CN113644533A - Holmium laser gain medium and holmium laser - Google Patents
Holmium laser gain medium and holmium laser Download PDFInfo
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- CN113644533A CN113644533A CN202110759840.6A CN202110759840A CN113644533A CN 113644533 A CN113644533 A CN 113644533A CN 202110759840 A CN202110759840 A CN 202110759840A CN 113644533 A CN113644533 A CN 113644533A
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- 229910052689 Holmium Inorganic materials 0.000 title claims abstract description 80
- KJZYNXUDTRRSPN-UHFFFAOYSA-N holmium atom Chemical compound [Ho] KJZYNXUDTRRSPN-UHFFFAOYSA-N 0.000 title claims abstract description 76
- 238000010521 absorption reaction Methods 0.000 claims abstract description 16
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/0602—Crystal lasers or glass lasers
- H01S3/0604—Crystal lasers or glass lasers in the form of a plate or disc
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/06—Construction or shape of active medium
- H01S3/0602—Crystal lasers or glass lasers
- H01S3/0612—Non-homogeneous structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
- H01S3/16—Solid materials
- H01S3/1601—Solid materials characterised by an active (lasing) ion
- H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
- H01S3/161—Solid materials characterised by an active (lasing) ion rare earth holmium
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
- H01S3/16—Solid materials
- H01S3/1601—Solid materials characterised by an active (lasing) ion
- H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
- H01S3/1616—Solid materials characterised by an active (lasing) ion rare earth thulium
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
- H01S3/16—Solid materials
- H01S3/163—Solid materials characterised by a crystal matrix
- H01S3/1631—Solid materials characterised by a crystal matrix aluminate
- H01S3/1638—YAlO3 (YALO or YAP, Yttrium Aluminium Perovskite)
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
- H01S3/16—Solid materials
- H01S3/163—Solid materials characterised by a crystal matrix
- H01S3/164—Solid materials characterised by a crystal matrix garnet
- H01S3/1643—YAG
Abstract
The invention discloses a holmium laser gain medium and a holmium laser, belongs to the technical field of laser, and can solve the problems of time consumption and energy consumption of a heat diffusion bonding process in the conventional gain medium. The holmium laser gain medium comprises: a substrate sheet, and a Ho-doped portion and a Tm-doped portion provided on the same surface of the substrate sheet; the Ho doping part and the Tm doping part are arranged side by side, and the end faces of the Ho doping part and the Tm doping part are attached; the Ho-doped part is a solid-state gain medium which can cover the emission wavelength of the Tm-doped part by an absorption band and can output Ho laser; the Tm-doped part is a solid-state gain medium which has an emission wavelength positioned in a resonance absorption band of the Ho-doped part and can output Tm laser. The invention is used for the holmium laser gain medium.
Description
Technical Field
The invention relates to a holmium laser gain medium and a holmium laser, and belongs to the technical field of laser.
Background
The laser wavelength (2.05-2.2 mu m) of the rare earth holmium (Ho) ion-doped solid-state laser safe to human eyes is positioned in an atmospheric window and a molecular fingerprint waveband, and can be coated with a large number of molecules (H)2O、N2O and CO2) The resonance absorption has wide application value and prospect in the fields of national defense safety, environmental monitoring, biological medical treatment and the like. Meanwhile, the laser wavelength longer than 2.1 mu m is far away from the cut-off absorption edge of the nonlinear optical crystal phosphorus germanium Zinc (ZGP) and OP, namely GaAs is near 2 mu m, and the output of the high-energy/power mid-infrared 3-5 mu m laser is facilitated. The all-solid-state Ho laser gain medium is subjected to Tm and Ho co-doped gain medium, single Ho ion doped gain medium and Tm/Ho bonded gain medium in sequence. Wherein, because Tm and Ho codoped gain medium has serious conversion loss in cooperation, effective Ho laser output (the highest power is lower than 1W) is difficult to realize at room temperature, single Ho ion doped gain medium is the most mainstream Ho laser gain medium at present, and high-beam quality and high-power Ho laser output can be realized, which mainly comprises Ho: YAG, Ho: YLF, Ho: YAP and Ho: Y2O3Etc. crystalline or ceramic materials. However, because Ho ions cannot cover the absorption band of the conventional LD in the 700-800 nm band, extra 1.9 μm pump sources with high manufacturing cost and complex process, such as a high-power Tm-doped all-solid-state or optical fiber laser, are needed for carrying out co-band pumping, so that the existing 2.1-micron Ho laser system has the problems of large volume, high manufacturing cost and the like. Aiming at the problems of the mainstream Ho laser gain medium, a Tm/Ho bonding gain medium capable of directly utilizing the conventional 800nm LD to realize high-efficiency Ho laser output is further developed, and at present, the Tm/Ho: YAG, Tm/Ho: YLF, Tm/Ho: YVO4And continuous power output of several watts is realized on the equal gain medium.
The main disadvantage of the gain medium is that the Tm-doped gain medium and the Ho-doped gain medium must be the same working substance to satisfy the lattice matching condition in crystal diffusion bonding. For gain media with natural birefringence properties, where there are single or two crystal axes, it is also required that Tm-doped and Ho-doped gain media must have uniform crystal cut directions and crystal axes must be parallel to each other to achieve a thermal diffusion bonding process that integrates the Tm-doped and Ho-doped gain media. Further, the process of the diffusion bonding process is complicated, and the crystal end faces for bonding of the Tm-doped and Ho-doped gain media need to be heated to near the melting temperature of the crystal to perform thermal bonding. The thermal bonding process has strict requirements on the working environment, and impurities or defects are easily introduced into a bonding interface to cause excessive increase of the loss of a gain medium, so that the laser efficiency is reduced and even light cannot be emitted. Therefore, the thermal diffusion bonding process for realizing the Tm/Ho bonding gain medium is a time-consuming and energy-consuming process, and the multi-stage bonding has the problems of low yield, high manufacturing cost and the like, and the freedom or flexibility of the design of the Ho laser gain medium is limited by the requirement that Tm and Ho doping gain media are required to be made of the same material.
Disclosure of Invention
The invention provides a holmium laser gain medium and a holmium laser, which can solve the problems of time consumption and energy consumption of the traditional heat diffusion bonding process in the gain medium.
In one aspect, the invention provides a holmium laser gain medium, which includes: a substrate sheet, and a Ho-doped portion and a Tm-doped portion provided on the same surface of the substrate sheet; the Ho doping part and the Tm doping part are arranged side by side and the end faces of the Ho doping part and the Tm doping part are attached;
the Ho-doped part is a solid-state gain medium which can cover the emission wavelength of the Tm-doped part by an absorption band and can output Ho laser;
the Tm-doped part is a solid-state gain medium which has an emission wavelength positioned in a resonance absorption band of the Ho-doped part and can output Tm laser.
Optionally, the doping concentration of Ho ions in the Ho doping part is between 0.2 at% and 2 at%.
Optionally, the doping concentration of Tm ions in the Tm doped portion is between 2 at% and 8 at%.
Optionally, the backing sheet is bonded to the Ho doped portion and the Tm doped portion by an adhesive layer.
Optionally, the substrate sheet is any one of sapphire, YAG, and fused quartz crystal.
Optionally, the thickness of the substrate sheet is 0.05mm to 1 mm.
Optionally, the Ho-doped part is any one of a laser crystal, ceramic and glass;
the Tm-doped part is any one of laser crystal, ceramic and glass.
In another aspect, the present invention provides a holmium laser, including: the laser device comprises a pumping module, a laser resonant cavity and a gain module; the gain module comprises the holmium laser gain medium;
the pumping module is used for emitting semiconductor pumping light;
the laser resonant cavity comprises a front cavity mirror and a rear cavity mirror; the holmium laser gain medium is arranged between the front cavity mirror and the rear cavity mirror;
and the semiconductor pump light generates holmium laser after passing through the front cavity mirror and the holmium laser gain medium, and the holmium laser is output through the rear cavity mirror.
Optionally, the pumping module includes a semiconductor laser, a multimode fiber and a collimating and focusing assembly;
the semiconductor laser is used for emitting semiconductor pump light;
the multimode optical fiber is used for transmitting the semiconductor pump light to the collimation focusing component;
the collimation focusing assembly is used for carrying out collimation focusing treatment on the semiconductor pump light.
Optionally, the collimating and focusing assembly is composed of two plano-convex lenses; the focal length of the collimation focusing assembly is between 30mm and 50 mm.
Optionally, the gain module further includes a cooling copper block, and the holmium laser gain medium is clamped by the cooling copper block; the cooling copper block is provided with a plurality of water nozzles, and the water nozzles are communicated with a cavity of the cooling copper block for clamping the holmium laser gain medium and form a gain medium water cooling loop with an external temperature control water tank.
Optionally, the temperature of the cooling water of the gain medium water-cooling loop is controlled between 5 ℃ and 30 ℃.
Optionally, the front cavity mirror and the rear cavity mirror adopt a flat concave cavity structure, the curvature of the rear cavity mirror is 50 mm-1000 mm, and the cavity length of the laser resonant cavity is 25 mm-80 mm.
Optionally, the front cavity mirror is a film layer plated with a high reflectivity to output wave bands of thulium laser and holmium laser and an anti-reflection effect to wave bands of the semiconductor pump light;
the coupled transmittance of the rear cavity mirror to holmium laser with the wave band of 2.05-2.2 μm is between 2% and 30%.
Optionally, a spectral filter is disposed between the holmium laser gain medium and the rear cavity mirror, and the spectral filter is used for anti-reflection Ho laser and high reflection Tm laser.
Optionally, a Q-adjusting element is disposed between the spectral filter and the rear cavity mirror.
The invention can produce the beneficial effects that:
the Ho laser gain medium provided by the invention integrates Tm-doped and Ho-doped gain media of different materials into an integrated Ho laser gain medium through a substrate slice-assisted cold bonding process, avoids the strict requirements that a time-consuming and energy-consuming thermal diffusion bonding process in the preparation process of a Tm/Ho bonding gain medium and the Tm-doped and Ho-doped gain media are required to be the same material and the same crystal axes are required to be parallel to each other, improves the freedom and flexibility of the design of the Ho laser gain medium, further enriches the gain medium system capable of realizing high-efficiency room-temperature Ho laser output through the direct pumping of a conventional 800nm semiconductor laser, can obviously reduce the overall cost of a Ho laser, and ensures the high efficiency, compactness and miniaturization of the system.
In an integrated Tm: YAG/Ho: YAP gain medium integrating Tm: YAG and Ho: YAP crystals, 6.7W of Ho laser output at room temperature is realized, the optical-to-Ho conversion efficiency of 785nmLD pump light is 26.8 percent, which is equivalent to the conversion efficiency of a resonance pump holmium laser adopting an expensive 1.9 mu m semiconductor laser, and the output power can be continuously amplified by increasing the pump power.
Drawings
Fig. 1 is a schematic structural diagram of a Ho laser gain medium according to an embodiment of the present invention;
fig. 2 is a schematic plan view of a Ho laser gain medium structure provided by an embodiment of the present invention;
FIG. 3 is a schematic diagram of polarization absorption spectrum of a Ho-doped part and laser wavelength of a Tm-doped part in a Ho laser gain medium provided by an embodiment of the present invention;
fig. 4 is a schematic diagram of a holmium laser based on a Ho laser gain medium according to an embodiment of the present invention;
fig. 5 is an output power curve of a holmium laser based on a Ho laser gain medium according to an embodiment of the present invention;
fig. 6 shows laser wavelengths of a holmium laser based on a Ho laser gain medium according to an embodiment of the present invention;
fig. 7 is measurement data of power stability of a holmium laser based on a Ho laser gain medium according to an embodiment of the present invention;
fig. 8 is a schematic diagram of a Q-switched laser based on a Ho laser gain medium according to an embodiment of the present invention;
FIG. 9 shows the average output power and the shortest pulse profile of a Q-switched laser based on a Ho laser gain medium according to an embodiment of the present invention;
fig. 10 shows the laser wavelength of a Q-switched laser based on a Ho laser gain medium according to an embodiment of the present invention;
fig. 11 shows the pulse width and repetition frequency variation law of a Q-switched laser based on a Ho laser gain medium according to an embodiment of the present invention;
fig. 12 is a pulse sequence chart of a Q-switched laser based on a Ho laser gain medium at the highest average power provided by an embodiment of the present invention.
List of parts and reference numerals:
1. a holmium laser gain medium; 11. a Ho doping part; 12. a Tm-doped part; 13. a substrate sheet; 14. an adhesive layer; 21. a front cavity mirror; 22. a rear cavity mirror; 23. a spectral filter; 31. a semiconductor laser; 32. a multimode optical fiber; 33. a collimating focusing assembly; 34. a semiconductor pump light; 41. tm laser; 42. a Ho laser; 5. and a Q-switching element.
Detailed Description
The present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.
An embodiment of the present invention provides a Ho laser gain medium, as shown in fig. 1 to 3, including: a Ho doped section 11, a Tm doped section 12 and a substrate sheet 13.
The Ho-doped part 11 is any solid-state gain medium, such as laser crystal, ceramic or glass, with an absorption band capable of covering the emission wavelength of the Tm-doped part 12 and capable of realizing output of the Ho laser 42; the crystals are selected from the group consisting of Ho: YAG, Ho: LuAG, Ho: YLF, Ho: LuLiF, Ho: YAP, Ho: KGW, Ho: YAB, Ho: GdVO4And Ho: YVO4Etc., ceramics such as Ho: YAG, Ho: Y2O3And Ho: Sc2O3And the like, glasses such as Ho-doped silicate, phosphate, or germanate glasses, and the like. The doping concentration of the Ho ions is between 0.2 at% and 2 at% to avoid fluorescence quenching at high doping concentrations. As an example, a Ho: YAP crystal having a doping concentration of 0.6 at% belonging to the orthorhombic system can be selected as the Ho doped portion 11.
The Tm-doped part 12 is any solid-state gain medium, such as laser crystal, ceramic or glass, with the emission wavelength located in the resonance absorption band of the Ho-doped part 11, and can realize the output of Tm laser 41; the crystal is Tm: YAG, Tm: LuAG, Tm: YLF, Tm: LuLiF, Tm: YAP, Tm: YAB, Tm: KGW, Tm: GdVO4And Tm: YVO4Etc., ceramics such as Tm: YAG, Tm: Y2O3And Tm: Sc2O3And the like, glasses such as Tm-doped silicate, phosphate, or germanate glasses, and the like. To achieve quantum efficiencies approaching 200% while avoiding fluorescence quenching under high Tm ion doping, the doping concentration of Tm ions is between 2 at.% and 8 at.%. As an example, a Tm: YAG crystal having a doping concentration of 3.5 at% belonging to a cubic system can be selected as the doped Tm portion 12.
The substrate sheet 13 is a solid optical material having a thickness of 0.05 to 1mm and a high thermal conductivity or capable of matching the thermal expansion coefficient and the thermal conductivity of the Tm-doped portion 12, such as sapphire, YAG, or fused quartz crystal. In the present embodiment, to match the thermal expansion coefficient of the Tm doped portion 12 having a high thermal effect, a 0.1mm thick YAG flake can be used.
The crystal lengths of the Tm-doped part 12 and the Ho-doped part 11 are determined qualitatively by measuring the emission spectrum of the Tm-doped part 12 and the absorption spectrum of the Ho-doped part 11 and analyzing the matching degree of the two, Tm-doped part 12 and Ho-doped part 11 gain media with different lengths are placed in a resonant cavity before the Tm-doped part 12 and the Ho-doped part 11 are not integrated with each other, and an intracavity pumping laser experiment is carried out to obtain the optimal laser efficiency to determine the lengths of the final Tm-doped part 12 and the Ho-doped part 11, wherein the parts do not need to be the same material. Illustratively, by measuring the absorption spectrum and the fluorescence spectrum of the crystals of the Tm-doped part 12 and the Ho-doped part 11, it is determined that a Tm: YAG crystal with a length of 10mm is used, the corresponding laser wavelength is 2020nm, and is just located in the flatter resonance absorption band of the Ho: YAP crystal, so that the Ho: YAP crystal is cut along the b-axis, and the single-pass absorption efficiency of the Ho-doped part 11 on the intracavity Tm laser 41 is improved by utilizing the stronger polarization absorption coefficient of the a-axis and c-axis of the crystal on the 2020nm wave band (as shown in FIG. 3). Based on the spectral data of fig. 3, different c-cut Ho: YAP crystals with lengths between 5mm and 10mm were placed in a resonant cavity such as a Tm: YAG crystal, the length of the Ho doped portion 11 was optimized by performing an intra-cavity pump laser experiment, measuring the laser efficiency, and finally determining that the Ho: YAP crystal length of the Ho doped portion 11 was 7 mm.
The respective portions are integrated by a cold bonding process in which both end faces of each of the Tm-doped portion 12 and the Ho-doped portion 11 are processed into a uniform shape size, illustratively, a square section of 3mm × 3mm, and subjected to optical-grade polishing (flatness λ/10, finish 5/10) and bonded to each other. The side surfaces of the Tm-doped and Ho-doped sections 11 on the same plane are coated with an optical material adhesive (i.e., an adhesive layer 14), and a backing sheet 13 is attached to effectively support the Tm-doped section 12 and the Ho-doped section 11 attached to each other, thereby forming an integrated Ho laser gain medium.
And further constructing a holmium laser based on the holmium laser gain medium 1 to realize high-efficiency room-temperature Ho laser 42 output. The holmium laser comprises a pumping module, a gain module and a laser resonant cavity, wherein the gain module and the laser resonant cavity are formed by a holmium laser gain medium 1.
The pumping module comprises a semiconductor laser 31, a multimode optical fiber 32 and a collimation and focusing assembly 33; the laser resonant cavity comprises a front cavity mirror 21 and a rear cavity mirror 22, and the rear cavity mirror 22 is used as a coupling output mirror; the holmium laser gain medium 1 is positioned between the front cavity mirror 21 and the rear cavity mirror 22; semiconductor pump light 34 excited by the semiconductor laser 31 passes through the multimode fiber 32 and is output to the collimating and focusing assembly 33, and light output by the collimating and focusing assembly 33 enters the holmium laser gain medium 1 through the front cavity mirror 21 to generate holmium laser which is output through the rear cavity mirror 22.
The semiconductor laser 31 is a semiconductor laser 31 having an output wavelength of about 800 nm; the specific output wavelength depends on different thulium (Tm) doped gain media, and according to the absorption characteristics of different Tm doped gain media, for example, the output wavelength of the 800nm semiconductor laser 31 can be 785nm for Tm: YAG and Tm: LuAG; for Tm, YLF and Tm, LuLiF, the output wavelength of the 800nm semiconductor laser 31 can be 792 nm; for Tm: YAP, the output wavelength of the 800nm semiconductor laser 31 may be 795 nm; the wavelength band far away from the absorption peak of the Tm-doped gain medium, such as 781nm or 808nm, can be used for side lobe pumping and the like. For the Tm-doped portion 12 being a YAG crystal, the output wavelength of the 800nm semiconductor laser 31 used in this embodiment is 785nm, and the output wavelength and the line width of the 800nm semiconductor laser 31 can also be locked at the optimal pump peak position of the Tm: YAG crystal portion, so as to significantly improve the optical-to-optical conversion efficiency of the holmium laser gain medium 1.
The multimode fiber 32 is an SMA interface, the core diameter is 400 microns, and the numerical aperture is 0.22; the collimation focusing assembly 33 is an imaging system formed by two plano-convex lenses, the focal length is within the range of 30-50 mm, and the focusing light spot of the pump light in the holmium laser gain medium 1 is matched with the light field distribution of the Tm laser 41 in the laser resonant cavity, so that the high-efficiency Ho laser 42 is generated and output.
The output port of the multimode fiber 32 is packaged in an aluminum lens barrel together with two plano-convex lenses constituting the collimating and focusing assembly 33 so as to be fixed to the optical alignment frame. When in use, two plano-convex lenses forming the collimation and focusing assembly 33 are filled in the lens barrel and fixed, and the collimation and focusing assembly 33 can be obtained; fixing an output end interface of the multimode optical fiber 32 to an input end of the aluminum material lens barrel, wherein when the output end interface of the multimode optical fiber 32 is connected with the input end of the aluminum material lens barrel, the distance between the end surface of the input end of the multimode optical fiber 32 and an incident surface of a first plano-convex lens of the collimation and focusing assembly 33 is equal to the back focal length of the first plano-convex lens, so as to ensure that the semiconductor pump light 34 incident on the first plano-convex lens is collimated, wherein the first plano-convex lens is a plano-convex lens which is close to the multimode optical fiber 32 in two plano-convex lenses; then, the lens barrel with two plano-convex lenses and connected with the multimode optical fiber 32 is fixed on an optical adjusting frame, and the optical adjusting frame preferably adopts a four-dimensional adjusting frame.
The laser resonant cavity is any resonant cavity which meets the holmium laser gain condition, enables the heat effect of a gain medium to be within the range of a stable region of the resonant cavity and can output holmium laser from the gain medium. For example, the shape can be a straight cavity, an L-shaped cavity, a multiple (3-fold, 4-fold, 5-fold, etc.) folded cavity; the straight cavity can be a flat cavity, a flat concave cavity or a concave-convex cavity, etc.
The laser resonant cavity included in the holmium laser shown in fig. 4 has a straight cavity structure, and the front cavity mirror 21 and the rear cavity mirror 22 included in the laser resonant cavity may be any cavity type structure capable of realizing stable output of the solid-state laser, such as a flat cavity, a flat concave cavity, or a concave-convex cavity.
For example, a front cavity mirror 21 and a rear cavity mirror 22 of the laser resonant cavity adopt a flat concave cavity structure, the curvature of the rear cavity mirror 22 is 50-1000 mm, and the cavity length of the laser resonant cavity is 25-80 mm; the front cavity mirror 21 is a film plated with high reflection on thulium laser and holmium laser output wave bands and is anti-reflection on a semiconductor pump light 34 wave band, the coupling transmittance of the rear cavity mirror 22 on holmium laser with wave bands of 2.05-2.2 mu m is 2-30%, holmium laser output with different wavelengths such as 2090nm, 2097nm, 2122nm and 2129nm can be realized through different coupling transmittances, and whether the film is enabled to simultaneously perform high reflection on the thulium laser wave bands can be selected according to whether dual-wavelength output of the thulium laser and the holmium laser is simultaneously realized.
When the holmium laser shown in fig. 4 is used, the symmetry centers of the front cavity mirror 21 and the rear cavity mirror 22 and the holmium laser gain medium 1 in the cooled copper block are adjusted to be on the same straight line by focusing through the He-Ne laser: the distance between the second surface of the front cavity mirror 21 and the first surface of the Tm-doped part 12 in the holmium laser gain medium 1 is less than 10mm, and the distance between the second surface of the Ho-doped part 11 in the holmium laser gain medium 1 and the first surface of the back cavity mirror 22 is 10-50 mm.
In practical application, the gain module further comprises a cooling copper block, and the cooling copper block is clamped with the gain medium; a plurality of water nozzles are arranged on the cooling copper block, are communicated with a cavity of the cooling copper block in a clamping mode with the holmium laser gain medium 1 and form a gain medium water cooling loop with an external temperature control water tank, and the temperature of cooling water is controlled to be 5-30 ℃. It should be noted that the temperature control water tank can also be used for cooling the semiconductor laser 31.
After the temperature of the semiconductor laser 31 and the holmium laser gain medium 1 is controlled by the temperature control water tank, low-power pumping is performed, for example, the power of pumping light is in the intensity range of 4-8W, and the position of a focusing spot of the pumping light of the collimation focusing assembly 33 on the Tm-doped part 12 is adjusted by the four-dimensional adjusting frame and the optical translation table, so that the maximum laser output power which can be obtained under the current pumping power is obtained.
The driving current of the semiconductor laser 31 is increased step by step, the maximum holmium laser output of 6.7W is obtained under the injection power of 25W, the corresponding slope efficiency is 38.3%, and the optical-optical conversion efficiency is 26.8%, as shown in fig. 5, which is equivalent to the conversion efficiency of the current 1.9 μm semiconductor laser 31 pumping holmium laser. The laser wavelength at the highest laser power was stable at 2129.2nm, as shown in fig. 6. The jitter range for the highest power monitored in 30 minutes was within 36.29mW, corresponding to a power instability of 0.54%.
Further, in order to realize the output of the Q-switched pulse, a spectral filter 23 which is used for increasing reflection of Ho laser 42 and can be used for increasing reflection of Tm laser 41 is inserted between the holmium laser gain medium 1 and the rear cavity mirror 22, and meanwhile, a Q-switched element 5 is inserted between the spectral filter 23 and the rear cavity mirror 22, so that a composite resonant cavity which can realize the output of the Q-switched pulse is formed.
The Q-switched element 5 includes any one of an electro-optic Q-switched switch, an acousto-optic Q-switched switch, a transition metal doped group-two-six compound crystal, a transition metal disulfide crystal, a transition metal diselenide crystal, a semiconductor saturable absorber, a graphene two-dimensional material, a carbon nanotube two-dimensional material, a topological insulator, and a saturable absorbing material that realizes Q-switched pulse output at a 2 μm band. Here, a Q-switched laser output with an average power of 743mW, a center wavelength of 2053nm, a pulse width of 123ns, and a repetition frequency of 14.2kHz was achieved using a Cr: ZnSe crystal with an initial transmittance of 92%, and the corresponding pulse peak power reached 0.42kW, as shown in fig. 9-12.
The embodiment introduces the design method of the Ho laser gain medium and the Ho laser, and demonstrates the high efficiency and reliability of the gain medium through continuous laser and Q-switched laser experiments.
Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.
Claims (10)
1. A holmium laser gain medium, comprising: a substrate sheet, and a Ho-doped portion and a Tm-doped portion provided on the same surface of the substrate sheet; the Ho doping part and the Tm doping part are arranged side by side and the end faces of the Ho doping part and the Tm doping part are attached;
the Ho-doped part is a solid-state gain medium which can cover the emission wavelength of the Tm-doped part by an absorption band and can output Ho laser;
the Tm-doped part is a solid-state gain medium which has an emission wavelength positioned in a resonance absorption band of the Ho-doped part and can output Tm laser.
2. The holmium laser gain medium according to claim 1, characterized in that the doping concentration of the Ho ions in the Ho-doped part is between 0.2 at% and 2 at%.
3. The holmium laser gain medium according to claim 1, characterized in that the Tm ion doping concentration in the Tm doped portion is between 2 at% and 8 at%.
4. The holmium laser gain medium according to claim 1, characterized in that the substrate sheet is bonded to the Ho-doped section and the Tm-doped section by an adhesive layer;
preferably, the substrate sheet is any one of sapphire, YAG and fused quartz crystal;
preferably, the substrate sheet has a thickness of 0.05mm to 1 mm.
5. The holmium laser gain medium according to claim 1, characterized in that the Ho-doped part is any one of a laser crystal, a ceramic and a glass;
the Tm-doped part is any one of laser crystal, ceramic and glass.
6. A holmium laser, comprising: the laser device comprises a pumping module, a laser resonant cavity and a gain module; the gain module comprises the holmium laser gain medium of any one of claims 1 to 5;
the pumping module is used for emitting semiconductor pumping light;
the laser resonant cavity comprises a front cavity mirror and a rear cavity mirror; the holmium laser gain medium is arranged between the front cavity mirror and the rear cavity mirror;
and the semiconductor pump light generates holmium laser after passing through the front cavity mirror and the holmium laser gain medium, and the holmium laser is output through the rear cavity mirror.
7. The holmium laser according to claim 6, wherein the pumping module includes a semiconductor laser, a multimode fiber and a collimating and focusing component;
the semiconductor laser is used for emitting semiconductor pump light;
the multimode optical fiber is used for transmitting the semiconductor pump light to the collimation focusing component;
the collimation focusing assembly is used for carrying out collimation focusing treatment on the semiconductor pump light;
preferably, the collimating and focusing assembly is composed of two plano-convex lenses; the focal length of the collimation focusing assembly is between 30mm and 50 mm.
8. The holmium laser of claim 6, wherein the gain module further comprises a cooled copper block sandwiching the holmium laser gain medium; the cooling copper block is provided with a plurality of water nozzles which are communicated with a cavity of the cooling copper block which clamps the holmium laser gain medium and form a gain medium water cooling loop with an external temperature control water tank;
preferably, the temperature of the cooling water of the gain medium water-cooling loop is controlled between 5 ℃ and 30 ℃.
9. The holmium laser according to claim 6, characterized in that the front cavity mirror and the back cavity mirror adopt a flat concave cavity structure, the curvature of the back cavity mirror is between 50mm and 1000mm, and the cavity length of the laser resonant cavity is between 25mm and 80 mm;
preferably, the front cavity mirror is a film layer which is plated with high reflectivity to output wave bands of thulium laser and holmium laser and is anti-reflection to wave bands of semiconductor pump light;
the coupled transmittance of the rear cavity mirror to holmium laser with the wave band of 2.05-2.2 μm is between 2% and 30%.
10. The holmium laser as claimed in claim 6, wherein a spectral filter is arranged between the holmium laser gain medium and the back cavity mirror, and the spectral filter is used for anti-reflection Ho laser and high reflection Tm laser;
preferably, a Q-switching element is arranged between the spectral filter and the rear cavity mirror.
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