Infrared band optical frequency conversion element and converter and laser using same

Abstract

The invention discloses an infrared band optical frequency conversion element and a converter and a laser using the infrared band optical frequency conversion element, nonlinear optical polycrystalline transparent ceramic is adopted, and a processing area and an unprocessed area which are periodically and regularly distributed are arranged in the nonlinear optical polycrystalline transparent ceramic in the light passing direction. The refractive indexes of the processing area and the unprocessed area are different, so that a phase grating with periodically distributed refractive indexes is formed; the processing area is used for providing phase differences among the fundamental frequency light, the signal light and the difference frequency light, and the processing area does not have a nonlinear optical effect. Difference frequency laser output of an infrared band can be realized, and optical frequency conversion is realized in nonlinear optical polycrystalline ceramic by adopting a periodic phase adding method.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to an infrared band optical frequency conversion element different from a traditional nonlinear optical single crystal, and a converter and a laser using the same. Background Art

[0002] Nonlinear optics is the study of nonlinear phenomena and their applications produced by media under the action of strong coherent light. Nonlinear optical frequency conversion includes up-conversion and down-conversion of laser frequency. Among them, difference frequency technology uses its frequency down-conversion effect to achieve the effect of reducing optical frequency and increasing wavelength. It is currently the most widely used means to achieve infrared laser output. The core foundation of difference frequency technology is nonlinear optical frequency conversion devices. At present, the requirement for achieving infrared difference frequency output is that the frequency conversion device needs to meet phase matching, and the main phase matching methods are birefringence phase matching and quasi-phase matching. However, the above two phase matching methods have many restrictions on nonlinear optical crystals, which limits the scope of application.

[0003] Nonlinear optical materials include single crystals and polycrystalline ceramics. Among them, single crystal refers to the particles inside the crystal body arranged regularly and periodically in three-dimensional space to form a single crystal polyhedron. This structure makes the particle arrangement of the single crystal in the whole crystal long-range orderly, the lattice continuous and consistent, and at the same time has the characteristics of anisotropy. Polycrystalline ceramics are different from single crystals. Polycrystalline ceramics are an inorganic material composed of multiple tiny grains. These grains are separated from each other by interfaces to form an aggregated state, and do not have the characteristics of long-range order and anisotropy. For nonlinear optical polycrystalline transparent ceramics, polycrystalline ceramics are relatively simple to prepare compared with single crystals, and the growth technology is mature. Large sizes (~ meter level) can be grown, avoiding problems such as crystal quality and size limitations. Therefore, polycrystalline ceramics have a good application foundation and prospects in the field of nonlinear optics. However, since the birefringence of transparent ceramics is zero, phase matching cannot be achieved, and the ceramics are polycrystalline particles, and the particle size and direction are mostly randomly distributed. Although random quasi-phase matching can be produced, its frequency conversion efficiency is low, which affects practical applications.

[0004] Therefore, how to provide an infrared band optical frequency conversion element based on nonlinear optical polycrystalline transparent ceramics and a converter and laser using the same is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the invention

[0005] Aiming at the deficiencies of existing nonlinear optical frequency conversion technology and nonlinear optical materials, the present invention takes nonlinear optical polycrystalline transparent ceramics as the research object and provides an infrared band optical frequency conversion element and a converter and laser using the same, which can realize difference frequency laser output in the infrared band and realize optical frequency conversion in nonlinear optical polycrystalline ceramics by adding a periodic phase method.

[0006] The present invention provides an infrared band optical frequency conversion element, which adopts nonlinear optical polycrystalline transparent ceramics. The nonlinear optical polycrystalline transparent ceramics are provided with periodically regularly distributed processed areas and unprocessed areas along the light transmission direction. The refractive indexes of the processed areas and the unprocessed areas are different, forming a phase grating with a periodic distribution of refractive indices; the processed areas are used to provide a phase difference between fundamental frequency light, signal light and difference frequency light, and the processed areas do not have a nonlinear optical effect.

[0007] According to the present invention, the polycrystalline ceramic in the optical frequency conversion device is provided with periodically distributed processed and unprocessed areas; the processed area has no nonlinear optical effect and only provides a phase difference, thereby blocking the "backflow" process of the difference frequency light to the fundamental frequency light, but the processed area can still provide a phase difference between the fundamental frequency light, the signal light and the difference frequency light, thereby compensating for the lack of phase mismatch of the nonlinear optical polycrystalline ceramic and realizing efficient difference frequency conversion.

[0008] Preferably, the phase gratings are arranged in parallel along the light transmission direction of the nonlinear optical polycrystalline transparent ceramic.

[0009] Preferably, the phase difference between the fundamental frequency light and the doubled frequency light provided by the processed area and the unprocessed area within one grating period is an odd multiple of π. By controlling the periodic phase difference added to the damaged area, the phase matching condition is met to achieve effective optical frequency conversion.

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

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

[0012] Preferably, the length of the processing area is controlled according to the wavelengths of the incident fundamental frequency light, signal light and difference frequency light and 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 processed 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 regulation system and an optical frequency conversion device arranged in sequence along an optical path; the optical frequency conversion device adopts the infrared band optical frequency conversion element;

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

[0017] Preferably, it further comprises 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, comprising the infrared band optical frequency converter, which is used to realize infrared band optical frequency conversion.

[0019] The infrared band optical frequency conversion element and the converter and laser using the same proposed by the present invention have the following beneficial effects compared with the prior art:

[0020] 1. The present invention adopts nonlinear optical polycrystalline ceramics, and the polycrystalline ceramics are provided with periodically regularly distributed processed and unprocessed areas; the processed area has no nonlinear optical effect, thereby blocking the conversion process of difference frequency light to fundamental frequency light, but the processed area can provide a phase difference between fundamental frequency light and difference frequency light. For example: a phase grating with a periodic distribution of refractive index can be formed inside the nonlinear optical polycrystalline ceramics through laser processing, ion etching and other technologies, thereby providing an additional periodic phase, compensating for the lack of phase mismatch of nonlinear optical polycrystalline ceramics, and realizing efficient difference frequency conversion. Not only is the structure simple, but it also has the advantages of easy processing, low cost, large size, etc., and can successfully realize optical frequency conversion in the infrared band.

[0021] 2. The present invention has no special requirements for the structure of nonlinear optical polycrystalline ceramics. All nonlinear optical polycrystalline ceramics within the allowable range of their transmittance 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, which greatly improves the advantages of mass production and application of polycrystalline ceramics.

[0022] 3. The present invention does not require the use of additional effects, such as the effect of an electric field. Optical frequency conversion in the infrared band can be achieved simply by processing a periodic grating in nonlinear optical polycrystalline ceramics. The method is very simple and has high processing accuracy and strong controllability.

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

[0024] 5. The present invention can optimize different wavelengths. It only needs to select appropriate nonlinear polycrystalline ceramics according to the required wavelength and provide an additional periodic phase matching it through processes such as laser lithography to achieve frequency conversion of the corresponding wavelength. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on the provided drawings without creative work.

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

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

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

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

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

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

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

[0033] Figure 8 It is the periodic arrangement diagram and statistical distribution diagram of the polycrystalline ceramic ZnSe after photolithography provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] The polycrystalline transparent ceramic used in the present invention is a nonlinear optical ceramic. Due to the isotropy of the polycrystalline ceramic, the frequency conversion device is cut along the growth direction of the polycrystalline ceramic by laser processing or ion beam etching, and the original structure inside the polycrystalline ceramic is periodically destroyed along the light transmission direction, so that the destroyed area has no nonlinear optical effect, and the "backflow" of nonlinear optical frequency conversion energy is prevented, thereby regulating the phase change between the three frequencies of base frequency light, signal light and difference frequency light. By controlling the phase difference of the base frequency light, signal light and difference frequency light, the phase relationship inside the polycrystalline ceramic is adjusted and phase matching is achieved, thereby obtaining effective optical frequency conversion.

[0036] The professional terms involved in the present invention are explained below:

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

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

[0039] Difference frequency light: output light, frequency is ω3=ω1-ω2;

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

[0041] Reflux: 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 laser processing or ion etching techniques to form gratings with periodic arrangements of different refractive indices.

[0043] A first aspect of an embodiment of the present invention provides an infrared band optical frequency conversion element, which uses nonlinear optical polycrystalline transparent ceramics. The nonlinear optical polycrystalline transparent ceramics are provided with periodically regularly distributed processed areas and unprocessed areas along the light transmission direction. The refractive indices of the processed areas and the unprocessed areas are different, forming a phase grating with a periodic distribution of refractive indices; the processed areas are used to provide a phase difference between fundamental frequency light, signal light and difference frequency light, and the processed areas do not have a nonlinear optical effect.

[0044] It should be noted that the periodically distributed phase grating of the present invention includes both processed amorphous areas and unprocessed areas. Since the refractive indices of these two parts are different, a periodic distribution of the refractive index 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, while in the processed area, coherent superposition of nonlinear optical effects cannot be achieved, and frequency conversion energy cannot be continuously enhanced, but a phase difference between fundamental frequency light and difference frequency light can be provided, thereby blocking the "backflow" process of difference frequency light energy to fundamental frequency light.

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

[0046] In one embodiment, the phase difference between the fundamental frequency light and the doubled frequency light provided by the processed area and the unprocessed area within one grating period is an odd multiple of π. By controlling the periodic phase difference added to the damaged area, the phase matching condition is met to achieve effective optical frequency conversion.

[0047] By changing the processing length of the damaged area, the phase difference between the fundamental frequency light / signal light and the double frequency light provided by the processing area within one grating period is The phase difference between the fundamental frequency light / signal light and the double frequency light provided by the unprocessed area is Both m and n are integers.

[0048] In one embodiment, the period of the phase grating is Λ=l a +l b , l a is the width of the unprocessed area of ​​the nonlinear optical polycrystalline transparent ceramic along the light transmission direction within a period, l b It is the width of the processing area of ​​nonlinear optical polycrystalline transparent ceramics along the light transmission direction. 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; 7 is the refractive index of the processed area. The phase of light transmitted inside the polycrystalline ceramic is controlled by controlling the processing length of the phase grating in the light transmission direction. The phase difference of the polycrystalline ceramic transmitted within one grating period can be expressed as Δφ=Δk·Λ, where Δk is the reciprocal lattice vector of the phase mismatch of the nonlinear optical ceramic.

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

[0050] In one embodiment, the phase grating is obtained by processing polycrystalline ceramics, that is, adding a periodic phase; the processing method includes but is not limited to laser micromachining, ion etching and other technologies that can achieve local destruction of polycrystalline ceramics. In this embodiment, the structure of the polycrystalline ceramic itself is destroyed to form a periodically regularly distributed processing area, so that the processing area does not have a nonlinear optical effect, thereby blocking the "backflow" process from the difference frequency light to the fundamental frequency light, but the area can still provide a phase difference between the fundamental frequency light and the difference frequency light.

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

[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. Cutting is performed along the growth direction of the polycrystalline ceramic, and two surfaces perpendicular to the cutting direction are polished. Along the light transmission direction, a periodic phase grating perpendicular to the light transmission direction is processed by laser lithography, ion etching and other technologies. According to the wavelength of the incident fundamental frequency light, signal light and difference frequency light and the refractive index dispersion equation of the nonlinear optical polycrystalline ceramic, the length of the processing area is controlled to provide an additional periodic phase, thereby satisfying the phase matching condition and realizing frequency conversion in the infrared band.

[0053] In one embodiment, the cross section of the processed 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 length of the nonlinear optical polycrystalline ceramic in the light transmission direction 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 band optical frequency conversion device:

[0057] The preparation process of the optical frequency conversion device: ZnS polycrystalline ceramics are used, and the processing is cut along the Z direction of the polycrystalline ceramic growth direction (001). The grating structure with periodic distribution of refractive index is formed by laser etching in the Z direction of the light transmission direction. The schematic diagram of adding periodic phase processing is shown in the figure. Figure 1 The photolithography area provides an additional periodic phase, where the width of the processed area and the unprocessed area is 35 or 30 μm. The statistical periodic processing distribution shows that the error is small, as shown in Figure 2As shown, Figure (a) is a microstructure diagram with a processing period of 70μm; Figure (b) is a microstructure diagram with a processing period of 60μm; Figure (c) is a statistical distribution diagram of the actual period size with a processing period of 70μm; Figure (d) is a statistical distribution diagram of the actual period size with a processing period of 60μm). The additional periodic phase difference of the fundamental frequency light, signal light and difference frequency light that can be provided in the processing area is π. The length of the polycrystalline ceramic in the entire processing area is 3mm, the cross-section is 5mm×5mm, and the light-transmitting surface is polished. The frequency doubling ability of the processed polycrystalline ceramics was tested using a 1030nm femtosecond laser. After microscopic observation, the frequency doubling ability of the processed area was zero, and only a phase difference was provided, while the unprocessed area had a very good frequency doubling ability, as shown Figure 3 shown.

[0058] Experimental setup Figure 4 As shown, it is composed of a pump source, a nonlinear light regulation system and ZnS polycrystalline ceramics; the pump source generates a first laser beam (fundamental frequency light, frequency is ω1); part of the laser beam passes through the nonlinear light regulation system to generate frequency-doubled light, and obtains a near-infrared optical parametric oscillation laser (signal light, frequency is ω2); the near-infrared optical parametric oscillation laser and the remaining part of the laser beam are colinear and synchronously incident on the optical frequency conversion device, and a difference frequency (frequency is ω3=ω1-ω2) is generated, and an infrared band difference frequency laser is obtained.

[0059] In the above-mentioned infrared band difference frequency laser based on ZnS polycrystalline ceramic, the nonlinear light regulation system includes a first half-wave plate, a telescope system, an optical parametric oscillator system and a convex lens arranged in sequence along the transmission direction of the laser beam; after the laser beam generated by the pump source passes through the first half-wave plate, the telescope system and the optical parametric oscillator system in sequence, a part of it passes through the optical parametric oscillator system to generate near-infrared optical parametric oscillator laser; the remaining part of the laser beam and the near-infrared optical parametric oscillator laser are synchronously incident on the convex lens for focusing, and then incident on the ZnS polycrystalline ceramic. A difference frequency is generated in the ZnS polycrystalline ceramic, and a tunable infrared band difference frequency laser is generated. After the infrared band difference frequency laser passes through the germanium plate, it is incident on the 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 titanyl phosphate (KTP), and the cutting angle is optical polishing of the light-transmitting surface, without coating or coating. If coated, it is coated with a dielectric film with high transparency to pump light and frequency doubling light; its cutting angle, that is, the angle between the light-transmitting direction of the crystal and the Z-axis direction of the KTP crystal is 90°, and the azimuth angle, that is, the angle between the projection of the light-transmitting direction of the crystal on the XY plane and the X-axis is 23.5°; the crystal length can be 1-20 mm, preferably, the crystal length is 5 mm.

[0061] By increasing the pump power, 4.0-10.0μm infrared laser output can be achieved, and the output wavelength is as follows Figure 5 shown.

[0062] Compared with traditional nonlinear optical single crystals, ZnS polycrystalline ceramics with periodic phases have a better comprehensive performance than mid-infrared nonlinear optical crystals La3Nb 0.5 Ga 5.5 O 14 (LGN) was used as the reference object. Figure 4 With the same experimental setup, based on the difference frequency technology, at 5.4 μm, the difference frequency laser output energy of ZnS polycrystalline ceramics is 2.8 times that of LGN single crystals. Figure 6 shown.

[0063] At the same time, in order to better compare the advantages of adding a periodic phase in the present invention, this embodiment compares the difference frequency laser output of the ZnS polycrystalline ceramic with a periodic phase added and the original ZnS polycrystalline ceramic. The ZnS polycrystalline ceramic with a periodic phase added has a higher output energy. In the range of 4.3 to 9.8 microns, the conversion efficiency is 7-18 times that of the original ZnS polycrystalline ceramic. Figure 7 shown.

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

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

[0066] ZnSe polycrystalline ceramic size 5×5×10mm 3 , where the width of the processed area and the unprocessed area in each cycle is 42.6μm. The phase difference between the fundamental frequency light, signal light and frequency-doubled light provided by the processed area is π. Increasing the pump power can achieve wide-tuned infrared band laser output. The device processing cycle is as follows: Figure 8 The remaining structures of the infrared band optical frequency conversion device in this embodiment are the same as those in the first embodiment.

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

[0068] ZnTe polycrystalline ceramic size 5×5×10mm 3 , wherein the width of the processed area and the unprocessed area in each cycle is 30-40 μm, the phase difference between the fundamental frequency light and the double frequency light provided by the processed area is π, and increasing the pump power can achieve wide-tuning infrared band laser output. The remaining structure of the infrared band optical frequency conversion device in this embodiment is the same as that in embodiment 1.

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

[0070] GaAs polycrystalline ceramic size 5×5×10mm 3 , wherein the width of the processed area and the unprocessed area in each cycle is 20-35 μm, the phase difference between the fundamental frequency light and the double frequency light provided by the processed area is π, and increasing the pump power can achieve wide-tuning infrared band laser output. The remaining structure of the infrared band optical frequency conversion device in this embodiment is the same as that in embodiment 1.

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

[0072] GaSe polycrystalline ceramic size 5×5×10mm 3 , wherein the width of the processed area and the unprocessed area in each cycle is 20-40 μm, the phase difference between the fundamental frequency light and the double frequency light provided by the processed area is π, and increasing the pump power can achieve wide-tuning infrared band laser output. The remaining structure of the infrared band optical frequency conversion device in this embodiment is the same as that in embodiment 1.

[0073] The second aspect of the embodiment of the present invention also provides an infrared band optical frequency converter, including: a pump source, a nonlinear light regulation system and an optical frequency conversion device arranged in sequence along the optical path; the optical frequency conversion device adopts an infrared band optical frequency conversion element of the first aspect of the embodiment; the pump source generates fundamental frequency light; part of the fundamental frequency light is frequency-doubled by the nonlinear light regulation system to obtain near-infrared optical parametric oscillation laser, that is, signal light; the signal light and the remaining part of the fundamental frequency light are colinear and synchronously incident on the optical frequency conversion device, and a difference frequency is generated to obtain an infrared band difference frequency laser.

[0074] In one embodiment, Figure 4 As shown, the nonlinear optical regulation system includes a first half-wave plate λ / 2, a telescope system TS, an optical parametric oscillator system KTP / SHG and KTP / OPO, and convex lenses L3 and L4 arranged in sequence along the transmission direction of the fundamental frequency light; the laser beam λ=1064nm generated by the pump source Nd:YAG laser passes through the first half-wave plate λ / 2, the telescope system and the optical parametric oscillator system in sequence, and a part of the laser beam passes through the optical parametric oscillator system KTP / OPO to generate a near-infrared optical parametric oscillator laser; the remaining part of the laser beam and the near-infrared optical parametric oscillator laser are synchronously incident on the convex lens for focusing, and then incident on the optical frequency conversion ceramic device sample. Since the polycrystalline ceramic in the optical frequency conversion device is provided with periodically regularly distributed processed and unprocessed areas; the processed area has no nonlinear optical effect, thereby blocking the "backflow" process of the difference frequency light to the fundamental frequency light, but the processed area can still provide the phase difference between the fundamental frequency light, the signal light and the difference frequency light, making up for the lack of phase mismatch of the nonlinear optical polycrystalline ceramic, and realizing efficient difference frequency conversion.

[0075] In one embodiment, it also includes a germanium plate and a detector; the infrared band difference frequency laser passes through the germanium plate 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 embodiments of the present invention further provides a laser, comprising an infrared band optical frequency converter according to the second aspect of the embodiments, for realizing infrared band optical frequency conversion.

[0077] The infrared band optical frequency conversion element and the converter and laser using the same provided by the present invention are introduced in detail above. The principle and implementation mode of the present invention are explained in this article by using specific examples. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

[0078] In this article, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the statement "comprise a ..." do not exclude the presence of other identical elements in the process, method, article or device including the elements.

Claims

1. An infrared band optical frequency conversion element, Features: A nonlinear optical polycrystalline transparent ceramic is used, wherein a periodically regularly distributed processed area and an unprocessed area are arranged inside the nonlinear optical polycrystalline transparent ceramic along the light transmission direction, and the refractive indexes of the processed area and the unprocessed area are different, forming a phase grating with a periodic distribution of the refractive index; the processed area is used to provide a phase difference between the fundamental frequency light, the signal light and the difference frequency light, and the processed area has no nonlinear optical effect.

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

3. The infrared band optical frequency conversion element according to claim 1, It is characterized in that The phase difference between the fundamental frequency light and the doubled frequency light provided by the processed area and the unprocessed area within one grating period is an odd multiple of π.

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

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

6. The infrared band optical frequency conversion element according to claim 1, It is characterized in that According to the wavelengths of the incident fundamental frequency light, signal light and difference frequency light and the refractive index dispersion equation of the nonlinear optical polycrystalline transparent ceramic, the length of the processing area is controlled to provide an additional periodic phase.

7. The infrared band optical frequency conversion element according to claim 1, It is characterized in that 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.

8. The infrared band optical frequency conversion element according to claim 1, It is characterized in that The cross section of the processed 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.

9. An infrared band optical frequency converter, It is characterized in that include: A pump source, a nonlinear light regulation system and an optical frequency conversion device are sequentially arranged along the optical path; the optical frequency conversion device adopts an infrared band optical frequency conversion element as described in any one of claims 1 to 8; The pump source generates fundamental frequency light; part of the fundamental frequency light is frequency-doubled by the nonlinear light regulation system to obtain near-infrared optical parametric oscillation laser, i.e., signal light; the signal light and the remaining part of the fundamental frequency light are colinear and synchronously incident on the optical frequency conversion device, and a difference frequency is generated to obtain an infrared band difference frequency laser.

10. A laser, It is characterized in that It comprises an infrared band optical frequency converter as described in claim 9, which is used to realize infrared band optical frequency conversion.

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