CN113381280B - A device and method for directly generating mid-infrared ultrafast vortex laser - Google Patents
A device and method for directly generating mid-infrared ultrafast vortex laser Download PDFInfo
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Abstract
一种中红外超快涡旋激光的直接产生装置及方法，沿着激光传播方向依次设置第一凸透镜、第二凸透镜、第一平凹镜、第一圆孔光阑、激光增益介质、第二圆孔光阑、第二平凹镜、第三平凹镜、第四平凹镜、锁模元件、输出耦合镜，锁模元件接收来自第四平凹镜的光束，用于启动中红外波段脉冲激光，选择输出横模模式，调控脉冲时域波形，微调重复频率；输出耦合镜，输出谐振腔内振荡激光光束，本发明发能够直接产生一阶涡旋激光，过程简单，操作方便，且产生的涡旋激光纯度高。
A device and method for directly generating a mid-infrared ultrafast vortex laser. A first convex lens, a second convex lens, a first plano-concave mirror, a first circular aperture diaphragm, a laser gain medium, a second circular aperture diaphragm, a second plano-concave mirror, a third plano-concave mirror, a fourth plano-concave mirror, a mode-locking element, and an output coupling mirror are sequentially arranged along the laser propagation direction. The mode-locking element receives a light beam from the fourth plano-concave mirror and is used for starting a mid-infrared band pulse laser, selecting an output transverse mode, regulating a pulse time domain waveform, and fine-tuning a repetition frequency. The output coupling mirror outputs an oscillating laser beam in a resonant cavity. The device and method can directly generate a first-order vortex laser, and the process is simple and the operation is convenient. The generated vortex laser has high purity.
Description
Technical Field
The invention relates to a vortex laser generating device, in particular to a device and a method for directly generating middle-infrared ultrafast vortex laser, and belongs to the technical fields of ultrafast laser and vortex beams.
Background
The vortex beam carries orbital angular momentum, the light intensity cross section of the vortex beam is distributed in a ring shape, the equiphase surface is spiral, and the phase center is a singular point. The expression of vortex beam contains phase factorL is the number of topological charges that are present,Is azimuthal, which is not found in the fundamental gaussian beam expression. Vortex beams can be generally classified into Laguerre Gaussian beams and Bessel Gaussian beams, the phase factor of which isThe phase factor in the Bessel Gaussian beam expression isThese features, particularly with orbital angular momentum, have led to the widespread use of vortex beams in the fields of optical communications, optical manipulation, super-resolution imaging, optical processing, quantum communications, and the like. The optical tweezers technology utilizes the orbital angular momentum of vortex beams to manipulate particles and even drive the particles to rotate; the traditional optical communication is to modulate the amplitude and the phase of light to meet the communication requirement, and the orbital angular momentum can be used for information transmission and reception, so that a new dimension is added for communication transmission.
The generation method of vortex laser mainly comprises two kinds of indirect generation and direct generation, wherein the indirect generation refers to the generation of vortex beams by utilizing some optical conversion elements and beam shaping elements, such as spiral phase plates, spatial light modulators, cylindrical lenses, calculation holographic plates and the like, the generation method generally utilizes a base film Gaussian beam for phase modulation, the amplitude is not changed, and the generation method can lead to the generation of vortex beams with lower purity due to the superposition of modes. The invention discloses a vortex ultrashort laser pulse amplification system and a vortex ultrashort laser pulse amplification method with a publication number of CN107357113B in 11/17 of 2017, wherein a pumping pulse mode converter/shaper and a broadband vortex laser pulse converter are utilized to convert a laser mode, so that the purity of the generated vortex laser is not high; the method for directly generating vortex laser is simpler in device, such as using thermal lens effect of gain medium, non-collinear pump, adding etalon in cavity, annular pump, double-end pump, etc., and the device for directly generating vortex laser disclosed in China patent No. 2018, 12, 18 has a publication number of CN109038196B, and the device for directly generating vortex laser directly generates vortex laser in different directions by using Faraday magneto-optical rotation mode to generate loss difference.
Therefore, a method for generating a vortex laser beam with high purity more simply and reliably is designed and gradually becomes a hot technical direction in the field of laser research.
Disclosure of Invention
The invention aims to provide a direct generation device and a method for medium infrared ultrafast vortex laser, which can directly generate first-order vortex laser, and have simple process and high purity.
In order to achieve the above purpose, the invention provides a direct generation device of middle infrared ultrafast vortex laser, which comprises a laser pumping source, a first convex lens, a second convex lens, a first flat concave mirror, a first round hole diaphragm, a laser gain medium, a second round hole diaphragm, a second flat concave mirror, a third flat concave mirror, a fourth flat concave mirror, a mode locking element and an output coupling mirror;
the laser pumping source is used for providing pumping laser;
The first convex lens is used for focusing the laser generated by the laser pumping source onto the second convex lens;
a second convex lens for focusing the light beam focused by the first convex lens onto the first concave mirror;
The first flat concave mirror and the second flat concave mirror jointly act to form a confocal resonant cavity system;
The first round hole diaphragm and the second round hole diaphragm are arranged on two sides of the laser gain medium;
the laser gain medium is arranged at the focus and receives vortex beam output of a middle infrared band generated by pumping laser of the first plano-concave mirror;
A second concave mirror receiving a light beam from the laser gain medium;
The third plano-concave mirror receives the pumping light beam of the first plano-concave mirror and reflects the pumping light beam to the fourth plano-concave mirror;
The fourth concave mirror reflects the received transmission light beam to the upper surface of the mode locking element;
The mode locking element receives the light beam from the fourth concave mirror, is used for starting the middle infrared band pulse laser, selecting and outputting a transverse mode, regulating and controlling the pulse time domain waveform, and finely adjusting the repetition frequency;
and the output coupling mirror is used for outputting the laser beam oscillated in the resonant cavity.
The laser resonant cavity is in a symmetrical cavity shape, the distance from the first flat concave mirror to the laser gain medium is d 1, the distance from the laser gain medium to the second flat concave mirror is d 2, the distance from the second flat concave mirror to the output coupling mirror is d 3, the distance from the first flat concave mirror to the third flat concave mirror is d 4, and the distance from the third flat concave mirror to the fourth flat concave mirror is d 5; the distance from the fourth concave mirror to the mode locking element is d 6; the included angle between the incident light and the reflected light at the first flat concave mirror is theta 1, the included angle between the incident light and the reflected light at the second flat concave mirror is theta 2, the included angle between the incident light and the reflected light at the third flat concave mirror is theta 3, the included angle between the incident light and the reflected light at the fourth flat concave mirror is theta 4, and the transmission matrix in the noon direction of the resonant cavity isThe transmission matrix in the sagittal direction isWherein M i represents a transmission matrix of a cavity mirror and a free space in the resonant cavity, and a meridian direction and a sagittal direction transmission matrix of the first plano-concave mirror (the focal length is f 1) are respectively: The meridian and sagittal transmission matrices for d 1 are: The meridional and sagittal transmission matrices of the laser gain medium (focal length f 2) are: the meridian and sagittal transmission matrices for d 2 are: The meridian direction and sagittal direction transmission matrices of the second concave mirror (focal length is f 3) are respectively: The meridian and sagittal transmission matrices for d 3 are: The output coupling mirror is a plane mirror, the transmission matrix is 1, omitted here; the meridian and sagittal transmission matrices for d 4 are: The meridian direction and sagittal direction transmission matrices of the third plano-concave mirror (focal length is f 4) are respectively: the meridian and sagittal transmission matrices for d 5 are: the meridional direction and sagittal direction transmission matrices of the fourth concave mirror (focal length is f 5) are respectively: The meridian and sagittal transmission matrices for d 6 are: The meridian and sagittal transmission matrices for the mode-locking element (focal length f 6) are: m T satisfies the following conditions Satisfy the following requirementsThe laser can be stably transmitted in the resonant cavity.
The invention also comprises a chiral selection element which is arranged between the third concave mirror and the fourth concave mirror or at any position in front of the output coupling mirror, wherein the chiral selection element is a filter with double refraction characteristics, and can select the chirality and the wavelength of vortex laser, realize nonlinear adjustment in a cavity, compensate chromatic dispersion in the cavity at other positions and adjust the angle of the nonlinear adjustment, so that the chiral adjustment and the wavelength tuning of ultra-fast vortex laser can be realized.
The laser pumping source is a high-power laser diode, and the output wavelength is matched with the absorption wavelength of the laser gain medium; the laser gain medium of the invention is one of anisotropic a-cut CaYAlO 4 crystal, anisotropic c-cut CaYAlO 4 crystal and isotropic YAG crystal doped by Tm 3+.
According to the invention, the inclination angle of the first flat concave mirror is 98-102% of the original angle (the included angle between the mirror surface and the pump light is 90 degrees), the inclination angle of the second flat concave mirror is 98-103% of the original angle (the included angle between the mirror surface and the pump light is 90 degrees), and vortex light beams can be transmitted in the resonant cavity.
The first round hole diaphragm and the second round hole diaphragm can be used for positioning the transmission laser in the resonant cavity and determining that the resonant cavity is in a collinear pumping mode; the first round hole diaphragm and the second round hole diaphragm can also be used for filtering, different diaphragm sizes correspond to different transverse mode modes in the resonant cavity, and the diaphragm diameter is 5mm at most; the signal to noise ratio of the diaphragm at different positions can be improved to realize Kerr lens mode locking.
The vertical inclination range of the third concave mirror can be changed, when the included angle between the incident light and the reflected light is 90-110% of that of theta 3, the vortex light beam can be transmitted in the resonant cavity, and the state of collinear pumping in the resonant cavity can not be changed when the lens angle is changed.
The vertical inclination range of the fourth concave mirror can be changed, when the included angle between the incident light and the reflected light is 90-110% of that of the theta 4, the vortex light beam is transmitted in the resonant cavity, and the state of collinear pumping in the resonant cavity can not be changed when the lens angle is changed; changing the length d 6 between the fourth concave mirror and the mode-locking element can produce a vortex laser output at 110.92% of the distance to produce laser light, and a different transverse mode can also occur when only adjusting the distance between the mode-locking element and the fourth concave mirror, the adjustment range being 93.2-111.13% of the distance to produce laser light.
The mode locking element is a semiconductor mode locking saturable absorber mirror, the modulation depth is any one of 1.2%, 2.4%, 3% and 5%, and the working wave band is 1850-2100nm; the transmissivity of the output coupling mirror is 2% or 5%, and the working wave band is 1850-2100nm.
A direct generation method of a medium infrared ultrafast vortex laser comprises the following steps:
① The laser pumping source generates pumping laser, and the first convex lens and the second convex lens with the same focal length adjust a certain angle and then aim the pumping beam until the pumping beam is formed on the first flat concave mirror; the angles of the first flat concave mirror, the laser gain medium and the second flat concave mirror are adjusted to enable the pumping mode in the resonant cavity to be collinear pumping, and the first round hole diaphragm and the second round hole diaphragm are adjusted to enable the pumping mode to be collinear pumping; the pump beam focused on the laser gain medium is absorbed by the gain medium to generate particle number inversion; adjusting the positions of the third concave mirror, the fourth concave mirror and the mode locking element to enable laser to resonate, and generating 2 mu m-mode ultra-fast laser of a fundamental mode;
② The laser generates resonance in the resonant cavity and has an amplifying effect on the pulse, and the laser is reflected by the third flat concave mirror and the fourth flat concave mirror to be incident on the mode locking element; generating a saturated absorption effect by adjusting the distance between the mode locking element and the fourth concave mirror, and generating 2 mu m ultra-short mode locking basic order pulse output;
③ The deviation angle of the laser in the output coupling mirror and the resonant cavity is regulated, the left and right angle regulating range is 1-3 degrees, and the upper and lower angle regulating range is 1-2 degrees to generate 2 mu m ultra-fast vortex light beams; the signal-to-noise ratio of vortex laser is improved by adjusting the sizes of the first round hole diaphragm and the second round hole diaphragm; changing the light intensity of the output vortex beam by using an output coupling mirror with the transmissivity of 2% or 5%; by adjusting the distance between the fourth concave mirror and the mode locking element, the transverse mode in the cavity can be controlled under the condition of not changing the collinear pumping state in the cavity, and the ultrafast laser with the specified transverse mode is output;
④ The chiral selection element is added, the inclination angle is changed to realize chiral selection and wavelength tuning, and the position is changed to control the intra-cavity dispersion and adjust the nonlinearity;
⑤ Detecting the light spot intensity distribution and interference patterns of the output laser by using a CCD camera and an interferometer; detecting time domain characteristics by using an oscilloscope and an autocorrelation instrument, and detecting frequency domain characteristics by using a spectrometer; the pulse repetition frequency and the signal to noise ratio are measured by a spectrum analyzer, and the parameters in the cavity are optimized, so that the ultra-fast vortex laser in the middle infrared band can be directly generated.
Compared with the prior art, the invention sequentially sets the first convex lens, the second convex lens, the first flat concave mirror, the first round hole diaphragm, the laser gain medium, the second round hole diaphragm, the second flat concave mirror, the third flat concave mirror, the fourth flat concave mirror, the mode locking element and the output coupling mirror along the laser propagation direction, the mode locking element receives the light beam from the fourth flat concave mirror and is used for starting the middle infrared band pulse laser, selecting the output transverse mode, regulating the pulse time domain waveform and fine adjusting the repetition frequency; the invention can obtain the middle infrared band ultrafast vortex laser pulse generated in the all-solid-state laser, the ultrafast vortex laser beam can be directly obtained without adding any shaping element in the device, the pulse width is in the order of a few picoseconds, the output power is in the order of hundreds of milliwatts, and the generated vortex laser is a linear polarization scalar beam; the invention can obtain the vortex laser and Gaussian beam with adjustable transverse mode, and a chiral selection device-a double refraction filter plate-is added outside the cavity, so that the chirality of the first-order vortex laser can be selected, the vortex laser beams with right and left rotations can be output, and secondly, the transverse mode modes of the Gaussian beam can be controlled by adjusting the distance between the fourth concave mirror and the mode locking element, so as to obtain Gaussian beam pulses with different transverse modes.
Drawings
FIG. 1 is a diagram of an apparatus for directly generating mid-infrared band ultra-fast vortex laser according to embodiment 1 of the present invention;
FIG. 2 is a diagram of a vortex laser spot detected with a camera in example 1 of the present invention;
FIG. 3 is a pattern-locked pulse image of the embodiment 1 of the present invention for directly generating mid-infrared band ultra-fast vortex laser;
FIG. 4 is a spectrum frequency domain and an autocorrelation curve of the embodiment 1 of the present invention for directly generating the middle infrared band ultra-fast vortex laser;
FIG. 5 is a radio frequency spectrum image of the embodiment 1 of the present invention for directly generating the middle infrared band ultra-fast vortex laser;
FIG. 6 is a view of another transverse mode spot pattern obtained in example 1 of the present invention;
FIG. 7 is a diagram of a chiral selection, wavelength tuning, dispersion control, nonlinear adjustment device for the infrared band ultrafast vortex laser in examples 2, 3, 4,5 of the present invention;
FIG. 8 is a schematic view showing the position or angle adjustment of the chiral selector in examples 2, 3, 4, and 5 according to the present invention;
fig. 9 is a diagram of simulated planar and spherical interference fringes according to example 1 of the present invention.
In the figure: 1. the laser pump comprises a laser pump source 2, a first convex lens 3, a second convex lens 4, a first flat concave mirror 5, a first round hole diaphragm 6, a laser gain medium 7, a second round hole diaphragm 8, a second flat concave mirror 9, a third flat concave mirror 10, a fourth flat concave mirror 11, a mode locking element 12, an output coupling mirror 13 and a chiral selection element.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in fig. 1, a direct generating device of middle infrared ultrafast vortex laser comprises a laser pumping source 1, a first convex lens 2, a second convex lens 3, a first flat concave mirror 4, a first round hole diaphragm 5, a laser gain medium 6, a second round hole diaphragm 7, a second flat concave mirror 8, a third flat concave mirror 9, a fourth flat concave mirror 10, a mode locking element 11 and an output coupling mirror 12;
a laser pump source 1 for providing pump laser;
A first convex lens 2 for focusing the laser generated by the laser pumping source 1 onto a second convex lens 3;
a second convex lens 3 for focusing the light beam focused by the first convex lens 2 onto the first plano-concave mirror 4;
The first concave mirror 4 and the second concave mirror 8 cooperate to form a confocal resonant cavity system;
The first round hole diaphragm 5 and the second round hole diaphragm 7 are arranged on two sides of the laser gain medium 6 and are used for confirming that the pumping mode in the resonant cavity is a collinear pumping mode, not an annular diaphragm, and can be used for improving the signal-to-noise ratio of laser in the cavity and realizing the mode locking of the hard diaphragm of the Kerr lens;
The laser gain medium 6 is arranged at the focus to receive vortex beam output of the middle infrared band generated by the pumping laser of the first concave mirror 4;
A second concave mirror 8 for receiving the light beam from the laser gain medium 6 and forming a confocal resonant cavity system by coacting with the first concave mirror 4;
the third concave mirror 9 receives the pump beam of the first concave mirror 4 and reflects it onto the fourth concave mirror 10;
the fourth concave plano-convex mirror 10 reflects the received transmission beam onto the mode locking element 11;
The mode locking element 11 receives the light beam from the fourth concave mirror 10, is used for starting the middle infrared band pulse laser, selecting and outputting a transverse mode, regulating and controlling the pulse time domain waveform, and finely adjusting the repetition frequency, and is one of key devices for generating ultra-fast vortex laser;
An output coupling mirror 12 for outputting the laser beam oscillated in the cavity.
The laser resonant cavity is in a symmetrical cavity shape, the distance from the first flat concave mirror to the laser gain medium is d 1, the distance from the laser gain medium to the second flat concave mirror is d 2, the distance from the second flat concave mirror to the output coupling mirror is d 3, the distance from the first flat concave mirror to the third flat concave mirror is d 4, and the distance from the third flat concave mirror to the fourth flat concave mirror is d 5; the distance from the fourth concave mirror to the mode locking element is d 6; the included angle between the incident light and the reflected light at the first flat concave mirror is theta 1, the included angle between the incident light and the reflected light at the second flat concave mirror is theta 2, the included angle between the incident light and the reflected light at the third flat concave mirror is theta 3, the included angle between the incident light and the reflected light at the fourth flat concave mirror is theta 4, and the transmission matrix in the noon direction of the resonant cavity isThe transmission matrix in the sagittal direction isWherein M i represents a transmission matrix of a cavity mirror and a free space in the resonant cavity, and a meridian direction and a sagittal direction transmission matrix of the first plano-concave mirror 4 (the focal length is f 1) are respectively: The meridian and sagittal transmission matrices for d 1 are: the meridional and sagittal transmission matrices of the laser gain medium 6 (focal length f 2) are: the meridian and sagittal transmission matrices for d 2 are: The meridian and sagittal transmission matrices of the second concave mirror 8 (focal length f 3) are: The meridian and sagittal transmission matrices for d 3 are: The output coupling mirror 12 is a plane mirror, the transmission matrix is 1, omitted here; the meridian and sagittal transmission matrices for d 4 are: The meridian and sagittal transmission matrices of the third concave mirror 9 (focal length f 4) are respectively: the meridian and sagittal transmission matrices for d 5 are: The meridional and sagittal transmission matrices of the fourth concave mirror 10 (focal length f 5) are respectively: The meridian and sagittal transmission matrices for d 6 are: The meridian and sagittal transmission matrices of mode-locking element 11 (focal length f 6) are: m T satisfies the following conditions M S satisfies the following conditionsThe laser can be stably transmitted in the resonant cavity.
As shown in fig. 7, the present invention further includes a chiral selection element 13 disposed between the third concave mirror 9 and the fourth concave mirror 10 or disposed at any position in front of the output coupling mirror 12, where the chiral selection element 13 is a filter with birefringence characteristics, and the chiral selection element 13 can select chirality and wavelength of the vortex laser, so as to implement nonlinear adjustment in the cavity, and compensate chromatic dispersion in the cavity at other positions, and adjust the angle thereof to chiral select and tune the wavelength of the ultra-fast vortex laser.
The laser pumping source 1 is a high-power laser diode, and the output wavelength is matched with the absorption wavelength of the laser gain medium 6; the laser gain medium 6 is one of anisotropic a-cut CaYAlO 4 crystal, anisotropic c-cut CaYAlO 4 crystal and isotropic YAG crystal doped by Tm 3+.
The inclination angle of the first flat concave mirror 4 is 98-102% of the original angle (the included angle between the mirror surface and the pump light is 90 degrees), the inclination angle of the second flat concave mirror 8 is 98-103% of the original angle (the included angle between the mirror surface and the pump light is 90 degrees), and vortex light beams can be transmitted in the resonant cavity.
The first round hole diaphragm 5 and the second round hole diaphragm 7 can be used for positioning the transmission laser in the resonant cavity, and determining that the resonant cavity is in a collinear pumping mode; the filter can also be used for filtering, different diaphragm sizes correspond to different transverse mode modes in the resonant cavity, and the diaphragm diameter is 5mm at most; the signal to noise ratio of the diaphragm at different positions can be improved to realize Kerr lens mode locking.
The vertical tilting range of the third concave-flat mirror 9 can be changed, when the included angle between the incident light and the reflected light is 90-110% of that of the theta 3, the vortex light beam can be transmitted in the resonant cavity, and the state of the collinear pumping in the resonant cavity can not be changed when the lens angle is changed.
The vertical tilting range of the fourth concave mirror 10 can be changed, when the included angle between the incident light and the reflected light is 90-110% of that of the theta 4, the vortex light beam can be transmitted in the resonant cavity, and the state of collinear pumping in the resonant cavity can not be changed when the lens angle is changed; varying the length d 6 between the fourth concave mirror 10 and the mode-locking element 11 can produce a swirling laser output at 110.92% of the distance at which the laser is produced, and a different transverse mode can also occur when only the distance between the mode-locking element 11 and the fourth concave mirror 10 is adjusted, the adjustment range being 93.2-111.13% of the distance at which the laser is produced.
The mode locking element 11 is a semiconductor mode locking saturable absorber mirror, the modulation depth is any one of 1.2%, 2.4%, 3% and 5%, and the working wave band is 1850-2100nm; the output coupling mirror 12 has a transmissivity of 2% or 5% and an operating band of 1850-2100nm.
A direct generation method of a medium infrared ultrafast vortex laser comprises the following steps:
① The laser pumping source 1 generates pumping laser, and the first convex lens 2 and the second convex lens 3 with the same focal length adjust a certain angle and then aim the pumping laser until the pumping laser is formed on the first flat concave mirror 4; the angles of the first flat concave mirror 4, the laser gain medium 6 and the second flat concave mirror 8 are adjusted to enable the pumping mode in the resonant cavity to be collinear pumping, and the first round hole diaphragm 5 and the second round hole diaphragm 7 are adjusted to enable the pumping mode to be collinear pumping; the pump beam focused on the laser gain medium 6 is absorbed by the gain medium to generate the particle number inversion; adjusting the positions of the third concave mirror 9, the fourth concave mirror 10 and the mode locking element 11 to enable laser to resonate and generate 2 mu m base-order mode ultrafast laser;
② The laser generates resonance in the resonant cavity and has an amplifying effect on the pulse, and the laser is reflected by the third concave mirror 9 and the fourth concave mirror 10 to be incident on the mode locking element 11; generating 2 mu m ultra-short mode locking fundamental order pulse output by adjusting the distance between the mode locking element 11 and the fourth concave mirror 10 to generate a saturable absorption effect;
③ The deviation angle of the laser in the output coupling mirror 12 and the resonant cavity is regulated, the left and right angle regulating range is 1-3 degrees, and the upper and lower angle regulating range is 1-2 degrees to generate 2 mu m ultra-fast vortex light beams; the signal-to-noise ratio of vortex laser is improved by adjusting the sizes of the first circular aperture diaphragm 5 and the second circular aperture diaphragm 7; changing the light intensity of the output vortex beam by using an output coupling mirror 12 having a transmittance of 2% or 5%; by adjusting the distance between the fourth concave mirror 10 and the mode locking element 11, the transverse mode in the cavity can be controlled without changing the collinear pumping state in the cavity, and the ultrafast laser with the specified transverse mode can be output;
④ By adding the chiral selection element 10, chiral selection and wavelength tuning are realized by changing the inclination angle, and the nonlinear is controlled and regulated by changing the position of the chiral selection element;
⑤ Detecting the light spot intensity distribution and interference patterns of the output laser by using a CCD camera and an interferometer; detecting time domain characteristics by using an oscilloscope and an autocorrelation instrument, and detecting frequency domain characteristics by using a spectrometer; the pulse repetition frequency and the signal to noise ratio are measured by a spectrum analyzer, and the parameters in the cavity are optimized, so that the ultra-fast vortex laser in the middle infrared band can be directly generated.
Example 1
As shown in fig. 1, a device for directly generating a mid-infrared vortex laser specifically includes:
the laser pump source 1 is a commercial 793nm optical fiber coupled laser diode, the fiber core diameter is 105 μm, the numerical aperture NA is 0.22, the power is 12W at most, and the generated pump light excites the laser gain medium 6 to generate laser output with the wave band of 2 μm.
The first convex lens 2 and the second convex lens 3 have a focal length of 100mm, collimate the pump light generated by the laser pump source 1, the distance between the first convex lens 2 and the laser pump source 1 is 100mm, and the distance between the first convex lens 2 and the second convex lens 3 is 50mm.
The distance d 1 between the laser gain medium 6 and the first concave mirror 4 is 35mm, the laser gain medium is an anisotropic a-cut CaYAlO 4 crystal doped by Tm 3+, the doping concentration is 4%, an anti-reflection coating is coated on the wave band of 1900-2100nm, anti-reflection films with the same wave band are arranged at two ends of the crystal, the length of the crystal is 6.1mm, the cross section area of stimulated radiation is about 3x3mm 2, and the laser gain medium can generate 2 mu m-wave band linear polarization ultrafast vortex laser after being stimulated by pump light.
The first flat concave mirror 4, the second flat concave mirror 8 and the third flat concave mirror 9 have the same curvature radius, the curvature radius is 100mm, the curvature radius of the fourth flat concave mirror 10 is 50mm, and the first flat concave mirror 4, the second flat concave mirror 8, the third flat concave mirror 9 and the fourth flat concave mirror 10 are plated with high reflection films in 1850-2100nm wave bands; the distance between the first flat concave mirror 4 and the second convex lens 3 is 35mm, and the included angle theta 1 between the incident light and the reflected light is smaller than 16 degrees; the distance d 2 between the second concave mirror 8 and the laser gain medium 6 is 49mm, and the included angle theta 2 =20° between the incident light and the reflected light; the distance d 4 between the third concave mirror 9 and the first concave mirror 4 is 491mm, and the included angle theta 3 between the incident light ray and the reflected light ray at the position of the third concave mirror 9 is smaller than 20 degrees; the distance d 5 between the fourth concave mirror 10 and the third concave mirror 9 is 98mm, the included angle theta 4 between the incident light and the reflected light at the position of the fourth concave mirror 10 is less than 18 degrees, the included angle theta 3 between the incident light and the reflected light at the position of the third concave mirror 9 is equal to theta 4 between the incident light and the reflected light at the position of the fourth concave mirror 10, and the transmission matrix in the noon direction of the resonant cavity isThe transmission matrix in the sagittal direction isWherein M i represents a transmission matrix of a cavity mirror and a free space in the resonant cavity, and a meridian direction and a sagittal direction transmission matrix of the first plano-concave mirror 4 (the focal length is f 1) are respectively: The meridian and sagittal transmission matrices for d 1 are: the meridional and sagittal transmission matrices of the laser gain medium 6 (focal length f 2) are: the meridian and sagittal transmission matrices for d 2 are: The meridian and sagittal transmission matrices of the second concave mirror 8 (focal length f 3) are: The meridian and sagittal transmission matrices for d 3 are: The output coupling mirror 12 is a plane mirror, the transmission matrix is 1, omitted here; the meridian and sagittal transmission matrices for d 4 are: The meridian and sagittal transmission matrices of the third concave mirror 9 (focal length f 4) are respectively: the meridian and sagittal transmission matrices for d 5 are: The meridional and sagittal transmission matrices of the fourth concave mirror 10 (focal length f 5) are respectively: The meridian and sagittal transmission matrices for d 6 are: The meridian and sagittal transmission matrices of mode-locking element 11 (focal length f 6) are: m T satisfies the following conditions M S satisfies the following conditionsThe laser can be stably transmitted in the resonant cavity.
The inner diameters of the first round hole diaphragm 5 and the second round hole diaphragm 7 are 5mm, and the inner diameters can be adjusted to be smaller.
The mode locking element 11 adopts a commercial semiconductor saturated absorption mirror (SESAM), the modulation depth is 1.2%, the cavity mode diameter on the SESAM is about 70 μm, and the distance from the fourth concave mirror 10 is 49mm.
The output coupling mirror 12 is a concave mirror having a transmittance of 2% or 5% in the 1850 to 2100nm band, and the distance d 3 between the second concave mirror 8 is 490mm.
The distance and angle of the cavity mirror in the resonant cavity meet the laser stable resonance condition, a common laser diode pump source on the market is used for pumping a laser gain medium, and middle-infrared band vortex laser is directly generated by adjusting the included angle between the output coupling mirror 12 and laser in the cavity and the distance between the mode locking element 11 and the fourth concave mirror 10.
In order to further describe the method for directly generating the mid-infrared band vortex laser according to the embodiment, the following description will be given with reference to the accompanying drawings and specific examples:
As shown in fig. 1, a high-power optical fiber coupling laser diode with the working wavelength of 793nm of a laser pumping source 1 is utilized to generate pumping laser, the pumping laser is collimated after passing through a first convex lens 2 and a second convex lens 3 with the same focal length, the pumping laser is focused on a laser gain medium 6 by a first flat concave mirror 4 and a second flat concave mirror 8, and the pumping laser is absorbed by the gain medium to generate particle number inversion;
Secondly, the laser generates resonance in the cavity and has amplification effect on the pulse, the laser is reflected by the third concave mirror 9 and the fourth concave mirror 10 and is incident on the mode locking element 11, the mode locking element is SESAM, and the mode locking element has saturation absorption effect, so that the pulse can be narrowed, the pulse width is reduced, and 2 mu m ultra-short pulse output is generated.
And secondly, by adjusting the deviation angle of the output coupling mirror 12 and the laser in the cavity, the left-right angle adjusting range is 1-3 degrees, and the upper-lower angle adjusting range is 1-2 degrees, so that ultra-fast vortex beams are easy to generate.
Next, when the distance between the mode locking element 11 and the fourth concave mirror 10 is 110.92% of the distance for generating laser, the mode locking element 11 corresponds to the vortex laser beam generated at the 115 position in fig. 1, as shown in fig. 2, the vortex laser beam measured under the condition that the pumping power is 4W is on the left, the vortex laser beam measured under the condition that the pumping power is 7W is on the right, the time domain mode locking pulse image at the moment is shown in fig. 3, the spectrum frequency domain image and the autocorrelation curve are shown in fig. 4 (a) and fig. 4 (b), the radio frequency spectrum image is shown in fig. 5, and the repetition frequency of the ultrafast vortex laser is 120.8MHz; the mode-locked pulse width was 2.92ps and the spectral width was 2nm measured at 9W pump power; the mode-locked pulse width was 1.97ps, the spectral width was 3.1nm, and the center wavelength was 1967nm measured at a pump power of 12W; the signal to noise ratio at the 3GHz and 600kHz sweep ranges is 70dB.
In addition to the LG 01 mode, six modes as in fig. 6 can be obtained by adjusting the distance between the mode-locking element 11 and the fourth concave mirror 110, the distances being 106.37%, 111.13%, 101.78%, 98.37%, 96.98%, 93.20% of the distance at which the laser is generated, respectively, the positions of the mode-locking element 11 in the resonant cavity corresponding to 114, 116, 113, 112, 111, 110, respectively.
The first round hole diaphragm 5 and the second round hole diaphragm 7 on two sides of the laser gain medium 6 are used for guaranteeing that the pumping mode is collinear pumping, so that the laser can generate middle infrared ultrafast vortex laser in the collinear pumping mode.
The method for directly generating the middle infrared vortex laser can measure the spatial intensity distribution of the light beam through a CCD camera (WinCamD-IR-BB, the pixel size is 17 mu m), and can monitor the transverse mode of an output light spot in real time.
Example 2
As shown in fig. 7, a device for controlling chirality of a middle infrared vortex laser specifically includes:
the laser pump source 1 is a commercial 793nm optical fiber coupled laser diode, the fiber core diameter is 105 μm, the numerical aperture NA is 0.22, the power is 12W at most, and the generated pump light excites the laser gain medium 6 to generate laser output with the wave band of 2 μm.
The first convex lens 2 and the second convex lens 3 have a focal length of 100mm, collimate the pump light generated by the laser pump source 1, the distance between the first convex lens 2 and the laser pump source 1 is 100mm, and the distance between the first convex lens 2 and the second convex lens 3 is 50mm.
The distance d 1 between the laser gain medium 6 and the first concave mirror 4 is 35mm, the laser gain medium is an anisotropic c-cut CaYAlO 4 crystal doped by Tm 3+, the doping concentration is 4%, an anti-reflection coating is coated on the wave band of 1900-2100nm, anti-reflection films with the same wave band are arranged at two ends of the crystal, the length of the crystal is 6.1mm, the cross section area of stimulated radiation is about 3x3mm 2, and the laser gain medium can generate linear polarized ultrafast vortex laser with the wave band of 2 mu m after being stimulated by pump light.
The first flat concave mirror 4, the second flat concave mirror 8 and the third flat concave mirror 9 have the same curvature radius, the curvature radius is 100mm, the curvature radius of the fourth flat concave mirror 10 is 50mm, and the first flat concave mirror 4, the second flat concave mirror 8, the third flat concave mirror 9 and the fourth flat concave mirror 10 are plated with high reflection films in 1850-2100nm wave bands; the distance between the first flat concave mirror 4 and the second convex lens 3 is 30mm, and the included angle theta 1 between the incident light and the reflected light is smaller than 16 degrees; the distance d 2 between the second concave mirror 8 and the laser gain medium 6 is 52mm, and the included angle theta 1 =20° between the incident light and the reflected light; the distance d 4 between the third concave mirror 9 and the first concave mirror 4 is 491mm, and the included angle theta 3 between the incident light ray and the reflected light ray at the position of the third concave mirror 9 is smaller than 20 degrees; the distance d 5 between the fourth concave mirror 10 and the third concave mirror 9 is 98mm, and the included angle theta 4 between the incident light ray and the reflected light ray at the position of the fourth concave mirror 10 is smaller than 18 degrees; the inner diameters of the first round hole diaphragm 5 and the second round hole diaphragm 7 are 5mm, and the inner diameters can be adjusted to be smaller.
The chiral selector 13 is a birefringent filter, which in this embodiment is used for chiral selection of vortex lasers, the chiral selector 13 being placed at any position between the third concave mirror 9 and the fourth concave mirror 10.
The mode locking element 11 adopts a commercial semiconductor saturated absorption mirror (SESAM), the modulation depth is 2.4%, the cavity mode diameter on the SESAM is about 70 μm, and the distance from the fourth concave mirror 10 is 49mm.
The output coupling mirror 12 is a concave mirror having a transmittance of 2% or 5% in the 1850 to 2100nm band, and the distance d 3 between the second concave mirror 8 is 490mm.
The distance and angle of the cavity mirror in the resonant cavity meet the laser stable resonance condition, a common laser diode pump source on the market is used for pumping a laser gain medium, and vortex lasers with different middle-infrared wave bands are generated by adjusting the transverse included angle between the chiral selection element 13 and laser in the cavity.
In order to further describe the method for controlling chirality of the mid-infrared band vortex laser in this embodiment, the following details are described with reference to the accompanying drawings and specific examples:
on the basis of generating vortex laser in embodiment 1, only the tangential direction of the laser gain medium 6 and the modulation depth of the mode locking element 11 are changed, a chiral selection element 13 is inserted at any position between the third concave mirror 9 and the fourth concave mirror 10, firstly, the left and right positions of the chiral selection element 13 are adjusted to enable the laser to be exactly incident to the center position of the chiral selection element, and the angle of the chiral selection element 13 is adjusted to enable the mirror surface of the chiral selection element to be exactly perpendicular to the laser in the resonant cavity; next, the angle of deflection of the mirror surface and the laser light in the resonant cavity is adjusted by the adjustment frame of the chiral selector 13, and as shown in fig. 8 (a), the original angle α is 90 °, the angle of each adjustment is about 0.3 °, the interference fringes of the mach-zehnder (M-Z) interferometer are monitored by the CCD camera to determine whether the chirality of the vortex laser light generated by the laser is present in example 2, and when the inclination angle of the chiral selector 13 is in the range of 96.67% -97.78%, the vortex laser light generated is The simulation result of MATLAB software for interference results of modes is shown in FIG. 9, the upper half part is a plane wave interference result, and the stripes are branched upwards; the lower half is the spherical wave interference result, which is clockwise right-handed fringes. When the tilt angle of the chiral selector 13 is in the range 101.67% -102.78% α, a resultantThe vortex laser of the mode, the upper right corner of figure 9 is the simulation result of plane wave interference thereof, and is a vertical stripe with a downward bifurcation; the lower right corner is the simulation result of spherical wave interference, and is a counterclockwise left-handed stripe. The measurement result in the experiment is identical with the simulation result.
Example 3
The present embodiment uses a common laser diode pump source to pump the laser gain medium, and generates vortex laser with different wavelengths by rotating the chiral selector 13.
To further illustrate the method of ultrafast vortex laser wavelength tuning of this embodiment 3, the following is described in detail with reference to fig. 7 and 8 and the specific example:
On the basis of example 2, only the laser gain medium 6 was changed to Tm 3+ doped YAG crystal, the modulation depth of the mode locking element was 3%, the chiral selection element 13 was still placed between the third concave plano-convex mirror 9 and the fourth concave plano-convex mirror 10, in the vortex beam with chirality generated in example 2, the inclination angle of the chiral selection element 13 was in the range of 96.11% -96.67% α and 102.78% -103.89% α, in this range, the left-handed and right-handed chiralities of the vortex laser were maintained, and the rotation angle of the chiral selection element 13 was adjusted, as shown in fig. 8 (b), the accuracy of each adjustment was about 0.2 °, and vortex laser outputs of different wavelengths could be obtained.
When the rotation angle of the chiral selector 13 is changed, the output wavelength is in the range of 1955-1970nm, the adjustable range is 15nm, the intra-cavity pumping mode is still collinear pumping in the process, and the mode of the output laser is LG 01 mode.
Example 4
In this embodiment, the laser gain medium is pumped by using a common laser diode pump source in the market, and the dispersion in the resonant cavity is compensated by changing the thickness of the chiral selector 13.
To further describe the dispersion compensation method of this embodiment 4, the following details will be described with reference to fig. 7 and 8 and the specific example:
On the basis of the embodiment 3, changing the laser gain medium 6 to be a CaYAlO 4 crystal doped with Tm 3+ and having an anisotropic a-cut mode locking element modulation depth of 5%, placing the chiral selector 13 at any position between the third concave mirror 9 and the fourth concave mirror 10 or between the output coupling mirror 12 and the second concave mirror 8, wherein the chiral selector 13 is a birefringent filter, in the embodiment, there are two birefringent filters, one is a quartz etalon, and the dispersion value is adjustable about 1.46; the other is YVO 4 wedge-shaped crystal, the dispersion value is about 1.95 and can be used as a chiral selection element 13 to be placed in the cavity to compensate the negative dispersion in the cavity, and the two crystals are made of transparent materials, so that the laser oscillation in the resonant cavity is ensured. Other methods also use grating pairs as dispersion controlling elements, but are not applicable due to the large power loss to the cavity which is detrimental to the formation of the vortex beam.
The dispersion value of the chiral selection element 13, that is, the front and back positions of the quartz etalon or the YVO 4 wedge-shaped crystal can be regulated and controlled, as shown in fig. 8 (c), the crystal with the optimal thickness is further selected to compensate the intra-cavity dispersion, the chiral selection element 13 is placed between the third concave mirror 9 and the fourth concave mirror 10, and when the position of the quartz crystal deviates from the focal length of 20-30%, the dispersion regulation effect is optimal when the YVO 4 wedge-shaped crystal deviates from the focal length of 15-30%; the dispersion can also be suitably compensated for by being placed between the output coupling mirror 12 and the second concave mirror 8.
Example 5
In this embodiment, the laser gain medium is pumped by using a common laser diode pump source in the market, and the nonlinearity in the resonant cavity is adjusted by changing the relative positions and the number of the chiral selector elements 13.
To further explain the dispersion control method of this embodiment 5, the following will be described in detail with reference to fig. 7 and 8 and the specific example:
on the basis of example 4, the laser gain medium 6 was changed to a Tm 3+ doped anisotropic c-cut CaYAlO 4 crystal, and the chiral selection element 13 was still placed between the third concave mirror 9 and the fourth concave mirror 10.
The chiral selector 13 is a birefringent filter, and the intra-cavity nonlinearity value is related to the front-back position of the birefringent filter and the number of the birefringent filters.
Wherein the placement of the chiral selection element 13 at the focal position of the third concave mirror 9 and the fourth concave mirror 10 (as shown in fig. 8 (d)) allows for adjustment of intra-cavity nonlinearity.
The number of chiral selection elements 13 also has an effect on the nonlinear value in the resonant cavity, the control effect is weakest when a birefringent filter is placed, the more the number is placed, the control effect is optimal, but the number is adjusted on the premise that laser in the resonant cavity normally oscillates and pulse is not split.
Claims (8)
1. The direct generation device of the middle infrared ultrafast vortex laser is characterized by comprising a laser pumping source (1), a first convex lens (2), a second convex lens (3), a first flat concave mirror (4), a first round hole diaphragm (5), a laser gain medium (6), a second round hole diaphragm (7), a second flat concave mirror (8), a third flat concave mirror (9), a fourth flat concave mirror (10), a mode locking element (11) and an output coupling mirror (12);
a laser pump source (1) for providing pump laser light;
the first convex lens (2) is used for focusing the laser generated by the laser pumping source (1) onto the second convex lens (3);
A second convex lens (3) for focusing the light beam focused by the first convex lens (2) onto the first plano-concave mirror (4);
the first flat concave mirror (4) and the second flat concave mirror (8) are combined to form a confocal resonant cavity system;
The first round hole diaphragm (5) and the second round hole diaphragm (7) are arranged on two sides of the laser gain medium (6);
the laser gain medium (6) is arranged at the focus and receives vortex beam output of the middle infrared band generated by pumping laser of the first concave mirror (4);
a second concave mirror (8) for receiving the light beam from the laser gain medium (6);
The third concave mirror (9) receives the laser beam of the first concave mirror (4) and reflects the laser beam onto the fourth concave mirror (10);
The fourth concave mirror (10) reflects the received transmission beam to the upper surface of the mode locking element (11);
The mode locking element (11) receives the light beam from the fourth concave mirror (10) and is used for starting the middle infrared band pulse laser, selecting and outputting a transverse mode, regulating and controlling the pulse time domain waveform and finely adjusting the repetition frequency;
an output coupling mirror (12) for outputting the laser beam oscillated in the resonant cavity;
The laser resonant cavity is in a symmetrical cavity shape, the distance from the first flat concave mirror (4) to the laser gain medium (6) is d 1, the distance from the laser gain medium (6) to the second flat concave mirror (8) is d 2, the distance from the second flat concave mirror (8) to the output coupling mirror (12) is d 3, the distance from the first flat concave mirror (4) to the third flat concave mirror (9) is d 4, and the distance from the third flat concave mirror (9) to the fourth flat concave mirror (10) is d 5; the distance from the fourth concave mirror (10) to the mold locking element (11) is d 6; the included angle between the incident light and the reflected light at the first concave mirror (4) is theta 1, the included angle between the incident light and the reflected light at the second concave mirror (8) is theta 2, the included angle between the incident light and the reflected light at the third concave mirror (9) is theta 3, the included angle between the incident light and the reflected light at the fourth concave mirror (10) is theta 4, and the distance and the angle between the cavity mirrors meet the stability condition of the resonant cavity;
The inclination angle of the first flat concave mirror (4) is 98-102% of the original angle, the inclination angle of the second flat concave mirror (8) is 98-103% of the original angle, and vortex light beams can be transmitted in the resonant cavity.
2. A direct generating device of mid-infrared ultrafast vortex laser according to claim 1, characterized in that it further comprises a chiral selection element (13) placed between the third plano-concave mirror (9) and the fourth plano-concave mirror (10) or in any position in front of the output coupling mirror (12), the chiral selection element (13) being a filter with birefringent properties.
3. The direct generating device of the mid-infrared ultrafast vortex laser according to claim 1, wherein the laser pumping source (1) is a high-power laser diode, and the output wavelength is matched with the absorption wavelength of the laser gain medium (6); the laser gain medium (6) is one of anisotropic a-cut CaYAlO 4 crystal, anisotropic c-cut CaYAlO 4 crystal and isotropic YAG crystal doped by Tm 3+.
4. The direct generating device of the mid-infrared ultrafast vortex laser according to claim 1, wherein the first round hole diaphragm (5) and the second round hole diaphragm (7) are used for positioning the transmission laser in the resonant cavity and determining that the resonant cavity is in a collinear pumping mode; the first round hole diaphragm (5) and the second round hole diaphragm (7) are used for filtering, different diaphragm sizes correspond to different transverse mode modes in the resonant cavity, and the diaphragm diameter is 5mm at most; the signal to noise ratio of the diaphragm at different positions can be improved to realize Kerr lens mode locking.
5. The direct generating device of the mid-infrared ultrafast vortex laser according to claim 1, wherein the vertical inclination range of the third concave mirror (9) can be changed, when the included angle between the incident light and the reflected light is 90-110% of theta 3, the vortex light beam can be transmitted in the resonant cavity, and the state of collinear pumping in the resonant cavity can not be changed by changing the lens angle.
6. The direct generating device of mid-infrared ultrafast vortex laser according to claim 1, wherein the vertical tilting range of the fourth concave mirror (10) can be changed, when the included angle between the incident light and the reflected light is 90-110% of that of theta 4, the vortex light beam is transmitted in the resonant cavity, and changing the lens angle does not change the state of collinear pumping in the resonant cavity; varying the length d 6 between the fourth concave mirror (10) and the mode-locking element (11) enables a vortex laser output to be produced at 110.92% of the distance at which the laser is produced, and a different transverse mode to occur when only the distance between the mode-locking element (11) and the fourth concave mirror (10) is adjusted, the adjustment range being 93.2-111.13% of the distance at which the laser is produced.
7. The direct generating device of the mid-infrared ultrafast vortex laser according to claim 1, wherein the mode locking element (11) is a semiconductor mode locking saturable absorber mirror, the modulation depth is any one of 1.2%, 2.4%, 3% and 5%, and the working band is 1850-2100nm; the transmissivity of the output coupling mirror (12) is 2% or 5%, and the working band is 1850-2100nm.
8. A method for generating a direct generating device based on the mid-infrared ultrafast vortex laser of claims 1-7, comprising the steps of:
① The laser pumping source (1) generates pumping laser, and the first convex lens (2) and the second convex lens (3) with the same focal length adjust a certain angle and then aim the pumping laser until the pumping laser is formed on the first flat concave mirror (4); the angles of the first flat concave mirror (4), the laser gain medium (6) and the second flat concave mirror (8) are adjusted to enable the pumping mode in the resonant cavity to be collinear pumping, and the first round hole diaphragm (5) and the second round hole diaphragm (7) are adjusted to enable the pumping mode to be collinear pumping; the pump beam focused on the laser gain medium (6) is absorbed by the gain medium to generate the particle number inversion; adjusting the positions of the third concave mirror (9), the fourth concave mirror (10) and the mode locking element (11) to enable laser to resonate and generate 2 mu m-mode ultrafast laser;
② The laser generates resonance in the resonant cavity and has an amplifying effect on the pulse, and the laser is reflected by the third flat concave mirror (9) and the fourth flat concave mirror (10) to be incident on the mode locking element (11); generating a 2 mu m ultra-short mode locking fundamental order pulse output by adjusting the distance between the mode locking element (11) and the fourth concave mirror (10) to generate a saturable absorption effect;
③ The deviation angle of laser in the resonant cavity is regulated by an output coupling mirror (12), the left and right angle regulating range is 1-3 degrees, and the upper and lower angle regulating range is 1-2 degrees to generate 2 mu m ultra-fast vortex light beams; the signal-to-noise ratio of vortex laser is improved by adjusting the sizes of the first circular aperture diaphragm (5) and the second circular aperture diaphragm (7); changing the light intensity of the output vortex beam by using an output coupling mirror (12) with a transmissivity of 2% or 5%; by adjusting the distance between the fourth concave mirror (10) and the mode locking element (11), the transverse mode in the cavity can be controlled without changing the collinear pumping state in the cavity, and the ultrafast laser with the specified transverse mode can be output;
④ By adding a chiral selection element (10), chiral selection and wavelength tuning are realized by changing the inclination angle, and the nonlinearity is controlled and regulated by changing the position of the chiral selection element;
⑤ Detecting the light spot intensity distribution and interference patterns of the output laser by using a CCD camera and an interferometer; detecting time domain characteristics by using an oscilloscope and an autocorrelation instrument, and detecting frequency domain characteristics by using a spectrometer; the pulse repetition frequency and the signal to noise ratio are measured by a spectrum analyzer, and the parameters in the cavity are optimized, so that the ultra-fast vortex laser in the middle infrared band can be directly generated.
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