Double-gain-medium Q-switched laser and constant-power pulse width adjusting method

Abstract

The invention relates to the technical field of lasers, and provides a double-gain-medium Q-switched laser and a constant-power pulse width adjusting method.The laser comprises a first pumping source, a second pumping source, an optical fiber beam combiner, a beam shaping system and a laser resonant cavity, the laser resonant cavity comprises a reflecting mirror, a first gain medium, a second gain medium, a polarization selector, a quarter-wave plate, a Q switch and an output mirror which are arranged in sequence; the first gain medium is used for absorbing first pumping light, the second gain medium is used for absorbing second pumping light, and the pumping power of the first pumping source and the pumping power of the second pumping source can be independently controlled. By changing the pumping power of the two pumping sources, real-time adjustment of the pulse width of the laser under the constant output power is achieved, the structure is compact, and control is easy and convenient.

Description

Technical Field

[0001] This invention relates to the field of laser technology, and in particular to a dual-gain dielectric Q-switched laser and a constant power pulse width modulation method. Background Technology

[0002] Short-pulse-width lasers have wide applications in industrial processing, spectral analysis, and nonlinear frequency conversion. Q-switching is a key technology for obtaining high peak power pulsed lasers. Among them, electro-optic Q-switching is widely used due to its advantages such as controllable pulse repetition frequency, fast switching speed, and narrow pulse width. However, the pulse width of traditional single-gain dielectric electro-optic Q-switched lasers is mainly determined by the cavity length, output mirror coupling rate, and parameters of the gain medium. Once the cavity structure is fixed, the output pulse width is also basically fixed, lacking flexibility. Different application scenarios have different requirements for laser pulse width. For example, laser cutting and drilling require matching laser pulse widths to the physicochemical properties of the processed material to achieve precise ablation effects and balance efficiency and quality.

[0003] Currently, achieving tunable pulse width typically requires multiple lasers with different cavity lengths, leading to high system costs, complex structures, and decreased stability. While pulse width can be fine-tuned by changing the pump power, the adjustment range is very limited and affects output power and stability. Therefore, existing technology lacks a Q-switched laser solution that is relatively simple in structure, moderately costly, capable of achieving a wide range of pulse width adjustment, and does not sacrifice output power and beam quality. Summary of the Invention

[0004] This invention provides a dual-gain dielectric Q-switched laser and a constant power pulse width adjustment method to solve the defects of existing Q-switched lasers, such as basically fixed pulse width, limited adjustment range, and the need to configure multiple devices with different cavity lengths to meet diverse pulse width requirements, resulting in high system cost and complex structure.

[0005] In a first aspect, the present invention provides a dual-gain dielectric Q-switched laser, comprising: The first pump source is used to emit first pump light with a wavelength of λ1; The second pump source is used to emit a second pump light with a wavelength of λ2, where λ1 ≠ λ2. The pump power of the first pump source and the second pump source are controlled independently. Both the first pump source and the second pump source are fiber-coupled lasers. An optical fiber combiner is provided, wherein the output ends of the first pump source and the second pump source are both connected to the optical fiber combiner, and the optical fiber combiner is used to couple the first pump light and the second pump light into a coaxial beam for emission. A beam shaping system is disposed on the output side of the fiber combiner along the optical path direction. The beam shaping system is used to shape the coaxial pump light output by the fiber combiner. A laser resonant cavity is disposed on the output side of the beam shaping system. The laser resonant cavity includes a mirror, a first gain medium, a second gain medium, a polarizer, a quarter-wave plate, a Q switch, and an output mirror arranged in sequence. The first gain medium is used to absorb the first pump light, and the second gain medium is used to absorb the second pump light. The first gain medium and the second gain medium have the same laser emission wavelength, but their stimulated emission cross sections are different. By adjusting the power ratio of the two pump sources, the laser pulse width can be adjusted in real time while maintaining a constant output laser power.

[0006] According to the dual-gain medium Q-switched laser provided by the present invention, the reflector is highly transparent to the first pump light and the second pump light, and highly reflective to the laser emitted by the first gain medium and the second gain medium.

[0007] According to the dual-gain dielectric Q-switched laser provided by the present invention, the first gain medium and the second gain medium have high transmittance to the first pump light, the second pump light and the laser in the laser resonator.

[0008] According to the dual-gain dielectric Q-switched laser provided by the present invention, the positions of the quarter-wave plate and the Q switch in the optical path are interchangeable.

[0009] According to the dual-gain dielectric Q-switched laser provided by the present invention, the Q-switch is an electro-optic modulator.

[0010] According to the dual-gain dielectric Q-switched laser provided by the present invention, the polarizer is used to filter s-polarized light or p-polarized light.

[0011] According to the dual-gain dielectric Q-switched laser provided by the present invention, the polarizer includes any one of a thin-film polarizer and a polarizing beam splitter.

[0012] According to the dual-gain medium Q-switched laser provided by the present invention, the first gain medium is bonded to or placed close to the second gain medium.

[0013] In a second aspect, the present invention provides a constant power pulse width modulation method, employing a dual-gain dielectric Q-switched laser as described in the first aspect, comprising the following steps: When the first pump source is working alone, the power of the first pump source is adjusted from the minimum to the maximum rated value, and the output power range P1 of the laser is recorded. When the second pump source is working alone, the power of the second pump source is adjusted from the minimum to the maximum rated value, and the output power range P2 of the laser is recorded. Take the intersection P of P1 and P2, and select a target value from it as the constant output power value; Simultaneously turn on the first pump source and the second pump source, and initially set the initial pump power of the first pump source and the initial pump power of the second pump source so that the laser power emitted by the laser resonator is equal to the target value. The pump power of the two pump sources is synchronously adjusted so that the pump power of one increases while the pump power of the other decreases accordingly. The laser output power of the laser is monitored in real time and maintained at the constant output power value, thereby achieving the adjustment of the constant power pulse width of the emitted laser.

[0014] This invention provides a dual-gain medium Q-switched laser, comprising: a first pump source, a second pump source, an optical fiber combiner, a beam shaping system, and a laser resonator. The invention uses the optical fiber combiner to couple the non-coaxial beams of the two pump sources into a coaxial beam, ensuring synchronous and precise incident projection of the pump light onto the dual-gain medium. The beam shaping system further shapes the coaxial pump light into a spot size adapted to the laser mode size of the resonator, significantly improving energy conversion efficiency. Simultaneously, the dual-gain medium and the two pump sources are integrated into a single laser resonator via the optical fiber combiner, eliminating the need for multiple independent lasers. Compared to traditional technologies, this results in a more compact system structure, smaller footprint, and lower deployment costs.

[0015] On the other hand, this invention achieves adjustable laser pulse width by setting two pump sources and two gain media with the same emission wavelength but different stimulated emission cross sections in the resonant cavity. The first gain medium absorbs the first pump light with wavelength λ1 and does not absorb or absorbs the second pump light with wavelength λ2 very weakly. The second gain medium absorbs the second pump light with wavelength λ2. The difference in stimulated emission cross sections between the two directly determines the photon emission rate. The medium with a larger cross section emits photons faster, corresponding to a narrow pulse width; the medium with a smaller cross section emits photons slower, corresponding to a wide pulse width. During operation, only the operating current of the first and second pump sources needs to be changed to achieve pulse width adjustment. No optical components or mechanical structures need to be changed. The operation is extremely simple and easy to implement computer program control and automation. Specifically, by independently adjusting the power ratio of the two pump sources, the total excitation energy of the dual-gain medium is kept stable. For example, when the power of the first pump source (corresponding to the low-section medium) is increased while the power of the second pump source (corresponding to the high-section medium) is decreased, the low-section medium dominates in energy accumulation and release, thus outputting a laser with a wider pulse width. Conversely, when the power of the second pump source is increased while the power of the first pump source is decreased, the high-section medium dominates, thus outputting a laser with a narrower pulse width. Throughout the adjustment process, the average power of the final emitted laser remains unchanged, ultimately achieving real-time and continuous adjustment of the laser pulse width without the need to replace optical components or mechanical structures, adapting to diverse needs in industrial processing, spectral analysis, and other scenarios. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A schematic diagram of a dual-gain dielectric Q-switched laser that selects s-polarized light is provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a dual-gain dielectric Q-switched laser that selects p-polarized light, provided as an embodiment of the present invention.

[0018] Figure label: 1. First pump source; 2. Second pump source; 3. Fiber combiner; 4. Beam shaping system; 5. Mirror; 6. First gain medium; 7. Second gain medium; 8. Polarizer; 9. Quarter-wave plate; 10. Q switch; 11. Output mirror. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] The following is combined with Figures 1-2 This invention describes a dual-gain dielectric Q-switched laser and a constant power pulse width modulation method.

[0021] This invention provides a dual-gain dielectric Q-switched laser, comprising: a first pump source 1, a second pump source 2, an optical fiber combiner 3, a beam shaping system 4, and a laser resonator.

[0022] The first pump source 1 is used to emit a first pump light with a wavelength of λ1; the second pump source 2 is used to emit a second pump light with a wavelength of λ2, and λ1≠λ2; both the first pump source 1 and the second pump source 2 are fiber-coupled lasers; the output ends of both the first pump source 1 and the second pump source 2 are connected to the fiber combiner 3, which is used to couple the first pump light and the second pump light into a coaxial beam for emission; the beam shaping system 4 is set along the optical path direction on the output side of the fiber combiner 3, and the beam shaping system 4 is used to shape the coaxial pump light output by the fiber combiner 3 into a spot size that matches the laser mode size of the resonant cavity.

[0023] The laser resonant cavity is located on the output side of the beam shaping system 4. The laser resonant cavity includes a mirror 5, a first gain medium 6, a second gain medium 7, a polarizer 8, a quarter-wave plate 9, a Q switch 10, and an output mirror 11 arranged in sequence. The first gain medium 6 is used to absorb the first pump light and does not absorb or absorbs the second pump light very weakly. The second gain medium 7 is used to absorb the second pump light. The first gain medium 6 and the second gain medium 7 have the same laser emission wavelength, but their stimulated emission cross sections are different. The pump power of the first pump source 1 and the second pump source 2 can be independently controlled. By adjusting the power ratio of the two pump sources, the laser pulse width can be adjusted in real time while maintaining a constant output laser power.

[0024] As can be seen from the above scheme, on the one hand, the present invention couples the non-coaxial beam of the dual pump sources into a coaxial beam through the fiber combiner 3, ensuring that the pump light is synchronously and accurately incident on the dual-gain medium; the beam shaping system 4 further shapes the coaxial pump light into a spot size that matches the laser mode size of the resonant cavity, significantly improving the energy conversion efficiency; at the same time, the dual-gain medium and the dual pump sources are integrated into a single laser resonant cavity through the fiber combiner 3, eliminating the need for splicing multiple independent lasers. Compared with traditional technologies, the system structure is more compact, occupies less space, and has lower deployment costs.

[0025] On the other hand, this invention achieves adjustable laser pulse width by setting two pump sources and two gain media with the same emission wavelength but different stimulated emission cross sections within the resonant cavity. The first gain medium 6 absorbs the first pump light and does not absorb or only weakly absorbs the second pump light. The second gain medium 7 absorbs the second pump light, and the difference in stimulated emission cross sections between the two directly determines the photon emission rate. A medium with a larger cross section emits photons faster, corresponding to a narrower pulse width; a medium with a smaller cross section emits photons slower, corresponding to a wider pulse width. During operation, pulse width adjustment can be achieved simply by changing the operating current of the first pump source 1 and the second pump source 2, without changing any optical components or mechanical structures. The operation is extremely simple and easy to implement computer program control and automation. Specifically... By independently adjusting the power ratio of the two pump sources, the total excitation energy of the dual-gain medium is kept stable. For example, when the power of the first pump source 1 (corresponding to the low-section medium) is increased while the power of the second pump source 2 (corresponding to the high-section medium) is decreased, the low-section medium dominates in energy accumulation and release, resulting in a laser with a wider pulse width. Conversely, when the power of the second pump source 2 is increased while the power of the first pump source 1 is decreased, the high-section medium dominates, resulting in a laser with a narrower pulse width. Throughout the adjustment process, the average power of the final emitted laser remains constant, ultimately achieving real-time and continuous adjustment of the laser pulse width without the need to replace optical components or mechanical structures, adapting to diverse needs in industrial processing, spectral analysis, and other scenarios. Furthermore, the dual-gain medium Q-switched laser only changes the pump power ratio when adjusting the pulse width, avoiding drastic fluctuations in the laser mode and ensuring output beam quality and long-term operational stability.

[0026] In some embodiments, the beam shaping system 4 includes, in sequence along the optical path, a first lens and a second lens. The first lens has a first focal length f1 for receiving and collimating the diverging beam from the pump source. The second lens has a second focal length f2 for focusing the collimated beam. The beam shaping system 4 amplifies the input pump spot by a ratio of 1:M, where M is the ratio of the second focal length f2 to the first focal length f1, i.e., M = f2 / f1.

[0027] It should be noted that the first lens and the second lens include, but are not limited to, either spherical lenses or aspherical lenses.

[0028] In this embodiment, the reflector 5 is highly transparent to the first pump light and the second pump light, and highly reflective to the laser emitted by the first gain medium 6 and the second gain medium 7; the output mirror 11 partially transmits the laser.

[0029] In some embodiments, the first gain medium 6 and the second gain medium 7 have high transmittance to the first pump light, the second pump light, and the laser in the resonant cavity. For example, the first gain medium 6 is an Nd:YAG crystal, and the second gain medium 7 is an Nd:YVO4 crystal. The stimulated emission cross section of the Nd:YAG crystal is smaller than that of the Nd:YVO4 crystal. The medium with the smaller stimulated emission cross section dominates the wide pulse width output, and the medium with the larger cross section dominates the narrow pulse width output. The first pump source 1 emits a first pump light with a wavelength of 808 nm, and the second pump source 2 emits a second pump light with a wavelength of 878 nm. The laser wavelength emitted by the two gain media is consistent, such as 1064 nm, and the transmittance of the output mirror 11 for the 1064 nm laser is 40%.

[0030] Furthermore, the first gain medium 6 and the second gain medium 7 are bonded or placed close together. This significantly reduces the axial dimension of the laser resonator, making the structure compact, especially suitable for volume-sensitive applications such as industrial processing and portable devices. At the same time, the coaxial beam coupled by the dual pump sources through the fiber combiner 3 is shaped by the beam shaping system 4. The compact placement of the dual gain media ensures that the pump spot does not change drastically over a short transmission distance, and can be adapted to the laser mode size at the first gain medium 6 and the second gain medium 7 respectively.

[0031] In this embodiment, the front and rear positions of the quarter-wave plate 9 and the Q switch 10 in the optical path can be interchanged. The quarter-wave plate 9 and the Q switch 10 work together to adjust the intracavity loss. Optionally, the Q switch 10 is an electro-optic modulator, for example, the Q switch 10 is a BBO crystal.

[0032] In this embodiment, the polarizer 8 includes, but is not limited to, any one of a thin-film polarizer or a polarizing beam splitter, and is used to filter laser light with a specific polarization state. For example... Figure 1 As shown, polarizer 8 is used to filter s-polarized light; as Figure 2 As shown, polarizer 8 is used to filter p-polarized light.

[0033] Specifically, polarizer 8 is a thin-film polarizer, which is small in size and thin in thickness, and does not require a lot of extra space. It can further reduce the overall size of the laser. Polarizer 8 has a reflectivity of ≥99.8% for s-polarized laser and a transmittance of ≥99% for p-polarized laser.

[0034] This invention also provides a constant power pulse width modulation method, using the aforementioned dual-gain dielectric Q-switched laser, comprising the following steps: Step S1: When the first pump source 1 is working alone, adjust the power of the first pump source 1 from the minimum to the maximum rated value, and record the output power range P1 of the laser; Step S2: When the second pump source 2 is working alone, adjust the power of the second pump source 2 from the minimum to the maximum rated value, and record the output power range P2 of the laser; Step S3: Take the intersection P of P1 and P2, and select a target value from it as the constant output power value; Step S4: Simultaneously turn on the first pump source 1 and the second pump source 2. In the initial state, set the initial pump power of the first pump source 1 and the initial pump power of the second pump source 2 so that the laser power emitted from the laser resonator is equal to the target value. Step S5: Synchronously adjust the pump power of the two pump sources, so that the pump power of one increases while the pump power of the other decreases accordingly, monitor and maintain the laser output power of the laser at a constant output power value in real time, and realize the adjustment of the constant power pulse width of the emitted laser.

[0035] The constant power pulse width modulation method based on the above-mentioned dual-gain dielectric Q-switched laser has the following advantages: 1. By controlling the pump ratio of the first pump source 1 and the second pump source 2, the energy can be mainly converted from which gain medium. By utilizing the combined effect of the first gain medium 6 and the second gain medium 7, pulsed laser with an adjustable range of tens of nanoseconds can be obtained.

[0036] 2. It is simple to control and highly flexible. The pulse width can be adjusted by simply changing the operating current of the first pump source 1 and the second pump source 2. No optical components or mechanical structures need to be changed. The operation is extremely simple and easy to achieve computer program control and automation.

[0037] 3. The two gain media are bonded or placed close together, and the corresponding pump sources are coupled through fiber combiner 3. During the adjustment process, the intracavity laser mode will not change drastically, ensuring the long-term stability of output power and beam quality.

[0038] 4. The structure is compact. Compared with building multiple lasers or using complex external pulse broadening devices, this invention achieves pulse width adjustment in a single resonant cavity, resulting in high system integration, lower cost, and greater market competitiveness.

[0039] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "method," "specific method," or "some methods," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or method is included in at least one embodiment or method of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or method. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or methods. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or methods described in this specification, as well as the features of different embodiments or methods.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-gain dielectric Q-switched laser, characterized in that, include: The first pump source (1) is used to emit the first pump light with a wavelength of λ1; The second pump source (2) is used to emit a second pump light with a wavelength of λ2, and λ1≠λ2. The pump power of the first pump source (1) and the second pump source (2) are controlled independently. Both the first pump source (1) and the second pump source (2) are fiber-coupled lasers. The fiber optic combiner (3) is used to couple the first pump light and the second pump light into a coaxial beam for emission. The output ends of the first pump source (1) and the second pump source (2) are both connected to the fiber optic combiner (3). A beam shaping system (4) is disposed on the output side of the fiber combiner (3) along the optical path direction. The beam shaping system (4) is used to shape the coaxial pump light output by the fiber combiner (3) to a size that matches the resonant cavity laser mode. A laser resonant cavity is disposed on the output side of the beam shaping system (4). The laser resonant cavity includes a mirror (5), a first gain medium (6), a second gain medium (7), a polarizer (8), a quarter-wave plate (9), a Q switch (10), and an output mirror (11) arranged in sequence. The first gain medium (6) is used to absorb the first pump light, and the second gain medium (7) is used to absorb the second pump light. The first gain medium (6) and the second gain medium (7) have the same laser emission wavelength, and their stimulated emission cross sections are different. By adjusting the power ratio of the two pump sources, the laser pulse width can be adjusted in real time while maintaining a constant output laser power.

2. The dual-gain dielectric Q-switched laser according to claim 1, characterized in that, The reflector (5) is highly transparent to the first pump light and the second pump light, and highly reflective to the laser emitted by the first gain medium (6) and the second gain medium (7).

3. The dual-gain dielectric Q-switched laser according to claim 1, characterized in that, The first gain medium (6) and the second gain medium (7) are highly transparent to the first pump light, the second pump light and the laser in the laser resonator.

4. The dual-gain dielectric Q-switched laser according to claim 1, characterized in that, The positions of the quarter-wave plate (9) and the Q switch (10) in the optical path can be interchanged.

5. The dual-gain dielectric Q-switched laser according to claim 4, characterized in that, The Q switch (10) is an electro-optic modulator.

6. The dual-gain dielectric Q-switched laser according to any one of claims 1-5, characterized in that, The polarizer (8) is used to filter s-polarized light or p-polarized light.

7. The dual-gain dielectric Q-switched laser according to claim 6, characterized in that, The polarizer (8) includes any one of a thin-film polarizer or a polarizing beam splitter.

8. The dual-gain dielectric Q-switched laser according to any one of claims 1-5, characterized in that, The first gain medium (6) is bonded to or placed close to the second gain medium (7).

9. A constant power pulse width adjustment method, characterized in that, The method of using a dual-gain dielectric Q-switched laser as described in any one of claims 1-8 includes the following steps: When the first pump source (1) works alone, the power of the first pump source (1) is adjusted from the minimum to the maximum rated value, and the output power range P1 of the laser is recorded. When the second pump source (2) works alone, the power of the second pump source (2) is adjusted from the minimum to the maximum rated value, and the output power range P2 of the laser is recorded. Take the intersection P of P1 and P2, and select a target value from it as the constant output power value; Simultaneously turn on the first pump source (1) and the second pump source (2), and set the initial pump power of the first pump source (1) and the initial pump power of the second pump source (2) in the initial state so that the laser power emitted by the laser resonator is equal to the target value; The pump power of the two pump sources is synchronously adjusted so that the pump power of one increases while the pump power of the other decreases accordingly. The laser output power of the laser is monitored in real time and maintained at the constant output power value, thereby achieving the adjustment of the constant power pulse width of the emitted laser.

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