Design method for preventing pumping source from damaging laser in double-end pumping and laser

Abstract

The invention provides a design method for preventing a pumping source from damaging a laser in double-end pumping and the laser, and the method comprises the steps: according to the absorption bandwidth delta of a gain medium and the 10dB line width delta lambda of the pumping source, the pumping wavelengths lambda1 and lambda2 are designed, the lambda1 and the lambda2 meet the condition that delta lambda < = d lambda < delta, and d lambda is the absolute value of the wavelength difference of the pumping light, namely d lambda = lambda1-lambda2; surface film layers of dichroic mirrors DM1 and DM2 are designed according to pump wavelengths lambda1 and lambda2, an antireflection film with high transmittance lambda1 plated on the two sides of the DM1 ensures the high passing rate of the lambda1, a high-reflection film with high reflection lambda2 plated on the single side reflects pump light lambda2 which is not absorbed by the gain medium, and the 10%-90% step width omega of the high-reflection film is smaller than or equal to delta lambda2. Similarly, the double surfaces of the DM2 are plated with high-transmittance lambda 2 antireflection films, the single surface of the DM2 is plated with a high-reflectivity lambda 1 high-reflectivity film, and the 10%-90% step width omega of the high-reflectivity film is smaller than or equal to delta lambda / 2; the required laser oscillator and amplifier are designed according to the designed lambda 1, lambda 2, DM1 and DM2.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically relating to a design method and a laser for avoiding pump source damage in dual-ended pumping. Background Technology

[0002] To improve output performance such as power / energy and beam quality, most lasers adopt a dual-pump structure. Compared with the single-pump structure, the dual-pump structure has the advantages of uniform pump light distribution and high pump peak power density. However, it also has the disadvantage of incomplete absorption of pump light by the laser crystal, which can cause the remaining pump light at one end to damage the pump source at the other end and affect the stable operation of the laser.

[0003] Currently, there are two main methods to avoid damage to the pump source caused by dual-ended pumping structures: 1. polarization isolation; 2. angle isolation. The first method requires the addition of optical components such as waveplates and polarizers to the pump shaping system, which is difficult to adjust and results in high pump light loss. The second method requires a high degree of matching between the laser and the structure (angle). Therefore, a simpler and more convenient method is needed to avoid damage to the pump source caused by dual-ended pumping structures and improve laser stability. Summary of the Invention

[0004] The purpose of this invention is to provide a design method and a laser for avoiding pump source damage in dual-ended pumping, thereby reducing pump source damage and improving laser stability.

[0005] To achieve this objective, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a design method for avoiding damage to a laser from the pump source in a dual-ended pumping process, comprising the following steps:

[0007] Select the laser gain medium to obtain the absorption bandwidth δ;

[0008] Select the pump source to obtain the linewidth Δλ;

[0009] Determine whether the linewidth Δλ satisfies Δλ≤δ. If it does, select pump wavelengths λ1 and λ2 within the absorption bandwidth δ of the gain medium and calculate the wavelength difference dλ. If it does not satisfy the condition, reselect the pump source and obtain the linewidth Δλ. If the linewidth Δλ of the selectable pump sources does not satisfy the condition, reselect the laser gain medium.

[0010] Pump wavelengths λ1 and λ2 are selected within the absorption bandwidth δ of the gain medium. The wavelength difference dλ is calculated, where dλ = |λ1 - λ2|. It is then determined whether the wavelength difference dλ satisfies the condition dλ ≥ Δλ. If it does, the surface film layers of the dichroic mirrors DM1 and DM2 are further designed. If it does not, the pump wavelengths λ1 and λ2 are reselected.

[0011] The surface coatings of the dichroic mirrors DM1 and DM2 are designed according to the pump wavelengths λ1 and λ2. DM1 is coated with a high-transmittance antireflection film on both sides to ensure the high transmittance of λ1, and a high-reflection film on one side with high reflectivity of λ2. Similarly, DM2 is coated with a high-transmittance antireflection film on both sides with high transmittance of λ2, and a high-reflection film on one side with high reflectivity of λ1.

[0012] Determine whether the transmittance T, reflectance R, and 10%-90% step width ω of the high-reflectivity film in DM1 and DM2 meet the requirements. If they do, design the required laser based on λ1, λ2, DM1, and DM2 determined in the above steps. If they do not meet the requirements, reselect the pump wavelengths λ1 and λ2. If neither the selected pump wavelengths λ1 nor λ2 corresponding to the DM1 and DM2 films meet the requirements, reselect the laser gain medium.

[0013] Based on the λ1 and λ2, DM1 and DM2 obtained from the above steps, design the required laser.

[0014] In some embodiments, the selection of the laser gain medium includes selecting one of Nd:glass, Nd:YAG crystal, Ho:YAG crystal, and Yb:YAG optical ceramic;

[0015] The laser gain medium is selected according to the actual needs of the application scenario;

[0016] In some embodiments, the determination of whether the transmittance T, reflectance R, and 10%-90% step width ω of the high-reflectivity film in DM1 and DM2 meet the requirements is as follows: If the requirements are met, the required laser is designed based on λ1, λ2, DM1, and DM2 determined in the above steps; if not, the pump wavelengths λ1 and λ2 are reselected; if neither the selected pump wavelengths λ1 nor λ2 corresponding to the DM1 and DM2 films meet the conditions, the laser gain medium is reselected, specifically including:

[0017] Determine whether the parameters of DM1 and DM2 films meet the following conditions: high transmittance T1 > 99.0% @ λ1, high reflectivity R > 95% @ λ2, high reflectivity 10%-90% step width ω ≤ Δλ / 2, film absorption coefficient < 100ppm. If these conditions are met, proceed with laser design. If not, select pump wavelengths λ1 and λ2 within the absorption bandwidth δ of the gain medium, calculate the wavelength difference dλ. If neither the DM1 nor DM2 films corresponding to the selectable pump wavelengths λ1 and λ2 meet the conditions, then reselect the laser gain medium.

[0018] In a second aspect, the present invention also provides a laser oscillator for avoiding damage to the pump source in dual-ended pumping, comprising: a laser gain medium, a first pump source, a first pump shaping system, a first dichroic mirror DM1, a second pump source, a second pump shaping system, a second dichroic mirror DM2, a high-reflectivity mirror, a polarizer, and a coupling output mirror;

[0019] With the plane perpendicular to the optical axis of the laser gain medium (i.e., the laser crystal) as the plane of symmetry, a first pump source, a first pump shaping system, and a first dichroic mirror DM1 are respectively arranged on both sides along the optical path; a second pump source, a second pump shaping system, and a second dichroic mirror DM2 are respectively arranged on both sides; the pump light emitted by the first pump source and the second pump source is incident into the laser crystal along the optical path; the incident or emitting surfaces of the first dichroic mirror DM1 and the second dichroic mirror DM2 are at a certain angle to the optical axis, generally 45 degrees, 30 degrees, and 60 degrees, and the two are symmetrically arranged with respect to the plane of symmetry; the reflected light from the first dichroic mirror DM1 is incident into a high-reflection mirror, and the reflected light from the second dichroic mirror DM2 is incident into a polarizer, and then output as laser light through a coupling output mirror.

[0020] In some embodiments, the oscillation cavity of the laser oscillator is a square cavity comprising the high-reflection mirror, the first dichroic mirror DM1, the laser gain medium, the second dichroic mirror DM2, the polarizer, and the coupling output mirror. The first optical arm length and the second optical arm length of the oscillation cavity are equal. The distance between the high-reflection mirror and the first dichroic mirror DM1 is the first optical arm length, and the distance between the coupling output mirror and the second dichroic mirror DM2 is the second optical arm length.

[0021] In some embodiments, the gain medium may be rod-shaped, including square bars, round bars, and slats.

[0022] In some embodiments, the certain angle is 45°.

[0023] This invention provides a design method and laser for avoiding pump source damage in dual-ended pumping, proposing to use pump wavelengths λ1 and λ2 to... 2， The method of designing the surface film of a two-color mirror by using the absorption bandwidth δ of the gain medium and the 10dB linewidth Δλ of the pump source, and then designing the required laser oscillator or amplifier, avoids the influence of the double-ended pump structure on the pump source. Compared with existing methods, it is simpler to operate, reduces the requirements for the laser and structure, improves the stability of the laser, and can design different lasers according to needs, making it widely applicable. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the design method for avoiding pump source damage in a dual-ended pump according to Example 1.

[0025] Figure 2 This is a schematic diagram of the laser oscillator in Example 2;

[0026] Figure 3 This is a schematic diagram of the high-steepness reflective film curves at 1880nm and 1908nm in Example 2.

[0027] Wherein, 1-first pump source (output pump wavelength λ1), 2-second pump source (output pump wavelength λ2), 31-first pump shaping system, 32-second pump shaping system, 4-Ho:YAG laser crystal, 5-first dichroic mirror DM1, 6-second dichroic mirror DM2, 7-polarizer, 8-high reflection mirror, 9-coupled output mirror, 10-first optical arm length, 11-second optical arm length. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments of this invention will be further described below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely for the purpose of aiding understanding of this invention and do not constitute a limitation thereof.

[0029] Example 1

[0030] This embodiment provides a design method for avoiding pump source damage to lasers in dual-ended pumping, such as... Figure 1 The steps include:

[0031] Step 1: Obtain the absorption bandwidth δ based on the laser gain medium;

[0032] Step 2: Select the pump source and obtain the linewidth Δλ. In this embodiment, a 10dB pump source is selected with a linewidth Δλ = 20nm; in some other embodiments, a 3dB pump source can be selected.

[0033] Step 3: Determine whether the linewidth Δλ satisfies Δλ≤δ. If it does, proceed to Step 4. If it does not, proceed to Step 2. If none of the selectable pump source linewidths Δλ satisfy the condition, return to Step 1.

[0034] Step 4: Select pump wavelengths λ1 and λ2 within the gain medium absorption bandwidth δ, and calculate the wavelength difference dλ, dλ=|λ1-λ2|;

[0035] Step 5: Determine whether the wavelength difference dλ satisfies the condition dλ≥Δλ. If it does, proceed to step 6; otherwise, return to step 4.

[0036] Step 6: Based on the pump wavelengths λ1 and λ2, design the surface coatings of the dichroic mirrors DM1 and DM2. DM1 is coated with a high-transmittance antireflection film on both sides to ensure the high transmittance of λ1, and a high-reflection film on one side with high reflectivity of λ2. Similarly, DM2 is coated with a high-transmittance antireflection film on both sides with high transmittance of λ2, and a high-reflection film on one side with high reflectivity of λ1.

[0037] Step 7: Determine whether the parameters of DM1 and DM2 membranes meet the following conditions: high-permeability membrane transmittance T1 > 99.0% @ λ1, high-reflectivity membrane reflectance R > 95% @ λ2, high-reflectivity membrane 10%-90% step width ω ≤ Δλ / 2, membrane absorption coefficient < 100ppm. If the conditions are met, proceed to Step 8. If not, return to Step 4. If neither the DM1 nor DM2 membranes corresponding to the selectable pump wavelengths λ1 and λ2 meet the conditions, return to Step 1.

[0038] Step 8: Based on the above designs of λ1 and λ2, DM1 and DM2, design the required laser, laser oscillator or laser amplifier.

[0039] Example 2

[0040] This embodiment provides a laser oscillator that avoids pump source damage in dual-ended pumping, such as... Figure 2 It includes: YAG laser crystal 4, first pump source 1, first pump shaping system 31, first dichroic mirror 5, second pump source 2, second pump shaping system 32, second dichroic mirror 6, high reflection mirror 8, polarizer 7, and coupling output mirror 9;

[0041] With the plane perpendicular to the optical axis of the YAG laser crystal 4 as the plane of symmetry, a first pump source 1, a first pump shaping system 31, a first dichroic mirror 5, a second pump source 2, a second pump shaping system 32, and a second dichroic mirror 6 are respectively arranged along the optical path on both sides. The pump light emitted by the first pump source 1 and the second pump source 2 is incident into the YAG laser crystal 4 along the optical path. The light-incident or light-outcident surfaces of the first dichroic mirror 5 and the second dichroic mirror 6 are at a certain angle to the optical axis, and the two are symmetrically arranged with respect to the plane of symmetry. The reflected light from the first dichroic mirror 5 is incident into the high-reflection mirror 8, and the reflected light from the second dichroic mirror 6 is incident into the polarizer 7, and then output as laser light through the coupling output mirror 9.

[0042] In this embodiment, the oscillation cavity of the laser oscillator is a square cavity consisting of a high-reflection mirror 8, a first dichroic mirror 5, a YAG laser crystal 4, a second dichroic mirror 6, a polarizer 7, and a coupling output mirror 9. The cavity length is 730 mm. The first optical arm length 10 and the second optical arm length 11 of the oscillation cavity are equal, both being 350 mm. The distance between the high-reflection mirror 9 and the first dichroic mirror 5 is the first optical arm length 10, and the distance between the coupling output mirror 9 and the second dichroic mirror 6 is the second optical arm length 11.

[0043] In this embodiment, the working principle of the laser oscillator is as follows: the pump light λ1 and λ2 output from pump source 1 and pump source 2 are absorbed by the Ho:YAG laser crystal 4 after passing through the pump shaping system 3. The pump light λ1 and λ2 that are not absorbed by the Ho:YAG laser crystal 4 are reflected out of the laser oscillator by the second dichroic mirror 6 and the first dichroic mirror 5, respectively, so as to avoid the unabsorbed pump light λ1 and λ2 from damaging the light-emitting surfaces of pump source 2 and pump source 1. The generated 1030nm laser oscillates and is output between the high-reflection mirror 8 and the coupling output mirror 9 (optical arm length 10 and optical arm length 11), and the optical arm length 10 and optical arm length 11 are equal.

[0044] Pump sources 1 and 2 are quasi-continuous pump sources. The highest average output power of a single pump source is 50W. The pump light wavelengths are λ1 = 1880nm and λ2 = 1908nm, with a wavelength difference dλ = 28nm. The linewidth of pump sources 1 and 2 is Δλ = 20nm. The core diameter of the output pigtail is 200μm, and the numerical aperture NA is 0.22.

[0045] The shaping system 3 consists of an 18mm focal length lens and a 90mm focal length lens. The 18mm focal length lens collimates the pump light output from the fiber coupler, and the 90mm focal length lens focuses the collimated pump light. After shaping, the pump light located at the center of the crystal has a diameter of approximately 1mm.

[0046] The Ho:YAG crystal has an absorption bandwidth δ of 120nm (1870nm~1990nm) at room temperature, a doping concentration of 1.0at.%, and dimensions of 30mm×2mm×2mm (length×width×height). The output laser wavelength is 2090nm.

[0047] The first dichroic mirror 5 has the following dimensions and coating requirements: Φ30mm×3mm, double-sided coating with a 45°HT@λ1=1880nm film, transmittance T>99.8%, and S1 side coated with a 45°HR@λ2=1908nm high-steepness reflective film, reflectance R>99.5%, film absorption coefficient<100ppm, and a 10%-90% step width ω=10nm. See details... Figure 3 .

[0048] The first dichroic mirror 5 has a transmission power to reflection power ratio of >1:199.4 (0.5% × 99.8% : 99.5%) for pump light λ2 = 1908nm.

[0049] The second dichroic mirror 6 has the following dimensions and coating requirements: Φ30mm×3mm, double-sided coating with a 45°HT@λ2=1908nm film, transmittance T>99.8%, and S1 side coated with a 45°HR@λ2=1880nm high-steep reflective film with a laser wavelength of 2090nm, reflectance R>99.5%, film absorption coefficient<100ppm, and a 10%-90% step width ω=10nm. See details... Figure 3 .

[0050] The second dichroic mirror 6 has a transmission power to reflection power ratio of >1:199.4 (0.5% × 99.8% : 99.5%) for pump light λ1 = 1880nm.

[0051] The polarizer 7 has the following dimensions and coating requirements: Φ30mm×4mm, "flat mirror", double-sided coating with 45°HT@λ1=1880nm&λ2=1908nm film, transmittance T>99.8%, S1 side coated with 45°HT@1030nm film, p-polarized light transmittance Tp>95%, s-polarized light transmittance Ts<0.2%, extinction ratio Tp:Ts>475, S2 side coated with 45°HT@1030nm film, transmittance T>99.8%.

[0052] The dimensions and coating requirements for the high-reflectivity mirror 8 are Φ25.4mm×6mm, a "flat mirror", with 0°HT@λ1=1880nm&λ2=1908nm coating on both sides, transmittance T>99.8%, and 0°HR@1030nm coating on the S1 side, reflectance R>99.9%.

[0053] The dimensions and coating requirements of the coupling output mirror 9 are Φ25.4mm×6mm, a "flat mirror", with 0°HT@λ1=1880nm&λ2=1908nm film layers on both sides, and a transmittance T>99.8%. The S1 side is coated with a 1030nm transmittance film layer with a transmittance T=20%, and the S2 side is coated with a 0°HT@1030nm film layer with a transmittance T>99.9%.

[0054] Both optical arms 10 and 11 are 350 mm long, and the laser cavity length Lcav is 730 mm.

[0055] The absorption bandwidth δ of the Ho:YAG crystal 4, the pump light wavelengths λ1 and λ2, the wavelength difference dλ, the linewidth Δλ, and the 10%-90% step width ω of the high-reflection coating of the first dichroic mirror 5 and the second dichroic mirror 6 all satisfy the logical relationship in Example 2.

[0056] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will be able to make various obvious changes, readjustments, and substitutions without departing from the scope of protection of the present invention. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A design method for avoiding pump source damage to a laser in dual-ended pumping, characterized in that, Including the following steps: Select the laser gain medium to obtain the absorption bandwidth δ; Select the pump source to obtain the linewidth Δλ; Determine whether the linewidth Δλ satisfies Δλ≤δ. If it does, select pump wavelengths λ1 and λ2 within the absorption bandwidth δ of the gain medium and calculate the wavelength difference dλ. If it does not satisfy the condition, reselect the pump source and obtain the linewidth Δλ. If the linewidth Δλ of the selectable pump sources does not satisfy the condition, reselect the laser gain medium. Within the absorption bandwidth δ of the gain medium, select pump wavelengths λ1 and λ2, and calculate the wavelength difference dλ, where dλ = |λ1 - λ2|. Determine whether the wavelength difference dλ satisfies the condition dλ≥Δλ. If it does, further design the surface film layers of the dichroic mirrors DM1 and DM2. If it does not, reselect the pump wavelengths λ1 and λ2. The surface coatings of the dichroic mirrors DM1 and DM2 are designed according to the pump wavelengths λ1 and λ2. DM1 is coated with a high-transmittance antireflection film on both sides to ensure the high transmittance of λ1, and a high-reflection film on one side with high reflectivity of λ2. Similarly, DM2 is coated with a high-transmittance antireflection film on both sides with high transmittance of λ2, and a high-reflection film on one side with high reflectivity of λ1. Determine whether the transmittance T, reflectance R, and 10%-90% step width ω of the high-reflectivity film in DM1 and DM2 meet the requirements. If they do, design the required laser based on Δλ2, DM1, and DM2 determined in the above steps. If they do not meet the requirements, reselect the pump wavelengths λ1 and λ2. If neither the DM1 nor DM2 films corresponding to the selected pump wavelengths λ1 and λ2 meet the requirements, reselect the laser gain medium. Based on the λ1 and λ2, DM1 and DM2 obtained from the above steps, design the required laser.

2. The design method for avoiding pump source damage to the laser in dual-ended pumping according to claim 1, characterized in that, The selected laser gain medium includes one of Nd:glass, Nd:YAG crystal, Ho:YAG crystal, and Yb:YAG optical ceramic.

3. The design method for avoiding pump source damage to the laser in dual-ended pumping according to claim 1, characterized in that, The determination of whether the transmittance T, reflectance R, and 10%-90% step width ω of the high-reflectivity film in DM1 and DM2 meet the requirements is as follows: If they meet the requirements, the required laser is designed based on λ1, λ2, DM1, and DM2 determined in the above steps; if they do not meet the requirements, the pump wavelengths λ1 and λ2 are reselected; if neither the selected pump wavelengths λ1 nor λ2 corresponding to the DM1 and DM2 films meet the conditions, the laser gain medium is reselected, specifically including: Determine whether the parameters of DM1 and DM2 films meet the following conditions: high transmittance T1 > 99.0% @ λ1, high reflectivity R > 95% @ λ2, high reflectivity 10%-90% step width ω ≤ Δλ / 2, film absorption coefficient < 100ppm. If these conditions are met, proceed with laser design. If not, select pump wavelengths λ1 and λ2 within the absorption bandwidth δ of the gain medium, calculate the wavelength difference dλ. If neither the DM1 nor DM2 films corresponding to the selectable pump wavelengths λ1 and λ2 meet the conditions, then reselect the laser gain medium.

4. A laser oscillator for avoiding pump source damage in dual-ended pumping, characterized in that, Designed according to the method described in claims 1-3, the system comprises: a laser gain medium, a first pump source, a first pump shaping system, a first dichroic mirror DM1, a second pump source, a second pump shaping system, a second dichroic mirror DM2, a high-reflection mirror, a polarizer, and a coupling output mirror; With the plane perpendicular to the optical axis of the laser gain medium (i.e., the laser crystal) as the plane of symmetry, a first pump source, a first pump shaping system, and a first dichroic mirror DM1 are respectively arranged on both sides along the optical path; a second pump source, a second pump shaping system, and a second dichroic mirror DM2 are respectively arranged on both sides; the pump light emitted by the first pump source and the second pump source are both incident into the laser crystal along the optical path; the incident or emitting surfaces of the first dichroic mirror DM1 and the second dichroic mirror DM2 are at a certain angle to the optical axis, and the two are symmetrically arranged with respect to the plane of symmetry; the reflected light from the first dichroic mirror DM1 is incident into a high-reflection mirror, and the reflected light from the second dichroic mirror DM2 is incident into a polarizer, and then output as laser light through a coupling output mirror.

5. The laser oscillator for avoiding pump source damage in dual-ended pumping according to claim 4, characterized in that, The oscillation cavity of the laser oscillator is a square cavity comprising the high-reflection mirror, the first dichroic mirror DM1, the laser gain medium, the second dichroic mirror DM2, the polarizer, and the coupling output mirror. The lengths of the first and second optical arms of the oscillation cavity are equal. The distance between the high-reflection mirror and the first dichroic mirror DM1 is the length of the first optical arm, and the distance between the coupling output mirror and the second dichroic mirror DM2 is the length of the second optical arm.

6. The laser oscillator for avoiding pump source damage in dual-ended pumping according to claim 5, characterized in that, The gain medium can be rod-shaped, including square bars, round bars, and slabs.

7. The laser oscillator for avoiding pump source damage in dual-ended pumping according to claim 6, characterized in that, The specified angle is 45°.

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