High-stability efficient frequency multiplication system and method

Abstract

The invention belongs to the technical field of lasers, and particularly discloses a high-stability efficient frequency multiplication system and method. Comprising a fundamental frequency light source; the frequency doubling module comprises a polarization beam splitter, a first half-wave plate, a focusing lens, a frequency doubling crystal, a dichroscope and a spectroscope which are sequentially arranged in the light beam propagation direction, and the dichroscope is used for transmitting frequency doubling light output by the frequency doubling crystal and reflecting residual fundamental frequency light; the phase control module is used for receiving the residual fundamental frequency light reflected by the dichroscope, carrying out phase and polarization adjustment on the residual fundamental frequency light and then inputting the residual fundamental frequency light to the frequency doubling module again for frequency doubling, so that the residual fundamental frequency light subjected to frequency doubling is the same as the original fundamental frequency light in phase and polarization direction; and the feedback control module is used for locking the maximum value of the frequency doubling light according to the beam splitting light so as to adjust the angle of the first half-wave plate and the phase control module, so that the power of the frequency doubling light output by the dichroscope is maximized. The frequency doubling conversion efficiency is higher, and the stability is good.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, and more specifically, relates to a highly stable and efficient frequency doubling system and method. Background Technology

[0002] High-power lasers have broad application needs in industrial fields. However, for visible and ultraviolet lasers, directly obtaining high-power lasers through gain media is quite difficult. Frequency doubling technology in nonlinear frequency conversion is an important means of extending the laser output wavelength. Currently, there are three main structural methods for high-power frequency doubling technology: intracavity resonant frequency doubling, extracavity resonant frequency doubling, and single-pass frequency doubling. Intracavity resonant frequency doubling involves adding a frequency doubling crystal to the laser resonant cavity. This means that high-power, high-beam-quality fiber lasers cannot be used for the fundamental frequency beam, and the fundamental frequency beam of commonly used solid-state lasers is affected by thermal effects, leading to beam quality degradation. Extracavity resonant frequency doubling has higher efficiency and allows for separate optimization of the fundamental frequency resonant cavity and the frequency doubling cavity. However, it requires strict control of the cavity length, design of a complex piezoelectric ceramic feedback control system, and unconverted fundamental frequency beams can return to the fundamental frequency beam link, easily causing laser damage. Single-pass frequency doubling has a simple structure, low cost, and is easy to integrate, making it the mainstream frequency doubling output scheme for kilowatts and above. However, its frequency doubling efficiency is relatively low compared to the other two schemes. Summary of the Invention

[0003] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a highly stable and efficient frequency doubling system and method. It utilizes a phase control module to regulate the phase of the unconverted fundamental frequency light, enabling it to be efficiently injected into the frequency doubling crystal for a second frequency doubling process. A feedback module controls the polarization state and coherent superposition of the fundamental frequency light, allowing for continuous recycling and maximizing frequency doubling efficiency. Compared to existing frequency doubling structures, this method offers higher conversion efficiency, better stability, and facilitates the generation and transmission of high-power frequency-doubled light.

[0004] To achieve the above objectives, according to one aspect of the present invention, a highly stable and efficient frequency multiplication system is proposed, comprising: A fundamental frequency light source, used to output fundamental frequency light; The frequency doubling module includes a polarizing beam splitter, a first half-wave plate, a focusing lens, a frequency doubling crystal, a dichroic mirror, and a beam splitter arranged sequentially along the beam propagation direction. The dichroic mirror is used to transmit the frequency-doubled light output by the frequency doubling crystal and reflect the remaining fundamental frequency light. The phase control module is used to receive the residual fundamental frequency light reflected by the dichroic mirror, and after adjusting the phase and polarization of the residual fundamental frequency light, it is re-inputted to the frequency doubling module for frequency doubling, so that the phase and polarization direction of the frequency-doubled residual fundamental frequency light are the same as those of the original fundamental frequency light. The feedback control module receives the split beam from the beam splitter and locks the maximum value of the frequency-doubled light based on the split beam, so as to adjust the angle and phase control module of the first half-wave plate, thereby maximizing the power of the frequency-doubled light output by the dichroic mirror.

[0005] As a further preferred embodiment, the phase control module includes a first high-reflection mirror, a second half-wave plate, a phase controller, and a second high-reflection mirror arranged sequentially along the propagation direction of the remaining fundamental frequency light beam.

[0006] As a further preferred embodiment, the feedback control module includes a photodetector and a controller.

[0007] As a further preferred embodiment, a thermal lens compensation unit is also included, located between the second high-reflectivity mirror and the polarization beam splitter, for dynamically shaping the wavefront curvature of the remaining fundamental frequency light through thermal compensation.

[0008] As a further preferred embodiment, the thermal lens compensation unit includes an electrically adjustable zoom lens group or an adaptive deformable mirror; the thermal lens compensation unit is connected to the controller, which is used to adjust the focal length or curvature of the thermal lens compensation unit according to the fundamental frequency light power output by the fundamental frequency light source or a preset thermal effect model, so that the waist position and mode field size of the recovered residual fundamental frequency light in the frequency doubling crystal match the newly incident fundamental frequency light.

[0009] As a further preferred embodiment, it also includes: a jitter locking unit for loading a modulation signal onto the phase controller and demodulating the error signal to achieve closed-loop locking.

[0010] As a further preferred embodiment, the jitter locking unit includes: A signal generator is used to generate a sinusoidal modulated signal of a specific frequency and output it to the phase controller; A lock-in amplifier, whose signal input terminal is connected to the photodetector and whose reference input terminal is connected to the signal generator, is used to perform phase-sensitive detection on the frequency-doubled light signal detected by the photodetector and output an error signal. A PID controller is used to generate a DC bias voltage based on the error signal, and then superimpose it with the sinusoidal modulation signal to drive the phase controller.

[0011] According to another aspect of the present invention, a highly stable and efficient frequency multiplication output method is also provided, comprising the following steps: S1: The fundamental frequency light is incident on the frequency doubling crystal to generate frequency doubling light, and at the same time, the unconverted residual fundamental frequency light is separated out; S2: Collimate, adjust the phase and polarization direction of the remaining fundamental frequency light so that the remaining fundamental frequency light has the same phase and polarization direction as the original fundamental frequency light; S3: The remaining fundamental frequency light after processing in S2 is re-injected into the frequency doubling crystal, and it interferes with the newly incident fundamental frequency light; S4: Acquire a portion of the frequency-doubled light as a feedback signal to lock the maximum value of the frequency-doubled light, and adjust the positive bias direction and phase of the fundamental light and the remaining fundamental light to maximize the output power of the frequency-doubled light.

[0012] As a further preferred embodiment, S2 further includes: dynamically shaping the wavefront curvature of the remaining fundamental frequency light through thermal compensation, so that the waist position and mode field size of the recovered remaining fundamental frequency light in the frequency doubling crystal match the newly incident fundamental frequency light.

[0013] As a further preferred embodiment, the dynamic shaping of the wavefront curvature of the remaining fundamental frequency light through thermal compensation specifically includes: monitoring the current fundamental frequency light power or the temperature of the frequency doubling crystal; calculating the current thermal focal length change of the frequency doubling crystal according to a preset thermal lens effect curve; driving the thermal lens compensation unit to change its equivalent focal length to compensate for the thermal focal length change, and maintaining the Rayleigh length of the remaining fundamental frequency light and the newly incident fundamental frequency light consistent within the frequency doubling crystal.

[0014] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages: 1. This invention effectively re-injects unconverted fundamental frequency light into the frequency doubling crystal for coherent superposition by constructing an external circulating optical path that includes phase control and feedback adjustment. While retaining the advantages of easy integration of the single-pass structure, it solves the problem of low frequency doubling efficiency, thereby achieving laser frequency doubling output with high power, high efficiency and high stability. 2. This invention designs a phase control module to collect the fundamental frequency light that was wasted during the single-pass frequency doubling process and re-injects it into the frequency doubling crystal. Through this recycling mechanism, the power density of the fundamental frequency light at the crystal is enhanced, thereby solving the technical problem of low frequency doubling efficiency caused by a single action in traditional single-pass frequency doubling structures and maximizing the frequency doubling efficiency.

[0015] 3. This invention utilizes a feedback module to sample and monitor the output frequency-doubled light, and adjusts the angle of the half-wave plate and the phase of the phase controller in the loop in real time based on the monitoring results, thereby locking the maximum value of the frequency-doubled light power. This active control mechanism ensures that the reinjected residual fundamental frequency light and the newly incident fundamental frequency light always satisfy the coherence condition inside the crystal, forming stable interference superposition and a uniform light field intensity distribution, thus guaranteeing the high stability of the frequency-doubled output.

[0016] 4. Compared with intracavity resonant frequency doubling technology, this invention adopts an external cavity structure, which allows the use of high beam quality fiber lasers as light sources and avoids the degradation of fundamental frequency beam quality caused by the thermal effect of the gain medium of solid lasers. At the same time, the structure of this invention facilitates the generation and transmission of high-power frequency-doubled light, overcoming the shortcomings of traditional high-power frequency doubling schemes that make it difficult to balance high efficiency and high beam quality. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a highly stable and efficient frequency multiplication system provided in an embodiment of the present invention.

[0018] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1-fundamental frequency light source, 2-polarizing beam splitter, 3-first half-wave plate, 4-focusing lens, 5-frequency doubling crystal, 6-dichroic mirror, 7-collimating lens, 8-first high-reflection mirror, 9-second half-wave plate, 10-phase controller, 11-second high-reflection mirror, 12-beam splitter, 13-photodetector, 14-feedback module. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0020] like Figure 1 As shown, this embodiment of the invention provides a highly stable and efficient frequency doubling system, including: a fundamental frequency optical source, a frequency doubling module, a phase control module, and a feedback module.

[0021] The fundamental frequency light source 1 used is a high-power linearly polarized narrow-linewidth laser. The higher its polarization extinction ratio, the higher its frequency doubling efficiency.

[0022] The high-efficiency frequency doubling technology employs an external single-pass frequency doubling structure. Its frequency doubling module consists of a fundamental frequency light source passing sequentially through a polarizing beam splitter (PBS) 2, a half-wave plate 3, a focusing lens 4, a frequency doubling crystal 5, and a dichroic mirror 6. The half-wave plate rotates the polarization direction of the fundamental frequency light to align it parallel to the optical axis of the frequency doubling crystal. The focusing lens focuses the collimated fundamental frequency light onto the center of the crystal, generating high power density. The focal length of the focusing lens must consider both the size of the output beam of the fundamental frequency light and the length of the frequency doubling crystal to ensure that the fundamental frequency light operates within the Rayleigh distance range in the frequency doubling crystal. To improve frequency doubling efficiency, within the damage threshold range of the frequency doubling crystal, a higher power density of the focused beam results in higher frequency doubling efficiency. The PBS, half-wave plate, and focusing lens all have high transmittance in the fundamental frequency band. Both ends of the frequency doubling crystal have high transmittance in both the fundamental frequency and frequency doubling bands, with a transmittance of not less than 99%. The dichroic mirror separates the fundamental frequency light and the frequency doubling light, exhibiting high reflectivity for the fundamental frequency light and high transmittance for the frequency doubling light.

[0023] The phase control module reuses the unconverted fundamental frequency light for further frequency doubling. A phase controller regulates the phase of the unconverted fundamental frequency light incident on the frequency doubling crystal, maximizing the frequency doubling efficiency. This module collimates the diverging light spot of the unconverted fundamental frequency light through a collimating lens 7. The first high-reflection mirror 8 and the second high-reflection mirror 11 reflect the unconverted fundamental frequency light onto the PBS (Polymer Surface Photocell), which then re-dops the light through the frequency doubling module, maximizing the utilization of the fundamental frequency light and improving the frequency doubling efficiency. Since the phase and polarization direction of the fundamental frequency light change after passing through the frequency doubling crystal, to ensure that the fundamental frequency light can still undergo frequency doubling after returning to the frequency doubling module through the high-reflection mirrors, a half-wave plate 9 adjusts the polarization direction of the fundamental frequency light, and a phase controller 10 controls the phase of the unconverted fundamental frequency light to match the initial incident phase, thus improving the frequency doubling efficiency.

[0024] After the frequency-doubled light is output from the dichroic mirror, it is sampled by the beam splitter 12. The sampled light is received by the photodetector 13 and enters the feedback module 14. The feedback module can lock the frequency-doubled light to its maximum value based on the intensity of the sampled light, and control and adjust the phase of the first half-wave plate, the second half-wave plate, and the phase controller to maximize the output power of the frequency-doubled light. It is important to note that the unconverted fundamental frequency light must form a stable interference with the newly incident fundamental frequency light in the crystal, and the intensity distribution of the superimposed light field must be uniform to participate in the frequency doubling process efficiently. Therefore, there are requirements for the selection of the frequency doubling crystal and the parameters of the fundamental frequency light. By adjusting the optical path of the unconverted fundamental frequency light through the phase control module through the feedback module, the two fundamental frequency beams are coherently superimposed, thereby improving the frequency doubling efficiency.

[0025] Based on the above embodiments, in a preferred embodiment of the present invention, regarding the mode field mismatch caused by the thermal lensing effect, when the fundamental frequency light power is very high, the frequency doubling crystal absorbs energy and generates a thermal gradient, and the crystal behaves like a thermal lens. This causes the beam waist position and size of the fundamental frequency light to drift. Traditional fixed optical paths cannot adapt to this change, resulting in a decrease in the overlap factor between the recovered fundamental frequency light and the newly incident light, and the frequency doubling efficiency saturates or even decreases with increasing power. In this embodiment, a thermal lens compensation unit is added to the above system. This thermal lens compensation unit is located between the second high-reflectivity mirror 11 and the polarization beam splitter 2, and is used to dynamically shape the wavefront curvature of the remaining fundamental frequency light through thermal compensation. Preferably, the thermal lens compensation unit includes an electrically adjustable zoom lens group or an adaptive deformable mirror; the thermal lens compensation unit is connected to the controller, which is used to adjust the focal length or curvature of the thermal lens compensation unit according to the fundamental frequency light power output by the fundamental frequency light source 1 or a preset thermal effect model, so that the beam waist position and mode field size of the recovered remaining fundamental frequency light in the frequency doubling crystal 5 match the newly incident fundamental frequency light.

[0026] Based on any of the above embodiments or combinations of embodiments, in this embodiment, to address the problems of unstable phase locking, the traditional "hill-climbing" locking algorithm having extremely low sensitivity (zero derivative) near the maximum tracking power value, and being easily affected by environmental noise causing phase drift, thus failing to achieve long-term stable coherent superposition, a jitter locking unit is also provided. This unit is used to load a modulation signal onto the phase controller 10 and demodulate the error signal to achieve closed-loop locking. Preferably, the jitter locking unit includes: a signal generator for generating a sinusoidal modulation signal of a specific frequency and outputting it to the phase controller 10; a lock-in amplifier, whose signal input terminal is connected to the photodetector 13 and its reference input terminal is connected to the signal generator, for performing phase-sensitive detection on the frequency-doubled light signal detected by the photodetector 13 and outputting an error signal; and a PID controller for generating a DC bias voltage based on the error signal, superimposing it with the sinusoidal modulation signal, and driving the phase controller 10.

[0027] Based on any of the above embodiments, this embodiment also provides a working process for a highly stable and efficient frequency multiplication system: The S1 fundamental frequency light is incident on the frequency doubling crystal to generate frequency doubling light, and the unconverted residual fundamental frequency light is separated out; S2 collimates the remaining fundamental frequency light and uses a thermal lens compensation unit to shape the beam. Specifically, the beam shaping includes: monitoring the current fundamental frequency light power or the temperature of the frequency doubling crystal; calculating the current thermal focal length change of the frequency doubling crystal based on a preset thermal lens effect curve; and driving the thermal lens compensation unit to change its equivalent focal length to compensate for the thermal focal length change, so as to keep the Rayleigh length of the remaining fundamental frequency light and the newly incident fundamental frequency light consistent within the frequency doubling crystal.

[0028] S3 uses a phase controller to perform phase modulation on the remaining fundamental frequency light after shaping and adjust its polarization state. In this step, adjusting the polarization state involves using a half-wave plate to rotate the polarization direction of the remaining fundamental frequency light by 90 degrees so that it can be reflected by the polarization beam splitter and combined with the newly incident fundamental frequency light transmitted through it.

[0029] S4 re-injects the processed residual fundamental frequency light into the frequency doubling crystal, where it interferes with the newly incident fundamental frequency light. In this step, the residual fundamental frequency light and the newly incident fundamental frequency light satisfy the constructive interference condition in the frequency doubling crystal, and the wavefront overlap integral factor of the two beams is maximized through the shaping in step S2.

[0030] The S5 acquires a portion of the frequency-doubled light as a feedback signal and uses jitter-locked technology to control the phase controller, locking the interferometric enhancement state. Specifically, the jitter-locked control involves applying a small-amplitude sinusoidal jitter signal to the phase controller. f mod Demodulate the frequency from the feedback signal. f mod The components of the phase mismatch are used to obtain an error signal that reflects the direction and magnitude of the phase mismatch. The DC bias voltage of the phase controller is adjusted by negative feedback so that the error signal is kept near zero, thereby keeping the frequency multiplication output power at its peak.

[0031] More specifically, this embodiment proposes an efficient frequency multiplication method, the specific process of which is as follows: Step 1: Fundamental frequency light injection and initial conversion. The P-polarized light emitted from the fundamental frequency light source passes through the PBS, is focused, and enters the frequency doubling crystal. Part of the light is converted into frequency-doubled light (such as green light), and the remaining unconverted fundamental frequency light (such as infrared light) is reflected and extracted by the dichroic mirror.

[0032] Step two, dynamic beam shaping and thermal compensation (the remaining fundamental frequency light is collimated into parallel light by a collimating lens. At this time, the system looks up the pre-stored thermal lens focal length data according to the current optical power level and drives the thermal lens compensation unit (e.g., moving the lens position). Specific operation: If the crystal thermal lensing effect is enhanced (focal length becomes shorter), the compensation unit correspondingly increases the divergence of the reinjected light, causing the focal point of the reinjected light in the crystal to shift backward and re-coincid with the focal point of the newly incident light.

[0033] Step three: After phase modulation and polarization adjustment, the beam passes through the second half-wave plate, where its polarization direction is rotated by 90° (becoming S-polarized) to meet the reflection conditions of the PBS. Simultaneously, the beam passes through a phase controller, whose piezoelectric ceramic precisely adjusts the position of the reflecting surface according to the driving voltage, changing the optical path with nanometer-level precision.

[0034] Step four: The remaining fundamental frequency light, coherently superimposed and reconverted to S-polarization, is reflected by the PBS and then combined with the transmitted P-polarized new fundamental frequency light. The two beams are vector-combined in the frequency doubling crystal according to the type I or type II phase matching condition. Since step two ensures spatial mode matching and step three (in conjunction with step five) ensures phase matching, the two beams undergo constructive interference. At this point, the fundamental frequency light field intensity within the crystal reaches its maximum, thereby greatly exciting nonlinear effects.

[0035] Step 5: The closed-loop jitter lockout system enters the locked state. Modulation: A frequency of [frequency value missing] is superimposed onto the phase controller. f The sinusoidal perturbation. Detection: The photodetector receives the frequency-doubled light, which contains both DC and AC components. Demodulation: The lock-in amplifier extracts the frequency... f The amplitude and phase of the AC component are calculated, and an error signal E(t) is output. When the frequency doubling efficiency is highest, the error signal E(t) = 0; when the phase deviates, E(t) is positive or negative. Feedback: The PID controller adjusts the DC bias voltage according to E(t), forcibly pulling the operating point back to E(t) = 0, which is the peak of the frequency doubling efficiency curve. This method, through a strategy of "shaping first, then adjusting phase, and then locking," transforms the residual fundamental frequency light, which was originally considered waste energy, into an effective pump source that can enhance the frequency doubling efficiency. In particular, the combination of steps two and five makes this method not only theoretically efficient but also extremely robust in practical engineering applications, solving the problem of existing technologies being "usable in the laboratory but unstable in engineering."

[0036] This invention employs the following working mechanisms: Thermal Lens Compensation Principle: Under the action of high-power (e.g., kilowatt-level) laser, the temperature at the center of the frequency doubling crystal increases, causing a radial gradient change in the refractive index, forming an equivalent "thermal lens." This causes the focal point of the remaining fundamental frequency light that was originally collimated and reinjected to shift forward, making it impossible for it to maintain mode overlap with the newly incident fundamental frequency light over the entire length of the crystal. The thermal lens compensation unit in this system generates a reverse wavefront curvature by changing the divergence angle of the reinjected beam, thus counteracting the effect of the crystal's thermal lens and forcing the two beams to maintain the same Rayleigh range and beam waist radius within the crystal. Dither Locking Principle: To address the low sensitivity problem at the power peak of the traditional "hill-climbing method," this system uses a signal generator to apply a perturbation (dither) to the phase controller. Since the frequency doubling efficiency and phase difference are nonlinear, the response slopes on both sides of the peak are opposite. Lock-in amplifiers can accurately determine whether the current phase is biased to the left or right by detecting the signal component in the output light that is at the same frequency as the perturbation (i.e., the first derivative), thereby generating a highly sensitive error signal for closed-loop control.

[0037] The system architecture achieves several beneficial effects, including overcoming power saturation: Through hardware-based thermal lensing compensation, the frequency doubling conversion efficiency does not roll off due to mode-field mismatch across the entire dynamic range from low to high power, achieving true linear high-power scaling. Environmental interference resistance: Employing jitter-locking technology and using phase-sensitive detection to extract useful signals from noise, the system can resist platform micro-vibrations and optical path changes caused by air convection, achieving long-term (>24 hours) power stability with an RMS noise level better than 0.5%.

[0038] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A highly stable and efficient frequency multiplication system, characterized in that, include: A fundamental frequency light source (1) is used to output fundamental frequency light; The frequency doubling module includes a polarization beam splitter (2), a first half-wave plate (3), a focusing lens (4), a frequency doubling crystal (5), a dichroic mirror (6), and a beam splitter (12) arranged sequentially along the beam propagation direction. The dichroic mirror (6) is used to transmit the frequency-doubled light output by the frequency doubling crystal (5) and reflect the remaining fundamental frequency light. The phase control module is used to receive the remaining fundamental frequency light reflected by the dichroic mirror (6), and after adjusting the phase and polarization of the remaining fundamental frequency light, it is re-inputted to the frequency doubling module for frequency doubling, so that the phase and polarization direction of the frequency-doubling remaining fundamental frequency light are the same as those of the original fundamental frequency light. The feedback control module is used to receive the beam splitter (12) and lock the maximum value of the frequency doubling light according to the split beam to adjust the angle and phase control module of the first half-wave plate (3) so that the frequency doubling light output by the dichroic mirror (6) is maximized.

2. The high-stability, high-efficiency frequency multiplication system according to claim 1, characterized in that, The phase control module includes a first high-reflection mirror (8), a second half-wave plate (9), a phase controller (10), and a second high-reflection mirror (11) arranged sequentially along the propagation direction of the remaining fundamental frequency light beam.

3. The high-stability, high-efficiency frequency multiplication system according to claim 2, characterized in that, The feedback control module includes a photodetector (13) and a controller (14).

4. The high-stability, high-efficiency frequency multiplication system according to claim 2, characterized in that, It also includes a thermal lens compensation unit, located between the second high-reflection mirror (11) and the polarization beam splitter (2), for dynamically shaping the wavefront curvature of the remaining fundamental frequency light through thermal compensation.

5. The high-stability, high-efficiency frequency multiplication system according to claim 4, characterized in that, The thermal lens compensation unit includes an electric zoom lens group or an adaptive deformable mirror; the thermal lens compensation unit is connected to the controller, which is used to adjust the focal length or curvature of the thermal lens compensation unit according to the fundamental frequency light power output by the fundamental frequency light source (1) or a preset thermal effect model, so that the waist position and mode field size of the recovered residual fundamental frequency light in the frequency doubling crystal (5) match the newly incident fundamental frequency light.

6. A highly stable and efficient frequency multiplication system according to any one of claims 1-5, characterized in that, Also includes: The jitter locking unit is used to load the modulation signal onto the phase controller (10) and demodulate the error signal to achieve closed-loop locking.

7. The high-stability, high-efficiency frequency multiplication system according to claim 6, characterized in that, The jitter locking unit includes: A signal generator is used to generate a sinusoidal modulated signal of a specific frequency and output it to the phase controller (10). A lock-in amplifier, whose signal input terminal is connected to the photodetector (13) and whose reference input terminal is connected to the signal generator, is used to perform phase-sensitive detection on the frequency-doubled light signal detected by the photodetector (13) and output an error signal; A PID controller is used to generate a DC bias voltage based on the error signal, and then superimpose it with the sinusoidal modulation signal to drive the phase controller (10).

8. A highly stable and efficient frequency multiplication output method, characterized in that, Includes the following steps: S1: The fundamental frequency light is incident on the frequency doubling crystal to generate frequency doubling light, and at the same time, the unconverted residual fundamental frequency light is separated out; S2: Collimate, adjust the phase and polarization direction of the remaining fundamental frequency light so that the remaining fundamental frequency light has the same phase and polarization direction as the original fundamental frequency light; S3: The remaining fundamental frequency light after processing in S2 is re-injected into the frequency doubling crystal, and it interferes with the newly incident fundamental frequency light; S4: Acquire a portion of the frequency-doubled light as a feedback signal to lock the maximum value of the frequency-doubled light, and adjust the positive bias direction and phase of the fundamental light and the remaining fundamental light to maximize the output power of the frequency-doubled light.

9. The high-stability, high-efficiency frequency multiplication output method according to claim 8, characterized in that, The S2 further includes: dynamically shaping the wavefront curvature of the remaining fundamental frequency light through thermal compensation, so that the waist position and mode field size of the recovered remaining fundamental frequency light in the frequency doubling crystal (5) match the newly incident fundamental frequency light.

10. The high-stability, high-efficiency frequency multiplication output method according to claim 9, characterized in that, The process of dynamically shaping the wavefront curvature of the remaining fundamental frequency light through thermal compensation specifically includes: monitoring the current fundamental frequency light power or the temperature of the frequency doubling crystal; calculating the current change in the thermal focal length of the frequency doubling crystal based on a preset thermal lens effect curve; driving the thermal lens compensation unit to change its equivalent focal length to compensate for the change in thermal focal length and maintain the Rayleigh length of the remaining fundamental frequency light and the newly incident fundamental frequency light consistent within the frequency doubling crystal.

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