Method and device for generating 639nm and 721nm dual-wavelength lasers by blue light pumping

Abstract

The present invention belongs to the field of visible light lasers, and specifically relates to a method and device for generating 639nm and 721nm dual-wavelength lasers by blue light pumping, including: using a blue light pumping source to generate blue light, collimating and focusing on a working crystal located in a resonant cavity through a 4F system, and generating 639nm and 721nm dual-wavelength laser outputs; wherein the working crystal is arranged at the optical waist of the resonant cavity, the resonant cavity is a critical cavity, and the transmittance to 639nm and 721nm is 3%-7%; the angle between the normal line of the output mirror surface of the resonant cavity and the incident light satisfies: the round-trip loss in the cavity caused by Fresnel reflection at 639nm and 721nm affected by the angle can make the threshold pump power ratio of the resonant cavity at 639nm and 721nm 1; the pumping light power of the blue light pumping source is greater than the threshold pumping power; the 4F system satisfies that the average spot of the light beam focused on the working crystal is smaller than the average spot of the working light. The present invention effectively fills the gap of dual-wavelength visible light lasers at 639nm and 721nm.

Description

Technical Field

[0001] The present invention belongs to the field of visible light lasers, and more specifically, relates to a method and device for generating 639nm and 721nm dual-wavelength lasers by blue light pumping. Background Art

[0002] With the continuous development of blue light semiconductor technology, the research of visible light lasers has become an important topic.

[0003] Visible lasers are widely used in medical diagnosis and treatment, laser display, free-space optical communication, deep-sea and atmospheric measurement, and other fields. For example, in medicine, retinal pigment epithelial cells have a strong absorption of green light, and green light lasers can be used for laser surgery for retinal diseases; yellow lasers with a wavelength of around 590nm have good effects in treating port-wine stains and skin hemangiomas because of their high absorption by hemoglobin. In communications, since seawater has the best transparency in the blue-green light band, blue-green lasers are considered to be the best light sources for underwater communications. Visible light lasers are currently mainly realized through the following ways: visible light laser diodes, frequency doubling based on nonlinear processes and optical parametric oscillators, and visible light up-conversion and down-conversion lasers doped with rare earth ions. However, LDs are not easy to produce high-energy or ultrafast lasers, and frequency-doubled lasers rely on nonlinear processes. The up-conversion technology mechanism is relatively complex, and its efficiency has no obvious advantage over frequency-doubled lasers. Down-conversion visible light lasers represented by Pr-doped lasers can efficiently generate blue, green, orange, red and deep red lasers, avoid the use of frequency-doubling crystals, have good stability, compact cavity structure, and are capable of all-fiber operation, which has attracted the attention of many researchers.

[0004] In 2021, the research group of Professor Cai Zhiping of Xiamen University reported that multi-wavelength laser oscillation of about 670nm was achieved by tilting the crystal and inserting different thicknesses of standards. By slightly tilting the Pr:YLF crystal to adjust the intracavity loss, a maximum output power of 2.52W was obtained at a dual wavelength of 670.1 / 674.8nm. By inserting an etalon with a thickness of 100μm at the Brinell angle, a dual-wavelength laser of 675.0 / 679.4 was obtained, with a maximum output power of 1.80W and a maximum slope efficiency of 34.1%. By vertically inserting an etalon with a thickness of 200μm and fine-tuning the tilt, a dual-wavelength laser of 670.1 / 679.1nm was obtained with a maximum output power of 0.36W. At the same time, it was reported that a three-wavelength laser of 670.4 / 674.8 / 679.4nm was obtained by tilting the crystal, with an output power of 1.78W. By inserting two etalons with a thickness of 100 μm and a thickness of 150 μm, a three-wavelength laser of 672.2 / 674.2 / 678.6 nm was obtained, with a maximum output power of 0.84 W. (Lin X, Feng Q, Zhu Y, et al. Diode-pumped wavelength-switchable visible Pr 3+:YLF laser and vortex laser around 670 nm [J]. Opto-Electronic Advances, 2021, 4 (4): 210006-1-210006-8.) In 2022, the group reported a semiconductor laser diode-pumped 604 nm continuous wave laser based on a low-doped Pr3+:YLF crystal. At 604 nm, the maximum output power was 3.28 W and the total slope efficiency was 34.2%. In addition, dual-wavelength lasers of 604 and 607 nm were achieved by adjusting the thermal lens effect of the crystal, and this process did not require any additional wavelength selection elements. This method was used to obtain a dual-wavelength laser of 604 and 607 nm with a maximum output power of 3.30 W (Lin X, Ji S, Feng Q, et al. Heat-induced wavelength-switchable high-power CW orange Pr3+:YLF lasers[J]. Journal of Luminescence, 2022, 243:118627.).

[0005] However, the wavelength bands currently available for dual-wavelength continuous wave operation do not include 639nm and 721nm. Summary of the invention

[0006] In view of the defects and improvement needs of the prior art, the present invention provides a method and device for generating 639nm and 721nm dual-wavelength lasers by blue light pumping, which aims to effectively fill the gaps of dual-wavelength visible light lasers at 639nm and 721nm.

[0007] To achieve the above object, according to one aspect of the present invention, a method for generating 639 nm and 721 nm dual-wavelength lasers by blue light pumping is provided, comprising:

[0008] A blue light pump source is used to generate blue light, which is collimated and focused onto the working crystal in the resonant cavity through the 4F system to generate dual-wavelength laser outputs of 639nm and 721nm;

[0009] The working crystal is arranged at the optical waist of the resonant cavity, and the resonant cavity is a critical cavity with a transmittance of 3%-7% at 639nm and 721nm; the angle between the normal line of the output mirror surface of the resonant cavity and the incident light satisfies: the round-trip loss in the cavity caused by Fresnel reflection at 639nm and 721nm affected by the angle can make the threshold pump power ratio of the resonant cavity at 639nm and 721nm 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.

[0010] Furthermore, the method further comprises: during the emission process of the dual-wavelength laser, controlling the proportion of the 639nm and 721nm lasers in the output light by disturbing the angle.

[0011] Furthermore, during the generation of the 639nm and 721nm dual-wavelength lasers, the working crystal and the blue light generating unit in the blue light pump source are both subjected to water cooling and heat dissipation treatment, and the water cooling temperature is set to 15°C.

[0012] Furthermore, the input mirror of the resonator is a plane mirror, and the output mirror of the resonator is a concave mirror.

[0013] Furthermore, the center of the working crystal coincides with the focus of the spherical focusing mirror F2 in the 4F system.

[0014] Furthermore, the input mirror of the resonant cavity has a transmittance of 99.7% in the absorption peak band of the working crystal, and a reflectance of 99.5% at 500-750 nm, the output mirror of the resonant cavity is a concave mirror with a curvature radius of 100 mm, and a transmittance of 3% at 500-750 nm, the cavity length of the resonant cavity is 100 mm, and the substrates of the input mirror and the output mirror of the resonant cavity are BK7 glass;

[0015] Then the angle between the normal line of the surface of the resonant cavity output mirror and the incident light is 7.5°.

[0016] The present invention also provides a device for generating 639nm and 721nm orthogonal polarization dual-wavelength lasers by blue light single tube pumping, 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 transmittance to 639nm and 721nm is 3%-7%;

[0017] The blue light pump source is used to generate blue light within the absorption peak band of the working crystal; the 4F system is used to collimate and focus the blue light onto the working crystal; the working crystal generates 639nm and 721nm dual-wavelength lasers in the resonant cavity, and outputs them through the output mirror of the resonant cavity; wherein the angle between the normal line of the output mirror surface of the resonant cavity and the incident light satisfies: the magnitude of the intracavity round-trip loss caused by Fresnel reflection at 639nm and 721nm affected by the angle can make the threshold pump power ratio of the resonant cavity at 639nm and 721nm 1; the pump light power of the blue light pump source is greater than the threshold pump power; the setting of 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.

[0018] Furthermore, it also includes: a water cooling device for performing water cooling and heat dissipation treatment on the working crystal and the blue light generating unit in the blue light pump source.

[0019] Furthermore, the input mirror of the resonant cavity has a transmittance of 99.7% in the absorption peak band of the working crystal, and a reflectance of 99.5% at 500-750 nm, the output mirror of the resonant cavity is a concave mirror with a curvature radius of 100 mm, and a transmittance of 3% at 500-750 nm, the cavity length of the resonant cavity is 100 mm, and the substrates of the input mirror and the output mirror of the resonant cavity are BK7 glass;

[0020] Then the angle between the normal line of the surface of the resonant cavity output mirror and the incident light is 7.5°.

[0021] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects:

[0022] (1) The method of the present invention adopts a combination of a 4F system and a resonant cavity. The 4F system is used to collimate and focus the blue light generated by a blue light pump source onto a working crystal located in the resonant cavity. The average spot of the light beam focused on the working crystal is smaller than the average spot of the working light. Due to the existence of the 4F system, the actual space setting and focusing requirements can be flexibly adjusted, so that the pump light injected into the working crystal and the working light can achieve good mode matching and optimize the slope efficiency. In addition, the resonant cavity is a critical cavity, and the transmittance of 639nm and 721nm is 3%-7%. The angle between the normal line of the output mirror surface of the resonant cavity and the incident light satisfies: the round-trip loss in the cavity caused by Fresnel reflection at 639nm and 721nm affected by the angle can make the threshold pump power ratio of the resonant cavity at 639nm and 721nm 1, and when the pump light power of the blue light pump source is greater than the above threshold pump power, dual-wavelength emission of 639nm and 721nm is achieved, effectively filling the gap of dual-wavelength visible light lasers at 639nm and 721nm.

[0023] (2) The present invention adopts a collimating and focusing system to improve the pumping efficiency and the power of the output light. The present invention adopts a collimating and focusing system to focus the pumping light on the center of the working material, and the working material is close to the input plane mirror to achieve the best mode matching between the pumping light and the working light, thereby improving the pumping efficiency. At the same time, the present invention has a higher output beam quality. The present invention adopts a collimating and focusing system to improve the beam quality of the pumping light. At the same time, the output beam quality is improved by adjusting the relative position and tilt angle of the two mirrors of the resonant cavity. Therefore, the present invention improves the poor output light beam quality in the traditional blue light pumping visible light system due to the imperfect design of the resonant cavity parameters.

[0024] (3) The present invention uses a special coated plane mirror and a concave mirror as the resonant cavity, wherein the input mirror of the resonant cavity has a transmittance of 99.7% in the absorption peak band of the working crystal and a reflectance of 99.5% at 500-750nm. The output mirror of the resonant cavity is a concave mirror with a curvature radius of 100mm and a transmittance of 3% at 500-750nm. The cavity length of the resonant cavity is 100mm. The substrates of the input and output mirrors of the resonant cavity are BK7 glass; the angle between the surface normal of the resonant cavity output mirror and the incident light is 7.5°. Dual wavelength operation at 639nm and 721nm is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A device for generating 639nm and 721nm orthogonally polarized dual-wavelength lasers by blue light pumping provided in an embodiment of the present invention;

[0026] Figure 2 A diagram of a resonant cavity structure provided by an embodiment of the present invention;

[0027] Figure 3 A schematic diagram of a collimation and focusing system provided in an embodiment of the present invention;

[0028] Figure 4 A schematic diagram of the structure of a Pr:YLF crystal water cooling block provided in an embodiment of the present invention;

[0029] Figure 5 A schematic structural diagram of a blue light single-tube water cooling plate provided in an embodiment of the present invention.

[0030] In all drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0031] 1 is a DC regulated power supply, 2 is a water-cooled copper substrate, 3 is a blue light single tube, 4 is an aspheric focusing mirror, 5 is a spherical focusing mirror F1, 6 is a spherical focusing mirror F2, 7 is an input plane mirror, 8 is a crystal water cooling module, 9 is a Pr:YLF crystal, 10 is an output coupling mirror, 11 is a long-wave pass filter, 12 is a polarization beam splitter, 13 is an indium foil, 14, 15, 16, 17 are all water-cooled tubes, 18, 19 are all water-cooled tube tees, and 20 is a water chiller. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Embodiment 1

[0034] A method for generating 639nm and 721nm orthogonally polarized dual-wavelength lasers by blue light pumping, comprising:

[0035] A blue light pump source is used to generate blue light, which is collimated and focused onto the working crystal in the resonant cavity through the 4F system to generate dual-wavelength laser outputs of 639nm and 721nm;

[0036] The working crystal is arranged at the optical waist of the resonant cavity; the resonant cavity is a critical cavity, which is easy to output dual-wavelength lasers at the same time, and the transmittance of 639nm and 721nm is 3%-7%; the angle between the normal line of the output mirror surface of the resonant cavity and the incident light satisfies: the size of the intracavity round-trip loss caused by Fresnel reflection at 639nm and 721nm affected by the angle can make the threshold pump power ratio of the resonant cavity at 639nm and 721nm 1; when calculating the threshold pump power, the intracavity round-trip loss corresponding to 639nm used is the loss of P wave caused by Fresnel reflection, and the intracavity round-trip loss corresponding to 721nm used 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 average spot of the focused light beam is smaller than the average spot of the working light.

[0037] The method is to directly generate dual-wavelength visible light of 639nm and 721nm for a blue light generating unit (such as a single blue light tube). The corresponding visible light laser structure includes a blue light pump source, a collimating and focusing system (i.e., a 4F system), a resonant cavity, and a working substance.

[0038] Preferably, the input mirror of the resonant cavity is a plane mirror, with a transmittance of 99.7% in the absorption peak band of the working crystal, and a reflectance of 99.5% at 500-750nm, the output mirror of the resonant cavity is a concave mirror with a radius of curvature of 100mm, and a transmittance of 3% at 500-750nm, the cavity length of the resonant cavity is 100mm, and the substrates of the input mirror and output mirror of the resonant cavity are BK7 glass; under this resonant cavity design, according to the angle between the surface normal of the resonant cavity output mirror and the incident light, the round-trip loss in the cavity caused by Fresnel reflection at 639nm and 721nm affected by the angle can make the threshold pump power ratio of the resonant cavity at 639nm and 721nm 1, and the angle between the surface normal of the resonant cavity output mirror and the incident light at the calculation point is 7.5°. Of course, in the dual-wavelength emission process, by adjusting the tilt angle of the output mirror with a small disturbance, the proportion of 639nm and 721nm lasers in the output light can be controlled.

[0039] Preferably, during the 639nm and 721nm dual-wavelength laser generation process, the working crystal and the blue light single tube in the blue light pump source are both subjected to water cooling treatment, and the water cooling temperature is set to 15° C. to control the wavelength drift of the blue light.

[0040] Preferably, the input mirror of the resonator is a plane mirror, and the output mirror of the resonator is a concave mirror, which facilitates the adjustment of the resonator.

[0041] Preferably, the center of the working crystal coincides with the focus of the spherical focusing mirror F2 in the 4F system, so as to achieve maximum absorption of the pump light by the crystal and further improve the frequency doubling efficiency.

[0042] In order to implement the above method and make it clearer, a set of devices is now provided and the above method is explained:

[0043] A laser device for generating dual-wavelength continuous wave laser by blue light pumping, such as Figure 1 As shown, it includes: a DC regulated power supply 1, a water-cooled copper substrate 2, a blue light single tube 3, an aspherical focusing mirror 4, a spherical focusing mirror F15, a spherical focusing mirror F26, an input plane mirror 7, a crystal water cooling module 8, a Pr:YLF crystal 9, an output coupling mirror 10, a long-wave filter 11, a polarization beam splitter 12, an indium foil 13, water-cooling tubes 14, 15, 16, 17, water-cooling tube three-way heads 18, 19, and a water chiller 20. Among them, the DC regulated power supply 1 and the blue light single tube 3 constitute a blue light pump source, the aspherical focusing mirror 4, the spherical focusing mirror F15, and the spherical focusing mirror F26 constitute a 4F system, and the input plane mirror 7 and the output coupling mirror 10 are respectively used as the input mirror and the output mirror of the resonant cavity to constitute the resonant cavity.

[0044] The DC regulated power supply 1 is used to generate a DC current to provide a pump for the blue light single tube 3; the water-cooled copper substrate 2 is used to provide water cooling for the blue light single tube 3; the blue light single tube 3 is used to generate a 444nm blue light to provide a pump for the Pr:YLF crystal 9; the aspheric focusing mirror 4 is used to focus the blue light emitted by the blue light single tube 3; the spherical focusing mirror F15 is used to collimate the focused light beam passing through the aspheric focusing mirror 4; the spherical focusing mirror F26 is used to focus the light collimated by the spherical focusing mirror F15; the input plane mirror 7 is used to form a resonant cavity, input pump light, and maintain the oscillation of the working light; the crystal water cooling module 8 is used to provide water cooling for the working crystal Pr:YLF crystal 9; Pr:YLF The crystal 9 is used as the working material of the dual-wavelength laser; the output coupling mirror 10 is used to form a resonant cavity and output the working light; the long-wave filter 11 is used to filter out the blue light that is not absorbed by the crystal in the output light; the polarization beam splitter 12 is used to separate the dual-wavelength output light of 639nm and 721nm; the indium foil 13 is used to wrap the Pr:YLF crystal 9 to improve the water cooling efficiency; the water cooling pipes 14, 15, 16, and 17 are used to pass water through the water-cooled copper substrate 2 and the crystal water cooling module 8; the water cooling pipe tees 18 and 19 are used to transfer the water cooling pipes passing through the water-cooled copper substrate 2 and the crystal water cooling module 8 into one pipe; the water cooler 20 is used to provide water cooling for the blue light single tube 3 and the Pr:YLF crystal 9;

[0045] Further, such as Figure 2As shown, the input plane mirror 7, the Pr:YLF crystal 9, and the output coupling mirror 10 are coordinated to complete the oscillation enhancement of the laser and stably emit dual-wavelength lasers of 639nm and 721nm. The input plane mirror 7 has a transmittance of 99.7% at 444nm and a reflectance of 99.5% at 500-750nm. The output coupling mirror 10 is a concave mirror with a curvature radius of 100mm, and a transmittance of about 3% (can be selected within 3%-7%) at 500-750nm. The two mirrors constitute a laser resonant cavity with a cavity length of 100mm. The substrates are all BK7 glass, the size is one inch, and they are all installed on a three-dimensional adjustment frame. The tilt angle θ of the output coupling mirror 10 is adjusted to adjust the loss of the resonant cavity at 639nm and 721nm. When the threshold pump power of the laser resonant cavity at 639nm and 721nm is the same, the two beams of light are emitted simultaneously. Ignoring the excited state absorption, the threshold ratio of the two transition wavelengths in the dual-wavelength operation can be expressed as:

[0046]

[0047] Among them, P th,1 is the threshold pump power of the resonant cavity at 639nm, P th,2 is the threshold pump power of the resonant cavity at 721 nm, R 1,2 are the reflectances of the output mirror at 639nm and 721nm, R1=R2=0.97, σ 1,2 is the stimulated emission cross section of Pr:YLF crystal at 639nm and 721nm: σ1 = 22.3*10 -20 cm 2 ,σ2=17.8*10 -20 cm 2 , L 1,2 is the round-trip loss in the cavity caused by Fresnel reflection at 639nm and 721nm, which is related to the incident angle and electric field polarization. In dual-wavelength operation, the two transition wavelengths 639nm and 721nm are σ polarization and π polarization, respectively, corresponding to P-wave and S-wave. The loss of P-wave and S-wave caused by Fresnel reflection can be expressed as:

[0048] L P =R P (n,θ)+[1-R P (n,θ)]·R P (1 / n,sin -1 (sinθ / n));

[0049] L S =R S (n,θ)+[1-R S (n,θ)]·R S (1 / n,sin-1 (sinθ / n));

[0050] in, n is the ratio of the refractive index of the concave mirror and air, and θ is the angle between the incident light and the surface normal of the output coupling mirror 10. Therefore, when the input plane mirror 7 has a transmittance of 99.7% at 444nm and a reflectance of 99.5% at 500-750nm, the output coupling mirror 10 is a concave mirror with a curvature radius of 100mm, and the transmittance at 500-750nm is about 3% (can be selected within 3%-7%), the two mirrors constitute a laser resonant cavity, the cavity length is 100mm, and the substrate is made of BK7 glass hardware design, the tilt angle θ of the output coupling mirror 10 that satisfies the threshold ratio of the two transition wavelengths to 1 is accurately calculated to be 7.5°.

[0051] At this time, when the tilt angle θ of the output coupling mirror 10 satisfies γ=1, the thresholds of the 639nm and 721nm transitions are the same, and dual-wavelength lasers are generated.

[0052] The principle of the method of this embodiment is described as follows:

[0053] If the excited state absorption is not considered, the laser threshold of the four-level continuous laser can be expressed as

[0054]

[0055] Among them, hv p is the pump photon energy, L is the round-trip loss in the laser cavity L = δ r +δ d =0.0152, R is the output mirror reflectivity, σ e is the stimulated emission cross section, τ f is the laser upper level fluorescence lifetime, ε p It represents the ratio of the number of particles reaching the upper energy level of the laser to the number of absorbed pump photons. For Pr:YLF, this term can be assumed to be 1. η a is the absorption efficiency of the pump light: η a =1-exp(-α·l), where α is the absorption coefficient of the laser medium to the pump light, and l is the length of the laser medium.

[0056] In this embodiment, the laser medium Pr:YLF crystal is set to have a length of l=5 mm, a doping concentration of 0.5 at%, and a density of 3.99 g / cm 3 , the molar mass is Avogadro's constant is N A =6.02×10 23 / mol, the lattice concentration N is calculated as follows:

[0057]

[0058] α = σ*N, where σ is the absorption cross section, set to 9×10 -20 cm 2 , we calculated that α = 6.282 cm -1 .

[0059] η a =1-exp(-α·l)=0.957;

[0060] S represents the integral term of the pump light mode and the laser mode on the cross section in the gain medium. For end-pumping and assuming that both the pump light and the laser are Gaussian beams, S can be approximately written as:

[0061]

[0062] Among them, ω0, ω p are the average spot radii of the pump light and the laser mode in the gain medium, respectively.

[0063] Set the cavity length L d =100mm, the diameter of the input plane mirror and the coupling output mirror is one inch, the radius of curvature of the coupling output mirror is 100mm, and S is taken as 0.0255mm 2 .

[0064] If the excited state absorption is not considered, the slope efficiency of the end-pumped four-level continuous laser can be expressed as:

[0065] η slope =η a η S ε p η m η c ;

[0066] η S =λ P / λ L ;

[0067]

[0068] Among them, η S is the Stokes factor, η m is the mode overlap efficiency, η c is the output coupling efficiency, λ P is the pump light wavelength, λ L is the laser wavelength.

[0069] In this embodiment, the pump light wavelength is 444 nm, and the stimulated emission cross section is 20×10 -20 cm 2 , the laser upper level fluorescence lifetime is 50μs, then:

[0070]

[0071] η slope =η a η S ε p η m η c =0.377;

[0072] In this embodiment, the rated output power of the blue light single tube 3 is 4W, which meets the pumping conditions, the resonant cavity can realize laser emission, and the slope efficiency can reach 37.7%.

[0073] When the output coupling mirror tilt angle satisfies θ=7.5°, the thresholds of the 639nm and 721nm transitions are the same, that is, γ=1, and dual-wavelength laser is generated.

[0074] Furthermore, the aspherical focusing mirror 4, the spherical focusing mirror F15, and the spherical focusing mirror F26 form a beam collimating and focusing system, and the relative positions of the mirrors are as follows: Figure 3 As shown, the purpose is to collimate and focus the pump light output by the blue light single tube into the crystal. Among them, the focal length of the aspherical focusing mirror 4 is 16mm, the focal length of the spherical focusing mirror F15 is 100mm, and the focal length of the spherical focusing mirror F26 is 75mm. The aspherical focusing mirror 4 and the spherical focusing mirror F15 are cofocal, that is, the distance between the two mirrors is 116mm. After the collimation and focusing system, the light beam can be focused to a size of 40*40μm 2 The light spot is improved, the mode overlap efficiency is improved, and the mode matching efficiency can reach 100%. The center of Pr:YLF crystal 9 coincides with the focus of spherical focusing mirror F26 and is close to the input plane mirror 7 to achieve the best mode matching. The doping concentration of Pr:YLF crystal 9 is 0.5.at.%, the size is 3*3*5mm, a-cut, and the light-transmitting end face is plated with a high-transmittance film in the blue light band.

[0075] Furthermore, the DC regulated power supply 1 is produced by Shenzhen Guce Electronic Technology Co., Ltd., model NPS605W, 0-60W / 5A.

[0076] Furthermore, the water-cooled copper substrate 2 is made of brass, such as Figure 5 As shown, two water cooling channels are opened at the upper and lower positions of the side of the copper plate, and the blue light single tube is fixed on the water cooling plate using a small patch, in order to water cool the blue light single tube, and the water cooler temperature is set to 15°C.

[0077] Furthermore, the blue light single tube 3 is a single tube in the Nichia blue light laser diode group NUBM06E, with a rated output power of 4W, a maximum operating current of 3.5W, a maximum operating voltage of 4.9V (at a constant current of 2.5A), a fast axis divergence angle of 0.4°, a slow axis divergence angle of 0.1°, a wavelength range of 440-450nm, and using wavelength control technology, the central wavelength under experimental conditions is 444nm.

[0078] Furthermore, the crystal water cooling module 8 is made of brass, such as Figure 4 As shown, the center is a 3.1*3.1*10mm through hole for placing the Pr:YLF crystal 9. The crystal water cooling module 8 contains a U-shaped water cooling channel for water cooling the Pr:YLF crystal 9. The water cooling machine temperature is set to 15°C.

[0079] Furthermore, the long-wave pass filter 11 has a cut-off wavelength of 480 nm and is placed behind the output coupling mirror 10 according to the light output direction, so as to filter out the pump light that is not absorbed by the Pr:YLF crystal 9 .

[0080] Furthermore, the polarization beam splitter 12 has an operating wavelength of 620nm-1000nm, and is coated with an anti-reflection film on its surface, with an extinction ratio (Tp:Ts):>1000:1. When a beam of polarized light is vertically incident on the polarization beam splitter 12 and is transmitted to the polarization splitting film, the light beam is divided into two beams, one beam of S polarized light is reflected, and one beam of P polarized light is transmitted.

[0081] Furthermore, the indium foil 13 is used to wrap the Pr:YLF crystal 9 to improve the water cooling efficiency.

[0082] Furthermore, the water cooling pipes 14, 15, 16, 17 are used to pass water through the water-cooled copper substrate 2 and the crystal water cooling module 8, and the diameter of the water cooling pipe is 6 mm.

[0083] Furthermore, the water-cooling pipe tees 18 and 19 are used to transfer the water-cooling pipes passing through the water-cooled copper substrate 2 and the crystal water-cooling module 8 into one pipe.

[0084] Furthermore, the water chiller 20 is used to cool the blue light single tube 3 and the Pr:YLF crystal 9, providing a heat dissipation of 50W / °C.

[0085] The method is to first use a blue light pump source to emit blue light with a central wavelength within the absorption peak of the working crystal. At the same time, the blue light generating unit needs to be cooled to control its wavelength drift; then, a beam collimation and focusing system composed of an aspherical focusing mirror, a spherical focusing mirror F1, and a spherical focusing mirror F2 is used to collimate and focus the beam, so that the pump light is focused to a size of 45*75um. 2The spot (smaller than the average spot of the working light) is used to meet the pumping condition. This spot is located at the center of the working crystal (Pr: YLF crystal). Under the action of the pump light, the working crystal achieves a population inversion. At the same time, the working crystal 9 is placed close to the input plane mirror of the resonant cavity to ensure that the pump light waist and the waist of the resonant cavity meet the best matching relationship and have a high mode overlap efficiency. Further, this placement method is conducive to laser emission. The distance between the output coupling mirror of the resonant cavity and the input plane mirror is 100mm. The resonant cavity is a critical cavity, which is easy to emit dual-wavelength lasers at the same time; the relative position of the input plane mirror and the output coupling mirror is slowly adjusted to make the gain obtained by the working light greater than the loss, meet the dual-wavelength emission conditions, and obtain 639nm and 721nm dual-wavelength lasers. The long-wave pass filter can be used to filter out the pump light that is not absorbed by the crystal, and the 639nm and 721nm dual-wavelength lasers can be separated by a polarization beam splitter; the water cooling system is used to dissipate heat for the blue light generating unit (such as a blue light single tube) and the working crystal.

[0086] In this embodiment, the blue light with a central wavelength of 444nm emitted by a blue light single tube installed on a water-cooled brass block is incident to the center of the working crystal after passing through a collimating and focusing system to provide pumping for the working substance; the input mirror is close to the working substance to achieve the best mode matching, the output mirror is 100mm away from the input mirror, the critical cavity is selected to facilitate the emission of dual-wavelength lasers, and the angle between the incident light and the normal of the incident plane is slowly adjusted. When the angle is 7.5°, the dual-wavelength laser is emitted; the emitted laser passes through a long-wave filter to filter out the pump light that is not completely absorbed by the crystal, and then passes through a polarization beam splitter to separate the two beams of light with perpendicular polarization; in the dual-wavelength emission process, the proportion of 639nm and 721nm lasers in the output light can be controlled by adjusting the tilt angle of the output coupling mirror 10. This embodiment utilizes the overall coordination between various components and the adjustment of component parameters to obtain a 639nm, 721nm dual-wavelength continuous wave laser device and method, which can achieve that the central wavelength of the pump light is stably located within the absorption peak of the working substance, the pump light is focused on the center of the working substance, and the pumping efficiency is improved. The design of the resonant cavity can achieve mode matching and wavelength selection, thereby improving the mode conversion efficiency and achieving stable dual-wavelength 639nm, 721nm continuous laser output.

[0087] The present invention uses an input plane mirror and a coupled output concave mirror with a curvature radius of 100 mm to form a laser resonant cavity, the cavity length is 100 mm, that is, the cavity is a critical cavity, the pump light pumps the working substance Pr:YLF, the working light realizes oscillation enhancement in the cavity, and the coupled output mirror outputs the working light. The present invention optimizes the lens parameters and relative positions of the plane input mirror and the coupled output concave mirror, further provides a lens with specific transmittance and refractive index for a specific wavelength, and controls the working substance to be located at the focus of the collimating and focusing system, the input plane mirror is close to the working substance to realize the best mode matching of the pump light and the working light, and improves the pumping efficiency, and at the same time, the tilt angle of the coupled output mirror is adjusted to realize the emission of dual-wavelength continuous light.

[0088] The above embodiment takes the collimating and focusing system with focal lengths of 16 mm, 100 mm, and 75 mm as an example. When the focal length of the collimating and focusing system lens is changed, dual-wavelength operation can also be achieved in the same way. At this time, the pump light power is greater than the threshold power, that is, P p >P th , Meet the dual wavelength emission conditions:

[0089] The present invention is applicable to blue light pumped 639nm, 721nm dual-wavelength lasers with any collimating and focusing lens parameters. Accordingly, the blue light single tube, input mirror, coupled output mirror, Pr:YLF crystal, polarization beam splitter and other components required for use in the present invention can be obtained according to the focal length of the collimating and focusing system and the curvature radius of the resonant cavity in practical applications, with reference to the relevant prior art; the output power of the blue light single tube, the resonant cavity element parameters, the parameters and size of the Pr:YLF crystal can be adjusted based on the principles of the present invention, as long as the working beam waist can achieve mode matching with the pump light, that is, the average spot of the working light is larger than the average spot of the focusing beam and meets the pumping conditions; at the same time, the Pr:YLF crystal is located at the focus of the collimating and focusing system, and the pump beam waist and the working beam waist both fall on the Pr:YLF crystal. The various other optical devices and optical components used in the present invention, except for special instructions, can all be commercially available products, or can be constructed based on relevant prior art; for example, the partial reflection film used in the present invention can be constructed with reference to the relevant prior art. In general, the present invention adjusts the method of blue light semiconductor pumping Pr:YLF crystal and the structural parameters of each component in the device, the curvature radius, reflectivity, tilt angle, etc. of the cavity mirror, and at the same time regulates the overall optical path and output wavelength of the corresponding laser.

[0090] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for generating 639nm and 721nm orthogonally polarized dual-wavelength lasers by blue light pumping, characterized in that: include: A blue light pump source is used to generate blue light, which is collimated and focused onto the working crystal in the resonant cavity through the 4F system to generate dual-wavelength laser outputs of 639nm and 721nm; The working crystal is arranged at the optical waist of the resonant cavity, the resonant cavity is a critical cavity, and the transmittance at 639nm and 721nm is 3%-7%; the angle between the normal line of the output mirror surface of the resonant cavity and the incident light satisfies: the round-trip loss in the cavity caused by Fresnel reflection at 639nm and 721nm affected by the angle can make the threshold pump power ratio of the resonant cavity at 639nm and 721nm 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; The input mirror of the resonant cavity is a plane mirror, the transmittance in the absorption peak band of the working crystal is 99.7%, the reflectance at 500-750nm is 99.5%, the output mirror of the resonant cavity is a concave mirror with a curvature radius of 100mm, and the transmittance at 500-750nm 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; Then the angle between the normal line of the surface of the resonant cavity output mirror and the incident light is 7.5°.

2. The method according to claim 1, characterized in that The method further comprises: during the emission process of the dual-wavelength laser, controlling the proportion of the 639nm laser and the 721nm laser in the output light by disturbing the included angle.

3. The method according to claim 1, characterized in that During the 639nm and 721nm dual-wavelength laser generation process, the working crystal and the blue light generating unit in the blue light pump source are both subjected to water cooling and heat dissipation treatment, and the water cooling temperature is set to 15°C.

4. The method according to claim 1, characterized in that The input mirror of the resonant cavity is a plane mirror, and the output mirror of the resonant cavity is a concave mirror.

5. The method according to claim 1, characterized in that The center of the working crystal coincides with the focus of the spherical focusing mirror F2 in the 4F system.

6. A device for generating 639nm and 721nm orthogonally polarized dual-wavelength lasers by blue light pumping, characterized in that: include: A blue light pump 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 transmittance to 639nm and 721nm is 3%-7%; The blue light pump source is used to generate blue light within the absorption peak band of the working crystal; the 4F system is used to collimate and focus the blue light onto the working crystal; the working crystal generates 639nm and 721nm dual-wavelength lasers in the resonant cavity, and outputs them through the output mirror of the resonant cavity; wherein the angle between the normal line of the output mirror surface of the resonant cavity and the incident light satisfies: the magnitude of the intracavity round-trip loss caused by Fresnel reflection at 639nm and 721nm affected by the angle can make the threshold pump power ratio of the resonant cavity at 639nm and 721nm 1; the pump light power of the blue light pump source is greater than the threshold pump power; the setting of 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; The input mirror of the resonant cavity is a plane mirror, the transmittance in the absorption peak band of the working crystal is 99.7%, the reflectance at 500-750nm is 99.5%, the output mirror of the resonant cavity is a concave mirror with a curvature radius of 100mm, and the transmittance at 500-750nm 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; Then the angle between the normal line of the surface of the resonant cavity output mirror and the incident light is 7.5°.

7. The device according to claim 6, characterized in that Also includes: The water cooling device is used to perform water cooling and heat dissipation treatment on the working crystal and the blue light generating unit in the blue light pump source.

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