halide crystal as well as a preparation method and application of the broadband infrared polarization device. The broadband infrared polarization device based on the mercurous halide crystal comprises a right-angle triangular prism based on the mercurous halide single crystal and a hexagonal prism based on the mercurous halide single crystal, and the mercurous halide is Hg < 2 > Cl2 or Hg < 2 > Br < 2 >. The mercurous halide crystal used in the invention is low in cost, can be prepared in a large size, and has stable physical and chemical properties; the transmission range of the infrared polarization device covers middle and far infrared bands, the transmission rate is high, and the birefringence is large; the polarization device based on the mercurous halide crystal can simultaneously realize polarization beam combination and beam splitting of visible-long wave infrared broadband, and has a high laser damage threshold, a high extinction ratio, high beam combination efficiency and high beam quality.

Description

Technical Field

[0001] The invention relates to a wide-band infrared polarization device based on mercurous halide crystals and a preparation method and application thereof, and belongs to the field of structural design of optical elements and processing of crystal elements. Background Art

[0002] 3-20μm mid-infrared coherent light sources have important applications in infrared detection, infrared guidance, infrared countermeasures and other fields. The development of infrared technology has increasingly urgent needs for high-power mid-infrared lasers. In particular, the rapid development of semiconductor quantum cascade lasers in recent years has made the size of mid-infrared lasers more compact and miniaturized, and the output spectral range is wider. However, the output power of mid-infrared lasers is generally small, which is difficult to meet the needs of infrared technology for high-power lasers. Laser beam combining technology is an effective method to achieve high-power laser output. It mainly includes spatial beam combining with aperture and polarization beam combining technology with common aperture. The beam combining laser of the former array structure has side lobes, which will cause far-field energy dispersion and cannot achieve high-power density laser beam combining. In addition to being able to achieve high-power laser output in the far field, the latter can achieve polarization coherent beam combining of lasers by using phase locking and laser resonance technology on this basis, and obtain a beam of circularly polarized light or linearly polarized light after beam combining, which doubles the power density while keeping the beam quality unchanged. Therefore, polarization beam combining technology has become a frontier research hotspot in the field of lasers. This technology can be applied to occasions that require high-power lasers, such as large laser interferometers, infrared detection, infrared countermeasures, lidar, long-distance laser communications and other laser fields.

[0003] The polarization beam combiner (PBC) based on birefringent crystal is the core component of common aperture polarization beam combining. The principle is roughly as follows: two linear polarized lights with perpendicular polarization directions pass through the two light-passing surfaces of the PBC device respectively, and are emitted from the other light-passing surface after beam combining inside the crystal, thereby realizing laser beam combining. Its advantages lie in its high laser damage threshold, high extinction ratio, high beam combining efficiency and high beam quality. In addition, the PBC device can also realize the polarization splitting function of the polarization beam splitter (PBS), and the device provides an escape window for the reflected polarized light. Compared with the traditional Glan Taylor prism, this beam splitter device with an escape window design reduces the accumulation of heat in the crystal and reduces the mutual influence caused by the reflection of the light path inside the crystal, thereby greatly improving the light damage resistance threshold of the device.

[0004] At present, the widely used matrix materials for crystal polarization devices include calcite, YVO4, rutile and MgF2 crystals, all of which have high birefringence and extinction properties, and can basically meet the needs of the ultraviolet-visible light band. However, calcite crystals are natural non-renewable resources. With the decrease in the amount of raw ore mining year by year, the price is becoming more and more expensive; rutile and YVO4 crystals are difficult to grow large-sized single crystals, which affects the production of large-sized devices. More importantly, the transmission range of the above crystals cannot cover the mid-to-far infrared bands, and it is difficult to meet the needs of mid-to-long-wave infrared polarization devices. Although the transmission range of MgF2 crystals can reach 8μm, its small birefringence limits the use of polarization devices. Therefore, exploring the scientific design of crystal materials and polarization devices with a wide light transmission range, high transmittance, high damage threshold, large birefringence, stable physical and chemical properties, low cost, and large-sized preparation from the visible to the long-wave infrared band is an important basis for realizing infrared polarization beam combining and splitting technology. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a wide-band infrared polarization device based on mercuric halide crystals, and a preparation method and application thereof. The mercuric halide crystals used in the present invention have low cost, can be prepared in large sizes, and have stable physical and chemical properties; the infrared polarization device has a transmission range covering the mid-to-far infrared band, has high transmittance, and has large birefringence; the polarization device based on mercuric halide crystals of the present invention can simultaneously realize polarization beam combining and beam splitting in the visible-long-wave infrared wide band, and has a high laser damage threshold, a high extinction ratio, a high beam combining efficiency, and a high beam quality.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A wide-band infrared polarization device based on mercury halide crystals comprises a right-angle triangular prism based on mercury halide single crystals and a hexagonal prism based on mercury halide single crystals; the mercury halide is Hg2Cl2 or Hg2Br2.

[0008] Preferably, according to the present invention, the lower left part of the device is a right-angled triangular prism, and the upper right part is a hexagonal prism. The right-angled triangular prism and the hexagonal prism are coupled face-to-face through air gaps, optical glue or deepening optical glue to form an overall device structure; the oblique surface of the right-angled triangular prism and the hexagonal prism are coupled face-to-face; the coupling surfaces of the right-angled triangular prism and the hexagonal prism are quadrilaterals, and maintain the same crystal orientation and flatness; the overall structure of the device is a cube structure with one corner cut off, wherein the cut surface is a rectangle. Preferably, the right-angled triangular prism and the hexagonal prism are coupled face-to-face through air gaps.

[0009] Preferably according to the present invention, the crystal orientations of the right-angled triangular prism and the hexagonal prism are consistent.

[0010] According to the preferred embodiment of the present invention, the material of the right-angled triangular prism and the hexagonal prism is a positive uniaxial Hg2Cl2 crystal or a positive uniaxial Hg2Br2 crystal, which belongs to the tetragonal system I 4 / mmm space group. The preparation of the positive uniaxial Hg2Cl2 crystal or the positive uniaxial Hg2Br2 crystal is prepared by the physical vapor transport (PVT) method disclosed in "A growth device and method for mercurous halide single crystal, ZL 201810601105.0".

[0011] Preferably, according to the present invention, the wavelength transmission range of the infrared polarization device based on mercurous chloride crystal is 0.38-25 μm, the transmittance in 0.8-14 μm is ≥81% (uncoated), the birefringence is 0.533@4.6 μm, and the refractive index dispersion equation is:

[0012]

[0013] Among them, n e and n o are the refractive indices of e-light and o-light respectively, λ is the wavelength, and the unit is μm.

[0014] According to the preferred embodiment of the present invention, the refractive index n of Hg2Cl2 single crystal at different wavelengths of o light and e light calculated according to the above refractive index dispersion equation is o and n e , birefringence △n, total reflection angle β and Brewster angle α are shown in the following table:

[0015]

[0016] Preferably, according to the present invention, the refractive index dispersion equation of the infrared polarization device based on mercurous bromide crystal is:

[0017]

[0018] Among them, n e and n o are the refractive indices of e-light and o-light respectively, λ is the wavelength, and the unit is μm.

[0019] According to the preferred embodiment of the present invention, the refractive index n of Hg2Br2 single crystal at different wavelengths of o light and e light calculated according to the above refractive index dispersion equation is o and n e , birefringence △n, total reflection angle β and Brewster angle α are shown in the following table:

[0020]

[0021] According to the present invention, at different target application wavelengths, the structural angle of the infrared polarization device is determined by the refractive index of two orthogonal polarized lights of the mercuric halide single crystal, Snell's law n1sinθ1=n2sinθ2, the total reflection condition β≥arcsin(n2 / n1), and Brewster's law α=arctan(n2 / n1). The above process is determined with reference to polarization optical physics, and the specific determination method is as follows: In order to realize the application of polarization beam combining, the structural angle θ of the device should be greater than the total reflection angle of e light and less than the total reflection angle of o light, satisfying β o =arcsin(1 / n o )>θ>β e =arcsin(1 / n e ), achieving total reflection of e-light and transmission of o-light. o , β e is the total reflection angle of o light and e light in the air gap, n e and n o are the refractive indices of e-light and o-light respectively.

[0022] Preferably, according to the present invention, the structural angle θ of the infrared polarization device based on mercurous chloride crystal is: 25.93° (total reflection angle of e light at 20μm) <θ < 30.61° (total reflection angle of o light at 0.633μm); the structural angle θ of the infrared polarization device based on mercurous bromide crystal is: 23.29° (total reflection angle of e light at 30μm) <θ < 28.25° (total reflection angle of o light at 0.633μm). Such a design can realize the total reflection (s polarization) of the e light component and the polarized transmission (p polarization) of the o light component in the wide band range of 0.633-20μm for the infrared polarization device based on mercurous chloride crystal and the range of 0.633-30μm for the infrared polarization device based on mercurous bromide crystal.

[0023] Preferably, at different application wavelengths, the structural angle θ of the infrared polarization device is the Brewster angle of the mercurous halide single crystal at the application wavelength. Brewster's law: When natural light is reflected and refracted on the dielectric interface, in general, both the reflected light and the refracted light are partially polarized light. When the incident angle is the Brewster angle, the reflected light is linearly polarized light, and the refraction angle is perpendicular to the reflection angle. The setting of the structural angle of the present invention eliminates the reflection loss at the prism coupling and the influence of beam interference on the device, achieves the highest reflectivity of e-light and the highest transmittance of o-light at this wavelength, and takes into account a high extinction ratio. According to the target application wavelength, the Brewster angle at this wavelength can be selected as the device structural angle to achieve optimal performance. The above structural angle range can meet the wide-band polarization beam splitting and beam combining of 0.633-20μm (mercurous chloride crystal device) or 0.633-30μm (mercurous bromide crystal device). In terms of polarization beam splitting function, at a specific wavelength, selecting the Brewster angle α=arctan(n1 / n2) of the wavelength can prevent the influence of beam interference, and at the same time obtain linear polarized light with higher polarization degree and transmittance ratio, so that the PBS device can achieve a higher extinction ratio at the target wavelength. According to the target wavelength and light source size of the beam splitter device, the structural angle and light transmission size BF, CD, DE and other parameters can be adjusted to design and process the mercurous halide crystal.

[0024] According to the present invention, the device structure angle θ is selected according to the principle that: Figure 3 , 4 The s light meets the total reflection condition in the mercurous halide hexagonal prism and is totally reflected at FG; while the p light, which does not meet the total reflection condition, can penetrate two mercurous halide crystal prisms through the air gap. For the polarization beam combining function, the preferred structural angle range in the technical solution can meet the 0.633-20μm (mercurous chloride crystal device) or 0.633-30μm (mercurous bromide crystal device) wide-band polarization beam combining. In terms of polarization beam splitting function, the use of the above structural angle range within the spectral range of 0.633-20μm (mercurous chloride crystal device) or 0.633-30μm (mercurous bromide crystal device) can also achieve arbitrary wavelength polarization beam splitting function.

[0025] According to the preferred embodiment of the present invention, the device structure is as follows: the ABCDE plane is the front side of the device, and the opposite and parallel side with the same size is the reverse side; the AB surface and the CD surface are the side surfaces of the device, and the AB surface and the CD surface are parallel to each other; the BC surface is the bottom surface of the device, and the AE surface is the top surface of the device, and the BC surface and the AE surface are parallel to each other; the ED surface is the inclined surface of the device; the FG surface is the coupling surface of the right-angle triangular prism and the hexagonal prism; the ABCDE plane and its opposite surface are (001) crystal planes, and the optical axis is perpendicular to the ABCDE plane; the AB surface and the CD surface are (110) crystal planes, which are light-transmitting surfaces, so that polarized light propagates perpendicular to the optical axis inside the crystal; the BC surface and the AE surface are (-110) crystal planes. The structural angle θ and the light-transmitting aperture determine the main parameters of the crystal device, and the crystal device parameters are as follows:

[0026] BF=CD=DE=AH(1)

[0027] ∠BFG=θ(2)

[0028] ∠ABC=∠BCD=∠BAE=90°(3)

[0029] CG=CD×tan(90-2θ)(4)

[0030] ∠CDE=180°-2θ(5)

[0031] Preferably, the infrared polarization device further comprises a housing; the housing packaging material is aluminum, stainless steel or other metals or polyoxymethylene resin, etc. The housing completely seals and protects the (001) crystal plane of the device, exposing three light-transmitting surfaces for light transmission by the polarization prism.

[0032] Preferably according to the present invention, the infrared polarization device is an infrared polarization beam combiner or an infrared polarization beam splitter.

[0033] The method for preparing the wide-band infrared polarization device based on mercurous halide crystal comprises the steps of: mercurous halide single crystal orientation, crystal cutting, grinding and shaping, fine polishing, prism coupling, and shell packaging to obtain the infrared polarization device.

[0034] Preferably, according to the present invention, mercury halide single crystal orientation: the grown mercury halide single crystal ingot usually has multiple natural cleavage planes, this crystal plane is the (110) plane, and the diffraction angle of this crystal plane is 14.06°. Based on this, an X-ray orientation instrument is selected to accurately orient the crystal. Finally, the (110) crystal plane and the mutually perpendicular (-110) crystal plane (the (110) plane and the (-110) plane of the mercury halide crystal have the same chemical environment, the same Bragg diffraction angle, and are two equivalent planes), as well as the (001) crystal plane are determined, thereby completing the crystal orientation. The orientation method of the present invention is simple to operate and has high orientation accuracy (the error is within 0.1°).

[0035] Preferably, according to the present invention, crystal cutting: the oriented mercury halide crystal ingot is cut to obtain a rectangular parallelepiped mercury halide crystal blank containing two equivalent (110) faces and a (001) face perpendicular thereto. The structural angle θ and the light-transmitting surface ED are also obtained by a cutting machine, and right-angled triangles and hexagonal mercury halide crystal blanks are obtained after cutting. Preferably, the cutting method of the mercury halide crystal ingot is diamond wire cutting or inner circle cutting. The cutting speed of the mercury halide crystal ingot is 0.05-5mm / min.

[0036] According to the preferred embodiment of the present invention, grinding and shaping: in order to remove the cutting line marks, a corundum grinding disc is used to grind the right-angle triangle and hexagonal mercurous halide crystal blanks, and a cerium oxide or aluminum oxide polishing liquid is used to complete the grinding. The polishing liquid is obtained by mixing polishing powder in a dispersion solvent, the polishing powder includes cerium oxide or aluminum oxide powder, and the dispersion solvent includes one or a mixture of two of ethanol, deionized water, methanol, ethylene glycol, ether, etc. The ratio of the mass of the polishing powder to the volume of the dispersion solvent is 0.05-1g / mL.

[0037] According to the preferred embodiment of the present invention, fine polishing: use fine-grained cerium oxide or aluminum oxide polishing liquid to polish the BF surface, ED surface, CD surface, and two FG bevels on the polishing asphalt, respectively, to perform precision polishing on a total of five surfaces, so that the crystal meets the surface quality requirements of high flatness and smoothness; after each polishing, the wafer is cleaned with a cleaning liquid and dried. Preferably, the cleaning liquid is a mixed solution of ethanol and petroleum ether, methanol, and ether. The polishing asphalt is an existing common commercial product. The particle size of fine-grained cerium oxide or aluminum oxide is 0.02-2μm, both of which are existing common commercial products. The dispersing solvent used in the polishing liquid includes one or a mixture of two of ethanol, deionized water, methanol, ethylene glycol, ether, etc. The concentration of cerium oxide or aluminum oxide in the polishing liquid is 0.01-1g / mL.

[0038] According to a preferred embodiment of the present invention, prism coupling is to couple a right-angled triangular prism and a hexagonal prism so that the two inclined surfaces of the crystal maintain a good parallel spacing and expose three light-transmitting surfaces BF, ED and CD.

[0039] The above-mentioned wide-band infrared polarization device based on mercuric halide crystal is used as an infrared polarization beam combiner for polarization laser beam combining, or as an infrared polarization beam splitter for polarization laser beam splitting.

[0040] According to the present invention, the design principle of the wide-band infrared polarization device based on mercuric halide crystal is as follows:

[0041] (1) Polarization beam combiner (PBC): The design optical path diagram of this polarization device is as follows: Figure 3 As shown in the figure, the principle of its function is as follows: p-polarized light is incident vertically on the BF plane into the right-angle triangular mercuric halide prism. Since the structural angle θ of the prism is designed to be the Brewster angle (βo >θ>β e ), which does not contain an s-polarization (parallel to the principal plane) component, and enters the hexagonal prism through the air gap at the coupling surface of the two FG prisms. The s-polarized light with a vibration direction perpendicular to the principal plane is incident vertically on the DE plane into the hexagonal prism with a structural angle of θ. It does not contain a p-polarization component and satisfies the total reflection relationship, so it is reflected on the FG surface and coincides with the p-polarization light path, completing a simple polarization beam combining. When controlling the phase and other conditions of the two polarized light beams, high-power polarization coherence can be achieved, and the beam combining technology of linear polarized light and circular polarized light can be obtained. Similarly, by adjusting the structural angle, laser polarization beam combining in different wavelength ranges can be achieved.

[0042] (2) Polarization beam splitter (PBS): This device is the reverse application of the polarization beam combiner. The optical path diagram is as follows: Figure 4 As shown in the figure, the principle of its function is as follows: when the light is incident perpendicular to the CD plane, the o (p polarized) light and e (s polarized) light inside the right-angle triangular prism, although they are not separated on the optical path, their speeds are inconsistent in the direction perpendicular to the optical axis, resulting in phase separation. When the two beams of light pass through the FG surface, they are divided into two polarized lights with polarization directions perpendicular to each other, namely, p light with polarization directions perpendicular to the main plane and s light parallel to the main plane, where the s light satisfies the total reflection relationship, is reflected and escapes from the DE surface of the hexagonal prism. The p light is refracted, enters the right-angle triangular prism through the air gap and emerges from the BF surface. By adjusting the structural angle θ of the prism to the Brewster angle, completely linear polarized light can be obtained to achieve polarization splitting.

[0043] In the present invention, the optical path diagram design of the polarization device is completed on the basis of the cut design of the mercurous halide crystal. The cut design diagram is a three-dimensional diagram, and the optical path diagram is a two-dimensional diagram of the cut.

[0044] The technical features and beneficial effects of the present invention are as follows:

[0045] (1) The mercurous halide (molecular formula: Hg2Cl2 or Hg2Br2) single crystal used in the present invention belongs to the tetragonal system I 4 / mmm space group, is a positive uniaxial crystal, has the advantages of easy acquisition of large-size high-quality single crystals, excellent crystal physical and chemical properties, easy processing, low cost, wide light transmission range, large birefringence, small dispersion in the medium and long wave infrared, high optical transmittance, etc., and is a type of broadband birefringence material in the medium and long wave infrared band with excellent performance. Among them, the mercurous chloride crystal device has a light transmission range of 0.38-25μm, a birefringence of 0.533@4.6μm, a small dispersion in the medium and long wave infrared, and an optical transmittance of up to 81% (uncoated).

[0046] (2) Since the existing crystal devices have small birefringence and cannot meet the needs of wide spectral coverage in the visible-long-wave infrared band, there is a problem of shortage of crystal device matrix materials in polarization beam combining and splitting technology. The present invention provides a wide-band infrared polarization device based on mercuric halide crystals. The polarization device design based on mercuric halide crystals in the present invention can realize polarization beam splitting and beam combining in a wide band (visible-long-wave infrared, 0.633-20μm or 0.633-30μm), especially in the medium and long-wave infrared bands. Its polarization beam splitting function can achieve the acquisition of high-power lasers, and the design of the Brewster structure angle can eliminate the influence of reflection loss and beam interference, which helps the device to have higher transmittance and extinction ratio in the whole band; the polarization beam combining function can stably realize polarization laser beam combining of visible-long-wave infrared band lasers. The polarization device based on mercuric halide crystals of the present invention has a high laser damage threshold, a high extinction ratio, a high beam combining efficiency and a high beam quality.

[0047] (3) The processing method based on the mercuric halide crystal device in the present invention is relatively gentle and can reduce the damage to the crystal. In addition, it can accurately meet the requirements of the design size of the crystal device based on the large-sized mercuric halide crystal with precise orientation and precise tilt angle. At the same time, the coupling process of the light-transmitting surface with high finish and high flatness is beneficial for the device to obtain a higher laser damage threshold and maintain a good beam quality in the laser beam combining or splitting function. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a photo of a large-sized Hg2Cl2 single crystal grown by the PVT method in the present invention.

[0049] Figure 2 This is a stereoscopic diagram of an infrared polarization device. The optical axis is shown in the figure.

[0050] Figure 3 The schematic diagram of the beam combining function of the infrared polarization beam combiner is shown in Figure 1, where the crystal optical axis is perpendicular to the plane shown. The arrowed lines in the figure represent the optical path, the black dots represent the s-light, and the short bidirectional arrows represent the p-light.

[0051] Figure 4 The figure is a schematic diagram of the beam splitting function of the infrared polarization beam splitter. The crystal optical axis is perpendicular to the plane shown. The arrowed line in the figure represents the light path, the black dot represents the s-light, and the short bidirectional arrow represents the p-light.

[0052] Figure 5 The device entity is a processed infrared polarization device based on mercurous chloride crystal.

[0053] Figure 6The relationship curve between the s-polarization and p-polarization reflectivity and the structural angle of the processed infrared polarization device based on mercurous chloride crystal at an air gap of 4.6μm. The horizontal axis in the figure is the structural angle and the vertical axis is the reflectivity.

[0054] Figure 7 This is the visible-long-wave infrared spectral transmission curve of the infrared polarization device based on mercurous chloride crystal. The horizontal axis in the figure is wavelength and the vertical axis is transmittance.

[0055] Figure 8 This is the optical path diagram of the beam combining test of the infrared polarization beam combiner based on mercurous chloride crystal.

[0056] Fig. 9 This is the spot profile at 130cm after the beam combining test of the infrared polarization beam combiner based on mercurous chloride crystal.

[0057] Fig.10 This is the rotational extinction performance curve of the infrared polarization beam splitter based on mercurous chloride crystal, where the abscissa is the rotation angle and the ordinate is the transmitted light power. DETAILED DESCRIPTION

[0058] The present invention is further described below in conjunction with specific embodiments and drawings, but the specific crystal device structure in the following embodiments cannot be regarded as a further limitation of the large-aperture infrared polarization device based on mercurous chloride crystal of the present invention.

[0059] In the embodiments, the materials and devices used are commercially available unless otherwise specified; the methods used are existing methods unless otherwise specified.

[0060] In the embodiment, the Hg2Cl2 single crystal is prepared by the physical vapor transport (PVT) method described in Example 5 of the public "A growth device and method for mercurous halide single crystal, ZL 201810601105.0". The appearance photo of the Hg2Cl2 single crystal is as follows Figure 1 As shown in the figure, the Hg2Cl2 single crystal is a positive uniaxial Hg2Cl2 crystal, belonging to the tetragonal system I 4 / mmm space group.

[0061] The Hg2Br2 single crystal is prepared by the physical vapor transport (PVT) method described in Example 6 of the public "A growth device and method for mercurous halide single crystal, ZL201810601105.0". The Hg2Br2 crystal is a positive uniaxial crystal.

[0062] Example 1

[0063] A wide-band infrared polarization beam combiner (PBC) or beam splitter (PBS) based on mercurous chloride crystal, the structure of which is as follows: Figure 2As shown, it includes a right-angle triangular prism based on Hg2Cl2 single crystal and a hexagonal prism based on Hg2Cl2 single crystal. The crystal orientations of the right-angle triangular prism and the hexagonal prism are consistent, and the direction of the optical axis is as follows: Figure 2 shown.

[0064] The wavelength transmission range of the device is 0.38-25μm, the transmittance in 0.8-14μm is ≥81% (uncoated), the birefringence is 0.533@4.6μm, and the refractive index dispersion equation is (where n e and n o are the refractive indices of e-light and o-light respectively, λ is the wavelength, in μm):

[0065]

[0066] The refractive index n of Hg2Cl2 single crystal at different wavelengths of o light and e light calculated according to the refractive index dispersion equation o and n e , birefringence △n, total reflection angle β and Brewster angle α are shown in the following table:

[0067]

[0068] When the target wavelength of the crystal device is 4.6 μm, the structural angle θ is determined to be the Brewster angle of Hg2Cl2 single crystal at the application wavelength of 27.75°.

[0069] The device structure is as follows:

[0070] The lower left part of the device is a right-angled triangular prism, and the upper right part is a hexagonal prism. The right-angled triangular prism and the hexagonal prism are face-to-face coupled through an air gap to form an overall device structure, and the coupling surfaces maintain the same crystal orientation and flatness; the oblique surface of the right-angled triangular prism and the hexagonal prism are face-to-face coupled; the coupling surfaces of the right-angled triangular prism and the hexagonal prism are quadrilaterals, and maintain the same crystal orientation and flatness; the overall structure of the device is a cubic structure with one corner cut off, in which the cross section is a rectangle. The ABCDE plane is the front of the device, and the opposite and parallel side with the same size is the back side; the AB and CD planes are the side surfaces of the device, and the AB and CD planes are parallel to each other; the BC plane is the bottom surface of the device, and the AE plane is the top surface of the device, and the BC and AE planes are parallel to each other; the ED plane is the inclined surface of the device; the FG plane is the coupling surface of the right-angle triangular prism and the hexagonal prism; the ABCDE plane and its opposite surface are (001) crystal planes, and the optical axis is perpendicular to the ABCDE plane; the AB and CD planes are (110) crystal planes, which are square light-transmitting surfaces, and the size of the CD plane is designed to be 10×10mm, so that the polarized light propagates perpendicular to the optical axis inside the crystal; the BC and AE planes are (-110) crystal planes. The structural angle θ and the light-transmitting aperture determine the main parameters of the crystal device. Figure 3 ,4 In the figure, the crystal device parameters are as follows:

[0071] BF=CD=DE=AH=10mm(1)

[0072] ∠BFG=θ=27.75°(2)

[0073] ∠ABC=∠BCD=∠BAE=90°(3)

[0074] CG=CD×tan(90°-2θ)=6.87mm(4)

[0075] ∠CDE=180°-2θ=124.50°(5)

[0076] The infrared polarization device also includes a shell; the shell packaging material is polyoxymethylene resin. The shell completely seals and protects the (001) crystal plane of the crystal prism, exposing the three-way light surface for the polarization prism to pass light.

[0077] The method for preparing the above-mentioned wide-band infrared polarization device based on mercurous chloride crystal comprises the steps of:

[0078] The infrared polarization device is obtained by orienting Hg2Cl2 single crystal, crystal cutting, grinding and shaping, fine polishing, prism coupling and shell packaging.

[0079] Orientation of Hg2Cl2 single crystal: The grown Hg2Cl2 single crystal ingot usually has multiple natural cleavage planes, the (110) plane, which has a diffraction angle of 14.06°. Based on this, an X-ray orientation instrument is used to accurately orient the crystal. Finally, the (110) crystal plane and the mutually perpendicular (-110) crystal plane (the (110) plane and (-110) plane of the Hg2Cl2 crystal have the same chemical environment, the same Bragg diffraction angle, and are two equivalent planes), as well as the (001) crystal plane are determined to complete the crystal orientation.

[0080] Crystal cutting: By using the internal angle relationship of the Hg2Cl2 crystal, the other diffraction surfaces of the Hg2Cl2 crystal can be determined by completing the two oriented (110) crystal planes. Diamond wire is used to cut the oriented Hg2Cl2 ingot, and paraffin is used to effectively fix the crystal on the cutting platform. The (001) crystal plane with a certain size perpendicular to the two (110) planes is cut out, and finally a rectangular Hg2Cl2 crystal blank with a size of 18×15×12mm is obtained, which includes two equivalent (110) planes and the optical axis plane (001) plane perpendicular to the plane. The structural angle θ and the light-transmitting surface ED are also obtained by diamond wire cutting, and right-angle triangle and hexagonal Hg2Cl2 crystal blanks are obtained after cutting. The cutting speed of Hg2Cl2 crystal is 3mm / min.

[0081] Grinding and shaping: In order to remove the cutting line marks and determine the angle relationship of θ = 27.75° and ∠CDE = 124.50°, a corundum grinding disc is used to grind the right-angle triangle and hexagonal Hg2Cl2 crystal blanks, and a grinding and polishing liquid is used during grinding. The specific composition of the grinding liquid is 10μm alumina powder and ethylene glycol solution, and the mass volume ratio is 0.1g / mL.

[0082] Fine polishing: Use fine-grained (particle size 0.03 μm) cerium oxide polishing liquid (ethanol solution of cerium oxide with a concentration of 0.03 g / mL). Perform precision polishing on the BF surface, ED surface, CD surface, and two FG bevels on the polishing asphalt, so that the crystal meets the surface quality requirements of high flatness and smoothness; after each polishing, the wafer is cleaned with a cleaning liquid and dried. The cleaning liquid is a mixed solution of ethanol and petroleum ether in a volume ratio of 1:1. The polishing asphalt is an existing common commercial product.

[0083] Prism coupling: The right-angle triangular prism and the hexagonal prism are coupled and connected to keep the two inclined surfaces of the crystal at a good parallel distance to obtain a perfect and stable air gap, and expose the three light-transmitting surfaces of BF, ED, and CD, completing the following steps: Figure 5 The processing of the infrared polarization beam combiner based on Hg2Cl2 crystal.

[0084] Shell packaging: The shell packaging material is polyoxymethylene resin. The shell completely seals and protects the (001) crystal face of the crystal prism, exposing the three-way light surface for the polarization prism to pass light.

[0085] Example 2

[0086] A wide-band infrared polarization beam combiner or beam splitter based on mercurous chloride crystal, such as Figure 2 As shown, the device structure of this embodiment is the same as that of embodiment 1, except that the target wavelength of the crystal device is different, which is 10.6 μm, and the structural angle θ is 27.89°. Figure 3 , 4 Other design parameters are:

[0087] BF=CD=DE=AH=10mm(1)

[0088] ∠BFG=θ=27.89°(2)

[0089] ∠ABC = ∠BCD = ∠BAE = 90° (3)

[0090] CG=CD×tan(90°-2θ)=6.80mm(4)

[0091] ∠CDE = 180° - 2θ = 124.22° (5)

[0092] The similarities between the crystal device processing and the embodiment 1 are not repeated here, the difference is that the cutting process of the crystal device is performed according to the design parameters in the above embodiment 2.

[0093] Example 3

[0094] A wide-band infrared polarization beam combiner or beam splitter based on mercuric bromide crystal, having a structure as follows Figure 2 As shown, the device structure is the same as that described in Example 1, except that the Hg2Cl2 single crystal is replaced by the Hg2Br2 single crystal.

[0095] The refractive index dispersion curve of the device is (where n e and n o are the refractive indices of e-light and o-light respectively, λ is the wavelength, in μm):

[0096]

[0097] The refractive index n of Hg2Br2 single crystal at important wavelengths for o-light and e-light calculated according to the refractive index dispersion equation o and n e , birefringence △n, total reflection angle β and Brewster angle α are shown in the following table:

[0098]

[0099] When the target wavelength of the crystal device is 1064nm, the structural angle θ is determined to be 25.95°; Figure 3 , 4 The other design parameters are:

[0100] BF=CD=DE=AH=10mm(1)

[0101] ∠BFG=θ=25.95°(2)

[0102] ∠ABC=∠BCD=∠BAE=90°(3)

[0103] CG=CD×tan(90°-2θ)=7.84mm(4)

[0104] ∠CDE = 180° - 2θ = 128.10° (5)

[0105] The other device structures are the same as those in Example 1.

[0106] The similarities between the crystal device processing and Example 1 are not repeated here. The difference is that the diffraction angles of the (110) crystal plane and the (001) crystal plane of the Hg2Br2 crystal are 13.5° and 16.06° respectively, and the cutting process is carried out according to the above-mentioned design parameters.

[0107] Test Example 1

[0108] The structural angle is critical to the transmittance performance of the infrared polarization beam combiner or beam splitter. According to the device structure of Example 1, the angle of the structural angle is changed, and the reflectivity of s-polarization and p-polarization at the air gap at 4.6 μm is calculated, as shown in FIG. Figure 6 As shown. When the structural angle is 27.75°, the reflection loss of the air gap is zero at the specified wavelength. In addition, when the structural angle is in the range of 26.75° to 28.80°, the reflection loss is still less than 0.1%, and total reflection of s-polarization can be achieved within this range, achieving optimal beam combining efficiency. The larger structural angle range enables the PBC device to have a larger field of view and use tolerance.

[0109] Test Example 2

[0110] A series of tests and characterizations were performed on the device processed in Example 1 of the present invention. The processing design of the device based on Hg2Cl2 crystal in the present invention has the following advantages compared with other crystal devices: the light transmittance range of the crystal device is 0.38-25μm, and the transmittance at 0.8-14μm can reach more than 81% without coating, reflecting the ultra-wide spectral transmittance range of Hg2Cl2 and the high transmittance obtained by the high crystal quality (such as Figure 7 shown).

[0111] In the polarization beam combining experiment, the polarization beam combining optical path is as follows: Figure 8 As shown in the figure, two 4.6μm semiconductor quantum cascade lasers were used to generate linearly polarized light beams. The powers of the two polarized light beams before beam combining were 18.04mW and 18.45mW respectively. After beam combining, 26.90mW of unpolarized light was obtained. The beam combining efficiency was 73.70% (uncoated). The spot profile is shown in the figure. Fig. 9 As shown, its beam quality factor Shows good beam quality.

[0112] Test Example 3

[0113] The optical component of the present invention can be used as a laser beam combining device as well as a laser beam splitting device. The beam splitter can be regarded as the reverse application of the beam combining device, and the optical path is the reverse optical path in the application of the beam combining device.

[0114] By using a PBS device based on a birefringent crystal polarizing prism, a polarization beam splitting technology with a high extinction ratio can be realized. The polarization beam splitting prism can split the incident non-polarized light into two linearly polarized lights with perpendicular polarizations.

[0115] The polarization beam splitting performance of the PBS crystal device manufactured in Example 1 of the present invention was characterized by relevant tests. The extinction ratios of 633nm, 1064nm and 10.6μm are: ER=41600@633nm (46.2dB); ER=39900@1064nm (46.0dB); ER=5900@10.6μm (37.7dB). Fig.10 The rotational extinction performance curves in the figure show the superiority of the infrared polarization beam combiner based on Hg2Cl2 crystal.

[0116] The above specific implementation methods are further explanations of the application of Hg2Cl2-type crystals as matrix materials in crystal polarization optical devices in the visible to infrared, especially in the mid- and far-infrared bands, and cannot be regarded as further limitations of the patent of the present invention. Non-substantial changes made by technical personnel in this field based on the content of the patent of the present invention should fall within the scope of protection of the patent of the present invention.

Claims

1. A wide-band infrared polarization device based on mercuric halide crystal, characterized in that: The invention comprises a right-angle triangular prism based on a mercury halide single crystal and a hexagonal prism based on a mercury halide single crystal; the mercury halide is Hg2Cl2 or Hg2Br2.

2. The wide-band infrared polarization device based on mercuric halide crystal according to claim 1, characterized in that: The lower left part of the device is a right-angled triangular prism, and the upper right part is a hexagonal prism. The right-angled triangular prism and the hexagonal prism are face-to-face coupled to each other through air gaps, optical glue or deepened optical glue to form an overall device structure; the oblique surface of the right-angled triangular prism and the hexagonal prism are face-to-face coupled to each other; the coupling surfaces of the right-angled triangular prism and the hexagonal prism are quadrilaterals, and maintain the same crystal orientation and flatness; the overall structure of the device is a cubic structure with one corner cut off, in which the cut surface is a rectangle; preferably, the right-angled triangular prism and the hexagonal prism are face-to-face coupled to each other through an air gap.

3. The wide-band infrared polarization device based on mercuric halide crystal according to claim 1, characterized in that: The crystal orientations of right-angled triangular prisms and hexagonal prisms are consistent.

4. The wide-band infrared polarization device based on mercuric halide crystal according to claim 1, characterized in that: The materials of the right-angled triangular prism and the hexagonal prism are positive uniaxial Hg2Cl2 crystal or positive uniaxial Hg2Br2 crystal, which belong to the tetragonal system I4 / mmm space group.

5. The wide-band infrared polarization device based on mercuric halide crystal according to claim 1, characterized in that: The wavelength transmission range of the infrared polarization device based on mercurous chloride crystal is 0.38-25μm, the transmittance in 0.8-14μm is ≥81% (uncoated), the birefringence is 0.533@4.6μm, and the refractive index dispersion equation is: Among them, n e and n o are the refractive indices of e-light and o-light respectively, λ is the wavelength, in μm; The refractive index dispersion equation of the infrared polarization device based on mercuric bromide crystal is: Among them, n e and n o are the refractive indices of e-light and o-light respectively, λ is the wavelength, and the unit is μm.

6. The wide-band infrared polarization device based on mercuric halide crystal according to claim 1, characterized in that: The structural angle θ of the infrared polarization device based on mercurous chloride crystal is: 25.93°<θ<30.61°; the structural angle θ of the infrared polarization device based on mercurous bromide crystal is: 23.29°<θ<28.25°; preferably, at different application wavelengths, the structural angle θ of the infrared polarization device is the Brewster angle of the mercurous halide single crystal at the application wavelength.

7. The wide-band infrared polarization device based on mercuric halide crystal according to claim 1, characterized in that: The device structure is as follows: the ABCDE plane is the front side of the device, and the opposite and parallel side with the same size is the back side; the AB and CD planes are the side faces of the device, and the AB and CD planes are parallel to each other; the BC plane is the bottom face of the device, and the AE plane is the top face of the device, and the BC and AE planes are parallel to each other; the ED plane is the inclined face of the device; the FG plane is the coupling face of the right-angle triangular prism and the hexagonal prism; the ABCDE plane and its opposite face are (001) crystal planes, and the optical axis is perpendicular to the ABCDE plane; the AB and CD planes are (110) crystal planes, which are the light-transmitting planes, so that the polarized light propagates perpendicular to the optical axis inside the crystal; the BC and AE planes are (-110) crystal planes; the structural angle θ and the light-transmitting aperture determine the main parameters of the crystal device, and the crystal device parameters are as follows: BF=CD=DE=AH(1) ∠BFG=θ(2)∠ABC=∠BCD=∠BAE=90°(3) CG=CD×tan(90-2θ)(4) ∠CDE=180°-2θ(5).

8. The wide-band infrared polarization device based on mercuric halide crystal according to claim 1, characterized in that: Includes one or more of the following conditions: i. The infrared polarization device also includes a housing; the housing completely seals and protects the (001) crystal plane of the device, exposing three light-transmitting surfaces for light transmission by the polarization prism; ii. The infrared polarization device is an infrared polarization beam combiner or an infrared polarization beam splitter.

9. The method for preparing a wide-band infrared polarization device based on mercuric halide crystal as claimed in any one of claims 1 to 8, comprising the steps of: orienting the mercuric halide single crystal, crystal cutting, grinding and shaping, fine polishing, prism coupling, and shell packaging to obtain the infrared polarization device.

10. The use of a wide-band infrared polarization device based on mercuric halide crystal according to any one of claims 1 to 8, characterized in that: It can be used as an infrared polarization beam combiner for polarization laser beam combining, or as an infrared polarization beam splitter for polarization laser beam splitting.

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