Light field laser with petal mode structure

Abstract

The invention discloses a petal mode structured light field laser. The laser comprises a pumping source, a pumping focusing optical module, a laser total reflective mirror, a laser gain medium, a first intra-cavity astigmatism mirror, a second intra-cavity astigmatism mirror and a laser output mirror. The length of a resonant cavity and the focal length and the position of a reflector / lens are selected, when the Gouy phase shift difference is accumulated to pi / 2, the light beam is converted from an HG0, m mode to an LG0, lOAM light beam, a second intra-cavity astigmatism mirror is placed at the position, the Gouy phase shift difference is fixed, and the laser between the second intra-cavity astigmatism mirror and a laser output mirror is the LG0, l light beam; during reverse transmission, the phase shift difference continues to be accumulated to pi, and an HG0, m mode with the direction rotating by 90 degrees relative to the original inclined HG0, m mode is formed; and when the output laser is transmitted to the laser output mirror and the Gouy phase shift difference is accumulated to 3pi / 2, an LG0,-l light beam is formed, that is, the output laser is in an LG0, + / -l petal mode synthesized by LG0, l and LG0,-l.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser, in particular to a petal mode structure light field laser. BACKGROUND

[0002] When the same order, opposite handedness Laguerre-Gaussian (LG) modes with the same intensity, namely LG 0,l and LG 0,-l modes, are coherently superimposed, a LG 0,±l mode beam with petal-shaped intensity distribution is generated, and the number of angular nodes is the topological charge l . The petal mode laser has very important applications in rotation measurement, fine processing and other fields due to its positive and negative orbital angular momentum (OAM) components and extremely special intensity distribution characteristics, and its generation method has become a research hotspot in laser physics [1] .

[0003] Direct generation of petal mode in a laser generally achieves selective excitation of specific high-order transverse modes by controlling gain and loss. For example, the pump light is shaped into a hollow ring, so that the LG 0,l and LG 0,-l modes with the largest overlap with the pump light have higher gain than other modes, and the LG 0,±l petal mode [2] can be realized; for another example, a defect point that cannot provide effective feedback to light is prepared in a mirror of a resonant cavity or other intracavity devices, i.e., the lower-order modes are "blocked", so that the laser can work in the higher-order LG 0,±l petal mode [3] that is not affected; in addition, by using the characteristic that the spot sizes of different order LG modes are different, a strong spherical aberration is introduced in the cavity to distinguish the light paths of different modes, and in combination with the design of the stable region of the resonant cavity, a high-order LG 0,±l petal mode [4] with a large range of adjustable order can be realized. In related reports, the highest order of LG 0,±l petal mode that can be generated in experiments is more than 300, and as the order of the mode increases, the intensity difference between adjacent orders decreases, making it difficult to realize the output of higher-order petal modes. On the other hand, the petal mode requires that the resonant cavity does not distinguish between the positive and negative handedness LG modes, so that the positive and negative handedness lasers with consistent intensity can be generated to form the petal mode, while the symmetry of the laser resonant cavity is inevitably broken, making the operation of the high-order LG 0,±l petal mode of the laser very sensitive to the collimation precision and disturbances, which limits the application.

[0004] Off-axis pumping is an important method for obtaining high-order transverse-mode structured optical field lasers. When a small pump light deviates from the axis of the resonant cavity, the high-order modes whose intensity maxima are closest to the pump light have higher pump overlap and corresponding effective gain compared to other modes, thus winning out and forming the laser output. Off-axis pumping eliminates the need for pump shaping, has a simple structure, and high conversion efficiency. Reports indicate that over 600-order Hermitian-Gaussian (HG) mode laser outputs have been achieved. [5] This is far higher than the highest order achievable in attempts to directly generate LG modes, and corresponding ultra-high-order LG mode laser output can be generated through astigmatic transformation (AMC). However, due to the off-axis pumping process of HG mode generation... x-y Symmetry breaking, resulting in a single HG m,n The mode is transformed into LG via AMC. p,l Pattern follows p =min( m , n ), l =| m - n The transformation relation of | can only produce LG with single chirality. p,l Pattern laser, cannot obtain LG 0,±l Petal mode.

[0005] References [1]Y. Zhang, A. Yan, Y. Qi, et al., High-order LG vortex Pr:YLF laseremitting in the visible wavelength range for the measurement of angularvelocity, Applied Physics Letters, 125(7), 071105 (2024). [2]YF Chen, YP Lan, SC Wang, Generation of Laguerre–Gaussianmodes in fiber-coupled laser diode end-pumped lasers, Appl. Phys. B, 72, 167-170 (2001). [3]Y. Zhang, Y. Qi, Q. Sheng, et al., Tunable vortex beams generation in visible band via Pr 3+:YLF laser with a spot defect, Applied PhysicsLetters, 123(25), 251117 (2023). [4]Q. Sheng, A. Wang, J. Geng, et al., Ultra-high-order Laguerre–Gaussian field generated directly from a laser cavity with spherical aberration, Laser & Photonics Reviews, 17(6), 2300369 (2023). [5]D. Zhan, Q. Sheng, T. Liu, et al., Over-600 th -order HG mode laserand LG vortex beam based on off-axis pumping, Proc. SPIE, 13711, 137110T(2025). Summary of the Invention

[0006] This invention provides a petal-mode structured light field laser. It employs an off-axis pumping method to excite an ultra-high-order HG mode laser. An in-cavity tilted spherical lens or spherical mirror is used to induce astigmatism in the intracavity oscillating beam, causing a one-way Gouy phase shift difference of π / 2 in the meridional and sagittal planes. This performs intracavity astigmatism transformation (AMC) on the oscillating laser, allowing it to switch back and forth between high-order HG and LG mode beams, thereby outputting a superimposed LG mode with positive and negative chirality. 0,±l Petal mode, see the description below: A petal-mode structured light field laser, the laser comprising: a pump source emitting pump light within the absorption band of a laser gain medium; the pump light being focused by a pump focusing lens optical module and entering the laser gain medium; the laser gain medium absorbing the pump light, forming population inversion, and generating laser gain. The laser total reflection mirror has high reflectivity for laser wavelength, and the laser output mirror has partial transmittance for laser wavelength; the first intracavity astigmatic mirror and the second intracavity astigmatic mirror, together with the laser total reflection mirror and the laser output mirror, constitute a laser resonant cavity; When the laser gain exceeds the laser resonator loss, the laser reaches the threshold and produces laser output. When the pump light incident position deviates from the optical axis of the laser resonator, the higher-order HG modes overlap significantly with the pump light, and the laser operates in higher-order HG modes. This causes the pump light to...x and y The directions are all deviated from the optical axis of the resonant cavity, exciting and x and y HG tilted at a 45° angle in all directions 0,m The mode, which is considered to be a phase-difference-free along-mode, x and y Direction HG m,0 and HG 0,m Overlay of patterns; and x and y HG tilted at a 45° angle in all directions 0,m After the pattern passes through the first intracavity astigmatism mirror, along x and y Direction HG m,0 and HG 0,m The mode components exhibit differences in Gouy phase shift during propagation; By selecting the resonant cavity length and the focal length and position of the mirror / lens, when the Gouy phase shift difference accumulates to π / 2, the beam is transformed by HG. 0,m Mode conversion to LG 0,l The OAM beam is positioned with a second intracavity astigmatism mirror at that location. The Gouy phase shift is fixed, and the laser beam between the second intracavity astigmatism mirror and the laser output mirror is the LG beam. 0,l beam; During reverse transmission, the phase shift difference continues to accumulate to π, resulting in a direction tilted relative to the original direction (HG). 0,m HG mode rotated 90° 0,m The mode; when it is transmitted to the laser output mirror, the Gouy phase shift difference accumulates to 3π / 2, forming LG. 0,-l The beam, i.e., the output laser, is LG. 0,l With LG 0,-l Synthetic LG 0,±l Petal mode.

[0007] The first intracavity astigmatic mirror and the second intracavity astigmatic mirror are tilted spherical mirrors or spherical lenses, which have high reflectivity or high transmittance for laser wavelengths.

[0008] Wherein, the beam of light is at an angle θ When the incident spherical mirror is tilted, the effective focal lengths on the meridional and sagittal planes are respectively f T =( R cos θ ) / 2 and f S = R / (2cos θ ),in R Let be the radius of curvature of the spherical mirror.

[0009] The laser gain medium is a bulk crystal, glass, or ceramic doped with rare earth ions or transition metal ions, or a solidified dye or encapsulated gas or liquid gain medium, or a gain medium that provides nonlinear gain through nonlinear processes such as optical parametric oscillation or stimulated Raman scattering.

[0010] The pump source is a semiconductor laser, a fiber laser, or a solid-state laser, and the laser mode is a fundamental transverse mode, a super-Gaussian or flat-top distribution of multiple transverse modes.

[0011] Furthermore, the emission wavelength of the pump source is within the absorption band of the laser gain medium or the transmission band and phase matching range of the nonlinear gain medium.

[0012] Furthermore, the output transmittance of the laser output mirror is less than 5%.

[0013] The beneficial effects of the technical solution provided by this invention are: 1. This invention generates higher-order LG by performing intracavity astigmatism transform on the HG mode. 0,±l Petal mode, compared to direct selection of LG based on pump shaping, amplitude template, etc. 0,±l Compared to the petal pattern approach, the implementation method is simpler, with a lower threshold and higher efficiency; 2. This invention generates higher-order LG by performing intracavity astigmatism transform on the HG mode. 0,±l The petal pattern has greater differentiation between adjacent patterns, making it easier to obtain higher-order LGs. 0,±l Petal mode output; 3. This invention generates higher-order LG by performing intracavity astigmatism transform on the HG mode. 0,±l The petal mode, with its strong intracavity astigmatism defining the eigenmode, is insensitive to the effects of resonant cavity collimation error and misalignment. 4. The present invention uses the astigmatism of a tilted spherical mirror / lens for AMC. Compared with AMC based on cylindrical lenses, the device is easier to obtain and the assembly and adjustment are simpler. Attached Figure Description

[0014] Figure 1 A schematic diagram of the optical path of a first embodiment of a petal-mode structured light field laser; Figure 2 This is a schematic diagram of the optical path of a second embodiment of a petal-mode structured light field laser. Figure 3 This is a schematic diagram showing the size of the light spot at various positions within the astigmatic resonant cavity in the first embodiment; Figure 4 For LG 0,±l A schematic diagram of a typical light intensity distribution in the petal pattern.

[0015] The attached diagram lists the components represented by each number as follows: 1: Pump source; 2: Pump focusing optical module; 3: Laser total reflection mirror; 4: Laser gain medium; 5: Astigmatism in the first cavity; 6: Astigmatism in the second cavity; 7: Laser output mirror. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0017] A petal-mode structured light field laser, comprising: a pump source 1, a pump focusing optical module 2, a laser total reflection mirror 3, a laser gain medium 4, a first intracavity astigmatism mirror 5, a second intracavity astigmatism mirror 6, and a laser output mirror 7.

[0018] Pump source 1 emits pump light within the absorption band of laser gain medium 4. After being focused by pump focusing optical module 2, the pump light enters laser gain medium 4, where it absorbs the pump light, resulting in population inversion and generating laser gain. Laser total reflection mirror 3 has high reflectivity to the laser wavelength, and laser output mirror 7 has partial transmittance to the laser wavelength. Together, they form a resonant cavity to provide feedback for the laser. The first intracavity astigmatic mirror 5 and the second intracavity astigmatic mirror 6 are tilted spherical mirrors or spherical lenses, which have high reflectivity (when using a mirror) or high transmittance (when using a lens) to the laser wavelength. Together with laser total reflection mirror 3 and laser output mirror 7, they form a laser resonant cavity. When the laser gain exceeds the laser resonator loss, the laser reaches the threshold and produces laser output. When the pump light incident position deviates from the optical axis of the laser resonator, the higher-order HG modes have greater overlap with the pump light compared to the fundamental mode, therefore the laser operates in a higher-order HG mode. x and y The directions are all deviated from the optical axis of the resonant cavity, that is, the excitation and x and y HG tilted at a 45° angle in all directions 0,m The mode, which can be viewed as a phase-difference-free along-mode, x and y Direction HG m,0 and HG 0,m Pattern superposition. The beam of light at an angle... θ When the incident spherical mirror is tilted, the effective focal lengths on the meridional and sagittal planes are respectively f T =( R cos θ ) / 2 and f S =R / (2cos θ ),in R Let be the radius of curvature of the spherical mirror (for a lens, the effective focal lengths on the meridional and sagittal planes are respectively...). f T = f cos θ and f S = f / cos θ ,in f (where the focal length is the lens), therefore the above and x and y HG tilted at a 45° angle in all directions 0,m After the pattern passes through the first intracavity astigmatism lens 5, along... x and y Direction HG m,0 and HG 0,m The mode components exhibit differences in Gouy phase shift during propagation. By appropriately selecting the resonant cavity length and the focal length and position of the mirror / lens, when the Gouy phase shift difference accumulates to π / 2, the beam is controlled by HG. 0,m Mode conversion to LG 0,l OAM beam ( m=l A second intracavity astigmatism mirror 6 is placed at this location, the Gouy phase shift difference is fixed, and the laser between the second intracavity astigmatism mirror 6 and the laser output mirror 7 is the LG laser. 0,l The beam. During reverse propagation, the phase shift difference continues to accumulate to π, resulting in a direction tilted relative to the original direction (HG). 0,m HG mode rotated 90° 0,m The mode; when it is transmitted to the laser output mirror, the Gouy phase shift difference accumulates to 3π / 2, forming LG. 0,-l The beam, i.e., the output laser, is LG. 0,l With LG 0,-l Synthetic LG 0,±l Petal mode.

[0019] Among them, the laser gain medium 4 of the laser is a bulk crystal, glass or ceramic doped with rare earth ions or transition metal ions, or a solidified dye or encapsulated gas or liquid gain medium, or a gain medium that provides nonlinear gain through nonlinear processes such as optical parametric oscillation or stimulated Raman scattering.

[0020] In this laser, the pump source 1 is a semiconductor laser, fiber laser, or solid-state laser, and the laser mode is a fundamental transverse mode, or a super-Gaussian or flat-top distribution of multiple transverse modes. The emission wavelength of the pump source 1 is within the absorption band or transmission band and phase-matching range of the laser gain medium 4, so that the laser gain medium 4 generates gain.

[0021] Preferably, the laser gain medium 4 should be a device with a relatively large aperture to avoid limiting the higher-order modes; correspondingly, the pump light at the laser gain medium 4 should have a small spot size, for example, significantly smaller than the size of the fundamental mode spot of the resonant cavity at that location, in order to improve the distinction between adjacent modes and improve the purity of the output higher-order modes; the laser output mirror 7 should be selected with a relatively low output transmittance to the laser (e.g., below 5%) to reduce the impact of inconsistent positive and negative chiral component ratios on the contrast of the petal mode.

[0022] Example 1 This invention provides a petal-mode structured light field laser, such as... Figure 1 As shown, the laser includes: a pump source 1, a pump focusing optical module 2, a laser total reflection mirror 3, a laser gain medium 4, a first intracavity astigmatism mirror 5, a second intracavity astigmatism mirror 6, and a laser output mirror 7. The system comprises: a pump source 1, a fiber-coupled semiconductor laser with a wavelength of 808 nm and a fiber core diameter of 62.5 μm; a pump focusing lens optical module 2, consisting of two plano-convex lenses, each with a focal length of 50 mm; a laser total reflection mirror 3, a plane mirror with one side facing the cavity coated with a 1064 nm laser wavelength high-reflection film and an 808 nm pump wavelength antireflection film, and the other side coated with the same film; and a laser gain medium 4, a neodymium-doped yttrium vanadate (Nd:YVO4) crystal cut along the a-axis, with an emission peak at 1064 nm and Nd... 3+ The doping concentration is 0.5-at.%, and the dimensions are 5mm × 5mm × 3mm. The laser output mirror 7 is a plane mirror, with one side coated with a 2% transmittance film for 1064nm laser wavelength and the other side coated with a 1064nm laser wavelength antireflection film. The length of the laser resonant cavity formed by the laser total reflection mirror 3 and the laser output mirror 7 is 227.6 mm. The first intracavity astigmatic mirror 5 and the second intracavity astigmatic mirror 6 are both concave mirrors with a radius of curvature of 100mm, coated with a 1064nm high reflectivity film. The distance between them is 100mm, and the radius of the fundamental mode spot at each position in the resonant cavity is as follows. Figure 3 As shown.

[0023] The 808 nm pump light emitted from pump source 1 is focused by pump focusing optical module 2 and then incident on the laser gain medium 4Nd:YVO4 crystal with a spot radius of 33 μm. The Nd in the Nd:YVO4 crystal... 3+Ions absorb the 808 nm pump light and are excited to the upper energy level of the laser, generating laser gain. When the pump light spot is located at the center of the crystal and coincides with the optical axis of the laser resonator formed by the laser total reflection mirror 3 and the laser output mirror 7, the overlap between the pump light and the fundamental transverse mode Gaussian beam is higher than the overlap with other higher-order modes. At this time, the laser operates in the fundamental mode. Adjusting the position of the pump light spot in the horizontal and vertical directions provides laser gain in the 45° tilt direction. At this time, the HG beam tilted at 45° relative to the horizontal plane is excited at the laser crystal. m,0 The pattern. After the light field passes through the first intracavity astigmatic mirror 5, due to its smaller effective focal length in the horizontal direction (stronger converging effect), the horizontal and vertical components exhibit different Gouy phase shifts during transmission, forming a Gouy phase shift difference. When the light field is transmitted to the second intracavity astigmatic mirror 6, the phase shift difference accumulates to π / 2, becoming LG. 0,l After the beam passes through the second intracavity astigmatism mirror 6, the Gouy phase shift difference is fixed, with a constant LG. 0,l Beam transmission. After the beam is reflected by the laser output mirror 7, the reflected light inside the cavity repeats the above process. After the reflected light passes sequentially through the second intracavity astigmatism mirror 6 and the first intracavity astigmatism mirror 5, the difference in Gouy phase shift between the horizontal and vertical components becomes π, and the intracavity optical field becomes HG, which is tilted by 45° compared to the initial value. m,0 The HG light field, rotated 90°, passes again in the forward direction through the first intracavity astigmatism mirror 5 and the second intracavity astigmatism mirror 6. The difference in Gouy phase shift becomes 3π / 2, becoming LG. 0,-l Therefore, the beam output after passing through laser output mirror 7 is LG. 0,l With LG 0,-l Synthetic, such as Figure 4 LG shown 0,±l Petal mode. Simply change the pump light in... x and y The offset of the direction relative to the axis of the resonant cavity can change LG. 0,±l The order of the petal pattern.

[0024] Example 2 This invention provides a petal-mode structured light field laser, such as... Figure 2 As shown, the laser includes: a pump source 1, a pump focusing optical module 2, a laser total reflection mirror 3, a laser gain medium 4, a first intracavity astigmatism mirror 5, a second intracavity astigmatism mirror 6, and a laser output mirror 7. The difference from Embodiment 1 is that the first intracavity astigmatism mirror 5 and the second intracavity astigmatism mirror 6 in this embodiment of the invention are spherical lenses coated with laser wavelength antireflection films, instead of spherical mirrors with high reflectivity to lasers. Astigmatism can still be provided when the lenses are tilted, thus allowing for a linear optical path structure and simplifying operation.

[0025] In the above embodiments, the laser gain medium 4 can be a neodymium-doped yttrium vanadate crystal, or a crystal or glass or ceramic matrix doped with rare earth ions such as ytterbium, thulium, erbium, titanium, iron, holmium, or transition metal ions such as yttrium aluminum garnet, potassium gadolinium tungstate, lithium yttrium fluoride, and zinc selenide. As long as it can absorb pump light and provide laser gain, it is acceptable. The embodiments of the present invention do not limit this.

[0026] Pump source 1 can be a multimode semiconductor laser, a single transverse mode semiconductor laser, or other types of lasers. The pump wavelength only needs to correspond to the pump absorption band of the laser gain medium 4. This embodiment of the invention does not impose any restrictions on this.

[0027] The doping concentration and size of the laser gain medium 4, the radius of curvature of the laser total reflection mirror 3 and the laser output mirror 5, and the distance between them can be selected from the parameters in the above embodiments, or other parameters, as long as the resonant cavity is within the stable region and the tilted laser gain medium 4 can introduce astigmatism to destroy the cylindrical symmetry of the resonant cavity.

[0028] Unless otherwise specified, the model numbers of the various devices in this embodiment of the invention are not specifically limited, including the type and parameters of gain, the material, radius of curvature, and transmittance of the lens, etc. Any device that can perform the above functions is acceptable.

[0029] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the sequence numbers of the above embodiments of the present invention are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0030] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A petal-mode structured light field laser, characterized in that, The laser includes: a pump source emitting pump light within the absorption band of a laser gain medium; the pump light being focused by a pump focusing lens optical module and then entering the laser gain medium; the laser gain medium absorbing the pump light, forming population inversion, and generating laser gain. The laser total reflection mirror has high reflectivity for laser wavelength, and the laser output mirror has partial transmittance for laser wavelength; the first intracavity astigmatic mirror and the second intracavity astigmatic mirror, together with the laser total reflection mirror and the laser output mirror, constitute a laser resonant cavity; When the laser gain exceeds the laser resonator loss, the laser reaches the threshold and produces laser output. When the pump light incident position deviates from the optical axis of the laser resonator, the higher-order HG modes overlap significantly with the pump light, and the laser operates in higher-order HG modes. This causes the pump light to... x and y The directions are all deviated from the optical axis of the resonant cavity, exciting and x and y HG tilted at a 45° angle in all directions 0,m The mode, which is considered to be a phase-difference-free along-mode, x and y Direction HG m,0 and HG 0,m Overlay of patterns; and x and y HG tilted at a 45° angle in all directions 0,m After the pattern passes through the first intracavity astigmatism mirror, along x and y Direction HG m,0 and HG 0,m The mode components exhibit differences in Gouy phase shift during propagation; By selecting the resonant cavity length and the focal length and position of the mirror / lens, when the Gouy phase shift difference accumulates to π / 2, the beam is transformed by HG. 0,m Mode conversion to LG 0,l The OAM beam is positioned with a second intracavity astigmatism mirror at that location. The Gouy phase shift is fixed, and the laser beam between the second intracavity astigmatism mirror and the laser output mirror is the LG beam. 0,l beam; During reverse transmission, the phase shift difference continues to accumulate to π, resulting in a direction tilted relative to the original direction (HG). 0,m HG mode rotated 90° 0,m The mode; when it is transmitted to the laser output mirror, the Gouy phase shift difference accumulates to 3π / 2, forming LG. 0,-l The beam, i.e., the output laser, is LG. 0,l With LG 0,-l Synthetic LG 0,±l Petal mode.

2. The petal-mode structured light field laser according to claim 1, characterized in that, The first and second intracavity astigmatic mirrors are tilted spherical mirrors or spherical lenses, which have high reflectivity or high transmittance for laser wavelengths.

3. A petal-mode structured light field laser according to claim 1, characterized in that, The beam of light is at an angle θ When the incident spherical mirror is tilted, the effective focal lengths on the meridional and sagittal planes are respectively f T =( R cos θ ) / 2 and f S = R / (2cos θ ),in R Let be the radius of curvature of the spherical mirror.

4. A petal-mode structured light field laser according to claim 1, characterized in that, The laser gain medium is a bulk crystal, glass, or ceramic doped with rare earth ions or transition metal ions, or a solidified dye or encapsulated gas or liquid gain medium, or a gain medium that provides nonlinear gain through nonlinear processes such as optical parametric oscillation or stimulated Raman scattering.

5. A petal-mode structured light field laser according to claim 1, characterized in that, The pump source is a semiconductor laser, fiber laser, or solid-state laser, and the laser mode is a fundamental transverse mode, a super-Gaussian or flat-top distribution of multiple transverse modes.

6. A petal-mode structured light field laser according to claim 1, characterized in that, The emission wavelength of the pump source is within the absorption band of the laser gain medium or the transmission band and phase matching range of the nonlinear gain medium.

7. A petal-mode structured light field laser according to claim 1, characterized in that, The laser output mirror is selected with an output transmittance of less than 5%.

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