CN115939919B

CN115939919B - Solid laser based on Kerr lens mode locking

Info

Publication number: CN115939919B
Application number: CN202310045559.5A
Authority: CN
Inventors: 张金伟; 杨婷婷; 武帆; 刘贺言
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2023-01-30
Filing date: 2023-01-30
Publication date: 2024-06-04
Anticipated expiration: 2043-01-30
Also published as: CN115939919A

Abstract

The invention discloses a solid laser based on Kerr lens mode locking, which is used for outputting high-stability femtosecond laser pulse capable of automatically starting Kerr lens mode locking, and belongs to the technical field of solid laser, and comprises the following steps: the laser comprises a pumping source, a laser crystal, a resonant cavity and an external cavity reflector; the pump laser output by the pump source is focused on the laser crystal through the pump light path; the laser generated by the laser crystal oscillates back and forth in the round-trip light path provided by the resonant cavity; the external cavity reflector is used for reflecting laser transmitted by the resonant cavity back to the resonant cavity, so that mode locking of the Kerr lens is started in a light disturbance mode. The invention solves the problem that the traditional Kerr lens mode locking requires a mode of applying mechanical disturbance by a worker to start mode locking, has higher stability, avoids the problem of light path deviation caused by long-term use and pushing of the resonant cavity mirror, and further can realize the high-stability and narrow-pulse-width femtosecond laser which has simple structure, easy operation and repeatable assembly.

Description

Solid laser based on Kerr lens mode locking

Technical Field

The invention belongs to the technical field of solid laser, and particularly relates to a solid laser based on Kerr lens mode locking.

Background

The ultra-fast laser has high peak power and narrow pulse width, so that the ultra-fast laser becomes an important research direction in the technical field of lasers, and has very wide and important application in the fields of basic scientific research, biomedical treatment, industrial processing, national defense and military and the like. The mode of generating ultrafast laser mainly comprises active mode locking and passive mode locking, wherein the pulse width generated by the active mode locking technology is generally in the picosecond order, and the passive mode locking technology is generally adopted for obtaining the ultrashort pulse in the femtosecond order. The mode locking mechanism of passive mode locking is a saturable absorption effect which can be achieved either by a real saturable absorber such as a semiconductor saturable absorber mirror (SESAM), carbon nanotubes, or graphene, or by a virtual saturable absorber such as a kerr lens mode locking. The passive mode-locked laser has the advantages of compact structure, stable performance and low cost, can generate ultra-short pulse with the magnitude of picosecond or even femtosecond, and can be widely applied to the fields of scientific research, medical treatment, industrial production and the like.

The current main way of generating ultrashort pulses is well developed by semiconductor saturated absorption mirror (SESAM) mode locking and kerr lens mode locking. The SESAM mode locking needs to prepare a mode locking device which combines a semiconductor saturable absorber and a reflecting mirror together, has strict selection on the laser wavelength, is easy to damage when generating high-power laser and has high cost; and the mode locking of the Kerr lens is equivalent to forming a virtual saturable absorber, so that a mode locking device does not need to be specially grown and manufactured, and the mode locking can be realized by only combining a Kerr medium with a nonlinear effect with the design of a resonant cavity, so that the Kerr lens mode locking has higher damage resistance threshold and lower price, and meanwhile, the modulation depth of the Kerr lens mode locking is larger, which is beneficial to generating ultra-fast laser with shorter pulse width. Therefore, kerr lens mode locking is a mode locking mode suitable for generating high-power and narrow-pulse-width ultrafast laser.

However, the mode locking of the Kerr lens requires fine design of the structure of the resonant cavity and careful adjustment, and the mode locking of the Kerr lens is generally not self-starting, generally requires that a worker applies a mechanical disturbance to start the mode locking state in experiments, is complex to operate, and uses a mode of mechanically vibrating the resonant cavity mirror for a long time, so that the optical path deviation is easy to cause, the stability is poor, which is definitely an important problem for limiting the development of ultra-fast laser of the mode locking of the Kerr lens in practical industrial application.

Disclosure of Invention

Aiming at the defects or improvement demands of the prior art, the invention provides a solid laser based on Kerr lens mode locking, which is used for solving the technical problem that the existing laser based on Kerr lens mode locking cannot be started automatically.

In order to achieve the above object, the present invention provides a solid laser based on kerr lens mode locking, comprising: the laser comprises a pumping source, a laser crystal, a resonant cavity and an external cavity reflector;

the pump laser output by the pump source is focused on the laser crystal through the pump light path; the laser generated by the laser crystal oscillates back and forth in the round-trip light path provided by the resonant cavity;

The external cavity reflector is used for reflecting laser transmitted by the resonant cavity back to the resonant cavity, so that mode locking of the Kerr lens is started in a light disturbance mode.

Further preferably, when the solid-state laser is a solid-state laser other than a disk laser, the resonant cavity includes:

The first end mirror and the second end mirror are arranged at two end parts of the resonant cavity and are used for reflecting the oscillation laser in the resonant cavity and providing a round-trip light path for the oscillation laser; wherein the first end mirror is a plane high-reflection mirror; the second end mirror is an output mirror;

The first concave mirror and the second concave mirror are arranged on the round trip light path, and form a tight focusing structure and are used for focusing oscillation laser in the resonant cavity onto the laser crystal so as to realize Kerr lens mode locking; the laser crystal is positioned between the first concave mirror and the second concave mirror;

and a high-dispersion mirror disposed on the round trip optical path for compensating dispersion introduced by the laser crystal and each optical element constituting the resonator.

Further preferably, when the solid-state laser is a disk laser, the resonant cavity includes:

the first concave mirror and the second concave mirror are arranged on the round trip light path, and form a tight focusing structure and are used for focusing oscillation laser in the resonant cavity to Kerr media so as to realize Kerr lens mode locking; wherein the Kerr medium is positioned between the first concave mirror and the second concave mirror;

A high-dispersion mirror disposed on the round trip optical path for compensating chromatic dispersion introduced by the laser crystal and each optical element constituting the resonant cavity;

the laser crystal is a disk-shaped laser crystal, and is used as a gain medium for generating laser light and as a return mirror for reflecting the oscillation laser light.

Further preferably, the resonant cavity further includes: and a diaphragm arranged on the round trip light path for improving diffraction loss in the resonant cavity.

In a preferred manner: the outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the first end mirror, which is back to the resonant cavity; the first end mirror is used for partially transmitting and partially reflecting the oscillation laser in the resonant cavity; the external cavity reflector is used for reflecting the laser transmitted by the first end mirror to enable the laser to return to the resonant cavity in the original path, so that the Kerr lens mode locking is started in a light disturbance mode;

the outer cavity reflector is a plane mirror or a concave mirror; one side of the outer cavity reflector, which is close to the first end mirror, is plated with a high-reflectivity film for oscillating laser, and the reflectivity is more than 99.9%;

One side of the first concave mirror and one side of the second concave mirror facing the resonant cavity are plated with high-reflectivity films for oscillating laser, and the reflectivity is more than 99.9%.

Further preferably, the outer cavity reflector and the first end mirror form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the first end mirror; when the outer cavity reflector is a plane mirror, the length of the outer cavity is in an integer multiple relation with the length of the resonant cavity; when the outer cavity reflector is a concave mirror, the outer cavity length is equal to the focal length of the outer cavity reflector.

Further preferably, one side of the first end mirror far away from the external cavity reflector is plated with a film which partially reflects and partially transmits the oscillation laser, and the transmittance range is 0.5% -20%; one side of the first end mirror, which is close to the outer cavity reflecting mirror, is plated with an antireflection film for oscillating laser, and the transmittance is more than 99.5%.

In a second preferred mode: the outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the second end mirror, which is away from the resonant cavity; at this time, the solid laser further includes a beam splitter located between the second end mirror and the external cavity mirror, and configured to partially transmit the laser light transmitted by the second end mirror, partially reflect the laser light onto the external cavity mirror, partially transmit the laser light reflected by the external cavity mirror, and partially reflect the laser light back to the second end mirror;

the second end mirror is used for partially transmitting and partially reflecting the oscillation laser in the resonant cavity; the external cavity reflector is used for reflecting the laser reflected by the splitter so that the laser returns to the resonant cavity in the original path, and thus, the Kerr lens mode locking is started in the form of light disturbance.

Wherein the outer cavity reflector is a plane mirror; one side of the outer cavity reflector, which is close to the second end mirror, is plated with a high-reflectivity film for oscillating laser, and the reflectivity is more than 99.9%;

Further preferably, the outer cavity reflector and the second end mirror form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the second end mirror; the length of the outer cavity is in integer multiple relation with the length of the resonant cavity.

In one preferred form, three: the outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the selected concave mirror, which is away from the resonant cavity;

The concave mirror is selected to partially transmit and partially reflect the oscillating laser light within the resonant cavity; the external cavity reflector is used for reflecting the laser transmitted by the selected concave mirror to enable the laser to return to the resonant cavity in the original path, so that the Kerr lens mode locking is started in a light disturbance mode;

the concave mirror is a first concave mirror or a second concave mirror;

the outer cavity reflector is a concave mirror, and one side of the outer cavity reflector, which is close to the selected concave mirror, is plated with a high-reflectivity film for oscillating laser, and the reflectivity is more than 99.9%; the focal length of the outer cavity reflector is greater than that of the selected concave mirror;

one side of the first end mirror surface facing the resonant cavity is plated with a high-reflection film for oscillating laser, and the reflectivity is more than 99.9%.

Further preferably, one side of the selected concave mirror surface facing the resonant cavity is plated with a film which partially reflects and partially transmits the oscillation laser, and the transmittance range is 0.5% -5%; one side of the selected concave mirror, which is back to the resonant cavity, is plated with an antireflection film for oscillating laser, and the transmittance is more than 99.5%.

Further preferably, the outer cavity reflector and the selected concave mirror form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the selected concave mirror; the external cavity length is the difference between the focal length of the external cavity mirror and the focal length of the selected concave mirror.

In a preferred mode four: when the solid laser is a solid laser except for a disc laser, the outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the laser crystal, which is away from the resonant cavity; the laser crystal and the resonant cavity are placed at Brewster angle and are used for reflecting part of the oscillation laser to the outer cavity reflecting mirror; the external cavity reflector is used for reflecting the laser reflected by the laser crystal to enable the original path of the laser to return to the resonant cavity, so that the Kerr lens mode locking is started in a light disturbance mode;

wherein the outer cavity reflector is a concave mirror; one side of the outer cavity reflector, which is close to the laser crystal, is plated with a high-reflectivity film for oscillating laser, and the reflectivity is more than 99.9%;

One side of the first concave mirror and one side of the second concave mirror facing the resonant cavity are plated with high-reflectivity films for oscillating laser, and the reflectivity is more than 99.9%;

Further preferably, the outer cavity reflector and the laser crystal form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the laser crystal; the length of the outer cavity is equal to the focal length of the outer cavity reflector.

In a fifth preferred mode: when the solid laser is a disc laser, the outer cavity reflector is arranged outside the resonant cavity, and the position Yu Keer medium is opposite to one side of the resonant cavity; the Kerr medium and the resonant cavity are placed at Brewster angle and are used for reflecting part of the oscillation laser to the outer cavity reflecting mirror; the external cavity reflector is used for reflecting laser reflected by the Kerr medium to enable the original path of the laser to return to the resonant cavity, so that the Kerr lens mode locking is started in a light disturbance mode;

Further preferably, the outer cavity reflector and the Kerr medium form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the Kerr medium; the length of the outer cavity is equal to the focal length of the outer cavity reflector.

In general, through the above technical solutions conceived by the present invention, the following beneficial effects can be obtained:

1. The invention provides a solid laser based on Kerr lens mode locking, which is characterized in that an external cavity reflector is arranged outside a resonant cavity to reflect laser transmitted by the resonant cavity back to the resonant cavity, so that Kerr lens mode locking is started in a light disturbance mode, self-starting of Kerr lens mode locking is realized, the mode locking is avoided by starting in a conventional mechanical vibration mode, meanwhile, the problem of light path deviation caused by mechanical vibration required to be carried out on the resonant cavity in a long-term use process is also avoided, and the solid laser has higher stability.

2. The solid laser based on Kerr lens mode locking provided by the invention has the advantages of low cost and low price, is suitable for the field of large-scale industrial devices such as industrial processing and production, and can realize laser pulse with narrower pulse width. Therefore, the Kerr lens mode-locked solid laser provided by the invention has the advantages of narrow pulse width and easiness in industrialization, and can be used for realizing a femtosecond laser with simple structure, easiness in operation, high stability and narrow pulse width, and easiness in repeated assembly.

3. The solid laser based on Kerr lens mode locking provided by the invention comprises but is not limited to a block solid laser and a disc laser, and is suitable for laser crystals with various shapes. Can meet the demands of unused applications, such as the compact solid-state laser is suitable for the industrial demands of compact structure and miniaturization, and the disk laser is suitable for the industrial demands of high power and high beam quality.

Drawings

Fig. 1 is a schematic diagram of an optical path structure of a kerr lens lock module-shaped solid laser according to an embodiment of the present invention when an external cavity is disposed outside a first end mirror and an external cavity mirror is a plane mirror;

Fig. 2 is a schematic diagram of an optical path structure of a kerr lens lock module-shaped solid laser according to an embodiment of the present invention when an external cavity is disposed outside a first end mirror and a reflection mirror of the external cavity is a concave mirror;

FIG. 3 is a schematic diagram of an optical path structure of a Kerr lens mode-locked disc laser according to an embodiment of the present invention when an external cavity is disposed outside a first end mirror and an external cavity mirror is a plane mirror;

FIG. 4 is a schematic diagram of an optical path structure of a Kerr lens mode-locked disc laser according to an embodiment of the present invention when an external cavity is disposed outside a first end mirror and an external cavity mirror is a concave mirror;

Fig. 5 is a schematic diagram of an optical path structure of a kerr lens lock module-shaped solid laser started by light disturbance when an external cavity is arranged outside a concave mirror according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of an optical path structure of a Kerr lens mode-locked disc laser started by optical disturbance when an external cavity is arranged outside a concave mirror according to an embodiment of the present invention;

fig. 7 is a schematic diagram of an optical path structure of a kerr lens lock module-shaped solid laser started by light disturbance when an external cavity is disposed outside a second end mirror according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of an optical path structure of a Kerr lens mode-locked disc laser with optical disturbance start when an external cavity is disposed outside a second end mirror according to an embodiment of the present invention;

Fig. 9 is a schematic diagram of an optical path structure of a kerr lens lock module-shaped solid laser started by light disturbance when an external cavity is disposed outside a laser crystal according to an embodiment of the present invention;

Fig. 10 is a schematic diagram of an optical path structure of a kerr lens mode-locked disc laser started by optical disturbance when an external cavity is placed outside a kerr medium according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.

In order to achieve the above object, the present invention provides a solid laser based on kerr lens mode locking, for achieving stable self-starting kerr lens mode locking femtosecond pulse output, comprising: the laser comprises a pumping source, a laser crystal, a resonant cavity and an external cavity reflector;

the pump source focuses the pump laser generated by the pump source onto the laser crystal through a pump light path, the laser crystal is used as a gain medium to generate laser, and meanwhile, the Kerr effect of the crystal is utilized to combine with the design of the resonant cavity to form laser pulses of Kerr lens mode locking. The external cavity reflector reflects laser transmitted by the resonant cavity back into the resonant cavity to start Kerr lens mode locking in a light disturbance mode.

When the solid-state laser is a solid-state laser other than a disk laser, the resonant cavity described above includes:

The first end mirror and the second end mirror are arranged at two end parts of the resonant cavity and are used for reflecting the oscillation laser in the resonant cavity and providing a round-trip light path for the oscillation laser; wherein the first end mirror is a plane high-reflection mirror; the second end mirror is an output mirror; specifically, the second end mirror is a plane mirror, and two sides of the second end mirror are plated with different dielectric films; one side of the second end mirror facing the resonant cavity is plated with a film which partially reflects and partially transmits the oscillating laser, and the transmittance range is 0.5% -20% (preferably 1% -20%). One side of the second end mirror, which is away from the resonant cavity, is plated with an antireflection film for oscillating laser, and the transmittance is more than 99.9%;

the first concave mirror and the second concave mirror are arranged on the round trip light path, and form a tight focusing structure and are used for focusing oscillation laser in the resonant cavity onto the laser crystal so as to realize mode locking of the Kerr lens; the laser crystal is positioned between the first concave mirror and the second concave mirror;

When the end face of the laser crystal is placed perpendicular to the resonant cavity, the two sides of the laser crystal are plated with antireflection films for oscillating laser; when the end face of the laser crystal and the resonant cavity are placed at Brewster angle, the two sides are not coated with films; laser crystals include, but are not limited to, yb: KYW, yb: KGW, yb: CALGO, yb: lu ₂O₃, yb: YAG, ybYGG, ho: YAG, cr: znS, cr: znSe, ti: sapphire, etc. The pump source includes, but is not limited to, a semiconductor laser, a fiber laser, a solid-state laser, etc. having an output wavelength in the range of 300nm to 5 μm.

When the solid-state laser is a disk laser, the resonant cavity includes:

A high-dispersion mirror arranged on the round trip light path for compensating the dispersion introduced by each optical element in the resonant cavity;

The laser crystal is a disc-shaped laser crystal, and is used as a gain medium for generating laser and a turning mirror for reflecting oscillation laser; one side of the disc-shaped laser crystal facing the resonant cavity is plated with an antireflection film of pumping laser and oscillation laser, and one side of the disc-shaped laser crystal facing away from the resonant cavity is plated with a high-reflection film of pumping laser and oscillation laser; in an alternative embodiment, the disc-shaped laser crystal is in a disc shape or an elliptic disc shape, the thickness is 10 mu m-1 mm, and the diameter is 3-30 mm; the material of the disk-shaped laser crystal includes, but is not limited to, yb, ho, YAG, tm, YAG, ho, KYW, yb CALGO, cr, znSe, yb, luScO ₃、Yb:Lu₂O₃, etc. which are suitable for processing into a disk-shaped laser crystal.

The Kerr medium is placed at Brewster angle with the resonant cavity. In an alternative embodiment, the Kerr medium is a material such as sapphire or fused silica having a thickness of 0.1mm to 10mm, which has a nonlinear Kerr effect. Preferably, the Kerr media is a sapphire sheet 1mm to 3mm thick.

Preferably, the resonant cavity further includes: and a diaphragm arranged on the round trip light path for improving diffraction loss in the resonant cavity. Specifically, according to the mode distribution in the resonant cavity, diaphragms with different sizes can be arranged at different positions in the cavity, so as to improve diffraction loss in the cavity and assist mode locking of the Kerr lens. In an alternative embodiment, the diaphragm aperture is 0.5mm to 5mm.

Specifically, in an alternative embodiment one:

The outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the first end mirror, which is back to the resonant cavity; the first end mirror is used for partially transmitting and partially reflecting the oscillation laser in the resonant cavity; the external cavity reflector is used for reflecting the laser transmitted by the first end mirror to enable the laser to return to the resonant cavity in the original path, so that the Kerr lens mode locking is started in a light disturbance mode;

Further preferably, the outer cavity reflector and the first end mirror form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the first end mirror; when the outer cavity reflector is a plane mirror, the length of the outer cavity is in an integer multiple relation with the length of the resonant cavity; at this time, the intensity of random pulses formed by continuous light in the resonant cavity is enhanced under the superposition of external synchronous pulses, and in the random pulses, the probability of reaching a mode locking threshold is increased, so that the mode locking starting capability is improved;

When the outer cavity reflector is a concave mirror, the length of the outer cavity is equal to the focal length of the outer cavity reflector, at the moment, the disturbance light is at a beam waist position at the first end mirror, so that the disturbance light is matched with a laser transverse mode in the resonant cavity, and the mode locking starting capability is improved; the disturbance light is laser reflected back to the resonant cavity by the outer cavity reflector.

Preferably, one side of the first end mirror far away from the outer cavity reflector is plated with a film which partially reflects and partially transmits the oscillation laser, and the transmittance range is 0.5% -20%; one side of the first end mirror, which is close to the outer cavity reflecting mirror, is plated with an antireflection film for oscillating laser, and the transmittance is more than 99.5%.

In an alternative embodiment two:

The outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the second end mirror, which is away from the resonant cavity; at this time, the solid laser further includes a beam splitter located between the second end mirror and the external cavity mirror, and configured to partially transmit the laser light transmitted by the second end mirror, partially reflect the laser light onto the external cavity mirror, partially transmit the laser light reflected by the external cavity mirror, and partially reflect the laser light back to the second end mirror;

Preferably, the outer cavity reflector and the second end mirror form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the second end mirror; the length of the outer cavity is in integer multiple relation with the length of the resonant cavity, at the moment, random pulses formed by continuous light in the resonant cavity are enhanced in strength under the superposition of external synchronous pulses, and in the random pulses, the probability of reaching a mode locking threshold is increased, so that the mode locking starting capability is improved; the disturbance light is laser reflected back to the resonant cavity by the external cavity reflector.

In an alternative embodiment three:

The outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the selected concave mirror, which is away from the resonant cavity; the concave mirror is selected to partially transmit and partially reflect the oscillating laser light within the resonant cavity; the external cavity reflector is used for reflecting the laser transmitted by the selected concave mirror to enable the laser to return to the resonant cavity in the original path, so that the Kerr lens mode locking is started in a light disturbance mode;

the concave mirror is a first concave mirror or a second concave mirror;

Preferably, one side of the selected concave mirror surface facing the resonant cavity is plated with a film which partially reflects and partially transmits the oscillation laser, and the transmittance range is 0.5-5%; one side of the selected concave mirror, which is back to the resonant cavity, is plated with an antireflection film for oscillating laser, and the transmittance is more than 99.5%.

Preferably, the outer cavity reflector and the selected concave mirror form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the selected concave mirror; the length of the outer cavity is the difference between the focal length of the outer cavity reflector and the focal length of the selected concave mirror; at this time, the disturbance light is at the beam waist position at the laser crystal (Kerr medium), so that the disturbance light is matched with the laser transverse mode in the resonant cavity, and the mode locking starting capability is improved; the disturbance light is laser reflected back to the resonant cavity by the outer cavity reflector.

In an alternative embodiment four:

when the solid laser is a solid laser except for a disc laser, the outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the laser crystal, which is away from the resonant cavity; the laser crystal and the resonant cavity are placed at Brewster angle and are used for reflecting part of the oscillation laser to the outer cavity reflecting mirror; the external cavity reflector is used for reflecting the laser reflected by the laser crystal to enable the original path of the laser to return to the resonant cavity, so that the Kerr lens mode locking is started in a light disturbance mode;

Preferably, the outer cavity reflector and the laser crystal form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the laser crystal; the length of the outer cavity is equal to the focal length of the outer cavity reflector; at the moment, the disturbance light is at a beam waist position at the laser crystal, so that the disturbance light is matched with a laser transverse mode in the resonant cavity, and the capability of starting mode locking is improved; the disturbance light is laser reflected back to the resonant cavity by the outer cavity reflector.

In an alternative embodiment five:

When the solid laser is a disc laser, the outer cavity reflector is arranged outside the resonant cavity, and the position Yu Keer medium is opposite to one side of the resonant cavity; the Kerr medium and the resonant cavity are placed at Brewster angle and are used for reflecting part of the oscillation laser to the outer cavity reflecting mirror; the external cavity reflector is used for reflecting laser reflected by the Kerr medium to enable the original path of the laser to return to the resonant cavity, so that the Kerr lens mode locking is started in a light disturbance mode;

Preferably, the outer cavity reflector and the Kerr medium form an outer cavity, and the length of the outer cavity is the distance between the outer cavity reflector and the Kerr medium; the length of the outer cavity is equal to the focal length of the outer cavity reflector; at the moment, the disturbance light is at a beam waist position at the Kerr medium, so that the disturbance light is matched with a laser transverse mode in the resonant cavity, and the mode locking starting capability is improved; the disturbance light is laser reflected back to the resonant cavity by the outer cavity reflector.

In order to further illustrate the solid-state laser provided by the present invention, the following describes a specific embodiment of a mode-locked solid-state laser based on four optical perturbations, and it should be noted that the present invention divides the solid-state laser into a disk laser and a solid-state laser other than the disk laser; solid state lasers other than disc lasers include: bulk solid state lasers, semiconductor lasers, and the like.

The solid-state lasers provided by the invention except the disc laser are exemplified by block-shaped solid-state lasers, and the laser crystals of the block-shaped solid-state lasers in the embodiment are in block-shaped solid shapes with side lengths of 1 mm-20 mm. Specifically, fig. 1 to 10 are optical path diagrams of a kerr lens lock module-shaped solid laser and a disc laser, respectively, which are started by optical disturbance when the external cavity is at different positions. Fig. 1 is a schematic diagram of an optical path structure of a kerr lens lock module-shaped solid laser started by light disturbance when an external cavity is arranged outside a first end mirror and an external cavity reflecting mirror is a plane mirror; FIG. 2 is a schematic view of the optical path structure of a Kerr lens lock module-shaped solid laser with the external cavity disposed outside the first end mirror and the external cavity mirror being a concave mirror; FIG. 3 is a schematic view of the optical path structure of the optical disturbance-activated Kerr-lens mode-locked disc laser when the external cavity is disposed outside the first end mirror and the external cavity mirror is a plane mirror; FIG. 4 is a schematic diagram of the optical path structure of a light disturbance-activated Kerr-lens mode-locked disc laser when the external cavity is disposed outside the first end mirror and the external cavity mirror is a concave mirror; FIG. 5 is a schematic view of the optical path structure of a light disturbance-activated Kerr-lens-lock module-like solid laser when the external cavity is placed outside the concave mirror; FIG. 6 is a schematic diagram of the optical path structure of a light-disturbance-activated Kerr-lens mode-locked disc laser when the external cavity is placed outside the concave mirror;

FIG. 7 is a schematic diagram of the optical path structure of a light disturbance activated Kerr lens lock module solid laser when the external cavity is placed outside the second end mirror; FIG. 8 is a schematic diagram of the optical path structure of an optical disturbance-activated Kerr-lens mode-locked disc laser when the external cavity is disposed outside the second end mirror; FIG. 9 is a schematic diagram of the optical path structure of a light-disturbance-activated Kerr-lens-lock module-like solid-state laser when the external cavity is placed outside the laser crystal; FIG. 10 is a schematic diagram of the optical path structure of an optical disturbance-activated Kerr lens mode-locked disk laser when the external cavity is placed outside the Kerr medium.

As can be seen from fig. 1,2, 5, 7 and 9, the optical disturbance-activated kerr lens lock module-like solid-state laser mainly includes a pump source 1 for supplying pump laser light to a laser crystal, a pump optical path 2 for focusing the pump laser light onto the laser crystal, a laser crystal 3 serving as a gain medium, a resonant cavity 11 defined by each optical element for supplying oscillating laser light to and from, and an external cavity 13 for supplying optical disturbance.

As can be seen from fig. 3, 4,6, 8 and 10, the optical disturbance-activated kerr lens mode-locked disc laser mainly includes a pump source 1 for supplying pump laser to a disc-shaped laser crystal, a pump optical path 2 for focusing the pump laser on the disc-shaped laser crystal, a disc-shaped laser crystal 7 serving as a gain medium, a kerr medium 3 for kerr lens mode-locking and placed at brewster's angle with the oscillating laser, a resonant cavity 11 defined by each optical element for supplying back and forth oscillating laser, and an external cavity 13 for supplying optical disturbance.

As can be seen from fig. 1 to 10, the resonant cavity 11 is substantially identical, with the difference being noted in the design of the outer cavity 13. In the embodiment provided by the present invention, the resonant cavity 11 includes: a first end mirror 9, a second end mirror 6, a high dispersion mirror 8 for providing dispersion, a first concave mirror 4 and a second concave mirror 5 for focusing the oscillating laser light onto a laser crystal (kerr medium), and a diaphragm 10 for improving the intra-cavity diffraction loss. In the case of a bulk solid-state laser,

The resonant cavity 11 also comprises a high reflection mirror 7; the side of the first concave mirror 4 facing the resonant cavity is plated with a high reflection film for oscillating laser and an anti-reflection film for pumping laser; one side of the first concave mirror 4 facing the pumping light path is coated with an antireflection film for pumping laser.

For a disk laser, the resonator 11 also includes a disk-shaped laser crystal 7 that serves as both a gain medium and a turning mirror; and the side of the disc-shaped laser crystal facing the resonant cavity is plated with a high-transmission film for the oscillation laser and the pumping laser, and the side of the disc-shaped laser crystal facing away from the resonant cavity is plated with a high-reflection film for the oscillation laser and the pumping laser.

In fig. 1 and 3, the outer cavity 13 is composed of the first end mirror 9 and the outer cavity plane mirror 12.

In fig. 2 and 4, the outer cavity 13 is composed of the first end mirror 9 and the outer cavity concave mirror 12.

In fig. 5 and 6, the outer cavity 13 is composed of the second concave mirror 5 and the outer cavity concave mirror 12.

In fig. 7 and 8, the outer cavity 13 is composed of the second end mirror 6, the beam splitter 14 and the outer cavity plane mirror 12.

In fig. 9 and 10, the external cavity 13 is composed of a laser crystal (kerr medium) 3 and an external cavity concave mirror 12.

Specifically, the optical paths of the optical disturbance-activated kerr lens lock module-shaped solid laser and the disc laser are mainly divided into a resonant cavity 11 and an external cavity 13. The resonant cavity 11 includes a first end mirror 9, a second end mirror 6, a high dispersion mirror 8, a first concave mirror 4, a second concave mirror 5, a high reflection mirror (disk laser crystal) 7, a laser crystal (kerr medium) 3, and a diaphragm 10. Wherein the first end mirror 9 and the second end mirror 6 as two end mirrors of the resonator 11 provide a round-trip light path for the oscillating laser light. The high dispersion mirror 8 serves to compensate for the dispersion introduced by the various optical elements within the cavity. The first concave mirror 4 and the second concave mirror 5 constitute a tight focusing structure to focus the laser light oscillated in the cavity on the laser crystal (kerr medium) 3. The diaphragm 10 assists the kerr lens to lock the mode by increasing diffraction loss in the cavity, and the placement position is not limited. For the bulk solid laser, when the end face of the laser crystal 3 is placed vertically to the resonant cavity 11, anti-reflection films for oscillating laser are coated on two sides, and when the end face of the laser crystal 3 and the resonant cavity 11 are placed at Brewster angle, the two sides are not coated with films. The high reflection mirror 7 serves as a return mirror for reflecting the oscillation laser light. For a disc laser, the kerr medium 3 is placed near the focus of the first concave mirror 4 and the second concave mirror 5 at the brewster angle. The disk-shaped laser crystal 7 can be used as a gain medium to generate laser light and as a return mirror of a resonant cavity for reflecting the oscillation laser light.

The outer cavity 13 can be divided into four cases according to the placement position:

When the external cavity is arranged outside the first end mirror (as shown in fig. 1-4), the external cavity 13 comprises the first end mirror 9 and the external cavity reflecting mirror 12, a part of transmission and partial reflection films for the oscillation laser are plated on the side of the first end mirror 9 facing the resonant cavity 11, and an antireflection film for the oscillation laser is plated on the side of the first end mirror 9 facing the external cavity 13. The side of the outer cavity mirror 12 facing the outer cavity 13 is coated with a high reflection film for the oscillating laser light. The length of the external cavity is not limited, and when the external cavity mirror 12 is a plane mirror, the external cavity length and the resonant cavity length are preferably in an integer multiple relationship; when the external cavity mirror 12 is a concave mirror, the external cavity length preferably coincides with the concave mirror focal length.

(II) when the external cavity is arranged outside the concave mirror (as shown in figures 5-6), the external cavity 13 comprises a second concave mirror 5 (or a first concave mirror 4) and an external cavity reflecting mirror 12, a part of the transmission and partial reflection film for the oscillation laser light is plated on the side of the second concave mirror 5 facing the resonant cavity 11, and an antireflection film for the oscillation laser light is plated on the side of the second concave mirror 5 facing the external cavity 13. The side of the outer cavity mirror 12 facing the outer cavity 13 is coated with a high reflection film for the oscillating laser light. The outer cavity mirror 12 is a concave mirror and has a focal length greater than that of the second concave mirror 5. The length of the outer cavity 13 is the difference between the focal length of the outer cavity concave mirror 12 and the focal length of the second concave mirror 5.

(III) when the external cavity is arranged outside the second end mirror (as shown in figures 7-8), the external cavity 13 comprises the second end mirror 6, the spectroscope 14 and the external cavity reflecting mirror 12, the side of the second end mirror 6 facing the resonant cavity 11 is plated with a partial reflection film and a partial transmission film for the oscillation laser, and the side of the second end mirror 6 facing the external cavity 13 is plated with an antireflection film for the oscillation laser. One side of the outer cavity reflector 12 facing the outer cavity 13 is plated with a high reflection film for oscillating laser, and the outer cavity reflector is a plane mirror. The length of the external cavity is not limited, and it is preferable that the length of the external cavity is an integer multiple of the length of the resonant cavity.

(IV) when the external cavity is arranged outside the laser crystal (Kerr medium) (as shown in figures 9-10), the external cavity 13 comprises a laser crystal (Kerr medium) 3 and an external cavity reflector 12, the laser crystal (Kerr medium) 3 is arranged in the resonant cavity 11 at the Brewster angle, part of oscillation laser in the cavity is reflected to the external cavity reflector 12, a high-reflection film for the oscillation laser is plated on one side of the external cavity reflector 12 facing the external cavity 13, the external cavity reflector is a concave mirror, and the length of the external cavity is consistent with the focal length of the external cavity concave mirror 12.

In the above four embodiments of the optical disturbance-activated kerr lens mode-locked solid laser, the design of the resonator 11 is substantially identical, and the main difference is in the design of the external cavity 13, so that the oscillation process of the resonator 11 will be described first and the optical disturbance-activated mode-locked process of the external cavity 13 will be described separately in conjunction with the specific examples of fig. 1 to 10.

First, the oscillation process of the optical disturbance-started kerr lens lock module-shaped solid laser and the disk laser will be described with reference to the specific examples of fig. 1 to 10.

For the solid laser, the semiconductor laser coupled and output by the optical fiber is selected as the pumping source 1, the pumping wavelength is 940nm, the pumping wavelength is focused on the laser crystal 3 through the pumping light path 2, and the laser crystal is Yb: KGW crystal with the wavelength of 5 multiplied by 5 mm. The 1030nm laser generated by KGW is incident on the second concave mirror 5, reflected to the high-reflection mirror 7 by the second concave mirror 5, reflected to the high-dispersion mirror 8 by the high-reflection mirror 7, reflected to the first end mirror 9 by the high-dispersion mirror 8, returned by the first end mirror 9, reaches the laser crystal 3 again and is incident on the first concave mirror 4 through the laser crystal 3, finally reflected to the second end mirror 6, wherein part of the laser is returned by the first end mirror 6 and forms oscillation in the resonant cavity 11, and part of the laser is transmitted through the second end mirror 6 and outputs stable mode-locked pulse laser.

For the disk laser, the semiconductor laser coupled and output by the optical fiber is selected as the pumping source 1, the pumping wavelength is 940nm, the pumping light is focused on the disk-shaped laser crystal 7 through the pumping light path 2, and the disk crystal is a disk-shaped Yb-YAG (doping concentration is 7%) laser crystal with the diameter of 10mm and the thickness of 220 mu m. The side of the disc-shaped laser crystal, which is opposite to the resonant cavity, is fixed on the heat sink, and the generated heat is taken away by a water cooling impact mode. The 1030nm laser generated by YAG laser crystal is incident on high dispersion mirror 8, reflected by high dispersion mirror 8 to first end mirror 9, first end mirror 9 returns the laser in the original path, reaches disc laser crystal 2 again and is reflected on second concave mirror 5, second concave mirror 5 reflects the laser to first concave mirror 4 through Kerr medium 3, finally reflected on second end mirror 6 by first concave mirror 4, wherein part of laser is reflected by second end mirror 6 and returns in the original path to form oscillation in resonant cavity 11, and part of laser outputs stable high power mode locking pulse laser through second end mirror 6.

The optical path of the light disturbance-initiated mode locking is then described in part for the external cavity 13 of fig. 1-10, respectively.

In fig. 1 to 4, the laser reflected to the first end mirror 9 is divided into two parts, one part is returned by the original path and oscillates in the resonant cavity 11, and the other part passes through the first end mirror 9 and reaches the outer cavity mirror 12, is reflected by the outer cavity mirror 12 and returned by the original path into the resonant cavity 11, and starts the kerr lens mode locking in the form of optical disturbance.

In fig. 5 to 6, the laser light reflected on the second concave mirror 5 is divided into two parts, one part is reflected on the laser crystal (kerr medium) 3, and the other part passes through the second concave mirror 5 and reaches the external cavity mirror 12, is reflected by the external cavity mirror 12 and returns to the resonant cavity 11 in the original path, and starts the kerr lens mode locking in the form of optical disturbance.

In fig. 7 to 8, the laser light transmitted through the second end mirror 6 is incident on the beam splitter 14, the laser light reaching the beam splitter 14 is divided into two parts, one part is transmitted through the beam splitter 14 and used for output, the other part is reflected to the external cavity mirror 12, reflected by the external cavity mirror 12 and returned to the resonant cavity 11 in the original way, and the kerr lens mode locking is started in a light disturbance mode.

In fig. 9 to 10, the laser light reflected by the second concave mirror 5 and reaching the laser crystal (kerr medium) 3 is divided into two parts, one part of the laser light passes through the laser crystal (kerr medium) 3 and is incident on the first concave mirror 4, and oscillates in the resonant cavity 11, and the other part of the laser light is reflected by the laser crystal (kerr medium) 3 to the external cavity mirror 12, reflected by the external cavity mirror 12 and returns to the resonant cavity 11 in the original path, and the kerr lens mode locking is started in the form of optical disturbance.

The invention provides a light disturbance start Kerr lens mode locking solid laser, which aims to realize light disturbance start Kerr lens mode locking, the design of a resonant cavity is not limited, and parameters of specific optical elements in the cavity are selected according to the design of the resonant cavity. Here, only a disk laser having a repetition rate of 100MHz is used as a specific example, and the relationship between the resonator and the external cavity is described in detail. According to the same method, a corresponding external cavity structure can be designed for any cavity type to realize that the Kerr lens is started to lock the mode by light disturbance and obtain stable femtosecond pulse output.

According to the above embodiment, for a disc laser with a repetition rate of 100MHz, the cavity length, i.e., the distance between the first end mirror 9 and the second end mirror 6, is 1.5m, the radii of curvature of the first concave mirror 4 and the second concave mirror 5 are both 150mm, the distance between the first concave mirror 4 and the first end mirror 9 is the long arm end of the cavity, the distance between the second concave mirror 5 and the second end mirror 6 is the short arm end, and the ratio of the long arm end to the short arm end is about 3.3:1. when the distance between the first concave mirror 4 and the second concave mirror 5 is between 150mm and 156mm, the resonant cavity is in a first stable region, and when the distance between the first concave mirror 4 and the second concave mirror 5 is between 175mm and 181mm, the resonant cavity is in a second stable region. Kerr lens mode locking can be achieved when the distance between the first concave mirror 4 and the second concave mirror 5 is in the vicinity of four positions of 150.5mm, 155.5mm, 175.5mm and 180.5 mm. Preferably, the kerr lens mode locking is most easily achieved at a distance of about 155.5mm between the first concave mirror 4 and the second concave mirror 5. The kerr medium 3 is preferably a sapphire sheet of 2mm thickness and the total negative dispersion in the cavity 11 is preferably-14000 fs2. The second end mirror 6 is coated with a part of the transmission film for the oscillation laser on the side facing the resonant cavity 11, the transmission rate range is 1% -20%, preferably, the transmission rate is 8% -10%, and the second end mirror 6 is coated with an antireflection film on the side facing away from the resonant cavity 11, and the transmission rate is more than 99.9%.

Only the external cavity design when the resonator 11 is in the above embodiment is described here. When the design of the outer cavity is shown in fig. 3, a part of the transmission film for the oscillation laser is plated on the side of the first end mirror 9 facing the resonant cavity 11, the transmission range is 0.5% -5%, preferably, the transmission is 0.5% -1.5%, and the antireflection film is plated on the side of the first end mirror 9 facing the outer cavity 13, and the transmission is more than 99.9%. The length of the outer cavity is not limited, and is preferably a value which is in integral multiple relation with 1.5 mm; when the design of the outer cavity is shown in fig. 4, a part of the transmission film for the oscillating laser is plated on the side of the first end mirror 9 facing the resonant cavity 11, the transmission range is 0.5% -5%, preferably, the transmission is 0.5% -1.5%, and the anti-reflection film is plated on the side of the first end mirror 9 facing the outer cavity 13, and the transmission is more than 99.9%. The outer cavity length is not limited and the radius of curvature of the outer cavity concave mirror 12 is not limited, preferably, when the radius of curvature of the outer cavity mirror 12 is 300mm, the outer cavity length is 150mm; when the design of the outer cavity is shown in fig. 6, a part of the transmission film for the oscillation laser is plated on the side of the second concave mirror 5 facing the resonant cavity 11, the transmission range is 0.5% -5%, preferably, the transmission is 0.5% -1.5%, and the antireflection film is plated on the side of the second concave mirror 5 facing the outer cavity 13, and the transmission is more than 99.9%. The radius of curvature of the outer cavity concave mirror 12 is larger than that of the second concave mirror 5, and the outer cavity length is the difference between the focal length of the outer cavity concave mirror and the focal length of the second concave mirror, preferably, when the radius of curvature of the outer cavity concave mirror 12 is 300mm, the outer cavity length is 75mm; when the external cavity design is as shown in fig. 8, the external cavity length is not limited, and preferably the external cavity length is an integer multiple of 1.5 m. When the external cavity design is as shown in fig. 10, the external cavity length and the radius of curvature of the external cavity concave mirror are not limited, and preferably, when the radius of curvature of the external cavity mirror 12 is 300mm, the external cavity length is 150mm.

The invention solves the problem that the traditional Kerr lens mode locking requires a worker to apply mechanical disturbance to start mode locking, and the method for starting Kerr lens mode locking by light disturbance has higher stability, avoids the problem of light path deviation caused by long-term use and pushing of a resonant cavity mirror, can obtain high-stability femtosecond laser pulse for starting Kerr lens mode locking by light disturbance, and further can realize a high-stability and narrow-pulse width femtosecond laser with simple structure, easy operation and repeated assembly. The optical disturbance start Kerr lens mode-locking solid laser provided by the invention has the advantages of simple structure, good practicality and operability, mass production, repeated assembly and the like, and can be widely applied to the fields of scientific research, industrial production, biomedicine and the like.

It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.

Claims

1. A solid state laser based on kerr lens mode locking, comprising: the laser comprises a pumping source, a laser crystal, a resonant cavity and an external cavity reflector;

The pump laser output by the pump source is focused on the laser crystal through a pump light path; the laser generated by the laser crystal oscillates back and forth in a round-trip light path provided by the resonant cavity;

The external cavity reflector is used for reflecting laser transmitted by the resonant cavity back to the resonant cavity, so that mode locking of the Kerr lens is started in a light disturbance mode;

when the solid-state laser is a solid-state laser other than a disk laser, the resonant cavity includes:

The first end mirror and the second end mirror are arranged at two end parts of the resonant cavity and are used for reflecting the oscillation laser in the resonant cavity and providing a round-trip light path for the oscillation laser; the first end mirror is a plane high-reflection mirror; the second end mirror is an output mirror;

When the solid-state laser is a disk laser, the resonant cavity includes:

The first concave mirror and the second concave mirror are arranged on the round trip light path, and form a tight focusing structure and are used for focusing the oscillation laser in the resonant cavity to Kerr media so as to realize Kerr lens mode locking; the Kerr medium is positioned between the first concave mirror and the second concave mirror;

At this time, the laser crystal is a disk-shaped laser crystal, and also serves as a turning mirror for reflecting the oscillation laser;

The outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the first end mirror, which is away from the resonant cavity; the first end mirror is used for partially transmitting and partially reflecting the oscillation laser in the resonant cavity; the external cavity reflector is used for reflecting the laser transmitted by the first end mirror to enable the laser to return to the resonant cavity in the original path, so that the Kerr lens mode locking is started in a light disturbance mode;

the outer cavity reflecting mirror is a plane mirror or a concave mirror;

When the outer cavity reflector is a plane mirror, the length of the outer cavity is in an integer multiple relation with the length of the resonant cavity; when the outer cavity reflector is a concave mirror, the length of the outer cavity is equal to the focal length of the outer cavity reflector; wherein the external cavity length is the distance between the external cavity reflector and the first end mirror.

2. The solid state laser of claim 1, wherein the resonant cavity further comprises: and a diaphragm arranged on the round trip light path for improving diffraction loss in the resonant cavity.

3. The solid state laser of claim 1 or 2, wherein a side of the external cavity mirror near the first end mirror is coated with a high reflection film for oscillating laser light, and the reflectivity is greater than 99.9%;

And one side of the first concave mirror and one side of the second concave mirror facing the resonant cavity are plated with high-reflectivity films for oscillating laser, and the reflectivity is more than 99.9%.

4. The solid state laser of claim 1 or 2, wherein a side of the first end mirror away from the external cavity mirror is coated with a partially reflective and partially transmissive film for the oscillating laser light, the transmittance ranging from 0.5% to 20%; one side of the first end mirror, which is close to the outer cavity reflecting mirror, is plated with an antireflection film for oscillating laser, and the transmittance is more than 99.5%.

5. A solid state laser based on kerr lens mode locking, comprising: the laser comprises a pumping source, a laser crystal, a resonant cavity and an external cavity reflector;

When the solid-state laser is a disk laser, the resonant cavity includes:

The second end mirror is used for partially transmitting and partially reflecting the oscillation laser in the resonant cavity; the external cavity reflector is used for reflecting the laser reflected by the spectroscope to enable the original path of the laser to return to the resonant cavity, so that the Kerr lens mode locking is started in a light disturbance mode;

Wherein the outer cavity reflector is a plane mirror;

the length of the outer cavity is in integer multiple relation with the length of the resonant cavity; wherein the length of the outer cavity is the distance between the outer cavity reflector and the second end mirror.

6. The solid state laser of claim 5, wherein the resonant cavity further comprises: and a diaphragm arranged on the round trip light path for improving diffraction loss in the resonant cavity.

7. The solid state laser of claim 5 or 6, wherein the side of the external cavity mirror near the second end mirror is coated with a high reflection film for oscillating laser light, the reflectivity is greater than 99.9%;

8. A solid state laser based on kerr lens mode locking, comprising: the laser comprises a pumping source, a laser crystal, a resonant cavity and an external cavity reflector;

When the solid-state laser is a disk laser, the resonant cavity includes:

the outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the selected concave mirror, which is away from the resonant cavity;

The concave mirror is used for partially transmitting and partially reflecting the oscillation laser in the resonant cavity; the external cavity reflector is used for reflecting the laser transmitted by the selected concave mirror to enable the original path of the laser to return to the resonant cavity, so that the Kerr lens mode locking is started in a light disturbance mode;

wherein the selected concave mirror is the first concave mirror or the second concave mirror;

The outer cavity reflecting mirror is a concave mirror; the focal length of the outer cavity reflector is larger than that of the selected concave mirror;

the length of the outer cavity is the difference between the focal length of the outer cavity reflector and the focal length of the selected concave mirror; the length of the outer cavity is the distance between the outer cavity reflecting mirror and the selected concave mirror.

9. The solid state laser of claim 8, wherein the resonant cavity further comprises: and a diaphragm arranged on the round trip light path for improving diffraction loss in the resonant cavity.

10. The solid state laser of claim 8 or 9, wherein the side of the external cavity mirror adjacent to the selected concave mirror is coated with a highly reflective film to the oscillating laser light and has a reflectivity of greater than 99.9%;

one side of the first end mirror facing the resonant cavity is plated with a high-reflectivity film for oscillating laser, and the reflectivity is more than 99.9%.

11. The solid state laser of claim 8 or 9, wherein a side of the selected concave mirror facing the resonant cavity is coated with a partially reflective and partially transmissive film for the oscillating laser light, the transmittance ranging from 0.5% to 5%; one side of the selected concave mirror, which is away from the resonant cavity, is plated with an antireflection film for oscillating laser, and the transmittance is more than 99.5%.

12. A solid state laser based on kerr lens mode locking, comprising: the laser comprises a pumping source, a laser crystal, a resonant cavity and an external cavity reflector;

when the solid-state laser is a solid-state laser other than a disk laser:

The resonant cavity includes:

The outer cavity reflector is arranged outside the resonant cavity and is positioned at one side of the laser crystal, which is away from the resonant cavity; the laser crystal and the resonant cavity are placed at a Brewster angle and are used for reflecting part of oscillation laser to the outer cavity reflector; the external cavity reflector is used for reflecting the laser reflected by the laser crystal to enable the laser to return to the resonant cavity in the original way, so that the Kerr lens mode locking is started in a light disturbance mode; at this time, the outer cavity reflecting mirror is a concave mirror;

the length of the outer cavity is equal to the focal length of the outer cavity reflector; the length of the outer cavity is the distance between the outer cavity reflector and the laser crystal;

When the solid-state laser is a disk laser:

The resonant cavity includes:

The external cavity reflector is arranged outside the resonant cavity and is positioned at one side of the Kerr medium, which is away from the resonant cavity; the Kerr medium and the resonant cavity are placed at a Brewster angle and are used for reflecting part of oscillation laser to the outer cavity reflector; the external cavity reflector is used for reflecting the laser reflected by the Kerr medium to enable the original path of the laser to return to the resonant cavity, so that Kerr lens mode locking is started in a light disturbance mode; at this time, the outer cavity reflecting mirror is a concave mirror;

The length of the outer cavity is equal to the focal length of the outer cavity reflector; the length of the outer cavity is the distance between the outer cavity reflector and the Kerr medium.

13. The solid state laser of claim 12, wherein the resonant cavity further comprises: and a diaphragm arranged on the round trip light path for improving diffraction loss in the resonant cavity.

14. The solid state laser according to claim 12 or 13, wherein when the solid state laser is a solid state laser other than a disc laser, a side of the external cavity mirror close to the laser crystal is plated with a high reflection film for oscillating laser light, and the reflectance is more than 99.9%; one side of the first concave mirror and one side of the second concave mirror facing the resonant cavity are plated with high-reflectivity films for oscillating laser, and the reflectivity is more than 99.9%; one side of the first end mirror facing the resonant cavity is plated with a high-reflectivity film for oscillating laser, and the reflectivity is more than 99.9%;

When the solid laser is a disc laser, a high-reflectivity film for oscillating laser is plated on one side of the outer cavity reflector, which is close to the laser crystal, and the reflectivity is more than 99.9%; one side of the first concave mirror and one side of the second concave mirror facing the resonant cavity are plated with high-reflectivity films for oscillating laser, and the reflectivity is more than 99.9%; one side of the first end mirror facing the resonant cavity is plated with a high-reflectivity film for oscillating laser, and the reflectivity is more than 99.9%.