An infrared band optical frequency conversion element and a converter and laser using the same.

Abstract

This invention discloses an infrared optical frequency conversion element and a converter and laser using the same. It employs a nonlinear optical polycrystalline transparent ceramic. The nonlinear optical polycrystalline transparent ceramic has periodically distributed processed and unprocessed regions along the light transmission direction. The processed and unprocessed regions have different refractive indices, forming a phase grating with a periodically distributed refractive index. The processed regions provide the phase difference between the fundamental frequency light, signal light, and difference frequency light, and these processed regions do not exhibit nonlinear optical effects. This invention enables difference frequency laser output in the infrared band by adding a periodic phase method to the nonlinear optical polycrystalline ceramic to achieve optical frequency conversion.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to an infrared band optical frequency conversion element that differs from traditional nonlinear optical single crystals, as well as a converter and laser that utilize the same. Background Technology

[0002] Nonlinear optics studies the nonlinear phenomena generated in a medium under the influence of strongly coherent light and their applications. Nonlinear optical frequency conversion includes up-conversion and down-conversion of laser frequencies. Difference frequency conversion (DFC) utilizes the down-conversion effect to reduce the optical frequency and increase the wavelength, making it the most widely used method for achieving infrared laser output. The core of DFC is the nonlinear optical frequency conversion device. Currently, achieving infrared difference frequency output requires the frequency conversion device to meet phase matching requirements. The main phase matching methods are birefringence phase matching and quasi-phase matching. However, both of these methods impose numerous limitations on the nonlinear optical crystals, restricting their application range.

[0003] Nonlinear optical materials include single-crystal and polycrystalline ceramics. Single-crystal ceramics refer to crystals in which particles are arranged regularly and periodically in three-dimensional space, forming a single crystalline polyhedron. This structure results in long-range order of particles throughout the crystal, a continuous and consistent lattice, and anisotropy. Polycrystalline ceramics, unlike single-crystal ceramics, are inorganic materials composed of multiple fine grains separated by interfaces, forming an aggregated state. They lack long-range order and anisotropy. For nonlinear optical applications, polycrystalline transparent ceramics are relatively simpler to prepare than single-crystal ceramics, with mature growth techniques, allowing for the growth of large sizes (~meter scale), avoiding limitations related to crystal quality and size. Therefore, polycrystalline ceramics have a good foundation and promising future in the field of nonlinear optics. However, because transparent ceramics have zero birefringence, phase matching cannot be achieved. Furthermore, the internal structure of ceramics consists of polycrystalline particles with random particle size and orientation. Although random quasi-phase matching can be achieved, the frequency conversion efficiency is low, affecting practical applications.

[0004] Therefore, how to provide an infrared band optical frequency conversion element based on nonlinear optical polycrystalline transparent ceramic, as well as converters and lasers using it, is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This invention addresses the shortcomings of existing nonlinear optical frequency conversion technologies and nonlinear optical materials. Taking nonlinear optical polycrystalline transparent ceramics as the research object, it provides an infrared band optical frequency conversion element and a converter and laser that utilize it. It can realize difference frequency laser output in the infrared band. The optical frequency conversion is achieved by adding a periodic phase method in the nonlinear optical polycrystalline ceramic.

[0006] The present invention provides an infrared band optical frequency conversion element, which adopts nonlinear optical polycrystalline transparent ceramic. The nonlinear optical polycrystalline transparent ceramic has periodically distributed processed regions and unprocessed regions arranged along the light transmission direction. The processed regions and the unprocessed regions have different refractive indices, forming a phase grating with periodically distributed refractive indices. The processed regions are used to provide the phase difference between the fundamental frequency light, the signal light and the difference frequency light, and the processed regions do not have nonlinear optical effects.

[0007] This invention utilizes the periodically distributed processed and unprocessed regions within the polycrystalline ceramic of the optical frequency conversion device. The processed region has no nonlinear optical effects and only provides a phase difference, thereby blocking the "backflow" process from the difference frequency light to the fundamental frequency light. However, the processed region can still provide the phase difference between the fundamental frequency light, the signal light, and the difference frequency light, compensating for the insufficient phase mismatch of the nonlinear optical polycrystalline ceramic and achieving efficient difference frequency conversion.

[0008] Preferably, the phase grating is arranged parallel to the light transmission direction of the nonlinear optical polycrystalline transparent ceramic.

[0009] Preferably, within one grating cycle, the processed region and the unprocessed region provide a phase difference between the fundamental frequency light and the frequency-doubled light that is an odd multiple of π. By controlling the additional periodic phase difference in the damaged region, the phase matching condition is satisfied, thereby achieving effective optical frequency conversion.

[0010] Preferably, the period Λ of the phase grating is 1 a +l b , l a The width of the unprocessed region along the light transmission direction of the nonlinear optical polycrystalline transparent ceramic within a period, l b It is the width of the processing area along the light transmission direction of the nonlinear optical polycrystalline transparent ceramic.

[0011] Preferably, the processing method for the processing area of ​​the nonlinear optical polycrystalline transparent ceramic includes laser micromachining or ion etching.

[0012] Preferably, the length of the processing region is controlled according to the wavelengths of the incident fundamental frequency light, signal light, and difference frequency light, as well as the refractive index dispersion equation of the nonlinear optical polycrystalline transparent ceramic, to provide an additional periodic phase.

[0013] Preferably, the nonlinear optical polycrystalline transparent ceramic includes any one of zinc sulfide ceramic, zinc selenide ceramic, zinc telluride ceramic, gallium arsenide ceramic, and gallium selenide ceramic.

[0014] Preferably, the cross-section of the processing area is a polished surface, and is coated with a high-transmittance film for fundamental frequency light, signal light and difference frequency light, or is not coated.

[0015] The present invention also provides an infrared band optical frequency converter, comprising: a pump source, a nonlinear light modulation system, and an optical frequency conversion device arranged sequentially along the optical path; wherein the optical frequency conversion device adopts the aforementioned infrared band optical frequency conversion element;

[0016] The pump source generates fundamental frequency light; a portion of the fundamental frequency light is frequency-doubled by the nonlinear light modulation system to obtain near-infrared parametric oscillating laser, i.e., signal light; the signal light and the remaining portion of the fundamental frequency light are collinear and synchronously incident on the optical frequency conversion device, and a difference frequency is generated to obtain infrared band difference frequency laser.

[0017] Preferably, it also includes a germanium sheet and a detector; the infrared band difference frequency laser passes through the germanium sheet and is incident on the detector; the detector is used to detect the parameters of the infrared band difference frequency laser.

[0018] The present invention also provides a laser, including the aforementioned infrared band optical frequency converter, for realizing infrared band optical frequency conversion.

[0019] The infrared band optical frequency conversion element and the converters and lasers using it proposed in this invention have the following advantages compared with the prior art:

[0020] 1. This invention employs nonlinear optical polycrystalline ceramics, with periodically distributed processed and unprocessed regions within the ceramic. The processed regions exhibit no nonlinear optical effects, thus blocking the conversion process from difference frequency light to fundamental frequency light. However, these processed regions provide the phase difference between the fundamental and difference frequency light. For example, a phase grating with a periodically distributed refractive index can be formed within the nonlinear optical polycrystalline ceramic using laser processing, ion etching, or other techniques, thereby providing an additional periodic phase to compensate for the insufficient phase mismatch of the nonlinear optical polycrystalline ceramic and achieving efficient difference frequency conversion. This invention not only has a simple structure but also offers advantages such as easy processing, low cost, and large size, successfully achieving optical frequency conversion in the infrared band.

[0021] 2. This invention does not have special requirements for the structure of nonlinear optical polycrystalline ceramics. All nonlinear optical polycrystalline ceramics within their permissible transmittance range can be processed to achieve optical frequency conversion in the infrared band. There is no need to consider issues such as crystal quality and uniformity, greatly improving the advantages of mass production and application of polycrystalline ceramics.

[0022] 3. This invention does not require any additional action, such as the action of an electric field. It can achieve optical frequency conversion in the infrared band simply by processing a periodic grating in nonlinear optical polycrystalline ceramic. The method is very simple, has high processing accuracy, and is highly controllable.

[0023] 4. The phase matching method of the additional periodic phase described in this invention can optimize the nonlinear optical polycrystalline ceramic, such as selecting a polycrystalline ceramic with a large effective nonlinear coefficient, thereby improving the frequency conversion efficiency.

[0024] 5. This invention can optimize different wavelengths. By selecting an appropriate nonlinear polycrystalline ceramic according to the required wavelength and providing an additional periodic phase that matches it through processes such as laser lithography, the frequency conversion of the corresponding wavelength can be achieved. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely embodiments of the present invention, and those skilled in the art can obtain other drawings based on the provided drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of polycrystalline ceramic processing provided in Embodiment 1 of the present invention.

[0027] Figure 2 These are the periodic arrangement diagram and statistical distribution diagram of polycrystalline ZnS ceramic after photolithography provided in Embodiment 1 of the present invention.

[0028] Figure 3 This is a microscopic frequency doubling test pattern of polycrystalline ceramic after photolithography provided in Embodiment 1 of the present invention.

[0029] Figure 4 This is a schematic diagram of the infrared difference frequency laser device provided in Embodiment 1 of the present invention.

[0030] Figure 5 This is the infrared frequency conversion spectrum calculation diagram provided in Embodiment 1 of the present invention.

[0031] Figure 6 This is a comparison diagram of the output of ZnS polycrystalline ceramic with added periodic phase processing and LGN single-crystal difference frequency laser provided in Embodiment 1 of the present invention.

[0032] Figure 7 This is a comparison chart of the conversion efficiency of the ZnS polycrystalline ceramic with added periodic phase processing and the original ZnS polycrystalline ceramic difference frequency laser provided in Embodiment 1 of the present invention.

[0033] Figure 8 These are the periodic arrangement diagram and statistical distribution diagram of polycrystalline ZnSe after photolithography provided in Embodiment 2 of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The polycrystalline transparent ceramic used in this invention is a nonlinear optical ceramic. Due to the isotropic nature of polycrystalline ceramics, the frequency conversion device is cut along the growth direction of the polycrystalline ceramic using methods such as laser processing or ion beam etching. This periodically destroys the original structure inside the polycrystalline ceramic along the light transmission direction, so that the destroyed area does not have nonlinear optical effects, preventing the "backflow" of nonlinear optical frequency conversion energy. This controls the phase change between the three frequencies of fundamental frequency light, signal light, and difference frequency light. By controlling the phase difference between the fundamental frequency light, signal light, and difference frequency light, the phase relationship inside the polycrystalline ceramic is adjusted and phase matching is achieved, thus obtaining effective optical frequency conversion.

[0036] The following explains the technical terms used in this invention:

[0037] Fundamental frequency light: The first pump beam, with a frequency of ω1;

[0038] Signal light: The second pump light, with a frequency of ω2;

[0039] Difference frequency light: Output light with a frequency of ω3 = ω1 - ω2;

[0040] Infrared light: refers to light with a wavelength greater than 3.0 micrometers;

[0041] Recirculation: The process of converting difference frequency light energy into fundamental frequency light;

[0042] Grating period: also known as grating constant, is formed by periodically processing the interior of polycrystalline ceramics using techniques such as laser processing or ion etching to create gratings with periodically arranged refractive indices.

[0043] The first aspect of this invention provides an infrared band optical frequency conversion element, which adopts a nonlinear optical polycrystalline transparent ceramic. The nonlinear optical polycrystalline transparent ceramic has a periodically distributed processed region and an unprocessed region arranged inside along the light transmission direction. The refractive indices of the processed region and the unprocessed region are different, forming a phase grating with a periodically distributed refractive index. The processed region is used to provide the phase difference between the fundamental frequency light, the signal light and the difference frequency light, and the processed region does not have a nonlinear optical effect.

[0044] It should be noted that the periodically distributed phase grating of the present invention includes both the processed amorphous region and the unprocessed region. The refractive indices of these two parts are different, which is why a periodic distribution of refractive indices is formed. In the unprocessed part, there is not only a phase difference, but also an effective nonlinear effect is retained, that is, the continuous conversion of fundamental frequency light to difference frequency light is guaranteed. In the processed region, coherent superposition of nonlinear optical effects cannot be achieved, nor can the frequency conversion energy be continuously enhanced, but it can provide a phase difference between the fundamental frequency light and the difference frequency light, thereby blocking the "backflow" process of difference frequency light energy to fundamental frequency light.

[0045] In one embodiment, the phase gratings are arranged parallel to the light transmission direction of the nonlinear optical polycrystalline transparent ceramic.

[0046] In one embodiment, the processed and unprocessed regions provide a phase difference of π between the fundamental and harmonic light within one grating cycle. By controlling the additional periodic phase difference in the damaged region, phase matching conditions are satisfied, thus achieving efficient optical frequency conversion.

[0047] By changing the processing length of the damaged region, the phase difference between the fundamental frequency / signal light and the frequency-doubled light provided by the processed region within one grating cycle is made as follows: The unprocessed area provides a phase difference between the fundamental frequency / signal light and the frequency-doubled light. Both m and n are integers.

[0048] In one embodiment, the period Λ of the phase grating is 1 a +l b , l a The width of the unprocessed region along the light transmission direction of a nonlinear optical polycrystalline transparent ceramic within a period, l b It refers to the width of the processed area along the light transmission direction in nonlinear optical polycrystalline transparent ceramics. For example... Figure 1 As shown, 1 is the fundamental frequency light; 2 is the signal light; 3 is the difference frequency light; 4 is the width of the unprocessed area; 5 is the width of the processed area; 6 is the refractive index of the unprocessed area; and 7 is the refractive index of the processed area. The phase of light propagating within the polycrystalline ceramic is controlled by adjusting the processing length of the phase grating in the light transmission direction. The phase difference propagating within one grating period of the polycrystalline ceramic can be expressed as Δφ = Δk·Λ, where Δk is the phase mismatch reciprocal vector of the nonlinear optical ceramic.

[0049] In this embodiment, the width l of the unprocessed portion a =0.1-100μm, width l of the processed part b =0.1-100μm.

[0050] In one embodiment, the phase grating is obtained by processing polycrystalline ceramics, i.e., adding periodic phases. Processing methods include, but are not limited to, laser micromachining, ion etching, and other techniques that can locally disrupt polycrystalline ceramics. This embodiment creates periodically distributed processing regions by disrupting the structure of the polycrystalline ceramic itself, thus eliminating nonlinear optical effects in these regions and blocking the "backflow" process from the difference frequency light to the fundamental frequency light. However, this region can still provide the phase difference between the fundamental frequency light and the difference frequency light.

[0051] In one embodiment, the length of the processing region is controlled based on the wavelengths of the incident fundamental light, signal light, and difference light, as well as the refractive index dispersion equation of the nonlinear optical polycrystalline transparent ceramic, to provide an additional periodic phase.

[0052] In one embodiment, the nonlinear optical polycrystalline transparent ceramic includes any one of zinc sulfide ceramic, zinc selenide ceramic, zinc telluride ceramic, gallium arsenide ceramic, and gallium selenide ceramic. The polycrystalline ceramic is cut along its growth direction, and the two surfaces perpendicular to the tangential direction are polished. A periodic phase grating perpendicular to the light transmission direction is fabricated using techniques such as laser lithography and ion etching. Based on the wavelengths of the incident fundamental light, signal light, and difference frequency light, and the refractive index dispersion equation of the nonlinear optical polycrystalline ceramic, the length of the fabricated region is controlled to provide an additional periodic phase, thereby satisfying the phase matching condition and achieving frequency conversion in the infrared band.

[0053] In one embodiment, the cross-section of the processing area is a polished surface, and is coated with a high-transmittance film for fundamental frequency light, signal light, and difference frequency light, or is not coated.

[0054] In one embodiment, the light transmission direction length of the nonlinear optical polycrystalline ceramic is 0.1-100 mm, more preferably 3-10 mm, and the cross-section of the polycrystalline ceramic is circular, square, or any shape.

[0055] The present invention will be further described below with reference to the accompanying drawings and embodiments, but is not limited thereto.

[0056] Example 1: ZnS polycrystalline ceramic infrared optical frequency conversion device:

[0057] Fabrication process of optical frequency conversion device: ZnS polycrystalline ceramic is used, and it is cut along the (001)Z direction of the polycrystalline ceramic growth direction. A grating structure with a periodic refractive index distribution is formed in the light transmission direction Z direction by laser etching. The periodic phase is added as shown in the schematic diagram. Figure 1 As shown. The photolithographic region provides an additional periodic phase, where both the processed and unprocessed areas are 35 or 30 μm wide. Statistical analysis of the periodic processing distribution shows relatively small errors, such as... Figure 2As shown in the figures, Figure (a) is the microstructure with a processing period of 70 μm; Figure (b) is the microstructure with a processing period of 60 μm; Figure (c) is the statistical distribution of the actual period size with a processing period of 70 μm; and Figure (d) is the statistical distribution of the actual period size with a processing period of 60 μm. The additional periodic phase difference between the fundamental frequency light, signal light, and difference frequency light provided by the processing area is π. The length of the polycrystalline ceramic in the entire processing area is 3 mm, the cross-section is 5 mm × 5 mm, and the light-transmitting surface is polished. The frequency doubling capability of the processed polycrystalline ceramic was tested using a 1030 nm femtosecond laser. After microscopic observation, the frequency doubling capability of the processed area was zero, only providing a phase difference, while the unprocessed area had a very good frequency doubling capability, such as... Figure 3 As shown.

[0058] Experimental setup such as Figure 4 As shown, it consists of a pump source, a nonlinear optical modulation system, and ZnS polycrystalline ceramic. The pump source generates a first laser beam (fundamental frequency light, frequency ω1). Part of the laser beam is passed through the nonlinear optical modulation system to generate frequency-doubled light, obtaining near-infrared parametric oscillating laser (signal light, frequency ω2). The near-infrared parametric oscillating laser and the remaining part of the laser beam are collinear and synchronously incident on the optical frequency conversion device, generating a difference frequency (frequency ω3 = ω1 - ω2), thus obtaining infrared band difference frequency laser.

[0059] In the aforementioned infrared-band difference-frequency laser based on ZnS polycrystalline ceramic, the nonlinear optical modulation system includes a first half-wave plate, a telescope system, an optical parametric oscillation system, and a convex lens arranged sequentially along the transmission direction of the laser beam. The laser beam generated by the pump source passes sequentially through the first half-wave plate, the telescope system, and the optical parametric oscillation system. A portion of this beam then passes through the optical parametric oscillation system to generate near-infrared optical parametric oscillating laser. The remaining portion of the laser beam and the near-infrared optical parametric oscillating laser are synchronously incident on the convex lens for focusing before being incident on the ZnS polycrystalline ceramic. A difference frequency is generated in the ZnS polycrystalline ceramic, producing a tunable infrared-band difference-frequency laser. This infrared-band difference-frequency laser passes through a germanium plate and is incident on a detector. The detector is used to detect the parameters of the infrared-band difference-frequency laser.

[0060] In this embodiment, the frequency doubling crystal is a single crystal potassium titanium phosphate (KTP), with the cutting angle being optically polished on the light-transmitting surface, and either uncoated or coated. If coated, it is coated with a dielectric film that is highly transparent to pump light and frequency doubling light; its cutting angle, i.e., the angle between the light-transmitting direction of the crystal and the Z-axis direction of the KTP crystal, is 90°, and its azimuth angle, i.e., the angle between the projection of the light-transmitting direction of the crystal onto the XY plane and the X-axis, is 23.5°; the crystal length can be 1-20 mm, preferably 5 mm.

[0061] Increasing the pump power can achieve 4.0-10.0μm infrared laser output, with output wavelengths such as... Figure 5 As shown.

[0062] Compared to traditional nonlinear optical single crystals, ZnS polycrystalline ceramics with added periodic phases exhibit superior overall performance, particularly the mid-infrared nonlinear optical crystal La3Nb. 0.5 Ga 5.5 O 14 (LGN) was used as a reference, and all adopted Figure 4 Using the same experimental setup, based on difference frequency technology, at 5.4 micrometers, the difference frequency laser output energy of ZnS polycrystalline ceramic is 2.8 times that of LGN single crystal. Figure 6 As shown.

[0063] Meanwhile, to better compare the advantages of adding a periodic phase in this invention, this embodiment compares the difference-frequency laser output of ZnS polycrystalline ceramics with added periodic phases and those of the original ZnS polycrystalline ceramics. The ZnS polycrystalline ceramics with added periodic phases exhibit higher output energy, and in the 4.3 to 9.8 micrometer wavelength range, the conversion efficiency is 7-18 times that of the original ZnS polycrystalline ceramics. Figure 7 As shown.

[0064] This invention not only demonstrates the advantages of ZnS polycrystalline ceramics with added periodic phases compared to single crystals, but also shows a significant improvement in difference frequency laser output compared to the original polycrystalline ceramics.

[0065] Example 2: ZnSe polycrystalline ceramic infrared optical frequency conversion device:

[0066] ZnSe polycrystalline ceramic has dimensions of 5×5×10mm. 3 In each cycle, the width of both the processed and unprocessed regions is 42.6 μm. The phase difference between the fundamental frequency light, signal light, and frequency-doubled light provided by the processed region is π. Increasing the pump power can achieve laser output in a wide-tunable infrared band. The device processing cycle is as follows: Figure 8 As shown. The remaining structure of the infrared band optical frequency conversion device in this embodiment is the same as in Embodiment 1.

[0067] Example 3: ZnTe polycrystalline ceramic infrared optical frequency conversion device:

[0068] The ZnTe polycrystalline ceramic has dimensions of 5×5×10mm. 3 In each cycle, the width of both the processed and unprocessed regions is 30-40 μm. The phase difference between the fundamental and frequency-doubled light provided by the processed region is π. By increasing the pump power, laser output in a wide-tunable infrared band can be achieved. The remaining structure of the infrared band optical frequency conversion device in this embodiment is the same as in Embodiment 1.

[0069] Example 4: GaAs polycrystalline ceramic infrared optical frequency conversion device:

[0070] The GaAs polycrystalline ceramic has dimensions of 5×5×10mm. 3 In each cycle, the width of both the processed and unprocessed regions is 20-35 μm. The phase difference between the fundamental and frequency-doubled light provided by the processed region is π. By increasing the pump power, laser output in a wide-tunable infrared band can be achieved. The remaining structure of the infrared band optical frequency conversion device in this embodiment is the same as in Embodiment 1.

[0071] Example 5: GaSe polycrystalline ceramic infrared optical frequency conversion device:

[0072] The GaSe polycrystalline ceramic has dimensions of 5×5×10mm. 3 In each cycle, the width of both the processed and unprocessed regions is 20-40 μm. The phase difference between the fundamental and frequency-doubled light provided by the processed region is π. By increasing the pump power, laser output in a wide-tunable infrared band can be achieved. The remaining structure of the infrared band optical frequency conversion device in this embodiment is the same as in Embodiment 1.

[0073] A second aspect of the present invention also provides an infrared band optical frequency converter, comprising: a pump source, a nonlinear optical modulation system, and an optical frequency conversion device arranged sequentially along an optical path; the optical frequency conversion device employs an infrared band optical frequency conversion element of the first aspect of the present invention; the pump source generates fundamental frequency light; a portion of the fundamental frequency light is frequency-doubled by the nonlinear optical modulation system to obtain near-infrared parametric oscillation laser, i.e., signal light; the signal light and the remaining portion of the fundamental frequency light are collinear and synchronously incident on the optical frequency conversion device, generating a difference frequency to obtain an infrared band difference frequency laser.

[0074] In one embodiment, such as Figure 4 As shown, the nonlinear optical modulation system includes a first half-wave plate λ / 2, a telescope system TS, optical parametric oscillation systems KTP / SHG and KTP / OPO, and convex lenses L3 and L4 arranged sequentially along the transmission direction of the fundamental frequency light. A laser beam with a pump source Nd:YAG laser has a wavelength of λ = 1064 nm. After passing through the first half-wave plate λ / 2, the telescope system, and the optical parametric oscillation system, a portion of the laser beam passes through the optical parametric oscillation system KTP / OPO to generate near-infrared optical parametric oscillation laser. The remaining portion of the laser beam and the near-infrared optical parametric oscillation laser are synchronously incident on the convex lens for focusing and then incident on the optical frequency conversion ceramic device sample. Because the polycrystalline ceramic in the optical frequency conversion device has periodically distributed processed and unprocessed regions, the processed region has no nonlinear optical effects, thus blocking the "backflow" process from the difference frequency light to the fundamental frequency light. However, the processed region can still provide the phase difference between the fundamental frequency light, the signal light, and the difference frequency light, compensating for the insufficient phase mismatch of the nonlinear optical polycrystalline ceramic and achieving efficient difference frequency conversion.

[0075] In one embodiment, the device further includes a germanium wafer and a detector; infrared-band difference frequency laser passes through the germanium wafer and is incident on the detector; the detector is used to detect the parameters of the infrared-band difference frequency laser.

[0076] A third aspect of the present invention also provides a laser, including an infrared band optical frequency converter of the second aspect of the present invention, for realizing infrared band optical frequency conversion.

[0077] The present invention provides a detailed description of an infrared band optical frequency conversion element and its application converters and lasers. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

[0078] In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without necessarily requiring or implying any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. An infrared band optical frequency conversion element, characterized in that: A nonlinear optical polycrystalline transparent ceramic is employed, wherein the interior of the nonlinear optical polycrystalline transparent ceramic has periodically distributed processed and unprocessed regions along the light transmission direction. The processed and unprocessed regions have different refractive indices, forming a phase grating with a periodically distributed refractive index. The processed regions are used to provide the phase difference between the fundamental frequency light, the signal light, and the difference frequency light, and the processed regions do not have nonlinear optical effects. The length of the processed regions is controlled according to the wavelengths of the incident fundamental frequency light, signal light, and difference frequency light, as well as the refractive index dispersion equation of the nonlinear optical polycrystalline transparent ceramic, to provide an additional periodic phase.

2. The infrared band optical frequency conversion element according to claim 1, characterized in that, The phase gratings are arranged parallel to the light transmission direction of the nonlinear optical polycrystalline transparent ceramic.

3. The infrared band optical frequency conversion element according to claim 1, characterized in that, Within one grating cycle, the processed region and the unprocessed region provide a phase difference between the fundamental frequency light and the frequency-doubled light. π An odd multiple of.

4. The infrared band optical frequency conversion element according to claim 1, characterized in that, The period of the phase grating Ʌ = l a + l b , l a It is the width of the unprocessed region along the light transmission direction of the nonlinear optical polycrystalline transparent ceramic within one cycle. l b It is the width of the processing area along the light transmission direction of the nonlinear optical polycrystalline transparent ceramic.

5. The infrared band optical frequency conversion element according to claim 1, characterized in that, The processing methods for the processing area of ​​the nonlinear optical polycrystalline transparent ceramic include laser micromachining or ion etching.

6. The infrared band optical frequency conversion element according to claim 1, characterized in that, The nonlinear optical polycrystalline transparent ceramic includes any one of zinc sulfide ceramics, zinc selenide ceramics, zinc telluride ceramics, gallium arsenide ceramics, and gallium selenide ceramics.

7. The infrared band optical frequency conversion element according to claim 1, characterized in that, The cross-section of the processing area is a polished surface, and is coated with a high-transmittance film for fundamental frequency light, signal light, and difference frequency light, or is not coated.

8. An infrared band optical frequency converter, characterized in that, include: A pump source, a nonlinear light modulation system, and an optical frequency conversion device are arranged sequentially along the optical path; the optical frequency conversion device is an infrared band optical frequency conversion element according to any one of claims 1-7. The pump source generates fundamental frequency light; a portion of the fundamental frequency light is frequency-doubled by the nonlinear light modulation system to obtain near-infrared parametric oscillating laser, i.e., signal light; the signal light and the remaining portion of the fundamental frequency light are collinear and synchronously incident on the optical frequency conversion device, and a difference frequency is generated to obtain infrared band difference frequency laser.

9. A laser, characterized in that, The invention includes an infrared band optical frequency converter as described in claim 8, used to realize infrared band optical frequency conversion.

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