Miniaturized laser frequency doubling device

Abstract

The utility model discloses a miniaturized laser frequency doubling device, which comprises a shell (1), a crystal (15) is arranged in the middle of the rear row in the shell (1), and an incident cavity mirror (M1) and an emergent cavity mirror (M2) are respectively arranged on the left side and the right side of the crystal (15); a first reflection cavity mirror (M3) and a second reflection cavity mirror (M4) are arranged on the left side and the right side of the front row respectively; pump light enters the resonant cavity through the left side window mirror (4) of the shell (1), penetrates the incidence cavity mirror (M1), is subjected to frequency multiplication through the crystal (15) and then penetrates the emergence cavity mirror (M2) and the right side window mirror (2) to output frequency multiplication light. The light which is subjected to frequency multiplication by the crystal (15) and is reflected by the emergent cavity mirror (M2) is sequentially reflected for multi-beam interference and then enters the incident cavity mirror (M1); reflected fundamental frequency light of the incident cavity mirror (M1) enters the HC cavity locking device. By adopting the butterfly-shaped cavity design that optical devices are arranged in multiple rows and columns, the size of the resonant cavity is greatly reduced, and integration and miniaturization of products are facilitated. The application range is wide.

Description

TECHNICAL FIELD

[0001] The utility model belongs to optical and electronic structure technical field, especially relate to a miniaturized laser frequency multiplication device. BACKGROUND

[0002] The full name of frequency multiplication SHG is Secondary Harmonic Generation, which is a second-order nonlinear optical phenomenon, also known as frequency multiplication. SHG is a nonlinear optical phenomenon, which refers to the interaction of two identical frequency photons (usually laser photons) with a nonlinear medium at the same time, generating a photon with a frequency twice that of the input light. For example, if the frequency of the input light is ω, the frequency of the output light is 2ω. This phenomenon only occurs when the medium has a non-central symmetric structure, because only in this structure, the second-order nonlinear susceptibility χ of the medium is not zero. From the quantum point of view, the SHG process can be understood as the "annihilation" of two photons and the "generation" of a higher energy photon. In this process, the laws of conservation of energy and momentum must be satisfied. Specifically, the total energy of the two input photons is equal to the energy of the output photon, that is where is the reduced Planck constant.

[0003] Phase matching is a key condition in the SHG process. In order to make the second harmonic signal strong enough, the phase of the input light and the output light must be matched. Phase matching can be achieved by adjusting the propagation direction of the light, the refractive index of the medium, or using a special crystal structure. In practical applications, the phase matching condition is usually satisfied by selecting appropriate crystal materials and optical path design. The realization of SHG phenomenon depends on materials with high second-order nonlinear susceptibility. Common nonlinear optical materials include crystals, polymers and nanomaterials. The non-central symmetric structure of these materials enables them to effectively generate second harmonic.

[0004] The commonly used frequency doubling material of the crystal is KTP (potassium titanyl phosphate, KTiOPO4), which has a large nonlinear coefficient, a large allowable temperature and an allowable angle; the commonly used frequency doubling material of the crystal is also BBO (low-temperature phase barium borate (β-BaB2O4)), which has a wide phase matching wavelength range (409.6-3500nm), a wide transmittance wavelength range (190-3500nm), a high frequency doubling conversion efficiency (equivalent to 6 times that of KDP crystal), good optical uniformity, high damage threshold and wide acceptance angle (about 55℃).

[0005] The current laser frequency multiplication device adopts optical devices arranged side by side along a line of light rays, and the volume of the resonant cavity is large, especially the longitudinal dimension is too large, which is greatly limited in the application of product integration and miniaturization. SUMMARY

[0006] The utility model discloses a miniaturized laser frequency multiplication device adopts the design of the butterfly cavity of optical device multi-line multi-column arrangement, greatly reduces the volume of resonant cavity, and is favorable to product integration miniaturization.

[0007] The utility model provides a technical scheme as follows:

[0008] A miniaturized laser frequency multiplication device, including the shell 1, the incident cavity mirror M1, the emission cavity mirror M2, the first reflection cavity mirror M3 and the second reflection cavity mirror M4 that constitute the resonant cavity are arranged in two rows in the shell 1,

[0009] The crystal 15 is arranged in the middle of the rear row in the shell 1, and the incident cavity mirror M1 and the emission cavity mirror M2 are arranged on the left and right sides of the crystal 15 respectively; the first reflection cavity mirror M3 and the second reflection cavity mirror M4 are arranged on the left and right sides of the front row in the shell 1; the interval of the incident cavity mirror M1 and the emission cavity mirror M2 is greater than the interval of the first reflection cavity mirror M3 and the second reflection cavity mirror M4;

[0010] The pump light transmits through the left side window mirror 4 of the shell 1 and is incident to the incident cavity mirror M1, the transmitted light of the incident cavity mirror M1 enters the resonant cavity, and the frequency-doubled light is output after transmitting through the emission cavity mirror M2 and the right side window mirror 2 after frequency doubling through the crystal 15; the light reflected by the emission cavity mirror M2 after frequency doubling is reflected by the first reflection cavity mirror M3 and the second reflection cavity mirror M4 in turn and then is incident to the incident cavity mirror M1 after multi-beam interference;

[0011] The reflected light of the incident cavity mirror M1 is output as the fundamental frequency light by the left side window mirror 4 and is incident to the HC cavity device.

[0012] Preferably, the bottom of the shell 1 is provided with a five-axis adjustment mechanism 12, and the crystal 15 is mounted on the five-axis adjustment mechanism 12 through a temperature control furnace device.

[0013] Preferably, the temperature control furnace device includes a crystal base adapter plate 11, a crystal base 8, a crystal clamp 10, a crystal pressing plate 9, a heating device, a refrigeration device and a temperature control interface 5.

[0014] The crystal base adapter plate 11 is mounted on the five-axis adjustment mechanism 12, and the crystal base 8 is mounted on the crystal base adapter plate 11; the crystal clamp 10 is mounted on the crystal base 8 and is pressed tightly through the crystal pressing plate 9.

[0015] The heating device is arranged in the crystal base 8 and below the crystal clamp 10, and the temperature control interface 5 is arranged on the shell of the shell 1 and is electrically connected to the heating device and the refrigeration device.

[0016] Preferably, the front and rear sides of the shell 1 are respectively provided with a first groove 3 and a second groove 7.

[0017] Preferably, the rear side of the shell 1 is provided with a window corresponding to the position of the internal five-axis adjustment mechanism 12, and the window is provided with a cover plate 6.

[0018] Preferably, the first reflective mirror M3 or the second reflective mirror M4 is provided with a piezoelectric transducer PZT; the back of the second reflective mirror M4 or the first reflective mirror M3 is provided with a first attenuation sheet AS1 and a first photodetector PD1.

[0019] Preferably, the HC lock cavity device comprises a second quarter-wave plate QWP2, a polarization beam splitter PBS, a second attenuation sheet AS2, a third attenuation sheet AS3, a second photodetector PD2, a third photodetector PD3 and a mirror M.

[0020] The fundamental frequency light output by the left side window mirror 4 is filtered by the second quarter-wave plate QWP2, is split by the polarization beam splitter PBS, one of the beams is incident on the second photodetector PD2 through the second attenuation sheet AS2, and the other beam is reflected by the mirror M, is incident on the third photodetector PD3 through the third attenuation sheet AS3.

[0021] Preferably, the left side window mirror 4 comprises a first quarter-wave plate QWP1, a first half-wave plate HWP1 and a convex lens L.

[0022] The pump light emitted by the semiconductor laser amplifier TA is incident on the incident mirror M1 through the first quarter-wave plate QWP1, the first half-wave plate HWP1 and the convex lens L in sequence.

[0023] Preferably, the right side window mirror 2 comprises a low-pass filter sheet LF.

[0024] Preferably, the incident mirror M1, the exit mirror M2, the first reflective mirror M3 and the second reflective mirror M4 are respectively installed on the bottom of the shell 1 through a boss 13.

[0025] As can be seen from the technical scheme provided by the above-mentioned utility model, the utility model embodiment provides a kind of miniaturization laser frequency doubling device, adopts the butterfly-shaped cavity design of optical device multi-line multi-column arrangement, greatly reduce the volume of resonant cavity, benefit product integration miniaturization.It is convenient to use and widely applicable. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical scheme of the embodiment of the utility model, the drawings needed in the embodiment description will be briefly introduced as follows, and obviously, the drawings in the following description are only some embodiments of the utility model, and those skilled in the art can obtain other drawings according to these drawings without creating creative labor.

[0027] Figure 1The embodiment of the utility model provides a small laser frequency multiplication device's external three-dimensional structure schematic diagram Figure 1

[0028] Figure 2 The embodiment of the utility model provides a small laser frequency multiplication device's external three-dimensional structure schematic diagram Figure 2

[0029] Figure 3 The embodiment of the utility model provides a small laser frequency multiplication device's internal structure schematic view

[0030] Figure 4 The embodiment of the utility model provides a small laser frequency multiplication device's optical path principle structure schematic view. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the utility model will be clearly and completely described below with reference to the drawings in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the utility model.

[0032] Firstly, the terms possibly used in the present text are explained as follows:

[0033] The term "and / or" means either one or both, for example, X and / or Y means three cases including "X", "Y" or "X and Y".

[0034] The terms "include", "contain", "have", "possess" or other similar semantic descriptions should be interpreted as non-exclusive inclusion. For example: including certain technical feature elements (such as raw materials, components, ingredients, carriers, dosage forms, materials, sizes, parts, components, mechanisms, devices, steps, processes, methods, reaction conditions, processing conditions, parameters, algorithms, signals, data, products or articles, etc.) should be interpreted as not only including the explicitly listed certain technical feature elements, but also including other technical feature elements not explicitly listed in the art.

[0035] The term "consisting of" means excluding any technical feature elements not explicitly listed. If this term is used in the claims, the term will make the claim closed, so that it does not contain technical feature elements other than the explicitly listed technical feature elements, except for conventional impurities related thereto. If the term only appears in a certain clause of the claim, it is only limited to the elements explicitly listed in that clause, and the elements described in other clauses are not excluded from the overall claim.

[0036] ​​The term "mass parts" is used to indicate the mass ratio relationship between components, for example: if it is described that X component is x mass parts and Y component is y mass parts, it means that the mass ratio of X component to Y component is x:y; 1 mass part can represent any mass, for example: 1 mass part can represent 1 kg or 3.1415926 kg, etc. The sum of the mass parts of all components does not necessarily equal 100 parts, and can be greater than 100 parts, less than 100 parts, or equal to 100 parts. Unless otherwise specified, the parts, proportions, and percentages described herein are by mass.

[0037] Unless otherwise explicitly specified or limited, the terms "mounting", "connecting", "connecting", "fixing" and the like should be understood broadly, for example: it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be connected inside two elements. For those skilled in the art, the specific meaning of the above terms in this article can be understood according to the specific circumstances.

[0038] When the concentration, temperature, pressure, size or other parameters are expressed in the form of a numerical range, the numerical range should be understood as specifically disclosing all ranges formed by any upper limit value, lower limit value, preferred value in the numerical range, regardless of whether the range is explicitly recorded; for example, if the numerical range "2-8" is recorded, the numerical range should be interpreted as including "2-7", "2-6", "5-7", "3-4 and 6-7", "3-5 and 7", "2 and 5-7", etc. Unless otherwise specified, the numerical ranges recorded herein include all integers and fractions within the numerical range, including the end values.

[0039] The terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. The orientation or positional relationship indicated is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of description and simplification of description, and does not mean or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting herein.

[0040] The embodiments of the utility model will be described in further detail below with reference to the drawings.

[0041] Embodiments

[0042] As Figures 1 to 4As shown, a miniaturized laser frequency doubling device includes a housing 1, which includes a lower housing 16 and an upper cover 14 to form a cavity housing. Inside the housing 1, there are arranged in two rows an incident cavity mirror M1, an exit cavity mirror M2, a first reflective cavity mirror M3, a second reflective cavity mirror M4, and a crystal 15 to form a resonant cavity. Here, the resonant cavity is formed by the incident cavity mirror M1, the exit cavity mirror M2, the first reflective cavity mirror M3, and the second reflective cavity mirror M4, and the crystal 15 is arranged in the resonant cavity.

[0043] In this example, the incident cavity mirror M1 is a plano-concave cavity mirror, which is a mirror body with one concave surface and one flat surface. The reflection coefficient R1(10) = 97.3%, the transmission coefficient T1(10) = 2.7% ± 0.5%, and it can be made of fused quartz. The diameter is 12.7 mm, the center thickness is 3 mm, and the concave surface has a curvature radius R = 80 mm. The transmittance of the concave surface is T = 2.7% ± 0.5% @ 808 nm, i.e., the parallel transmittance (PT) of the concave surface is 2.7% at a wavelength of 808 nm, with an allowable error of ± 0.5%. The incident angle range is "10 degrees to 45 degrees incident". The incident angle represents the angle between the light irradiating the surface of the lens and the normal line of the lens. The transmittance of the flat surface is AR R < 0.5% @ 808 nm, i.e., the flat surface is coated with an anti-reflection film (AR), and the reflectance is less than 0.5% at a wavelength of 808 nm.

[0044] The exit cavity mirror M2 is a plano-concave cavity mirror, which is a mirror body with one concave surface and one flat surface, and is also a plano-concave dichroic mirror. The concave reflection coefficient R2(10) ≥ 99.5%, and it can be made of fused quartz. The diameter is 12.7 mm, the center thickness is 3 mm, and the concave surface has a curvature radius R = 80 mm. The concave reflectance HR R > 99.5% @ 808 nm, HT T > 97% @ 404 nm, i.e., the concave surface has a high reflectance (HR) of more than 99.5% at a wavelength of 808 nm and a high transmittance (HT) of more than 97% at a wavelength of 404 nm. The transmittance of the flat surface is AR R < 0.5% @ 404 nm, i.e., the flat surface is coated with an anti-reflection film (AR), and the reflectance is less than 0.5% at a wavelength of 404 nm. The transmission coefficient T2(10) = 97%.

[0045] The first reflective cavity mirror M3 is a flat mirror, and the reflection coefficient R3(10) ≥ 99.5%, such as single-side HR @ 750-1100 nm (R > 99.6% @ 808 nm), i.e., the lens is coated with a high reflection film (HR) on one side, and has high reflection characteristics in the wavelength range of 750-1100 nm, with a reflectance of more than 99.6% at a wavelength of 808 nm.

[0046] The second reflecting mirror M4 is a plane mirror with a reflection coefficient R4(10)≧99.5%, such as single-side HR@750-1100nm(R>99.6%@808nm), that is, the mirror is coated with a high reflection film (HR) on one side, has high reflection characteristics in the wavelength range of 750-1100nm, and the reflectivity at 808nm is greater than 99.6%.

[0047] The first reflecting mirror M3 has a first attenuating sheet AS1 and a first photodetector PD1 on the non-reflecting surface; or the second reflecting mirror M4 has a first attenuating sheet AS1 and a first photodetector PD1 on the non-reflecting surface; and the first reflecting mirror M3 or the second reflecting mirror M4 further has a piezoelectric transducer PZT.

[0048] The piezoelectric transducer PZT is generally a piezoelectric ceramic, which is used to adjust the length of the resonant cavity.

[0049] The crystal 15 is a PPKTP (periodically poled potassium titanyl phosphate) crystal, which is a key nonlinear optical crystal for frequency doubling. The PPKTP crystal is a non-naturally occurring artificial crystal. Based on the quasi-phase matching (QPM) theory, the nonlinear polarization rate of the crystal is periodically modulated to compensate for the wave vector mismatch caused by dispersion in nonlinear frequency conversion, which can greatly improve the nonlinear optical effect coefficient. In this example, an O-type third-order PPKTP crystal is used. The O-type third-order refers to the type of interaction and the order of polarization period in the nonlinear optical process. O-type indicates a specific polarization state and interaction mode in the optical process, and third-order indicates the modulation order of the polarization period.

[0050] The crystal 15 is arranged in the middle of the rear row in the shell 1, and the incident mirror M1 and the exit mirror M2 are arranged on the left and right sides of the crystal 15 respectively; the first reflecting mirror M3 and the second reflecting mirror M4 are arranged on the left and right sides of the front row in the shell 1 respectively; the distance between the incident mirror M1 and the exit mirror M2 is greater than the distance between the first reflecting mirror M3 and the second reflecting mirror M4; the specific positions need to meet the propagation route of the pump light below, including transmission and reflection.

[0051] The incident mirror M1, the exit mirror M2, the first reflecting mirror M3, and the second reflecting mirror M4 constituting the resonant cavity are arranged in a multi-row and multi-column arrangement of butterfly cavities, which greatly reduces the volume of the resonant cavity and is beneficial to product integration and miniaturization. It is easy to use and has a wide range of applications.

[0052] The pump light passes through the left side window mirror 4 of the shell 1 and is incident to the incident mirror M1. Here, the left side window mirror 4 includes a first quarter wave plate QWP1, a first half wave plate HWP1, and a convex lens L.

[0053] In this example, the first quarter wave plate QWP1 is used to change the polarization state of light, adjust the polarization of the pump laser to meet quasi-phase matching.

[0054] The first half wave plate HWP1 is used to change the polarization state of light, and the polarization of the pump laser is adjusted again to meet quasi-phase matching.

[0055] The focal length f of the convex lens L is 150 mm, which functions to focus the mode matching.

[0056] The pump light emitted by the semiconductor laser amplifier TA passes through the first quarter wave plate QWP1, the first half wave plate HWP1 and the convex lens L in turn and is incident on the incident cavity mirror M1. In this paper, the wavelength of the pump light is taken as an example.

[0057] The transmitted light through the incident cavity mirror M1 enters the resonant cavity. Here, the transmitted light refers to the light that can be transmitted from the incident cavity mirror M1, and the light that cannot be transmitted and is reflected is less, which is processed later. The transmitted light passes through the crystal 15 times and is output through the exit cavity mirror M2 and the right side window mirror 2. The wavelength of the frequency doubled light is 404 nm. Most of the transmitted light through the exit cavity mirror M2 is frequency doubled light, which is output after frequency doubling. The light reflected by the exit cavity mirror M2 after frequency doubling passes through the first reflecting mirror M3 and the second reflecting mirror M4 in turn and is reflected to perform multi-beam interference, and then is incident on the incident cavity mirror M1 again, and is reflected into the crystal 15 again. The crystal 15 is periodically polarized to realize the generation of frequency doubled laser with quasi-phase matching.

[0058] The reflected light of the incident cavity mirror M1 is output by the left side window mirror 4 to the HC locking cavity device.

[0059] In this example, the right side window mirror 2 includes a low-pass filter LF, which functions to low-pass filter and filter out the fundamental frequency light, allowing the frequency doubled light to pass through.

[0060] In this example, the HC locking cavity device includes a second quarter wave plate QWP2, a polarization beam splitter PBS, a second attenuator AS2, a third attenuator AS3, a second photodetector PD2, a third photodetector PD3 and a reflecting mirror M.

[0061] In this example, the second quarter wave plate QWP2 is used to change the polarization state of light, adjust the polarization of the pump laser to meet quasi-phase matching.

[0062] The polarization beam splitter PBS (Polarizing Beam Splitter) splits the light according to the polarization state of the light.

[0063] The first attenuator sheet AS1, the second attenuator sheet AS2, the third attenuator sheet AS3, the attenuator sheet, can be used to adjust the intensity of light, suitable for detection.

[0064] The first photoelectric detector PD1, the second photoelectric detector PD2, the third photoelectric detector PD3, the photoelectric detector, is used for detecting the optical signal.

[0065] The fundamental frequency light output by the left side window mirror 4 is filtered by the second quarter wave plate QWP2, then split by the polarizing beam splitter PBS, one of the beams is incident on the second photoelectric detector PD2 through the second attenuator sheet AS2, and the other beam is reflected by the mirror M, then incident on the third photoelectric detector PD3 through the third attenuator sheet AS3.

[0066] The detection result signals output by the second photoelectric detector PD2 and the third photoelectric detector PD3 are input to the controller, and the feedback adjustment signal is adjusted by the piezoelectric transducer PZT to adjust the length of the resonant cavity.

[0067] The mirror M is a plane mirror, the reflection wavelength of the mirror is 808nm, the reflection coefficient R4(10) is greater than or equal to 99.5%, such as single face HR@750-1100nm(R>99.6%@808nm), that is, the lens is coated with a high reflection film (HR) on one side, which has high reflection characteristics in the wavelength range of 750-1100nm, and the reflectivity at 808nm is greater than 99.6%.

[0068] A specific size structure is referred to Figure 4 The center distance between the incident mirror M1 and the exit mirror M2 is 10.2cm; the center distance between the first reflecting mirror M3 and the second reflecting mirror M4 is 6.1cm; the front and back distance between the center lines of the incident mirror M1 and the exit mirror M2 and the center lines of the three mirrors M3 and the second reflecting mirror M4 is 7.38cm.

[0069] In this example, the inner bottom of the shell 1 is provided with a five-axis adjustment mechanism 12, which can be fixed to the inner bottom of the shell 1 by bolt connection. The crystal 15 is mounted on the five-axis adjustment mechanism 12 through the temperature control furnace device. The five-axis adjustment mechanism 12 is an adjustment mechanism with 5 degrees of freedom, which can adjust the xyz three-axis rotation and xy axis translation. The position of the crystal 15 on the five-axis adjustment mechanism 12 can be fine-tuned to optimize the frequency doubling efficiency. The specific mechanical structure of the five-axis adjustment mechanism 12 is prior art or well-known technology, which can be purchased from the horlabs py005 of the Sunray Optics Company, and this patent only applies, and will not be described in detail.

[0070] In this example, the temperature control furnace device includes crystal base adapter plate 11, crystal base 8, crystal clamp 10, crystal pressure plate 9, heating device, refrigeration device and temperature control interface 5. The crystal base adapter plate 11 is installed on the five-axis adjustment mechanism 12, and the crystal base adapter plate 11 can be fixed on the terminal moving part of the five-axis adjustment mechanism 12 by bolt connection, obtaining the movement adjustment ability of 5 degrees of freedom. The crystal base 8 is installed on the crystal base adapter plate 11, which can be connected by bolt. The refrigeration device is arranged between the crystal base adapter plate 11 and the crystal base 8, and the refrigeration device can adopt a Peltier coated with silicon grease. The crystal clamp 10 is installed on the crystal base 8, which can be connected by bolt, and is pressed by the crystal pressure plate 9, which can be pressed by bolt connection. The heating device is arranged in the crystal base 8 and below the crystal clamp 10, and the heating device can adopt a thermistor.

[0071] The temperature control interface 5 is arranged on the shell of the shell 1, and is electrically connected with the heating device and the refrigeration device. At the same time, the temperature control interface 5 is also internally electrically connected with the first photoelectric detector PD3, the second photoelectric detector PD2 and the third photoelectric detector PD3; the temperature control interface 5 is also externally electrically connected with the controller of the miniaturized laser frequency doubling device, realizing the temperature control of the temperature control furnace device and the control of the length and other parameters of the resonant cavity.

[0072] In this example, the front and rear sides of the shell 1 are respectively provided with the first groove 3 and the second groove 7. Specifically, the first groove 3 and the second groove 7 are arranged at the lower part of the lower shell 16, and the miniaturized laser frequency doubling device can be fixed on the structure such as bread board by using the pressing block and other connecting structures through the first groove 3 and the second groove 7.

[0073] In this example, the rear side of the shell 1 is provided with a window corresponding to the position of the internal five-axis adjustment mechanism 12, and the window is provided with a cover plate 6. That is, the rear side of the lower shell 16 is provided with a window corresponding to the position of the internal five-axis adjustment mechanism 12, and the cover plate 6 is used to adjust the position of the crystal 15 through the five-axis adjustment mechanism 12. The cover plate 6 prevents light from entering and affecting the work.

[0074] In this example, the incident cavity mirror M1, the exit cavity mirror M2, the first reflection cavity mirror M3 and the second reflection cavity mirror M4 are respectively installed on the inner bottom of the shell 1 through a boss 13.

[0075] Working principle

[0076] SHG is a kind of second-order nonlinear optical effect, which refers to the interaction of two photons with the same frequency (fundamental frequency, ω) in a nonlinear medium, and a photon with doubled frequency (second harmonic, 2ω) is generated. The core condition is to meet the phase matching, that is, the propagation speed of the fundamental frequency light and the second harmonic light in the medium is consistent, to avoid the periodic backflow of energy due to phase mismatch. PPKTP crystal is suitable for high-power and visible light band application, and has good temperature stability. The application improves the circulating power of the fundamental frequency light by constructing a butterfly-shaped resonant cavity, so that the SHG power based on the PPKTP crystal is greatly improved. By flexibly adjusting the polarization period and temperature of the PPKTP crystal, the requirements of various laser systems can be adapted, and the progress in the fields of laser technology and quantum information is promoted. Specifically, as shown in Figure 4 , reference Figures 1 to 3 , the pump light emitted by the semiconductor laser amplifier TA, taking the wavelength of the pump light as 808nm for example, the pump light successively passes through the first quarter wave plate QWP1, the first half wave plate HWP1 and the convex lens L to be incident on the incident mirror M1. The transmitted light through the incident mirror M1 enters the resonant cavity, and the transmitted light here passes through the crystal 15 frequency multiplication and then transmits through the exit mirror M2 and the right side window mirror 2 to output the frequency multiplication light; the wavelength of the frequency multiplication light is 404nm. Most of the transmitted light through the exit mirror M2 is the transmitted light, which is output as the frequency multiplication light. The light reflected by the exit mirror M2 after passing through the crystal 15 is reflected by the first reflecting mirror M3 and the second reflecting mirror M4 in turn, and then enters the incident mirror M1 again, and then is reflected into the crystal 15. The light incident into the crystal 15 is periodically polarized to realize the crystal with quasi-phase matching to generate the frequency multiplication laser of the second harmonic.

[0077] In this example, an O-type third-order PPKTP crystal is used to generate blue laser light by using the cavity-outside-enhanced SHG scheme of the 0-type third-order QPM PPKTP crystal. Stable output of the frequency multiplication light is obtained by improving the circulating pump power in the cavity.

[0078] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any skilled person in the art can easily think of changes or replacements within the technical range disclosed in the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A miniaturized laser frequency doubling device, characterized in that, It comprises a shell (1), and the incident cavity mirror (M1), the exit cavity mirror (M2), the first reflecting cavity mirror (M3) and the second reflecting cavity mirror (M4) are arranged in two rows in the shell (1) to form a resonant cavity. The rear middle part of the shell (1) is provided with a crystal (15), and the incident cavity mirror (M1) and the exit cavity mirror (M2) are arranged on the left and right sides of the crystal (15) respectively; the left and right sides of the front row in the shell (1) are provided with the first reflecting cavity mirror (M3) and the second reflecting cavity mirror (M4) respectively; the interval of the incident cavity mirror (M1) and the exit cavity mirror (M2) is greater than the interval of the first reflecting cavity mirror (M3) and the second reflecting cavity mirror (M4). The pump light transmits through the left side window mirror (4) of the shell (1) and enters the incident cavity mirror (M1), the transmitted light of the incident cavity mirror (M1) enters the resonant cavity, and the frequency-doubled light is output through the exit cavity mirror (M2) and the right side window mirror (2) after frequency doubling of the crystal (15); the light reflected by the exit cavity mirror (M2) after frequency doubling of the crystal (15) is reflected by the first reflecting cavity mirror (M3) and the second reflecting cavity mirror (M4) in turn, and then enters the incident cavity mirror (M1) after multi-beam interference. The reflected light of the incident cavity mirror (M1) is output as the fundamental frequency light by the left side window mirror (4) and enters the HC cavity locking device.

2. The miniaturized laser frequency doubling device of claim 1, wherein, The bottom of the shell (1) is provided with a five-axis adjustment mechanism (12), and the crystal (15) is mounted on the five-axis adjustment mechanism (12) through a temperature control furnace device.

3. The miniaturized laser frequency doubling device of claim 2, wherein, The temperature control furnace device comprises a crystal base adapter plate (11), a crystal base (8), a crystal clamp (10), a crystal pressing plate (9), a heating device, a refrigeration device and a temperature control interface (5). The crystal base adapter plate (11) is mounted on the five-axis adjustment mechanism (12), and the crystal base (8) is mounted on the crystal base adapter plate (11); the crystal clamp (10) is mounted on the crystal base (8) and is pressed tightly through the crystal pressing plate (9). The heating device is arranged in the crystal base (8) and below the crystal clamp (10), and the temperature control interface (5) is arranged on the shell (1) and is electrically connected with the heating device and the refrigeration device.

4. The compact laser frequency doubling device of claim 1, wherein, The front and rear sides of the shell (1) are respectively provided with a first groove (3) and a second groove (7).

5. The compact laser frequency doubling device of claim 1, wherein, The rear side of the shell (1) is provided with a window corresponding to the position of the five-axis adjustment mechanism (12) inside, and the window is provided with a cover plate (6).

6. The compact laser frequency doubling device of claim 1, wherein, The first reflecting cavity mirror (M3) or the second reflecting cavity mirror (M4) is provided with a piezoelectric transducer (PZT); the second reflecting cavity mirror (M4) or the first reflecting cavity mirror (M3) is provided with a first attenuation sheet (AS1) and a first photodetector (PD1) on the back.

7. The compact laser frequency doubling device of claim 1, wherein, The HC cavity locking device comprises a second quarter wave plate (QWP2), a polarization beam splitter (PBS), a second attenuation sheet (AS2), a third attenuation sheet (AS3), a second photodetector (PD2), a third photodetector (PD3) and a mirror (M). The fundamental light output by the left side window mirror (4) is filtered by the second quarter wave plate (QWP2), split by the polarizing beam splitter (PBS), one of the beams is incident on the second photoelectric detector (PD2) through the second attenuating sheet (AS2), and the other beam is reflected by the mirror (M) to be incident on the third photoelectric detector (PD3) through the third attenuating sheet (AS3).

8. The compact laser frequency doubling device of claim 1, wherein, The left side window mirror (4) comprises a first quarter wave plate (QWP1), a first half wave plate (HWP1) and a convex lens (L). The pump light emitted by the semiconductor laser amplifier (TA) is incident on the incident cavity mirror (M1) through the first quarter wave plate (QWP1), the first half wave plate (HWP1) and the convex lens (L) in sequence.

9. The compact laser frequency doubling device of claim 1, wherein, The right side window mirror (2) comprises a low-pass filter sheet (LF).

10. The compact laser frequency doubling device of claim 1, wherein, The incident cavity mirror (M1), the exit cavity mirror (M2), the first reflecting cavity mirror (M3) and the second reflecting cavity mirror (M4) are respectively installed on the bottom of the shell (1) through a boss (13).

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