A laser frequency doubling device

Abstract

This invention discloses a laser frequency doubling generator, which, along the laser propagation direction, sequentially comprises: a fundamental frequency module, a frequency doubling generation module, a dual-wavelength reflector, a frequency doubling laser sampling mirror, and a frequency doubling power sampling sensor. The frequency doubling generation module contains a frequency doubling temperature-controlled furnace, which holds a nonlinear crystal. The fundamental frequency module provides fundamental frequency laser light. The frequency doubling generation module performs nonlinear conversion on the fundamental frequency laser light. The frequency doubling laser sampling mirror reflects the frequency doubling laser light into the frequency doubling power sampling sensor. The frequency doubling power sampling sensor determines the current power of the frequency doubling laser light. The frequency doubling temperature-controlled furnace adjusts the temperature of the nonlinear crystal when the current power is less than a preset target power, so that the current power reaches the target power. This invention solves the angle mismatch problem in dual-channel frequency doubling and improves the conversion efficiency of dual-channel frequency doubling.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a laser frequency doubling device. Background Technology

[0002] Current technologies generally employ laser frequency doubling to obtain shorter wavelength lasers. In solid-state lasers, frequency-doubled lasers are obtained by utilizing the second nonlinear effect generated by a nonlinear crystal under the influence of a strong laser. To achieve higher second-harmonic conversion efficiency, double-pass frequency doubling is typically used: the fundamental laser passes through the nonlinear crystal twice, increasing the nonlinear interaction length and significantly improving conversion efficiency. The reason is that laser divergence causes phase mismatch, requiring the divergence angle to be controlled within a certain range, i.e., the receiving angle. The receiving angle is inversely proportional to the length of the crystal along the optical axis; the longer the crystal, the smaller the receiving angle, and the higher the beam quality requirements for the fundamental light. Assuming a crystal of length L with a receiving angle of α, using a double-pass frequency doubling scheme, the first and second passes are equivalent to two independent frequency doubling conversions, both with a receiving angle of α. If a single-pass frequency doubling conversion is used, it's equivalent to a crystal length of 2L, but the receiving angle becomes α / 2. This means the incident laser divergence angle must be even smaller, i.e., the beam waist is larger, resulting in lower power density and consequently lower nonlinear conversion efficiency.

[0003] Therefore, under the same crystal length conditions, dual-pass frequency doubling can achieve approximately twice the conversion efficiency of single-pass frequency doubling. However, existing dual-pass frequency doubling generators are prone to angle mismatch during frequency doubling conversion. During nonlinear conversion, the conversion efficiency of dual-pass frequency doubling is unstable, leading to a significant reduction in conversion efficiency. Summary of the Invention

[0004] This invention provides a laser frequency doubling generator to solve the technical problem that existing laser frequency doubling generators are prone to angle mismatch, resulting in low conversion efficiency of dual-pass frequency doubling.

[0005] To address the aforementioned technical problems, this invention provides a laser frequency doubling generator, which, along the laser propagation direction, sequentially comprises: a fundamental frequency module, a frequency doubling generator module, a dual-wavelength reflector, a frequency doubling laser sampling mirror, and a frequency doubling power sampling sensor.

[0006] The frequency doubling module is equipped with a frequency doubling temperature control furnace; the frequency doubling temperature control furnace holds a nonlinear crystal.

[0007] The baseband module is used to provide baseband laser;

[0008] The frequency doubling module is used to perform a first nonlinear conversion and a second nonlinear conversion on the fundamental frequency laser to generate a frequency doubling laser.

[0009] The dual-wavelength reflector is used to reflect the frequency-doubled laser generated by the first nonlinear conversion and the remaining fundamental frequency laser back to the frequency-doubled generation module, so that the frequency-doubled generation module can perform a second nonlinear conversion on the remaining fundamental frequency laser to generate frequency-doubled laser.

[0010] The frequency-doubled laser sampling mirror is used to transmit the frequency-doubled laser as a dual-pass frequency-doubled laser and reflect a low-power frequency-doubled laser into the frequency-doubled power sampling sensor.

[0011] The frequency-doubled power sampling sensor is used to determine the current power of the incoming frequency-doubled laser.

[0012] The frequency doubling temperature control furnace is used to provide a constant temperature environment for the nonlinear crystal, and when the current power is less than the preset target power, the temperature of the nonlinear crystal is adjusted so that the current power reaches the target power.

[0013] As a preferred embodiment, the laser frequency doubling device further includes: a PZT two-dimensional adjustment stage, a polarizer, and a position sensor detector;

[0014] The dual-wavelength reflector is mounted on the PZT two-dimensional adjustment stage; along the direction of laser propagation, the polarizer and the position sensor are sequentially arranged after the frequency doubling module;

[0015] The polarizer is used to reflect the remaining fundamental frequency laser after the low-power second nonlinear conversion into the position sensing detector.

[0016] The position sensor detector is used to determine the current spot position coordinates of the remaining fundamental frequency laser that has entered;

[0017] The PZT two-dimensional adjustment stage is used to adjust the two-dimensional angle to maximize the efficiency of the second nonlinear conversion. During the operation of the laser frequency doubling device, when the current spot position coordinates are inconsistent with the preset target spot position coordinates, the angle of the dual-wavelength reflector is adjusted so that the current spot position coordinates are consistent with the target spot position coordinates.

[0018] As a preferred embodiment, the frequency doubling module is further configured to adjust the spatial orientation of the frequency doubling temperature control furnace when the nonlinear crystal is at a preset initial temperature, so that the fundamental frequency laser undergoes a first nonlinear conversion within the nonlinear crystal to generate a frequency doubling laser, thereby achieving phase matching;

[0019] The remaining fundamental frequency laser reflected back by the dual-wavelength mirror is subjected to a second nonlinear conversion to generate frequency-doubled laser, and the pitch and horizontal yaw of the dual-wavelength mirror are adjusted to maximize the power of the generated frequency-doubled laser.

[0020] Specifically, when the power of the generated frequency-doubled laser reaches its maximum value, the power of the frequency-doubled laser determined by the frequency-doubled power sampling sensor at this time is taken as the target power, and the current spot position coordinates of the remaining fundamental frequency laser determined by the position sensor at this time are taken as the target spot position coordinates.

[0021] As a preferred embodiment, the laser frequency doubling device further includes: an optical isolator, a first fundamental frequency half-wave plate, a fundamental frequency sampling mirror, a fundamental frequency power sampling sensor, a dichroic mirror, an electric translational lifting platform, a second fundamental frequency half-wave plate, and a waste light collector;

[0022] Along the propagation direction of the laser, the optical isolator, the first fundamental frequency half-wave plate, the fundamental frequency sampling mirror, the fundamental frequency power sampling sensor, and the dichroic mirror are sequentially arranged between the fundamental frequency module and the frequency doubling generation module; the second fundamental frequency half-wave plate is arranged before the polarizer; and the waste light collector is arranged after the polarizer.

[0023] The incident surface of the dichroic mirror is coated with an anti-reflection film for the fundamental frequency laser, and the exit surface is coated with a high-reflection film for the frequency-doubled laser.

[0024] The optical isolator is used to isolate the fundamental frequency laser generated by the fundamental frequency module, isolate the fundamental frequency laser transmitted in the reverse direction, and transmit the fundamental frequency laser transmitted in the forward direction into the first fundamental frequency half-wave plate.

[0025] The first fundamental frequency half-wave plate is used to change the polarization of the fundamental frequency laser to horizontal linear polarization before it enters the fundamental frequency sampling mirror;

[0026] The fundamental frequency sampling mirror is used to transmit fundamental frequency laser light into the dichroic mirror and reflect low-power fundamental frequency laser light into the fundamental frequency power sampling sensor.

[0027] The fundamental frequency power sampling sensor is used to monitor whether the incoming fundamental frequency laser is normal;

[0028] The dichroic mirror is used to transmit the fundamental frequency laser into the frequency doubling generation module, and to reflect all the frequency doubling lasers generated by the first and second nonlinear conversions in the frequency doubling generation module into the frequency doubling laser sampling mirror. The remaining fundamental frequency laser in the frequency doubling generation module is transmitted sequentially into the first fundamental frequency half-wave plate and the optical isolator, so that the first fundamental frequency half-wave plate and the optical isolator change the polarization of the remaining fundamental frequency laser to vertical linear polarization, and then reflect it into the second fundamental frequency half-wave plate.

[0029] The second fundamental frequency half-wave plate is used to polarize the remaining fundamental frequency laser before it enters the polarizer;

[0030] The waste light collector is used to collect the remaining fundamental frequency laser transmitted through the polarizer.

[0031] As a preferred embodiment, the laser frequency doubling device further includes: an electrically operated translational lifting platform;

[0032] The dichroic mirror, frequency doubling module, dual-wavelength reflector, and PZT two-dimensional adjustment stage are installed on the electric translation and lifting platform;

[0033] The electric translational lifting platform is used to provide vertical linear motion for the dichroic mirror, frequency doubling module, dual-wavelength reflector, and PZT two-dimensional adjustment platform.

[0034] As a preferred embodiment, the frequency multiplier module is also equipped with a temperature control furnace connection mechanical component;

[0035] The temperature control furnace connecting mechanical components are respectively connected to the frequency doubling temperature control furnace and the electric translation lifting platform by screws;

[0036] When the temperature control furnace connecting mechanical components are connected to the frequency doubling temperature control furnace and the electric translation lifting platform, preset debugging and locking requirements must be met.

[0037] The debugging and locking requirements include debugging requirements and locking requirements; the debugging requirements are: after the temperature control furnace connecting mechanical component is connected to the frequency doubling temperature control furnace, the frequency doubling temperature control furnace does not produce any offset in other directions when rotating clockwise and counterclockwise around the x-axis by a preset angle;

[0038] The locking requirement is as follows: when the temperature control furnace connecting mechanical component is connected to the frequency multiplier temperature control furnace, the temperature control furnace connecting mechanical component and the frequency multiplier temperature control furnace are tightly locked with screws until the locking distance between the temperature control furnace connecting mechanical component and the frequency multiplier temperature control furnace is less than the preset distance. When the temperature control furnace connecting mechanical component is connected to the electric translational lifting platform, the temperature control furnace connecting mechanical component and the electric translational lifting platform are tightly locked with screws until the locking distance between the temperature control furnace connecting mechanical component and the electric translational lifting platform is less than the preset distance.

[0039] As a preferred embodiment, the nonlinear crystal is processed in the following manner:

[0040] Along a preset cutting direction, a wedge angle of the same angle is cut at the input and output ends of the nonlinear crystal respectively; wherein, the wedge angle separates the spot of the reflected light and the main optical path, and at each point of use of the nonlinear crystal, the reflected light can pass completely through the nonlinear crystal without hitting the side of the nonlinear crystal.

[0041] As a preferred embodiment, the nonlinear crystal is further processed in the following manner:

[0042] Within a preset allowable temperature range for noncritical phase matching, the operating temperature of the nonlinear crystal is adjusted to have an offset from the preset theoretical phase matching temperature value; wherein, the offset is calculated based on the angle required for the nonlinear crystal to just separate two wavelengths of light;

[0043] The spatial orientation of the nonlinear crystal is adjusted so that the spatial orientation compensates for the angle.

[0044] As a preferred embodiment, the nonlinear crystal includes: BBO crystal, LBO crystal, CLBO crystal or KBBF crystal.

[0045] Compared with the prior art, the embodiments of the present invention have the following beneficial effects:

[0046] This invention provides a laser frequency doubling generator, comprising, in sequence along the laser propagation direction: a fundamental frequency module, a frequency doubling generation module, a dual-wavelength reflector, a frequency doubling laser sampling mirror, and a frequency doubling power sampling sensor; the frequency doubling generation module contains a frequency doubling temperature control furnace; the frequency doubling temperature control furnace holds a nonlinear crystal; the fundamental frequency module provides a fundamental frequency laser; the frequency doubling generation module performs nonlinear conversion on the fundamental frequency laser to generate a frequency doubling laser; the frequency doubling laser sampling mirror transmits the frequency doubling laser as a dual-pass frequency doubling laser and reflects a low-power frequency doubling laser into the frequency doubling power sampling sensor; the frequency doubling power sampling sensor determines the current power of the incoming frequency doubling laser; the frequency doubling temperature control furnace adjusts the temperature of the nonlinear crystal when the current power is less than a preset target power, so that the current power reaches the target power.

[0047] This invention incorporates a frequency-doubled laser sampling mirror and a frequency-doubled power sampling sensor. The sampling mirror reflects the dual-channel frequency-doubled laser sample obtained from the frequency-doubled generation module into the power sampling sensor, which determines the current power of the dual-channel frequency-doubled laser. Then, based on the current power, it compares it with a preset target power. When the current power is less than the target power, the temperature of the nonlinear crystal in the frequency-doubled generation module is adjusted in real time to increase the power of the dual-channel frequency-doubled laser to the target power. This solves the angle mismatch problem in dual-channel frequency doubling and improves the conversion efficiency. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the structure of a laser frequency doubling generator according to an embodiment of the present invention;

[0049] Figure 2 This is a schematic diagram showing the number and range of crystal shift points;

[0050] Figure 3 This is a schematic diagram of the internal structure of the frequency multiplier module;

[0051] Figure 4 This is a schematic diagram of the first processing method for nonlinear crystals;

[0052] Figure 5 This is a schematic diagram of the second processing method for nonlinear crystals; Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0055] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0056] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0057] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0058] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0059] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0060] Example 1

[0061] Please refer to Figure 1 The diagram below shows a laser frequency doubling generator according to an embodiment of the present invention. The device includes, in sequence along the laser propagation direction, a fundamental frequency module, a frequency doubling generator module, a dual-wavelength reflector, a frequency doubling laser sampling mirror, and a frequency doubling power sampling sensor.

[0062] The frequency doubling module is equipped with a frequency doubling temperature control furnace; the frequency doubling temperature control furnace holds a nonlinear crystal.

[0063] The baseband module is used to provide baseband laser;

[0064] The frequency doubling module is used to perform a first nonlinear conversion and a second nonlinear conversion on the fundamental frequency laser to generate a frequency doubling laser.

[0065] The dual-wavelength reflector is used to reflect the frequency-doubled laser generated by the first nonlinear conversion and the remaining fundamental frequency laser back to the frequency-doubled generation module, so that the frequency-doubled generation module can perform a second nonlinear conversion on the remaining fundamental frequency laser to generate frequency-doubled laser.

[0066] The frequency-doubled laser sampling mirror is used to transmit the frequency-doubled laser as a dual-pass frequency-doubled laser and reflect a low-power frequency-doubled laser into the frequency-doubled power sampling sensor.

[0067] The frequency-doubled power sampling sensor is used to determine the current power of the incoming frequency-doubled laser.

[0068] The frequency doubling temperature control furnace is used to provide a constant temperature environment for the nonlinear crystal, and when the current power is less than the preset target power, the temperature of the nonlinear crystal is adjusted so that the current power reaches the target power.

[0069] Preferably, the laser frequency doubling device further includes: a PZT two-dimensional adjustment stage, a polarizer, and a position sensor detector; the dual-wavelength reflector is mounted on the PZT two-dimensional adjustment stage; along the laser propagation direction, the polarizer and the position sensor detector are sequentially arranged after the frequency doubling module; the polarizer is used to reflect the remaining fundamental frequency laser after the second nonlinear conversion with low power into the position sensor detector; the position sensor detector is used to determine the current spot position coordinates of the entering remaining fundamental frequency laser; the PZT two-dimensional adjustment stage is used to adjust the two-dimensional angle to maximize the efficiency of the second nonlinear conversion, and during the operation of the laser frequency doubling device, when the current spot position coordinates are inconsistent with the preset target spot position coordinates, the angle of the dual-wavelength reflector is adjusted to make the current spot position coordinates consistent with the target spot position coordinates.

[0070] Preferably, the laser frequency doubling generator further includes: an optical isolator, a first fundamental frequency half-wave plate, a fundamental frequency sampling mirror, a fundamental frequency power sampling sensor, a dichroic mirror, an electrically operated translational lifting platform, a second fundamental frequency half-wave plate, and a waste light collector; along the laser propagation direction, the optical isolator, the first fundamental frequency half-wave plate, the fundamental frequency sampling mirror, the fundamental frequency power sampling sensor, and the dichroic mirror are sequentially arranged between the fundamental frequency module and the frequency doubling generator module; the second fundamental frequency half-wave plate is arranged before the polarizer; the waste light collector is arranged after the polarizer; the incident surface of the dichroic mirror is coated with an anti-reflection film for the fundamental frequency laser, and the exit surface is coated with a high-reflection film for the frequency doubling laser; the optical isolator is used to isolate the fundamental frequency laser generated by the fundamental frequency module, isolate the fundamental frequency laser propagating in the opposite direction, and transmit the fundamental frequency laser propagating in the forward direction into the first fundamental frequency half-wave plate; the first fundamental frequency half-wave plate is used to change the polarization of the fundamental frequency laser to horizontal linear polarization before it enters the laser. The fundamental frequency sampling mirror is used to transmit fundamental frequency laser light into the dichroic mirror and reflect low-power fundamental frequency laser light into the fundamental frequency power sampling sensor. The fundamental frequency power sampling sensor is used to monitor whether the incoming fundamental frequency laser light is normal. The dichroic mirror is used to transmit fundamental frequency laser light into the frequency doubling generation module and reflect all frequency doubling laser light generated by the first and second nonlinear conversions in the frequency doubling generation module into the frequency doubling laser sampling mirror. The remaining fundamental frequency laser light in the frequency doubling generation module is transmitted sequentially into the first fundamental frequency half-wave plate and the optical isolator, so that the first fundamental frequency half-wave plate and the optical isolator change the polarization of the remaining fundamental frequency laser light to vertical linear polarization before reflecting it into the second fundamental frequency half-wave plate. The second fundamental frequency half-wave plate is used to polarize the remaining fundamental frequency laser light before it enters the polarizer. The waste light collector is used to collect the remaining fundamental frequency laser light transmitted by the polarizer.

[0071] There are two problems with the existing dual-pass frequency doubling generator: (1) When it performs frequency doubling conversion, it is easy to have angle mismatch. During the nonlinear conversion process, the conversion efficiency of dual-pass frequency doubling is unstable, resulting in a significant reduction in the conversion efficiency of dual-pass frequency doubling; (2) The frequency doubling light will have low-power reflected light on the two light-passing surfaces of the crystal. The reflected light is reflected multiple times in the crystal and returns to the fundamental frequency module along the original optical path, which will cause damage to the components on the front optical path and interfere with the beam quality.

[0072] To address the first problem mentioned above, this invention proposes a novel laser frequency doubling generator that can adaptively solve the angle mismatch problem in dual-pass frequency doubling, thereby improving the conversion efficiency of dual-pass frequency doubling. For example... Figure 1As shown, in the laser frequency doubling device of the present invention, the following components are arranged sequentially along the laser emission direction: (1) a fundamental frequency module, (2) an optical isolator, (3) a first fundamental frequency half-wave plate, (4) a fundamental frequency sampling mirror, (5) a fundamental frequency power sampling sensor, (6) a dichroic mirror, (7) a frequency doubling generation module, (8) a dual-wavelength 0° reflector, (9) a PZT two-dimensional adjustment stage, (10) an electric translational lifting stage, (11) a frequency doubling laser sampling mirror, (12) a frequency doubling power sampling sensor, (13) a second fundamental frequency half-wave plate, (14) a 45° polarizer, (15) a position sensor detector, and (16) a waste light collector.

[0073] Among them, (1) the fundamental frequency module is used to provide a linearly polarized fundamental frequency laser with a certain power, pulse width and repetition rate. Figure 1 The fundamental frequency laser shown is horizontally linearly polarized, but it can also be in other polarization states. If the fundamental frequency laser is in another polarization state, a half-wave plate needs to be inserted between (1) the fundamental frequency module and (2) the optical isolator to change the polarization of the fundamental frequency laser and rotate it to horizontal linear polarization.

[0074] The fundamental frequency laser is transmitted through optical isolator (2), which allows forward-propagating light to pass through while isolating reverse-propagating light. (2) can also be a combination of other optical devices with the same function. Then it passes through the first fundamental frequency half-wave plate (3). Figure 1 The fundamental frequency half-wave plate shown is a half-wave plate designed for the fundamental frequency wavelength. By rotating the wave plate, the angle between the polarization direction of the incident light and the optical axis of the wave plate is adjusted, thus changing the polarization of the emitted laser to horizontal linear polarization. It should be noted that the first fundamental frequency half-wave plate in (3) is rotated horizontally because the frequency doubling crystal in (7) requires the fundamental frequency to be horizontally linearly polarized, while the fundamental frequency sampling mirror in (4) has no requirement for the polarization direction.

[0075] Then, through the (4) fundamental frequency sampling mirror, (4) the fundamental frequency sampling mirror is used to transmit most of the power of the fundamental frequency laser and reflect a small portion of the power of the fundamental frequency laser into the (5) fundamental frequency power sampling sensor; (4) can be any optical element that meets the sampling requirements. The function of the (5) fundamental frequency power sensor is to collect the small signal power of the fundamental frequency laser and feed it back to the monitoring program in real time to monitor whether the (1)-(3) fundamental frequency optical path is working properly.

[0076] (4) The transmitted light from the fundamental frequency sampling mirror is transmitted through the (6) dichroic mirror. Figure 1 The dichroic mirror shown has a 45° incident angle. Its incident surface is coated with a fundamental frequency antireflection film, and its exit surface is coated with a frequency doubling high reflectivity film, so that a beam of dual-wavelength laser light is transmitted by one wavelength and reflected by the other after passing through the dichroic mirror. (6) The incident angle of the dichroic mirror can also be other non-0° values, and (6) can also be other optical elements with the same dichroic function.

[0077] The incident fundamental frequency laser undergoes a first nonlinear conversion in the (7) frequency doubling generation module, generating a first second harmonic. The frequency-doubled laser generated by the first nonlinear conversion, together with the remaining fundamental frequency laser, is reflected back to the (7) frequency doubling generation module along the original optical path by the (8) dual-wavelength 0° reflector. The remaining fundamental frequency light undergoes a second nonlinear conversion into a second harmonic in the nonlinear crystal, completing the second frequency doubling conversion. The efficiency of the second nonlinear conversion is not much different from that of the first nonlinear conversion. Here, the (8) dual-wavelength reflector is installed on the (9) PZT two-dimensional adjustment stage. The adjustment frame is manually adjusted to achieve the purpose of adjusting the lens. The function of the (9) PZT two-dimensional adjustment stage is to receive instructions and perform real-time micro-adjustment of the angle to correct the return optical path.

[0078] The frequency-doubled laser and the remaining fundamental laser obtained from the two nonlinear transformations return along the incident light path. At the incident surface in front of the dichroic mirror (6), the frequency-doubled laser is reflected at 90° and then reflected by the sampling mirror of the frequency-doubled laser (11) into the frequency-doubled power sensor detector (12). The transmitted light of (11) is the final output laser.

[0079] After the double-pass frequency doubling is completed, the remaining fundamental frequency laser is transmitted through the dichroic mirror (6) and returns along the original optical path. It passes through the first fundamental frequency half-wave plate (3) and the optical isolator (2). The polarization state of the fundamental frequency laser is rotated to vertical linear polarization by the first fundamental frequency half-wave plate (3) and the optical isolator (2), and is reflected out of the original optical path by 90°. Among them, the first fundamental frequency half-wave plate and the optical isolator (2) rotate the polarization by 45° in sequence to complete the transformation from horizontal to vertical.

[0080] The polarization state of the fundamental frequency laser is then converted by the second fundamental frequency half-wave plate (13) and enters the 45° polarizer (14). The function of (13) is to adjust the reflected power of the 45° polarizer (14), and it can also be other components with the same function. By rotating the wave plate to change the polarization direction of the fundamental frequency laser entering the polarizer, making it close to horizontal linear polarization, most of the power can be transmitted through the polarizer, and a small part of the power can be reflected into the position sensor. The specific rotation angle and the amount of power reflected into the position sensor are determined by the power threshold of the position sensor, which is a range value rather than a fixed value.

[0081] (14) The low-power fundamental frequency laser reflected by the 45° polarizer enters the (15) position sensor after power attenuation. The function of the (15) position sensor is to calibrate the position coordinates of the laser spot and provide real-time feedback. The light transmitted by the (14) 45° polarizer enters the (16) garbage light collector.

[0082] Preferably, the laser frequency doubling device further includes: an electric translational lifting platform; the dichroic mirror, the frequency doubling module, the dual-wavelength reflector, and the PZT two-dimensional adjustment platform are mounted on the electric translational lifting platform; the electric translational lifting platform is used to provide linear motion in the vertical dimension (x and y) for the dichroic mirror, the frequency doubling module, the dual-wavelength reflector, and the PZT two-dimensional adjustment platform.

[0083] The laser frequency doubling device also includes: (10) an electric translation lifting platform, (6)-(9) are all installed on the (10) electric translation lifting platform. The (10) electric translation lifting platform can be translated and lifted, providing high-precision linear motion in two vertical dimensions for the (6) dichroic mirror, (7) frequency doubling module, (8) dual-wavelength reflector and (9) PZT two-dimensional adjustment platform.

[0084] The shift code can be written through the set program, and the program controls the electric displacement lifting platform (10) to move or lift, so as to realize the synchronous shift function of crystal and vulnerable device ((6) dichroic mirror and (8) dual wavelength 0° reflector). In combination with other devices, the life of the laser generator can be greatly extended.

[0085] The following is an explanation of the shift-point encoding:

[0086] The number of shift points and their corresponding coordinates are designed based on the size of the input light spot and the dimensions of the crystal. The point positions are represented by codes. Please refer to [reference needed]. Figure 2 This is a schematic diagram showing the number and range of crystal shift points. Figure 2 The crystal has 3×3 usable points, coded as 1, 2, 3...9. The points of (6) the dichroic mirror and (8) the dual-wavelength 0° reflector are consistent with the crystal. When changing points, the crystal point position can be used as the reference. When it is necessary to change points, the point coordinate code is entered in the program. The program controls the operation of the electric lifting and translation stage, which moves (6)-(9) together to realize the synchronous point movement of the crystal and the vulnerable optical components.

[0087] Preferably, the frequency multiplier module further includes a temperature control furnace connection mechanical assembly; the temperature control furnace connection mechanical assembly is connected to the frequency multiplier temperature control furnace and the electric translational lifting platform respectively via screws; wherein, when the temperature control furnace connection mechanical assembly is connected to the frequency multiplier temperature control furnace and the electric translational lifting platform, preset debugging and locking requirements must be met; the debugging and locking requirements include debugging requirements and locking requirements; the debugging requirement is: after the temperature control furnace connection mechanical assembly is connected to the frequency multiplier temperature control furnace, when the frequency multiplier temperature control furnace rotates clockwise and counterclockwise around the x-axis by a preset angle, no other [features] are generated. Directional offset; the locking requirement is as follows: when the temperature control furnace connecting mechanical component is connected to the frequency multiplier temperature control furnace, the temperature control furnace connecting mechanical component and the frequency multiplier temperature control furnace are tightly locked with screws until the locking distance between the temperature control furnace connecting mechanical component and the frequency multiplier temperature control furnace is less than the preset distance; and when the temperature control furnace connecting mechanical component is connected to the electric translational lifting platform, the temperature control furnace connecting mechanical component and the electric translational lifting platform are tightly locked with screws until the locking distance between the temperature control furnace connecting mechanical component and the electric translational lifting platform is less than the distance.

[0088] Please refer to Figure 3 The diagram shows the internal structure of the frequency multiplier module (7). The frequency multiplier module mainly includes a frequency multiplier temperature control furnace (7-1) and a temperature control furnace connecting mechanical assembly (7-2). The function of the frequency multiplier temperature control furnace (7-1) is to clamp and fix the nonlinear crystal and provide a constant temperature environment, as well as to achieve high-precision temperature regulation. (7-2) is a set of mechanical components (including one or more mechanical parts). The design function requirement of this component is that the frequency multiplier temperature control furnace (7-1) and the temperature control furnace connecting mechanical assembly (7-2) can be connected by screws, and the electric displacement lifting platform (7-2) and (10) can be connected by screws, and the debugging and locking requirements can be met.

[0089] The debugging and locking requirements include debugging requirements and locking requirements. The debugging requirement is that the (7-1) frequency doubling temperature control furnace can rotate clockwise and counterclockwise around the x-axis by a certain angle, and the rotation process does not cause the (7-1) frequency doubling temperature control furnace to deviate in other directions. The angle adjustment range is related to different crystal parameters. The locking requirement is that after the (7-1) frequency doubling temperature control furnace is debugged, it is locked by tightening screws with a locking accuracy of ≤0.01mm. The screw tightening and locking accuracy of the (7-2) temperature control furnace connecting mechanical components and (10) electric displacement lifting platform is ≤0.01mm.

[0090] Preferably, the nonlinear crystal is processed in the following way: along a preset cutting direction, a wedge angle of the same angle is cut at the input end and the output end of the nonlinear crystal respectively; wherein, the wedge angle separates the spot of the reflected light and the main optical path, and at each point of use of the nonlinear crystal, the reflected light can completely pass through the nonlinear crystal without hitting the side of the nonlinear crystal.

[0091] Preferably, the nonlinear crystal is further processed by: adjusting the operating temperature of the nonlinear crystal to have an offset from the preset theoretical phase-matching temperature within a preset allowable temperature range for a type of noncritical phase matching; wherein the offset is calculated based on the angle required for the nonlinear crystal to just separate two wavelengths of light;

[0092] The spatial orientation of the nonlinear crystal is adjusted so that the spatial orientation compensates for the angle.

[0093] Preferably, the nonlinear crystal includes: BBO crystal, LBO crystal, CLBO crystal or KBBF crystal.

[0094] The nonlinear crystal installed in the (7-1) frequency doubling temperature control furnace can be a BBO crystal, LBO crystal, CLBO crystal, KBBF crystal, or other nonlinear crystals that can be phase matched. The nonlinear crystal can be of any suitable size.

[0095] To address the second problem mentioned above, this invention eliminates ghost light interference by processing the nonlinear crystal in the (7) frequency doubling module. There are two methods for processing the nonlinear crystal:

[0096] I. Please refer to Figure 4 This is a schematic diagram of the first processing method for nonlinear crystals. The input and output terminals of the crystal are cut with a wedge angle of the same angle in the y-axis direction. The wedge angle of the crystal is a small angle, which can separate the spot of the reflected light and the main optical path, while ensuring that the reflected light can pass through the crystal completely at every point of use without hitting the side of the crystal.

[0097] II. Please refer to Figure 5 This is a schematic diagram illustrating the second processing method for nonlinear crystals. The nonlinear crystal has no wedge angles at both ends. The azimuth angle φ (the angle between the projection of the light propagation direction onto the xoy plane and the x-axis) of the crystal is a theoretical value. The angle θ between the light propagation direction and the z-axis is a small deviation from the theoretical value. Figure 5The example negative biaxial nonlinear crystal LBO has a theoretical phase-matching temperature of 149°C at 1064 nm for a type of noncritical phase matching, with a walk-off angle of 0°. A 1°C temperature change corresponds to a 0.4° change in the φ angle. Therefore, the operating temperature can be designed to deviate by a certain value within the allowable temperature range for a type of noncritical phase matching, and the required angle can be compensated by adjusting the spatial orientation of the crystal, such as... Figure 5 As shown, the temperature offset here is calculated based on the angle required to separate the two wavelengths of light exactly.

[0098] The second processing method described above is applicable to nonlinear crystals that are sensitive to temperature mismatch. By appropriately reciprocating spatial orientation and temperature, the ghost beam can be eliminated and avoided. Both crystal processing methods described above can ensure that the returning ghost beam does not overlap with the original fundamental frequency laser path in front of the (7) frequency doubling generation module, thereby eliminating the influence of the ghost beam and protecting the front optical path.

[0099] Preferably, the frequency doubling generation module is further configured to adjust the spatial attitude of the frequency doubling temperature control furnace when the nonlinear crystal is at a preset initial temperature, so that the fundamental frequency laser undergoes a first nonlinear conversion within the nonlinear crystal to generate a frequency-doubled laser, achieving phase matching; perform a second nonlinear conversion on the remaining fundamental frequency laser reflected back from the dual-wavelength mirror to generate a frequency-doubled laser, and adjust the pitch and horizontal yaw of the dual-wavelength mirror to maximize the power of the generated frequency-doubled laser; wherein, when the power of the generated frequency-doubled laser reaches its maximum value, the power of the frequency-doubled laser determined by the frequency doubling power sampling sensor at this time is taken as the target power, and the current spot position coordinates of the remaining fundamental frequency laser determined by the position sensor at this time are taken as the target spot position coordinates.

[0100] This invention provides an adaptive adjustment function to solve the problem of angle mismatch in dual-pass frequency doubling. The adaptive adjustment function of the frequency doubling laser generator is described below.

[0101] 1. Debugging and calibration stage

[0102] During the commissioning phase of the frequency doubling laser generator, the operating temperature of the nonlinear crystal is first set as the initial temperature (the operating temperature of the nonlinear crystal is a range, which is related to the cutting angle of the crystal along the crystal axis; the initial temperature can be set within the range). Then, the pitch and horizontal yaw of the temperature control furnace (7-1) are adjusted to achieve phase matching of the first stage of frequency doubling, resulting in the highest frequency doubling efficiency. Since the crystal is installed inside the temperature control furnace, the two are considered as a whole, and the attitude (pitch and horizontal yaw) of the temperature control furnace can be adjusted. After the first stage of frequency doubling is completed, the pitch and horizontal yaw of the dual-wavelength 0° reflector (8) are installed and adjusted to maximize the frequency doubling power reflected at the dichroic mirror (6), and the second stage of frequency doubling is completed. In the first stage of frequency doubling, the pitch and horizontal yaw of the temperature control furnace are adjusted to achieve phase matching, i.e., the highest power. In the second stage of frequency doubling, the maximum power output is achieved by adjusting the pitch and horizontal yaw of the dual-wavelength reflector.

[0103] After the laser is debugged, the temperature of the (7-1) frequency doubling temperature control furnace is calibrated as the initial temperature; the power value obtained by the (12) frequency doubling power sensor is calibrated as the initial power value; and the coordinates of the frequency doubling spot obtained by the (15) position sensor are calibrated as the initial coordinates.

[0104] 2. Usage Phase

[0105] For nonlinear crystals that can use both critical phase matching and non-critical phase matching in harmonic generation, a feedback mechanism can be used to achieve automatic calibration of PZT micro-angle and automatic temperature tuning of the nonlinear crystal, ensuring constant output power throughout the life cycle.

[0106] (1) The position sensor can record the initial coordinates of the fundamental frequency laser reflected during the calibration of the second pass frequency doubling. Then, during the operation of the frequency doubling laser generator, if the (15) position sensor detects that the spot coordinate offset exceeds the allowable range, the (10) two-dimensional micro-motion stage driven by the piezoelectric ceramic actuator (PZT) will be used to adjust and compensate the (8) dual-wavelength 0° reflector. The advantage of this device is that it can achieve submicron or nanometer-level high-precision displacement through a simple control method, monitor and fine-tune in real time, ensure the conversion efficiency of the second pass frequency doubling of the laser, and improve power stability.

[0107] (2) The nonlinear crystal is installed in the (7-1) frequency doubling temperature control furnace. The function of the (7-1) frequency doubling temperature control furnace is to precisely control the temperature of the nonlinear crystal to achieve non-critical phase matching. (12) The frequency doubling power sampling sensor determines the current power of the generated dual-pass frequency doubling laser. The power of the current laser is monitored by the PD. During the operation of the frequency doubling laser generator, if the PD detects a decrease in its current power, it intervenes in the (7-1) frequency doubling temperature control furnace through the ATC (Automatic Temperature Control) function. The power is corrected by controlling the temperature of the nonlinear crystal in the (7-1) frequency doubling temperature control furnace, thereby ensuring the conversion efficiency of the laser's dual-pass frequency doubling and improving power stability.

[0108] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention for those skilled in the art.

Claims

1. A laser frequency doubling generator, characterized in that, Along the direction of laser propagation, the components are arranged in sequence as follows: fundamental frequency module, frequency doubling generation module, dual-wavelength reflector, frequency doubling laser sampling mirror, and frequency doubling power sampling sensor; The frequency doubling module is equipped with a frequency doubling temperature control furnace; the frequency doubling temperature control furnace holds a nonlinear crystal. The baseband module is used to provide baseband laser; The frequency doubling module is used to perform a first nonlinear conversion and a second nonlinear conversion on the fundamental frequency laser to generate a frequency doubling laser. The dual-wavelength reflector is used to reflect the frequency-doubled laser generated by the first nonlinear conversion and the remaining fundamental frequency laser back to the frequency-doubled generation module, so that the frequency-doubled generation module can perform a second nonlinear conversion on the remaining fundamental frequency laser to generate frequency-doubled laser. The frequency-doubled laser sampling mirror is used to transmit the frequency-doubled laser as a dual-pass frequency-doubled laser and reflect a low-power frequency-doubled laser into the frequency-doubled power sampling sensor. The frequency-doubled power sampling sensor is used to determine the current power of the incoming frequency-doubled laser. The frequency doubling temperature control furnace is used to provide a constant temperature environment for the nonlinear crystal, and when the current power is less than the preset target power, the temperature of the nonlinear crystal is adjusted so that the current power reaches the target power.

2. The laser frequency doubling generator as described in claim 1, characterized in that, Also includes: PZT two-dimensional adjustment stage, polarizer and position sensor detector; The dual-wavelength reflector is mounted on the PZT two-dimensional adjustment stage; along the direction of laser propagation, the polarizer and the position sensor are sequentially arranged after the frequency doubling module; The polarizer is used to reflect the remaining fundamental frequency laser after the low-power second nonlinear conversion into the position sensing detector. The position sensor detector is used to determine the current spot position coordinates of the remaining fundamental frequency laser that has entered; The PZT two-dimensional adjustment stage is used to adjust the two-dimensional angle to maximize the efficiency of the second nonlinear conversion. During the operation of the laser frequency doubling device, when the current spot position coordinates are inconsistent with the preset target spot position coordinates, the angle of the dual-wavelength reflector is adjusted so that the current spot position coordinates are consistent with the target spot position coordinates.

3. The laser frequency doubling generator as described in claim 2, characterized in that, The frequency doubling module is also used to adjust the spatial orientation of the frequency doubling temperature control furnace when the nonlinear crystal is at a preset initial temperature, so that the fundamental frequency laser undergoes a first nonlinear conversion in the nonlinear crystal to generate a frequency doubling laser, thereby achieving phase matching; The remaining fundamental frequency laser reflected back by the dual-wavelength mirror is subjected to a second nonlinear conversion to generate frequency-doubled laser, and the pitch and horizontal yaw of the dual-wavelength mirror are adjusted to maximize the power of the generated frequency-doubled laser. Specifically, when the power of the generated frequency-doubled laser reaches its maximum value, the power of the frequency-doubled laser determined by the frequency-doubled power sampling sensor at this time is taken as the target power, and the current spot position coordinates of the remaining fundamental frequency laser determined by the position sensor at this time are taken as the target spot position coordinates.

4. The laser frequency doubling generator as described in claim 3, characterized in that, Also includes: Optical isolator, first fundamental frequency half-wave plate, fundamental frequency sampling mirror, fundamental frequency power sampling sensor, dichroic mirror, electric translation and lifting platform, second fundamental frequency half-wave plate, and waste optical collector; Along the propagation direction of the laser, the optical isolator, the first fundamental frequency half-wave plate, the fundamental frequency sampling mirror, the fundamental frequency power sampling sensor, and the dichroic mirror are sequentially arranged between the fundamental frequency module and the frequency doubling generation module; the second fundamental frequency half-wave plate is arranged before the polarizer; and the waste light collector is arranged after the polarizer. The incident surface of the dichroic mirror is coated with an anti-reflection film for fundamental frequency laser light, and the exit surface is coated with a high-reflection film for frequency-doubled laser light. The optical isolator is used to isolate the fundamental frequency laser generated by the fundamental frequency module, isolate the fundamental frequency laser transmitted in the reverse direction, and transmit the fundamental frequency laser transmitted in the forward direction into the first fundamental frequency half-wave plate. The first fundamental frequency half-wave plate is used to change the polarization of the fundamental frequency laser to horizontal linear polarization before it enters the fundamental frequency sampling mirror; The fundamental frequency sampling mirror is used to transmit fundamental frequency laser light into the dichroic mirror and reflect low-power fundamental frequency laser light into the fundamental frequency power sampling sensor. The fundamental frequency power sampling sensor is used to monitor whether the incoming fundamental frequency laser is normal; The dichroic mirror is used to transmit the fundamental frequency laser into the frequency doubling generation module, and to reflect all the frequency doubling lasers generated by the first and second nonlinear conversions in the frequency doubling generation module into the frequency doubling laser sampling mirror. The remaining fundamental frequency laser in the frequency doubling generation module is transmitted sequentially into the first fundamental frequency half-wave plate and the optical isolator, so that the first fundamental frequency half-wave plate and the optical isolator change the polarization of the remaining fundamental frequency laser to vertical linear polarization, and then reflect it into the second fundamental frequency half-wave plate. The second fundamental frequency half-wave plate is used to polarize the remaining fundamental frequency laser before it enters the polarizer; The waste light collector is used to collect the remaining fundamental frequency laser transmitted through the polarizer.

5. The laser frequency doubling generator as described in claim 4, characterized in that, Also includes: Electric translational lifting platform; The dichroic mirror, frequency doubling module, dual-wavelength reflector, and PZT two-dimensional adjustment stage are installed on the electric translation and lifting platform; The electric translational lifting platform is used to provide vertical linear motion for the dichroic mirror, frequency doubling module, dual-wavelength reflector, and PZT two-dimensional adjustment platform.

6. The laser frequency doubling generator as described in claim 5, characterized in that, The frequency multiplier module is also equipped with a temperature control furnace connection mechanical component; The temperature control furnace connecting mechanical components are respectively connected to the frequency doubling temperature control furnace and the electric translation lifting platform by screws; When the temperature control furnace connecting mechanical components are connected to the frequency doubling temperature control furnace and the electric translation lifting platform, preset debugging and locking requirements must be met. The debugging and locking requirements include debugging requirements and locking requirements; the debugging requirements are: after the temperature control furnace connecting mechanical component is connected to the frequency doubling temperature control furnace, the frequency doubling temperature control furnace does not produce any offset in other directions when rotating clockwise and counterclockwise around the x-axis by a preset angle; The locking requirement is as follows: when the temperature control furnace connecting mechanical component is connected to the frequency multiplier temperature control furnace, the temperature control furnace connecting mechanical component and the frequency multiplier temperature control furnace are tightly locked with screws until the locking distance between the temperature control furnace connecting mechanical component and the frequency multiplier temperature control furnace is less than the preset distance. When the temperature control furnace connecting mechanical component is connected to the electric translational lifting platform, the temperature control furnace connecting mechanical component and the electric translational lifting platform are tightly locked with screws until the locking distance between the temperature control furnace connecting mechanical component and the electric translational lifting platform is less than the preset distance.

7. The laser frequency doubling generator as described in claim 1, characterized in that, The nonlinear crystal is processed in the following way: Along a preset cutting direction, a wedge angle of the same angle is cut at the input and output ends of the nonlinear crystal respectively; wherein, the wedge angle separates the spot of the reflected light and the main optical path, and at each point of use of the nonlinear crystal, the reflected light can pass completely through the nonlinear crystal without hitting the side of the nonlinear crystal.

8. The laser frequency doubling generator as described in claim 7, characterized in that, The nonlinear crystal is further processed in the following manner: Within a preset allowable temperature range for noncritical phase matching, the operating temperature of the nonlinear crystal is adjusted to have an offset from the preset theoretical phase matching temperature value; wherein, the offset is calculated based on the angle required for the nonlinear crystal to just separate two wavelengths of light; The spatial orientation of the nonlinear crystal is adjusted so that the spatial orientation compensates for the angle.

9. The laser frequency doubling generator as described in claim 8, characterized in that, The nonlinear crystals include: BBO crystals, LBO crystals, CLBO crystals, or KBBF crystals.

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