CN115459038A - Method and device for generating 639nm and 721nm dual-wavelength laser by blue light pumping - Google Patents

Method and device for generating 639nm and 721nm dual-wavelength laser by blue light pumping Download PDF

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CN115459038A
CN115459038A CN202211201526.7A CN202211201526A CN115459038A CN 115459038 A CN115459038 A CN 115459038A CN 202211201526 A CN202211201526 A CN 202211201526A CN 115459038 A CN115459038 A CN 115459038A
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resonant cavity
light
blue light
mirror
working
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夏燃
袁琴云
徐盛博
李仪芳
段长城
陈曦
郑毅
徐刚
胡烜瑜
郑暤翾
唐霞辉
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Huazhong University of Science and Technology
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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
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
    • H01S3/0813—Configuration of resonator
    • 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
    • H01S3/02—Constructional details
    • H01S3/04—Arrangements for thermal management
    • H01S3/0407—Liquid cooling, e.g. by water
    • 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
    • H01S3/08—Construction or shape of optical resonators or components thereof
    • H01S3/08054—Passive cavity elements acting on the polarization, e.g. a polarizer for branching or walk-off compensation

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Abstract

The invention belongs to the field of visible light laser, and particularly relates to a method and a device for generating 639nm and 721nm dual-wavelength laser by blue light pumping, which comprise the following steps: a blue light pumping source is adopted to generate blue light, and the blue light is collimated and focused on a working crystal in a resonant cavity through a 4F system to generate 639nm and 721nm dual-wavelength laser output; wherein the working crystal is arranged at the optical waist of the resonant cavity, the resonant cavity is a critical cavity, and the transmissivity to 639nm and 721nm is 3% -7%; the included angle between the normal of the surface of the output mirror of the resonant cavity and the incident ray satisfies the following conditions: the size of round-trip loss in the cavity caused by Fresnel reflection at positions 639nm and 721nm influenced by the included angle can enable the threshold pump power ratio of the resonant cavity at positions 639nm and 721nm to be 1; the pump light power of the blue light pump source is greater than the threshold pump power; the 4F system satisfies that the average light spot of the light beam focused on the working crystal is smaller than that of the working light. The invention effectively fills the blank of the dual-wavelength visible laser at 639nm and 721nm.

Description

Method and device for generating 639nm and 721nm dual-wavelength laser by blue-ray pumping
Technical Field
The invention belongs to the field of visible light laser, and particularly relates to a method and a device for generating 639nm and 721nm dual-wavelength laser by blue light pumping.
Background
With the continuous development of blue light semiconductor technology, the research of visible light lasers becomes an important topic.
Visible lasers are widely used in the fields of medical diagnosis and treatment, laser display, free space optical communication, deep sea and atmospheric measurements, and the like. For example, in medical treatment, the retinal pigment epithelial cells have strong absorption of green light, and green laser can be used for laser surgery treatment of retinopathy; the yellow laser with the wavelength of 590nm has good effect on treating port of port wine stains and cutaneous hemangioma because of high absorptivity of hemoglobin. In communication, since seawater has the best transparency in the blue-green band, blue-green laser is considered as the best light source for underwater communication. Visible lasers are currently implemented mainly by the following several approaches: visible light laser diodes, frequency doubling and optical parametric oscillators based on nonlinear processes, visible light up-conversion and down-conversion lasers doped with rare earth ions. The LD is not easy to generate large energy or ultrafast laser, the frequency doubling laser depends on a nonlinear process, the up-conversion technical mechanism is complex, and the efficiency of the frequency doubling laser has no obvious advantage compared with the efficiency of the frequency doubling laser. The down-conversion visible light laser represented by the Pr-doped laser can efficiently generate blue light, green light, orange light, red light and deep red light lasers, avoids the use of a frequency doubling crystal, has good stability and compact cavity structure, realizes full optical fiber under certain conditions, and attracts the eyes of a plurality of researchers.
In 2021, professor chu shich, university of mansion, reports that multi-wavelength laser oscillation of about 670nm was achieved by tilting the crystal and inserting etalons of different thicknesses. YLF crystal is slightly tilted to adjust the intracavity loss, and the maximum output power of 2.52W is obtained at the dual wavelength of 670.1/674.8 nm. A Brinell angle is used to insert an etalon with a thickness of 100 μm, and a dual-wavelength laser of 675.0/679.4 is obtained, with a maximum output power of 1.80W and a maximum slope efficiency of 34.1%. By vertically inserting an etalon having a thickness of 200 μm and finely adjusting the tilt, a two-wavelength laser of 670.1/679.1nm was obtained with a maximum output power of 0.36W. Meanwhile, it is reported that a three-wavelength laser of 670.4/674.8/679.4nm is obtained by tilting the crystal, and the output power is 1.78W. A672.2/674.2/678.6 nm three-wavelength laser with a maximum output power of 0.84W was obtained by inserting two etalons with a thickness of 100 μm and a thickness of 150 μm. (Lin X, feng Q, zhu Y, et al. Diode-pumped wavetength-switchable visible Pr3+: YLF laser and vortex laser around 670nm J. Opto-Electronic Advances,2021,4 (4): 210006-1-210006-8.) 2022, which in turn reported a semiconductor laser diode pumped 604nm continuous wave laser based on lowly doped Pr3+: YLF crystals. At 604nm, the maximum output power is 3.28W and the total skew efficiency is 34.2%. In addition, the dual-wavelength laser of 604nm and 607nm is realized by adjusting the thermal lens effect of the crystal, and the process does not need any additional wavelength selection element. A dual wavelength laser of 604 and 607nm is obtained by this method, with a maximum output power of 3.30W (Lin X, ji S, feng Q, et al, heat-induced wavelength-switched high-power CW orange Pr3+: YLFs [ J ]. Journal of Luminescence,2022, 243.
However, the current bands for achieving dual wavelength continuous wave operation do not include 639nm and 721nm.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a method and a device for generating 639nm and 721nm dual-wavelength laser by blue light pumping, and aims to effectively make up the blank of the dual-wavelength visible laser at 639nm and 721nm.
To achieve the above object, according to one aspect of the present invention, there is provided a method for generating 639, 721nm dual-wavelength laser by blue light pumping, comprising:
a blue light pumping source is adopted to generate blue light, and the blue light is collimated and focused on a working crystal in a resonant cavity through a 4F system to generate dual-wavelength laser output of 639nm and 721 nm;
the working crystal is arranged at the light waist of the resonant cavity, the resonant cavity is a critical cavity, and the transmissivity to 639nm and 721nm is 3% -7%; the included angle between the normal line of the output mirror surface of the resonant cavity and the incident ray satisfies the following conditions: the threshold pump power ratio of the resonant cavity at 639nm and 721nm is 1 due to the round-trip loss in the cavity caused by fresnel reflection at 639nm and 721nm influenced by the included angle; the pump light power of the blue light pump source is greater than the threshold pump power; the 4F system satisfies: the average spot of the light beam focused onto the working crystal is smaller than the average spot of the working light.
Further, the method further comprises: and in the emitting process of the dual-wavelength laser, the occupation proportion of the 639nm laser and the 721nm laser in output light is controlled by disturbing the included angle.
Further, in the 639nm and 721nm dual-wavelength laser generation process, the working crystal and the blue light generation unit in the blue light pumping source are all subjected to water cooling heat dissipation treatment, and the water cooling temperature is set to be 15 ℃.
Further, the input mirror of the resonator is a plane mirror, and the output mirror of the resonator is a concave mirror.
Further, the center of the working crystal coincides with the focus of the spherical focusing lens F2 in the 4F system.
Further, the transmittance of the input mirror of the resonant cavity in the absorption peak wavelength band of the working crystal is 99.7%, the reflectance at 500-750 nm is 99.5%, the output mirror of the resonant cavity is a concave mirror with a curvature radius of 100mm, the transmittance at 500-750 nm is 3%, the cavity length of the resonant cavity is 100mm, and the substrates of the input mirror and the output mirror of the resonant cavity are BK7 glass;
the angle between the normal of the output mirror surface of the resonant cavity and the incident light is 7.5 °.
The invention also provides a device for generating 639nm and 721nm orthogonal polarization dual-wavelength laser by using the blue light single-tube pump, which comprises the following components: a blue light pumping source, a 4F system, a resonant cavity and a working crystal; the working crystal is arranged at the optical waist of the resonant cavity, the resonant cavity is a critical cavity, and the transmissivity to 639nm and 721nm is 3% -7%;
the blue light pump source is used for generating blue light in the absorption peak wave band of the working crystal; the 4F system is used for collimating and focusing the blue light onto the working crystal; the working crystal generates dual-wavelength laser of 639nm and 721nm in the resonant cavity and outputs the laser through an output mirror of the resonant cavity; the included angle between the normal line of the surface of the output mirror of the resonant cavity and the incident ray satisfies the following conditions: the size of round-trip loss in the cavity caused by Fresnel reflection at positions 639nm and 721nm influenced by the included angle can enable the threshold pump power ratio of the resonant cavity at positions 639nm and 721nm to be 1; the pump light power of the blue light pump source is greater than the threshold pump power; the 4F system is set up as follows: the average spot of the light beam focused onto the working crystal is smaller than the average spot of the working light.
Further, still include: and the water cooling device is used for carrying out water cooling heat dissipation treatment on the working crystal and the blue light generating unit in the blue light pumping source.
Further, the transmittance of the input mirror of the resonant cavity in the absorption peak wavelength band of the working crystal is 99.7%, the reflectance at 500-750 nm is 99.5%, the output mirror of the resonant cavity is a concave mirror with a curvature radius of 100mm, the transmittance at 500-750 nm is 3%, the cavity length of the resonant cavity is 100mm, and the substrates of the input mirror and the output mirror of the resonant cavity are BK7 glass;
the angle between the normal of the output mirror surface of the resonant cavity and the incident light is 7.5 °.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) The method adopts the combination of the 4F system and the resonant cavity, the 4F system is used for collimating and focusing blue light generated by a blue light pumping source onto the working crystal positioned in the resonant cavity, and the average light spot of light beams focused onto the working crystal is smaller than the average light spot of working light; in addition, the resonant cavity is a critical cavity, and the transmissivity to 639nm and 721nm is 3% -7%; the included angle between the normal of the surface of the output mirror of the resonant cavity and the incident ray satisfies the following conditions: the size of round-trip loss in the cavity caused by Fresnel reflection at positions 639nm and 721nm influenced by the included angle can enable the threshold pumping power ratio of the resonant cavity at positions 639nm and 721nm to be 1, and under the condition that the pumping light power of the blue light pumping source is greater than the threshold pumping power, dual-wavelength emission at positions 639nm and 721nm is achieved, and the blanks of the dual-wavelength visible light laser at positions 639nm and 721nm are effectively made up.
(2) The invention adopts a collimation focusing system, improves the pumping efficiency and improves the power of output light. The invention adopts a collimation focusing system to focus the pump light on the center of the working substance, and the working substance is close to the input plane mirror to realize the optimal mode matching of the pump light and the working light, thereby improving the pumping efficiency. Meanwhile, the invention has higher output beam quality. The invention adopts a collimation focusing system, improves the beam quality of the pump light, and simultaneously improves the quality of the output beam by adjusting the relative position and the inclination angle of two mirrors of the resonant cavity, thereby improving the condition of poor quality of the output beam caused by imperfect design of the resonant cavity parameters in the traditional blue light pump visible light system.
(3) The invention adopts a special coated plane mirror and a concave mirror as a resonant cavity, wherein the transmissivity of an input mirror of the resonant cavity at the absorption peak wave band of a working crystal is 99.7 percent, the reflectivity at a position of 500-750 nm is 99.5 percent, an output mirror of the resonant cavity is a concave mirror with the curvature radius of 100mm, the transmissivity at the position of 500-750 nm is 3 percent, the length of the resonant cavity is 100mm, and the substrates of the input mirror and the output mirror of the resonant cavity are BK7 glass; the angle between the normal of the output mirror surface of the resonant cavity and the incident ray is 7.5 degrees. The dual-wavelength operation at 639nm and 721nm is realized.
Drawings
Fig. 1 is a device for generating 639, 721nm cross-polarized dual-wavelength laser by blue light pumping according to an embodiment of the present invention;
FIG. 2 is a diagram of a resonant cavity according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of a collimating and focusing system according to an embodiment of the present invention;
fig. 4 shows Pr: the structure schematic diagram of the YLF crystal water-cooling block;
fig. 5 is a schematic structural diagram of a blue light single-tube water-cooling plate according to an embodiment of the present invention.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:
1 is DC voltage-stabilizing power supply, 2 is for leading to water cold copper base plate, and 3 is the blue light single tube, and 4 are aspheric surface focusing mirror, and 5 are spherical surface focusing mirror F1, and 6 are spherical surface focusing mirror F2, and 7 are the input level crossing, and 8 are crystal water-cooling module, and 9 are Pr: the device comprises a YLF crystal, an output coupling mirror 10, a long-wave pass filter 11, a polarization beam splitter 12, indium foil 13, water cooling tubes 14, 15, 16 and 17, water cooling tube three-way heads 18 and 19 and a water cooling machine 20.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example one
A method of generating 639, 721nm cross-polarized dual wavelength laser by blue pumping, comprising:
a blue light pumping source is adopted to generate blue light, and the blue light is collimated and focused on a working crystal in a resonant cavity through a 4F system to generate dual-wavelength laser output of 639nm and 721 nm;
wherein, the working crystal is arranged at the optical waist of the resonant cavity; the resonant cavity is a critical cavity, dual-wavelength laser is easy to output simultaneously, and the transmissivity to 639nm and 721nm is 3% -7%; the included angle between the normal line of the output mirror surface of the resonant cavity and the incident ray satisfies the following conditions: the size of round-trip loss in the cavity caused by Fresnel reflection at positions 639nm and 721nm influenced by the included angle can enable the threshold pump power ratio of the resonant cavity at positions 639nm and 721nm to be 1; when the threshold pumping power is calculated, the round-trip loss value in the cavity corresponding to 639nm is the loss of P wave caused by Fresnel reflection, and the round-trip loss value in the cavity corresponding to 721nm is the loss of S wave caused by Fresnel reflection; the pump light power of the blue light pump source is greater than the threshold pump power; the 4F system satisfies: the focused beam average spot is smaller than the working beam average spot.
The method is to directly generate visible light with dual wavelengths of 639nm and 721nm aiming at a blue light generating unit (such as a blue light single tube), and the corresponding visible light laser structure comprises a blue light pumping source, a collimation focusing system (namely a 4F system), a resonant cavity and a working substance.
Preferably, the input mirror of the resonant cavity is a plane mirror, the transmittance in the wave band of the absorption peak of the working crystal is 99.7%, the reflectance at 500-750 nm is 99.5%, the output mirror of the resonant cavity is a concave mirror with the curvature radius of 100mm, the transmittance at 500-750 nm is 3%, the cavity length of the resonant cavity is 100mm, and the substrates of the input mirror and the output mirror of the resonant cavity are BK7 glass; under the design of the resonant cavity, the included angle between the normal line of the output mirror surface of the resonant cavity and the incident ray satisfies the following conditions: the size of round-trip loss in the cavity caused by Fresnel reflection at the positions of 639nm and 721nm influenced by the included angle can ensure that the threshold value pumping power ratio of the resonant cavity at the positions of 639nm and 721nm is 1, and the included angle between the normal of the output mirror surface of the resonant cavity and the incident ray at the calculated position is 7.5 degrees. Of course, the proportion of 639nm and 721nm laser light in the output light can be controlled by adjusting the tilt angle of the output mirror with a slight disturbance during the two-wavelength emission.
Preferably, in the dual-wavelength laser generation process of 639nm and 721nm, the working crystal and the single blue light tube in the blue light pumping source are both subjected to water cooling heat dissipation treatment, and the water cooling temperature is set to 15 ℃ to control the wavelength drift of the blue light.
Preferably, the input mirror of the resonator is a flat mirror and the output mirror of the resonator is a concave mirror, facilitating the tuning of the resonator.
Preferably, the center of the working crystal coincides with the focal point of the spherical focusing mirror F2 in the 4F system. So as to realize the maximum absorption of the pump light by the crystal and further improve the frequency doubling efficiency.
In order to implement and make the above method more clear, a set of apparatuses is now provided and the above method is described:
a laser device for generating dual-wavelength continuous wave laser by blue light pumping, as shown in fig. 1, comprising: direct current constant voltage power supply 1, logical water-cooling copper base plate 2, blue light single tube 3, aspheric surface focusing mirror 4, spherical surface focusing mirror F15, spherical surface focusing mirror F26, input level crossing 7, crystal water-cooling module 8, pr: the device comprises a YLF crystal 9, an output coupling mirror 10, a long wave pass filter 11, a polarization beam splitter 12, indium foils 13, water cooling tubes 14, 15, 16 and 17, water cooling tube tee joints 18 and 19 and a water cooling machine 20. The direct-current stabilized power supply 1 and the blue light single tube 3 form a blue light pumping source, the aspheric surface focusing mirror 4, the spherical surface focusing mirror F15 and the spherical surface focusing mirror F26 form a 4F system, and the input plane mirror 7 and the output coupling mirror 10 are respectively used as an input mirror and an output mirror of the resonant cavity to form the resonant cavity.
The direct current stabilized voltage supply 1 is used for generating direct current to provide a pump for the blue light single tube 3; the water-cooling copper substrate 2 is used for providing water cooling for the blue light single tube 3; the blue monotube 3 is used to generate 444nm blue light to Pr: YLF crystal 9 provides the pump; the aspheric focusing lens 4 is used for focusing light beams for the blue light emitted by the blue light single tube 3; the spherical focusing lens F15 is used for collimating the focusing light beam passing through the aspheric focusing lens 4; the spherical focusing lens F26 is used for focusing the light collimated by the spherical focusing lens F15; the input plane mirror 7 is used for forming a resonant cavity, inputting pump light and maintaining the oscillation of working light; the crystal water cooling module 8 is used for supplying working crystals Pr: the YLF crystal 9 provides water cooling; pr: the YLF crystal 9 is used as a working substance of the dual-wavelength laser; the output coupling mirror 10 is used for forming a resonant cavity and outputting working light; the long-wave pass filter 11 is used for filtering out blue light which is not absorbed by the crystal in the emergent light; the polarization beam splitter 12 is used for separating dual-wavelength emergent light of 639nm and 721nm; the indium foil 13 is used for wrapping Pr: YLF crystal 9, improving water cooling efficiency; the water cooling pipes 14, 15, 16 and 17 are used for supplying water to the water-cooled copper substrate 2 and the crystal water-cooling module 8; the water-cooling tube tee joints 18 and 19 are used for switching the water-cooling tube for water cooling of the copper substrate 2 and the crystal water-cooling module 8 into a tube; the water cooler 20 is used for cooling the blue light single tube 3 and Pr: the YLF crystal 9 provides water cooling;
further, as shown in fig. 2, the input plane mirrors 7, pr: the YLF crystal 9 and the output coupling mirror 10 cooperate with each other to complete the oscillation enhancement of the laser and stably emit dual-wavelength laser with the wavelength of 639nm and 721nm. The input plane mirror 7 has a transmittance of 99.7% at 444nm, a reflectance of 99.5% at 500-750 nm, the output coupling mirror 10 is a concave mirror with a radius of curvature of 100mm, and the transmittance at 500-750 nm is about 3% (selectable within 3% -7%), the two mirrors form a laser resonator, the length of the resonator is 100mm, the substrate is BK7 glass, both having a size of one inch and being mounted on a three-dimensional adjusting frame, the tilt angle θ of the output coupling mirror 10 is adjusted to adjust the loss of the resonator at 639nm and 721nm, when the threshold pump powers of the laser resonator at 639nm and 721nm are the same, the two beams are emitted simultaneously, regardless of the excited state absorption, and the threshold ratio of the two transition wavelengths in the two-wavelength operation can be expressed as:
Figure BDA0003872215780000081
wherein, P th,1 For threshold pump power at 639nm of the resonant cavity, P th,2 For threshold pump power of the resonator at 721nm, R 1,2 Reflectivity, R, of the output mirror at 639nm and 721nm, respectively 1 ＝R 2 ＝0.97，σ 1,2 Pr is the stimulated radiation cross section size of YLF crystal at 639nm and 721nm, sigma 1 ＝22.3*10 -20 cm 2 ，σ 2 ＝17.8*10 -20 cm 2 ，L 1,2 The magnitude of the intra-cavity round-trip loss due to fresnel reflections at 639nm and 721nm is related to the angle of incidence and the polarization of the electric field. The two transition wavelengths 639nm and 721nm in dual-wavelength operation are sigma-polarized and pi-polarized, respectively, for P-wave and S-wave, respectively, and the loss caused by fresnel reflection for P-wave and S-wave can be expressed as:
L P ＝R P (n,θ)+[1-R P (n,θ)]·R P (1/n,sin -1 (sinθ/n))；
L S ＝R S (n,θ)+[1-R S (n,θ)]·R S (1/n,sin -1 (sinθ/n))；
wherein,
Figure BDA0003872215780000091
n is the ratio of the refractive indices of the concave mirror and air, and θ is the angle between the incident ray and the normal to the surface of the output coupling mirror 10. Therefore, in the hardware design that the input plane mirror 7 has a transmittance of 99.7% at 444nm and a reflectance of 99.5% at 500 to 750nm, the output coupling mirror 10 is a concave mirror with a radius of curvature of 100mm, and the transmittance at 500 to 750nm is about 3% (selectable within 3% to 7%), the two mirrors constitute a laser resonator, the cavity length is 100mm, and the substrate is BK7 glass, the tilt angle θ of the output coupling mirror 10 that satisfies the threshold ratio 1 of the two transition wavelengths is accurately calculated to be 7.5 °.
At this time, when the tilt angle θ of the output coupling mirror 10 satisfies γ =1, the thresholds of transition at 639nm and 721nm are the same, and the two-wavelength laser light is generated.
The principle of the method of the embodiment is explained as follows:
if the excited state absorption is not considered, the laser threshold of the four-level continuous laser can be expressed as
Figure BDA0003872215780000092
Wherein, hv p Is the pump photon energy, L is the round-trip loss L = δ in the laser cavity r +δ d =0.0152,R is output mirror reflectivity, σ e Is the section of stimulated radiation, tau f Is the upper level fluorescence lifetime of the laser,. Epsilon p Representing the ratio of the number of particles reaching the upper level of the laser to the number of absorbed pump photons, this term can be assumed to be 1 for Pr: YLF. Eta a Is the absorption efficiency of the pump light [. Eta. ] a And (= 1-exp (- α · l)), where α is an absorption coefficient of the laser medium for the pump light, and l is a length of the laser medium.
In the embodiment, the length l =5mm of the laser medium Pr is set, the doping concentration is 0.5a.t.%, and the density is 3.99g/cm 3 In a molar mass of
Figure BDA0003872215780000101
Avogadro constant N A ＝6.02×10 23 The site concentration N is calculated as follows:
Figure BDA0003872215780000102
α = σ × N, where σ is the absorption cross section, set at 9 × 10 -20 cm 2 Calculated as α =6.282cm -1 。
η a ＝1-exp(-α·l)＝0.957；
S represents an integral term of the pump light mode and the laser mode on the cross section in the gain medium, and for end pumping, S can be approximately written as:
Figure BDA0003872215780000103
wherein, ω is 0 、ω p The average spot radius of the pump light, respectively the laser mode, within the gain medium.
Set cavity length L d =100mm, the diameters of the input plane mirror and the coupling output mirror are one inch, and the coupling output mirror is curvedThe radius of curvature is 100mm, in this case S =0.0255mm 2 。
If the excited state absorption is not considered, the slope efficiency of the end-pumped four-level continuous laser can be expressed as:
η slope ＝η a η S ε p η m η c ；
η S ＝λ P /λ L ；
Figure BDA0003872215780000104
wherein eta S Is the Stokes factor, η m Efficiency of mode overlap, η c For output coupling efficiency, λ P Is the wavelength of the pump light, λ L Is the laser wavelength.
The wavelength of the pump light is 444nm and the section of the stimulated radiation is 20 multiplied by 10 -20 cm 2 And the laser upper level fluorescence lifetime is 50 mus, then:
Figure BDA0003872215780000111
η slope ＝η a η S ε p η m η c ＝0.377；
in the embodiment, the rated output power of the blue light single tube 3 is 4W, the pumping condition is met, the resonant cavity can realize laser emission, and the tilting efficiency can reach 37.7%.
When the tilt angle of the output coupling mirror satisfies θ =7.5 °, the threshold values of the transitions at 639nm and 721nm are the same, i.e., γ =1, the dual-wavelength laser is generated.
Further, the aspheric focusing lens 4, the spherical focusing lens F15, and the spherical focusing lens F26 constitute a light beam collimating and focusing system, and the relative positions of the lenses are as shown in fig. 3, which aims to collimate and focus the pump light output by the blue light single tube into the crystal. Wherein, the focal length of the aspheric focusing lens 4 is 16mm, the focal length of the spherical focusing lens F15 is 100mm, the focal length of the spherical focusing lens F26 is 75mm, and the aspheric focusing lens 4 and the spherical condenserThe focusing lens F15 is in a common focus point, namely the distance between the two lenses is 116mm, and the light beams can be focused to 40X 40 μm after passing through the collimation focusing system 2 The mode overlapping efficiency is improved, and the mode matching efficiency can reach 100%. Pr: the center of the YLF crystal 9 coincides with the focus of the spherical focusing mirror F26 and is close to the input plane mirror 7 to realize the best mode matching, and the ratio of Pr: YLF crystal 9 has doping concentration of 0.5.at.%, size of 3X 5mm, a-cut, and blue light wave band high-transmittance film plated on the light-transmitting end face.
Further, the direct-current stabilized power supply 1 is produced by fixed electronics technology Limited of Shenzhen, model number NPS605W,0-60W/5A.
Further, lead to water-cooling copper base plate 2 and be the brass material, as shown in fig. 5, two water-cooling passageways are opened to copper side upper and lower position, and the blue light single tube utilizes little paster to fix on the water-cooling board, aims at carrying out the water-cooling to the blue light single tube, and the water cooler temperature sets up to 15 ℃.
Furthermore, the blue light single tube 3 is a single tube in a Nissan blue light laser diode group NUBM06E, the rated output power is 4W, the maximum working current is 3.5W, the maximum working voltage is 4.9V (when the constant current is 2.5A), the fast axis divergence angle is 0.4 degrees, the slow axis divergence angle is 0.1 degrees, the wavelength range is 440-450 nm, and the central wavelength is 444nm under the experimental conditions by using a wavelength control technology.
Further, the crystal water cooling module 8 is made of brass, and as shown in fig. 4, has a through hole with a center of 3.1 × 10mm, and is used for placing Pr: YLF crystal 9, contain U type water-cooling passageway in the crystal water-cooling module 8, to Pr: the YLF crystal 9 was water cooled and the water cooler temperature was set at 15 ℃.
Further, a long-wave pass filter 11 is arranged behind the output coupling mirror 10 according to the light emitting direction after being cut to 480nm wavelength, and is used for filtering the light which is not filtered by Pr: YLF crystal 9 absorbs the pump light.
Further, the working wavelength of the polarization beam splitter 12 is 620nm-1000nm, the surface is coated with an antireflection film, the extinction ratio (Tp: ts): 1000 is 1, one polarized light beam vertically enters the polarization beam splitter 12, when the polarized light beam is transmitted to the polarization beam splitting film, the light beam is divided into two beams, one beam is reflected by the S polarized light, and the other beam is transmitted by the P polarized light.
Further, the indium foil 13 is used for wrapping Pr: YLF crystal 9, improve water cooling efficiency.
Furthermore, water cooling pipes 14, 15, 16 and 17 are used for supplying water to the water cooling copper substrate 2 and the crystal water cooling module 8, and the diameter of each water cooling pipe is 6mm.
Further, the water-cooling tube three-way heads 18 and 19 are used for switching the water-cooling tube for water cooling of the copper substrate 2 and the crystal water-cooling module 8 into a tube.
Further, a water-cooled engine 20 is used to provide a power for the blue light monotube 3 and Pr: the YLF crystal 9 cools to provide a heat sink of 50W/deg.C.
The method comprises the steps that a blue light pump source is used for emitting blue light with the central wavelength located in an absorption peak of a working crystal, and meanwhile, a blue light generating unit needs to be cooled to control the wavelength drift; then, a light beam collimation and focusing system consisting of an aspheric focusing lens, a spherical focusing lens F1 and a spherical focusing lens F2 is used for carrying out collimation and focusing on the light beam, so that the pump light is focused to 45 × 75um 2 The light spot (smaller than the average light spot of the working light) is positioned in the center of the working crystal (Pr: YLF crystal) to meet the pumping condition, the working crystal realizes the population inversion under the action of the pumping light, and meanwhile, the working crystal 9 is closely arranged on the input plane mirror of the resonant cavity to ensure that the light waist of the pumping light and the light waist of the resonant cavity meet the optimal matching relation and have higher mode overlapping efficiency. The distance between an output coupling mirror and an input plane mirror of the resonant cavity is 100mm, and the resonant cavity is a critical cavity and is easy for dual-wavelength laser to emit out simultaneously; the relative position of the input plane mirror and the output coupling mirror is slowly adjusted to enable the gain obtained by the working light to be larger than the loss, the dual-wavelength emergent condition is met, dual-wavelength laser of 639nm and 721nm is obtained, a long-wave pass filter can be used for filtering pump light which is not absorbed by the crystal, and the polarization beam splitter can be used for separating the dual-wavelength laser of 639nm and 721 nm; the water cooling system dissipates heat for the blue light generating unit (such as a blue light single tube) and the working crystal.
In the embodiment, blue light with the central wavelength of 444nm emitted by a blue light single tube arranged on a water-cooling brass block is incident to the center of a working crystal after passing through a collimation focusing system to provide pumping for a working substance; the input mirror is close to the working substance to realize the best mode matching, the distance between the output mirror and the input mirror is 100mm, the critical cavity is selected to be beneficial to the emergence of the dual-wavelength laser, the included angle between the incident light and the normal of an incident plane is slowly adjusted, and when the included angle is 7.5 degrees, the dual-wavelength laser is emergent; the emergent laser passes through a long-wave pass filter to filter pump light which is not completely absorbed by the crystal, and then passes through a polarization beam splitter to separate two beams of light with vertical polarization; the proportion of 639nm and 721nm laser light in the output light can be controlled by adjusting the tilt angle of the output coupling mirror 10 during the two-wavelength emission process. In this embodiment, the 639nm and 721nm dual-wavelength continuous wave laser devices and methods obtained by using the overall matching among the components and the adjustment of the element parameters can realize that the central wavelength of the pump light is stably located in the absorption peak of the working substance, and the pump light is focused at the center of the working substance, thereby improving the pumping efficiency. The design of the resonant cavity can realize mode matching and wavelength selection, thereby improving the mode conversion efficiency and realizing stable dual-wavelength 639nm and 721nm continuous laser output.
The laser resonant cavity consists of an input plane mirror and a coupling output concave mirror with the curvature radius of 100mm, the cavity length is 100mm, namely the cavity is a critical cavity, pumping light pumps working substances Pr and YLF, oscillation enhancement of the working light in the cavity is realized, and the coupling output mirror outputs the working light. The invention carries out the optimization design of the lens parameters and the relative positions of the plane input mirror and the coupling output concave mirror, further provides a lens with specific transmissivity and refractive index for specific wavelength, controls the working substance to be positioned on the focus of the collimation focusing system, and the input plane mirror is close to the working substance to realize the best mode matching of the pumping light and the working light, thereby improving the pumping efficiency, and simultaneously, adjusts the inclination angle of the coupling output mirror to realize the exit of the dual-wavelength continuous light.
The above embodiment takes the collimating focusing system with focal lengths of 16mm, 100mm and 75mm as an example, and when the focal length of the collimating focusing system lens is changed, the dual-wavelength operation can be realized in the same way; at this time, the pump light power is greater than the threshold power, i.e., P p >P th ，
Figure BDA0003872215780000141
The dual-wavelength emergent condition is satisfied:
Figure BDA0003872215780000142
the invention is suitable for blue light pumping 639nm,721nm dual-wavelength lasers of any collimating and focusing lens parameter, correspondingly, the components such as a blue light single tube, an input mirror, a coupling output mirror, a Pr: YLF crystal, a polarization beam splitter and the like which are required to be used in the invention can be obtained by referring to the related prior art according to the focal length of a collimating and focusing system and the curvature radius of a resonant cavity in practical application; the light output power of the blue light single tube, the parameters of resonant cavity elements, pr, YLF crystal and the size can be adjusted based on the principle of the invention, as long as the working beam waist can realize mode matching with the pump light, namely the working light average spot is larger than the focusing light average spot and the pumping condition is satisfied; meanwhile, the Pr-YLF crystal is positioned at the focus of the collimation focusing system, and the pumping beam waist and the working beam waist are both positioned on the Pr-YLF crystal. Other various optical devices and optical components used in the present invention may be commercially available or may be constructed based on the related art, except for those specifically described; for example, the partially reflective film used in the present invention can be constructed with reference to the related art. On the whole, the invention adjusts the structural parameters of each component in the method and the device for the blue light semiconductor pumping Pr: YLF crystal, the curvature radius, the reflectivity, the inclination angle and the like of the cavity mirror, and simultaneously adjusts and controls the whole light path and the light-emitting wavelength of the corresponding laser.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (9)

1. A method for generating 639nm and 721nm cross-polarized dual-wavelength laser by blue light pumping, comprising:
a blue light pumping source is adopted to generate blue light, and the blue light is collimated and focused on a working crystal in a resonant cavity through a 4F system to generate 639nm and 721nm dual-wavelength laser output;
the working crystal is arranged at the optical waist of the resonant cavity, the resonant cavity is a critical cavity, and the transmissivity to 639nm and 721nm is 3% -7%; the included angle between the normal line of the output mirror surface of the resonant cavity and the incident ray satisfies the following conditions: the size of round-trip loss in the cavity caused by Fresnel reflection at positions 639nm and 721nm influenced by the included angle can enable the threshold pump power ratio of the resonant cavity at positions 639nm and 721nm to be 1; the pump light power of the blue light pump source is greater than the threshold pump power; the 4F system satisfies: the average spot of the light beam focused on the working crystal is smaller than the average spot of the working light.
2. The method of claim 1, further comprising: and in the emitting process of the dual-wavelength laser, the occupation proportion of the 639nm laser and the 721nm laser in output light is controlled by disturbing the included angle.
3. The method as claimed in claim 1, wherein during the generation of the dual-wavelength laser of 639nm and 721nm, the working crystal and the blue light generating unit in the blue light pump source are both subjected to water cooling heat dissipation treatment, and the water cooling temperature is set to 15 ℃.
4. The method of claim 1, wherein the input mirror of the resonator is a flat mirror and the output mirror of the resonator is a concave mirror.
5. The method of claim 1, wherein the center of the working crystal coincides with the focal point of a spherical focusing mirror F2 in the 4F system.
6. The method of any one of claims 1 to 5, wherein the input mirror of the resonant cavity is a flat mirror, the transmittance is 99.7% in the band of the absorption peak of the working crystal, the reflectance is 99.5% at 500 to 750nm, the output mirror of the resonant cavity is a concave mirror with a radius of curvature of 100mm, and the transmittance is 3% at 500 to 750nm, the cavity length of the resonant cavity is 100mm, and the substrates of the input mirror and the output mirror of the resonant cavity are BK7 glass;
the angle between the normal of the output mirror surface of the resonant cavity and the incident light ray is 7.5 °.
7. An apparatus for blue pumping to generate 639, 721nm cross-polarized dual-wavelength laser, comprising: a blue light pumping source, a 4F system, a resonant cavity and a working crystal; the working crystal is arranged at the optical waist of the resonant cavity, the resonant cavity is a critical cavity, and the transmissivity to 639nm and 721nm is 3% -7%;
the blue light pump source is used for generating blue light in the absorption peak wave band of the working crystal; the 4F system is used for collimating and focusing the blue light onto the working crystal; the working crystal generates dual-wavelength laser of 639nm and 721nm in the resonant cavity and outputs the laser through an output mirror of the resonant cavity; the included angle between the normal line of the surface of the output mirror of the resonant cavity and the incident ray satisfies the following conditions: the size of round-trip loss in the cavity caused by Fresnel reflection at positions 639nm and 721nm influenced by the included angle can enable the threshold pump power ratio of the resonant cavity at positions 639nm and 721nm to be 1; the pump light power of the blue light pump source is greater than the threshold pump power; the 4F system is set up as follows: the average spot of the light beam focused on the working crystal is smaller than the average spot of the working light.
8. The apparatus of claim 7, further comprising: and the water cooling device is used for carrying out water cooling heat dissipation treatment on the working crystal and the blue light generating unit in the blue light pumping source.
9. The apparatus of claim 7 or 8, wherein the input mirror of the resonant cavity is a flat mirror, the transmittance is 99.7% in the absorption peak wavelength band of the working crystal, the reflectance is 99.5% at 500 to 750nm, the output mirror of the resonant cavity is a concave mirror with a radius of curvature of 100mm, and the transmittance is 3% at 500 to 750nm, the cavity length of the resonant cavity is 100mm, and the substrates of the input mirror and the output mirror of the resonant cavity are BK7 glass;
the angle between the normal of the output mirror surface of the resonant cavity and the incident light is 7.5 °.
CN202211201526.7A 2022-09-29 2022-09-29 Method and device for generating 639nm and 721nm dual-wavelength laser by blue light pumping Pending CN115459038A (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107994448A (en) * 2017-12-01 2018-05-04 华侨大学 A kind of white light laser
WO2020001050A1 (en) * 2018-12-11 2020-01-02 山东大学 Phonon band edge emission-based all solid state high power slab laser

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN107994448A (en) * 2017-12-01 2018-05-04 华侨大学 A kind of white light laser
WO2020001050A1 (en) * 2018-12-11 2020-01-02 山东大学 Phonon band edge emission-based all solid state high power slab laser

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
YUAN, QINYUN 等: "Direct generation of orthogonally polarized dual-wavelength orbital Poincaré modes at 639 nm and 721 nm in a blue-diode pumped Pr:YLF laser", OPTICS LASER TECHNOLOGY, 30 April 2023 (2023-04-30) *

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