Intracavity quadruplicated frequency laser and implementation method

Abstract

The invention discloses an intracavity quadruplicated frequency laser which comprises a polarization rotation reflection module, a fundamental frequency light gain amplification module, a light conversion module and a double frequency light energy storage cavity. An optical filter, a fundamental frequency optical gain amplification module, a first polarization splitting prism, a frequency doubling conversion module, an output cavity mirror, a second polarization splitting prism and a polarization adjustment module are sequentially arranged on one side of the polarization rotation reflection module along an optical path. The first polarization splitting prism, the frequency doubling conversion module, the output cavity mirror, the second polarization splitting prism and the polarization adjustment module form a light conversion module; the frequency doubling light energy storage cavity is connected in parallel with the light conversion module and surrounds the outside of the frequency doubling conversion module, and the phase compensator is arranged between the third light splitting lens and the fourth light splitting lens. The problems of reverse light interference, poor polarization state control, unstable resonance conditions and the like in a light path are solved, and the output performance and the stability of the laser are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser technology, in particular to a cavity four frequency multiplication laser and a realization method. BACKGROUND

[0002] In the field of laser, it has important application value to obtain high-power and narrow linewidth laser output with specific wavelength, such as in the field of high-precision laser processing, spectral analysis in scientific research, biomedical imaging, etc. The cavity frequency multiplication technology is one of the effective means to realize the laser output with specific wavelength, and through multi-stage frequency multiplication, the fundamental frequency light can be converted into the required high harmonic light. When realizing four frequency multiplication, for example, converting 1064nm fundamental frequency light into 266nm laser, the traditional cavity frequency multiplication laser has the problems that, due to the large gain bandwidth of the gain medium such as Yb fiber, the long fundamental wave oscillation ring cavity will cause multiple wavelengths in the gain bandwidth range to meet the fundamental wave resonance condition, so that the spectral linewidth of the output laser is wide and the monochromaticity is poor. In addition, the problems of reverse light interference in the optical path, poor polarization state control and unstable resonance condition will also affect the output performance and stability of the laser. Therefore, it is urgent to improve the traditional cavity frequency multiplication laser to solve the above problems. SUMMARY

[0003] The purpose of the present application is to provide a cavity four frequency multiplication laser and a realization method to solve the problems proposed in the background.

[0004] To achieve the above purpose, the present application provides the following technical scheme: a cavity four frequency multiplication laser, comprising a polarization rotation reflection module, a fundamental frequency light gain amplification module, an optical conversion module and a two frequency multiplication light energy storage cavity, the polarization rotation reflection module comprising a first Faraday rotator and a total reflection cavity mirror, the polarization rotation reflection module is sequentially provided with a filter, the fundamental frequency light gain amplification module, a first polarization beam splitter prism, a frequency multiplication conversion module, an output cavity mirror, a second polarization beam splitter prism and a polarization adjustment module along the optical path along one side, the first polarization beam splitter prism, the frequency multiplication conversion module, the output cavity mirror, the second polarization beam splitter prism and the polarization adjustment module constitute the optical conversion module;

[0005] The two frequency multiplication light energy storage cavity is ring-shaped, comprising a first light splitting mirror, a second light splitting mirror, a third light splitting mirror, a fourth light splitting mirror and a phase compensator, the two frequency multiplication light energy storage cavity is connected in parallel to the optical conversion module and surrounds the outside of the frequency multiplication conversion module, and the phase compensator is arranged between the third light splitting mirror and the fourth light splitting mirror.

[0006] Preferably, the polarization rotation reflection module comprises a first Faraday rotator and a total reflection cavity mirror, the fundamental frequency light gain amplification module comprises a first optical fiber collimator, a pump source, an optical beam combiner, a gain optical fiber and a second optical fiber collimator, and the pump light generated by the pump source is coupled to the gain optical fiber by the optical beam combiner.

[0007] Preferably, the first polarization beam splitting prism is a double-layer polarization beam splitting prism structure, comprising two layers of polarization beam splitting films for separating P-polarized and S-polarized fundamental light; the frequency doubling conversion module comprises a first frequency doubling crystal for frequency doubling the fundamental light to generate second-harmonic light and a second frequency doubling crystal for frequency doubling the second-harmonic light to generate fourth-harmonic light.

[0008] Preferably, the polarization adjustment module comprises an optical rotator for rotating the polarization direction of the fundamental light by 45° and a second Faraday rotator for rotating the polarization direction of the fundamental light by 45° non-reciprocal.

[0009] Preferably, the pump source, the light combiner and the gain fiber form a unidirectional pump or a bidirectional pump.

[0010] Preferably, the gain fiber is provided with gain ions, the gain ions comprise any one or more of neodymium ions, erbium ions, germanium ions, praseodymium ions, holmium ions, europium ions, ytterbium ions, dysprosium ions and thulium ions; and the matrix material of the gain fiber is silicate glass, fluoride glass, sulfide glass, phosphate glass, tellurite glass or oxyfluoride glass.

[0011] Preferably, the first and second frequency doubling crystals are LBO, BBO, KTP, PPLN or KBBF, the phase compensator is a wave plate, an electro-optic phase modulator, an acousto-optic phase modulator, a liquid crystal phase modulator or a fiber Bragg grating phase compensator, and the optical rotator is a quartz optical rotator or a liquid crystal optical rotator.

[0012] Preferably, the matching mode of the first and second frequency doubling crystals is angle phase matching or temperature phase matching.

[0013] Another technical scheme of the present application provides an implementation method of the intracavity four-frequency laser, comprising the following steps:

[0014] S1. Start the pump source, the pump light emitted by the pump source is injected into the gain fiber through the light combiner, the gain fiber absorbs the pump light to generate particle number inversion, thereby generating initial oscillation laser;

[0015] S2. The initial oscillation laser is transmitted to the optical filter through the first fiber collimator, the optical filter filters the initial oscillation laser, only allowing the fundamental light to pass through, and filtering out other wavelength oscillation laser;

[0016] S3. The fundamental light is incident to the polarization rotation reflection module, and after being reflected by the polarization rotation reflection module, it returns to the optical filter, and in the reflection process, the polarization direction of the fundamental light is rotated by 90°;

[0017] S4. The fundamental light after the polarization direction rotation transmits the filter and returns to the fundamental light gain amplification module, is collimated and output from the second optical fiber collimator after amplification by the fundamental light gain amplification module, and is incident on the first polarization beam splitter prism;

[0018] S5. The S polarization component of the fundamental light is output to the first beam splitter after being reflected on the two polarization beam splitting films of the first polarization beam splitter prism, and then transmits the first frequency doubling crystal, the second frequency doubling crystal and the second beam splitter, and is output to the output cavity mirror and reflected by the output cavity mirror to the second polarization beam splitter prism;

[0019] After the reflection of the second polarization beam splitter prism, the S polarization component of the fundamental light is input to the optical rotator, the polarization direction of the S polarization component of the fundamental light is rotated clockwise by 45° along the direction of light transmission, and then the S polarization component of the fundamental light is input to the second Faraday rotator, at this time, the polarization direction of the S polarization component of the fundamental light is rotated counterclockwise by 45° along the direction of light transmission and becomes P polarization fundamental light, the P polarization fundamental light transmits the first polarization beam splitter prism, becomes the amplified S polarization component of the fundamental light after passing through the fundamental light gain amplification module, the filter and the polarization rotation reflection module, and the S polarization component of the fundamental light is input to the first polarization beam splitter prism, and then oscillation is formed in the cavity;

[0020] S6. The S polarization component of the fundamental light is continuously oscillated in step S5, and the power is gradually increased, when the power reaches the frequency doubling threshold, frequency doubling reaction occurs in the first frequency doubling crystal to generate second-order frequency doubling light;

[0021] S7. The second-order frequency doubling light is reflected by the second beam splitter, the fourth beam splitter, the third beam splitter and the first beam splitter in the second-order frequency doubling light energy storage cavity in turn after transmitting the second frequency doubling crystal, forms reciprocating circulation transmission in the cavity, the phase of the second-order frequency doubling light is changed under the action of the phase compensator, and the high Q value resonance condition of the energy storage ring cavity is met, the power of the second-order frequency doubling light is continuously increased after frequency doubling in the first frequency doubling crystal;

[0022] S8. When the power of the second-order frequency doubling light reaches the frequency doubling threshold, frequency doubling reaction occurs in the second frequency doubling crystal to generate fourth-order frequency doubling light, and the fourth-order frequency doubling light is output from the output cavity mirror after transmitting the second beam splitter.

[0023] Preferably, the center wavelength of the pump source in step S1 is 976 nm, and the gain optical fiber is a ytterbium-doped quartz optical fiber.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] 1. The polarization rotation reflection module of the present application comprises a first Faraday rotator and a total reflection mirror, which can realize non-reciprocal rotation of the fundamental frequency light direction, thereby suppressing the interference of the reverse light on the oscillation of the fundamental frequency light and reducing the loss of the optical path; the optical filter only allows the fundamental frequency light to pass through, filtering out the pump light, spontaneous radiation and other stray light, effectively narrowing the spectral linewidth of the fundamental frequency light and improving the monochromaticity, while improving the output performance and stability of the laser.

[0026] 2. The present application adopts a ring-shaped light conversion module closed structure, wherein the ring-shaped closed light path enables the fundamental frequency light to circulate in the cavity, obtain energy through the fundamental frequency light gain amplification module, and improve the power; the first polarization beam splitter and the second polarization beam splitter only allow the target polarization state fundamental frequency light to participate in oscillation, excluding the interference of non-target polarization light, and the polarization adjustment module can accurately regulate the polarization direction of the fundamental frequency light to ensure that the fundamental frequency light always meets the oscillation condition in the cycle.

[0027] 3. The present application sets a second harmonic light energy storage cavity in the oscillation cavity, and places a phase compensator in the second harmonic light energy storage cavity, so that the second harmonic light meets the high Q value resonance condition of the second harmonic light energy storage cavity, and the energy of the second harmonic light is continuously enhanced, thereby improving the frequency doubling efficiency and output power of the fourth harmonic light. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of the overall structure of the present application;

[0029] Figure 2 is an amplification structure of the light conversion module and the second harmonic light energy storage cavity and a schematic diagram of the S-polarized light path.

[0030] Figure 3 is an amplification structure of the light conversion module and the second harmonic light energy storage cavity and a schematic diagram of the P-polarized light path.

[0031] In the figure:

[0032] 1 - polarization rotation reflection module; 101 - total reflection mirror; 102 - first Faraday rotator; 2 - optical filter;

[0033] 3 - fundamental frequency light gain amplification module; 301 - first optical collimator; 302 - gain optical fiber; 303 - optical beam combiner; 304 - pump source; 305 - second optical fiber collimator;

[0034] Second harmonic light energy storage cavity: 5 - first beam splitter; 8 - second beam splitter; 13 - third beam splitter; 14 - phase compensator; 15 - fourth beam splitter;

[0035] Optical conversion module: 4 - first polarizing beam splitter prism; 6 - first frequency doubling crystal; 7 - second frequency doubling crystal; 9 - output cavity mirror; 10 - second polarizing beam splitter prism; 11 - optical rotator; 12 - second Faraday rotator;

[0036] 16 - frequency doubling conversion module; 17 - polarization adjustment module. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0038] Embodiment one

[0039] Please refer to Figures 1-2The application provides an intracavity four-frequency multiplication laser, which comprises a polarization rotation reflection module 1, a fundamental light gain amplification module 3, an optical conversion module and a second-harmonic light energy storage cavity. The polarization rotation reflection module 1 comprises a first Faraday rotator 102 and a total reflection mirror 101. The polarization rotation reflection module 1 is sequentially provided with a filter 2, the fundamental light gain amplification module 3, a first polarization splitting prism 4, a frequency doubling conversion module 16, an output mirror 9, a second polarization splitting prism 10 and a polarization adjustment module 17 along an optical path on one side. The first polarization splitting prism 4, the frequency doubling conversion module 16, the output mirror 9, the second polarization splitting prism 10 and the polarization adjustment module 17 form the optical conversion module. The second-harmonic light energy storage cavity is annular and comprises a first light splitting mirror 5, a second light splitting mirror 8, a third light splitting mirror 13, a fourth light splitting mirror 15 and a phase compensator 14. The second-harmonic light energy storage cavity is connected in parallel to the optical conversion module and surrounds the outside of the frequency doubling conversion module 16. The phase compensator 14 is arranged between the third light splitting mirror 13 and the fourth light splitting mirror 15. The second-harmonic light can pass through the light splitting mirror reflectivity to optimize the second-harmonic light accumulation efficiency in the energy storage cavity, and the optical conversion module does not affect each other, which greatly improves the overall debugging flexibility of the system. The phase compensator 14 is a key element for maintaining the high Q value of the energy storage cavity, and the position design directly affects the compensation efficiency. The phase compensator 14 is arranged between the third light splitting mirror 13 and the fourth light splitting mirror 15, which can directly modulate the phase of the second-harmonic light in the cycle, accurately compensate the optical path deviation and ensure that the cavity always meets the high Q value resonance condition. The principle realized by the embodiment is that the intracavity four-frequency multiplication laser first obtains the fundamental light by passing the pump light through the particle number inversion. After the initial fundamental light is filtered by the filter 2, the polarization direction is rotated by 90° and reflected back to the filter 2. After passing through the filter 2 again, the light enters the optical conversion module and completes the first gain amplification. The optical conversion module comprises the first polarization splitting prism 4, the frequency doubling conversion module 16, the output mirror 9, the second polarization splitting prism 10 and the polarization adjustment module 17, which form a closed loop. The first polarization splitting prism 4 separates the S and P polarization components of the fundamental light and only allows the S polarization component to enter the cavity. After the S polarization fundamental light is reflected by the frequency doubling conversion module 16 and the output mirror 9, the light enters the polarization adjustment module 17 through the second polarization splitting prism 10. The polarization direction is converted into the P polarization, the light passes through the first polarization splitting prism 4 and returns to the fundamental light gain amplification module 3. After being amplified again, the polarization direction is restored to the S polarization, forming an amplification, circulation and re-amplification closed loop oscillation and continuously improving the fundamental light power.When the S-polarized fundamental light power reaches the threshold, the first frequency doubling crystal 6 of the frequency doubling conversion module 16 doubles it to second-order frequency-doubled light. It is worth noting that the initial second-order frequency-doubled light power is low and cannot be directly doubled to fourth-order frequency-doubled light. Therefore, it needs to enter the second-order frequency-doubled light energy storage cavity connected in parallel to the light conversion module and be highly reflected to circulate and transmit in the cavity. The phase compensator 14 between the third beam splitter 13 and the fourth beam splitter 15 compensates the phase deviation in real time, ensures that the second-order frequency-doubled light meets the high-Q resonance condition, and reduces energy loss. The fundamental light continuously generates new second-order frequency-doubled light in the first frequency doubling crystal 6, providing gain for the energy storage cavity, so that the second-order frequency-doubled light power accumulates rapidly. When the second-order frequency-doubled light power in the energy storage cavity reaches the threshold, the second frequency doubling crystal 7 of the frequency doubling conversion module 16 doubles it to fourth-order frequency-doubled light. The fourth-order frequency-doubled light transmits through the second beam splitter 8 and the output cavity mirror 9 which highly transmit the fourth-order frequency-doubled light, and is finally output outside the cavity. In this embodiment, a narrow-band optical filter 2 is arranged in the optical path, which effectively narrows the spectral linewidth of the fundamental light, so that the output fourth-order frequency-doubled laser has high monochromaticity and meets the demand of high-precision application. High stability, the polarization rotation reflection module 1 is used to ensure that the light propagates unidirectionally in the cavity, suppresses the interference of reverse light, and the phase compensator 14 accurately compensates the resonance condition of the second-order frequency-doubled light energy storage ring cavity, thereby improving the output stability of the laser. High-efficiency frequency doubling, the design of the energy storage ring cavity and the configuration of each element enable the frequency doubling process from the fundamental light to the second-order frequency-doubled light and then to the fourth-order frequency-doubled light to be carried out efficiently, thereby improving the energy conversion efficiency. Further, the fundamental light gain amplification module 3 includes a first optical fiber collimator 301, a pump source 304, an optical combiner 303, a gain optical fiber 302, and a second optical fiber collimator 305. The pump light generated by the pump source 304 is coupled to the gain optical fiber 302 by the optical combiner 303. The first optical fiber collimator 301 can collimate the divergent fundamental light output by the gain optical fiber 302 into a parallel light beam, ensuring that the fundamental light efficiently enters the subsequent optical path and reducing transmission loss caused by beam divergence. The second optical fiber collimator 305 re-focuses and couples the parallel fundamental light returned from the external optical path back to the gain optical fiber 302. This module design avoids mode distortion caused by beam divergence and provides a high-quality light source for subsequent frequency doubling conversion. Further, the first polarization beam splitter 4 is a double-layer polarization beam splitter structure including two layers of polarization beam splitter films for separating P-polarized and S-polarized fundamental light. Through the cooperative action of the two layers of polarization beam splitter films, the S-polarized and P-polarized components in the fundamental light are completely separated, avoiding polarization crosstalk from affecting subsequent oscillation and frequency doubling processes. The frequency doubling conversion module 16 includes the first frequency doubling crystal 6 for doubling the fundamental light and generating second-order frequency-doubled light and the second frequency doubling crystal 7 for doubling the second-order frequency-doubled light and generating fourth-order frequency-doubled light. Further, the polarization adjustment module 17 includes a rotatory polarizer 11 for rotating the polarization direction of the fundamental light by 45° and a second Faraday rotator 12 for rotating the polarization direction of the fundamental light by 45° non-reciprocal rotation.This design makes the S-polarized fundamental light realize polarization state cyclic conversion and reciprocating oscillation, while the P-polarized fundamental light cannot realize oscillation, as shown in the following formula. Figure 3 The design ensures that only S-polarized fundamental light participates in effective oscillation, improving the purity and stability of oscillation. Preferably, the pump source 304, the light combiner 303 and the gain fiber 302 form a one-way pumping or a two-way pumping. The one-way pumping refers to that the pump light is injected from one end of the gain fiber 302, coupled through the light combiner 303, transmitted in a single direction in the gain fiber 302 and absorbed by the doped ions. The one-way pumping system has a simple structure, can avoid the interference of reverse light and improve the stability in a low-power scenario. The two-way pumping refers to that the pump light is injected from both ends of the gain fiber 302, transmitted in opposite directions in the gain fiber 302 and superimposedly absorbed. The two-way pumping makes the pump light superimposed in the middle region of the fiber, finally realizes uniform population inversion in the whole fiber length, greatly improves the energy conversion efficiency of the gain fiber 302 and can avoid local high temperature concentration, significantly reduces the negative effects of thermal effects. In some embodiments, the gain fiber 302 is provided with gain ions, and the gain ions include any one or more of neodymium ions, erbium ions, germanium ions, praseodymium ions, holmium ions, europium ions, ytterbium ions, dysprosium ions and thulium ions; the matrix material of the gain fiber 302 is silicate glass or fluoride glass or sulfide glass or phosphate glass or tellurite glass or oxyfluoride glass ceramic, realizing flexible output of different wavelength fundamental light to adapt to multiple scenarios and providing a high-power, high-stability and low-loss fundamental light basic working principle for four-frequency conversion.

[0040] The first frequency doubling crystal 6 and the second frequency doubling crystal 7 are LBO, BBO, KTP, PPLN or KBBF. This design realizes efficient conversion of fundamental light to second-harmonic light and then to fourth-harmonic light by matching the requirements of frequency doubling wavelength, power and stability. The phase compensator 14 is a wave plate, an electro-optic phase modulator, an acousto-optic phase modulator, a liquid crystal phase modulator or a fiber Bragg grating phase compensator. Its function is to dynamically offset the phase deviation of light during transmission in the cavity, ensure that the second-harmonic light meets the resonance condition in the energy storage cavity and maintain a high Q value to realize efficient energy accumulation. The optical rotator 11 is a quartz optical rotator or a liquid crystal optical rotator, which can accurately control the polarization state of light, ensure that the frequency doubling crystal meets the phase matching condition, reduce polarization-related loss and finally guarantee the output power and stability of the frequency doubling light. Preferably, the matching mode of the first frequency doubling crystal 6 and the second frequency doubling crystal 7 is angle phase matching or temperature phase matching. Angle matching is suitable for environments with wide wavelength adaptation and high power tolerance, has high flexibility and is suitable for multiple scenarios. Temperature phase matching is suitable for long-term stable environments, such as industrial production equipment. The stability of temperature phase matching can guarantee the frequency doubling efficiency of the equipment to be stable during continuous work. In actual production environment, the matching mode of the frequency doubling crystal can be flexibly selected to achieve better results.Figures 1-2The embodiment is different from the first embodiment in that the embodiment provides an implementation method of the intracavity four-frequency multiplication laser, and the implementation method comprises the following steps: S1, starting a pump source 304, pump light emitted by the pump source 304 is injected into a gain optical fiber 302 through a light combiner 303, the gain optical fiber 302 absorbs the pump light to generate particle number inversion, and initial oscillation laser is generated; S2, the initial oscillation laser is transmitted to a filter 2 through a first optical fiber collimator 301, the filter 2 performs filtering processing on the initial oscillation laser, only allows base frequency light to pass through, and filters out other wavelength oscillation laser; S3, the base frequency light is incident to a polarization rotation reflection module 1, returns to the filter 2 after being reflected through the polarization rotation reflection module 1, and the polarization direction of the base frequency light is rotated by 90° in the reflection process; S4, the base frequency light whose polarization direction is rotated transmits through the filter 2, returns to a base frequency light gain amplification module 3, and is output in parallel from a second optical fiber collimator 305 after being amplified through the base frequency light gain amplification module 3, and is incident to a first polarization beam splitter prism 4; S5, S polarization component base frequency light in the base frequency light is reflected on two polarization beam splitting films of the first polarization beam splitter prism 4 respectively after being reflected on the two polarization beam splitting films, is output to a first beam splitter 5, then transmits through a first frequency doubling crystal 6, a second frequency doubling crystal 7 and a second beam splitter 8 respectively, is output to an output cavity mirror 9 and is reflected to a second polarization beam splitter prism 10 by the output cavity mirror 9; the S polarization component base frequency light is input to a rotatory polarizer 11 after being reflected by the second polarization beam splitter prism 10, the polarization direction of the S polarization component base frequency light is rotated by 45° clockwise along the direction of light transmission, and then is input to a second Faraday rotator 12, at this time, the polarization direction of the S polarization component base frequency light is rotated by 45° counterclockwise along the direction of light transmission and becomes P polarization base frequency light, the P polarization base frequency light transmits through the first polarization beam splitter prism 4, becomes amplified S polarization component base frequency light after passing through the base frequency light gain amplification module 3, the filter 2 and the polarization rotation reflection module 1, and the S polarization component base frequency light is input to the first polarization beam splitter prism 4, and oscillation is formed in the cavity; S6, the S polarization component base frequency light is continuously oscillated through the step S5, the power gradually increases, when the power reaches the frequency doubling threshold, frequency doubling reaction occurs in the first frequency doubling crystal 6, and second frequency doubling light is generated; S7, the second frequency doubling light is reflected by the second beam splitter 8, a fourth beam splitter 15, a third beam splitter 13 and the first beam splitter 5 in turn after transmitting through the second frequency doubling crystal 7, forms reciprocating circulation transmission in the cavity, the phase of the second frequency doubling light is changed under the action of a phase compensator 14, and the high Q value resonance condition of the energy storage ring cavity is met, the second frequency doubling light is frequency doubled in the first frequency doubling crystal 6, and the power is constantly increased; S8, when the power of the second frequency doubling light reaches the frequency doubling threshold, frequency doubling reaction occurs in the second frequency doubling crystal 7, and fourth frequency doubling light is generated, and the fourth frequency doubling light is output from the output cavity mirror 9 after transmitting through the second beam splitter 8, and the fourth frequency doubling light is obtained.The above implementation method introduces the whole process from emitting pump light to low-power fundamental light, to high-power divergent fundamental light, to high-power parallel fundamental light, to second-harmonic light, to fourth-harmonic light. Further, the center wavelength of the pump source 304 in step S1 is 976 nm, and the gain fiber 302 is a ytterbium-doped quartz fiber. 976 nm is a high-absorption cross-section pump wavelength of gain ions. The photon energy corresponding to this wavelength precisely matches the energy level difference of the gain ions from the ground state to the excited state, which can directly and efficiently excite the ground state gain ions to the excited state, avoiding the problem of additional energy level transitions and energy loss when pumping at other wavelengths, and further improving the efficiency and stability of the laser output.

[0041] It should be noted that the relational terms herein such as first and second, and the like, are used solely to distinguish one entity or action from another, without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0042] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. An intracavity four-fold frequency-doubled laser, characterized in that, Comprise: A polarization rotation reflection module, a fundamental light gain amplification module, an optical conversion module, and a second-harmonic light energy storage cavity, the polarization rotation reflection module comprises a first Faraday rotator and a total reflection mirror, a filter, a fundamental light gain amplification module, a first polarization beam splitter prism, a frequency doubling conversion module, an output mirror, a second polarization beam splitter prism, and a polarization adjustment module are sequentially arranged along the optical path on one side of the polarization rotation reflection module, the first polarization beam splitter prism, the frequency doubling conversion module, the output mirror, the second polarization beam splitter prism, and the polarization adjustment module constitute the optical conversion module; The second-harmonic light energy storage cavity is annular, comprising a first light splitting mirror, a second light splitting mirror, a third light splitting mirror, a fourth light splitting mirror, and a phase compensator, the second-harmonic light energy storage cavity is connected in parallel to the optical conversion module and surrounds the outside of the frequency doubling conversion module, and the phase compensator is arranged between the fourth light splitting mirror and the third light splitting mirror.

2. The intracavity fourth harmonic laser of claim 1, wherein, The fundamental light gain amplification module comprises a first optical fiber collimator, a pump source, an optical combiner, a gain optical fiber, and a second optical fiber collimator, the pump light generated by the pump source is coupled to the gain optical fiber by the optical combiner.

3. The intracavity fourth harmonic laser of claim 1, wherein, The first polarization beam splitter prism is a double-layer polarization beam splitter prism structure, comprising two layers of polarization beam splitter films for separating P-polarized and S-polarized fundamental light; the frequency doubling conversion module comprises a first frequency doubling crystal for frequency doubling the fundamental light and generating second-harmonic light and a second frequency doubling crystal for frequency doubling the second-harmonic light and generating fourth-harmonic light.

4. The intracavity fourth harmonic laser of claim 1, wherein, The polarization adjustment module comprises a rotatory polarizer for rotating the polarization direction of the fundamental light by 45° and a second Faraday rotator for rotating the polarization direction of the fundamental light by 45° non-reciprocal rotation.

5. The intracavity fourth harmonic laser of claim 2, wherein, The pump source, the optical combiner, and the gain optical fiber form unidirectional pumping or bidirectional pumping.

6. The intracavity fourth harmonic laser of claim 2, wherein, The gain optical fiber is provided with gain ions, the gain ions comprise any one or more of neodymium ions, erbium ions, germanium ions, praseodymium ions, holmium ions, europium ions, ytterbium ions, dysprosium ions, and thulium ions; and the matrix material of the gain optical fiber is one of silicate glass, fluoride glass, sulfide glass, phosphate glass, tellurite glass, or oxyfluoride glass.

7. The intracavity fourth harmonic laser of claim 3, wherein, The first frequency doubling crystal and the second frequency doubling crystal are LBO, BBO, KTP, PPLN, or KBBF, and the phase compensator is a wave plate, an electro-optic phase modulator, an acousto-optic phase modulator, a liquid crystal phase modulator, or a fiber Bragg grating phase compensator.

8. The intracavity fourth harmonic laser of claim 3, wherein, The matching mode adopted by the first frequency doubling crystal and the second frequency doubling crystal is angle phase matching or temperature phase matching.

9. The method of claim 1-8, wherein the intracavity fourth harmonic generator is implemented by, The method comprises the following steps: S1. Start the pump source, the pump light emitted by the pump source is injected into the gain optical fiber through the optical combiner, the gain optical fiber absorbs the pump light to generate particle number inversion, thereby generating initial oscillation laser; S2. The initial oscillation laser is transmitted to the filter through the first optical fiber collimator, the filter filters the initial oscillation laser, only allows the fundamental light to pass through, and filters out other wavelength oscillation laser; S3. The fundamental light is incident to the polarization rotation reflection module, and after being reflected by the polarization rotation reflection module, the fundamental light returns to the optical filter, and the polarization direction of the fundamental light is rotated by 90° during the reflection; S4. The polarization direction rotated fundamental light transmits through the optical filter, returns to the fundamental light gain amplification module, and after being amplified by the fundamental light gain amplification module, is collimated and output from the second optical fiber collimator, and is incident to the first polarization beam splitter prism; S5. After the S-polarization component fundamental light is reflected by the two layers of polarization beam splitting films of the first polarization beam splitter prism, the S-polarization component fundamental light is output to the first beam splitter, and then transmits through the first frequency doubling crystal, the second frequency doubling crystal and the second beam splitter, and is output to the output cavity mirror and reflected by the output cavity mirror to the second polarization beam splitter prism; After the S-polarization component fundamental light is reflected by the second polarization beam splitter prism, the S-polarization component fundamental light is input to the optical rotator, the polarization direction of the S-polarization component fundamental light is rotated clockwise by 45° along the direction of light transmission, and then the S-polarization component fundamental light is input to the second Faraday rotator, at this time, the polarization direction of the S-polarization component fundamental light is rotated counterclockwise by 45° along the direction of light transmission, thereby becoming P-polarization fundamental light, the P-polarization fundamental light transmits through the first polarization beam splitter prism, and after passing through the fundamental light gain amplification module, the optical filter and the polarization rotation reflection module, becomes amplified S-polarization component fundamental light, the S-polarization component fundamental light is input to the first polarization beam splitter prism, and then oscillation is formed in the cavity; S6. The S-polarization component fundamental light is continuously oscillated by the step S5, and the power gradually increases, when the power reaches the frequency doubling threshold, frequency doubling reaction occurs in the first frequency doubling crystal, and second harmonic light is generated; S7. The second harmonic light is reflected by the second beam splitter, the fourth beam splitter, the third beam splitter and the first beam splitter in the second harmonic light storage cavity in turn, and forms reciprocating circulation transmission in the cavity, under the action of the phase compensator, the phase of the second harmonic light is changed, and the high Q value resonance condition of the storage ring cavity is met, the second harmonic light is frequency doubled in the first frequency doubling crystal, and the power is continuously increased; S8. When the power of the second harmonic light reaches the frequency doubling threshold, frequency doubling reaction occurs in the second frequency doubling crystal, and fourth harmonic light is generated, the fourth harmonic light transmits through the second beam splitter, and is output from the output cavity mirror, and the fourth harmonic light is obtained.

10. The intracavity fourth harmonic laser implementation method of claim 9, wherein: The center wavelength of the pump source in the step S1 is 976 nm, and the gain optical fiber is an ytterbium-doped quartz optical fiber.

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