MJ-level pulse laser generating device

Abstract

The invention discloses an mJ-level pulse laser generating device which comprises a pump laser, a collimating mirror, a focusing mirror, an input mirror, a gain medium and an output mirror which are sequentially arranged, the pump laser outputs divergent pump laser, the collimating mirror converts the divergent pump laser into collimated laser, the focusing mirror converts the collimated laser into focused laser, and the output mirror outputs the focused laser. The focused laser is transmitted to the gain medium through the input mirror, and the gain medium amplifies the focused laser to obtain an amplified laser beam; the gain medium is a crystal doped with rare earth ions; one surface, facing the gain medium, of the output mirror is dispensed with an anti-saturation absorption material comprising a ground state energy level, an excited state energy level and a higher state energy level, a band gap between the excited state energy level and the ground state energy level is zero, and a band gap smaller than target energy exists between the excited state energy level and the higher state energy level; and the output mirror outputs target energy pulse laser generated based on a passive Q-switching mode of an anti-saturated absorption material. According to the scheme, the anti-saturation absorption material and the proper gain medium are combined, so that the generation of large-energy pulses is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy pulse, and particularly relates to an mJ-level pulsed laser generating device. Background Art

[0002] Pulsed lasers, especially high-energy pulsed lasers, have important applications in information transmission, laser shock peening, etc. At present, obtaining high-energy pulsed lasers is mainly achieved through pulsed laser amplification. The seed laser for single-pulse laser amplification plays a decisive role in the overall amplification effect. If the seed laser can reach higher energy, the overall amplification level and complexity can be reduced in subsequent amplification. Moreover, during the amplification process, the shape of the pulse may also change. Therefore, directly generating a high-energy pulsed laser light source is very important. The pulse energy depends on the average output power of the laser on the one hand and the pulse repetition frequency of the laser on the other hand. In terms of increasing the average output power, the main methods include improving the efficiency of the pump laser, increasing the gain of the gain medium, and improving the heat dissipation of the gain medium. In terms of reducing the repetition frequency of the laser, there are mainly active modulation devices (acousto-optic Q-switching, electro-optic Q-switching, etc.) based on low repetition frequencies or crystals doped with rare-earth ions with high saturation flux as absorbers of the passive Q-switching system. Among them, the Q-value represents the loss of the laser and is an important method for generating pulsed lasers. The Q-switching method can obtain a narrower pulse width and higher peak power compared with electrical control, and has a lower repetition frequency compared with mode-locked lasers. However, currently, the repetition frequency of the pulsed lasers obtained by various Q-switching methods is usually in the kHz order of magnitude, and the obtained pulse energy is usually in the μJ or even nJ order of magnitude, and the single-pulse energy of the current high-energy lasers rarely reaches the mJ order of magnitude.

[0003] Therefore, providing a device and method that can generate pulsed lasers of the mJ order of magnitude is a technical problem that urgently needs to be solved. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide an mJ-level pulsed laser generating device, which solves the problem of the relatively low order of magnitude of the pulse energy in the prior art.

[0005] The present application discloses an mJ-level pulsed laser generating device, which includes a pump laser, a collimating mirror, a focusing mirror, an input mirror, a gain medium, and an output mirror arranged in sequence. The pump laser is used to output divergent pump laser with divergent characteristics. The collimating mirror is used to convert the divergent pump laser into collimated laser. The focusing mirror is used to convert the collimated laser into focused laser. The focused laser is transmitted to the gain medium through the input mirror. The gain medium is used to amplify the focused laser to obtain an amplified laser beam. Among them, target coatings are provided on two opposite side surfaces of the input mirror. The target coating opposite to the focusing mirror has a target transmittance for the focused laser, and the target coating opposite to the gain medium has a target reflectivity for the amplified laser beam. The gain medium is a crystal doped with Cr 3+ ions. An anti-saturation absorption material is drop-coated on the surface of the output mirror facing the gain medium. The anti-saturation absorption material includes a ground state energy level, an excited state energy level, and a higher state energy level. The band gap between the ground state energy level and the excited state energy level is zero. There is a band gap less than the target energy between the excited state energy level and the higher state energy level, showing a second-order saturation characteristic. The output mirror is used to output target energy pulsed laser generated by the passive Q-switching method based on the anti-saturation absorption material.

[0006] In some embodiments, there is a band gap of 1 eV target energy between the excited state energy level and the higher state energy level.

[0007] In some embodiments, the anti-saturation absorption material is a HfTe 2 two-dimensional material.

[0008] In some embodiments, the collimating mirror is a plano-convex lens, including a collimating mirror plane and a collimating mirror convex surface. The focusing mirror is a plano-convex lens, including a focusing mirror plane and a focusing mirror convex surface. The collimating mirror convex surface is opposite to the focusing mirror convex surface.

[0009] In some embodiments, the input mirror is configured as a plano-plano lens with two planar sides or the input mirror is configured as a plano-concave lens with one planar side and one concave side. The concave side of the plano-concave lens faces the gain medium. The output mirror is configured as a plano-plano lens.

[0010] In some embodiments, the pump laser is a semiconductor laser emitting at a wavelength of 638 nm. The gain medium is a chrysoberyl crystal with a target Cr 3+ ion doping concentration. The wavelength of the target energy pulsed laser output by the output mirror is 755 nm, and the pulse energy is greater than 10 mJ.

[0011] In some embodiments, both the pump laser and the gain medium are cooled by water cooling.

[0012] In some embodiments, the pump laser is a semiconductor laser emitting at a wavelength of 976 nm, the gain medium is a Yb:YAG crystal, and the target energy pulsed laser output by the output mirror has a wavelength of 1064 nm and a pulse energy greater than 10 mJ.

[0013] In some embodiments, the pump laser is cooled by air cooling, and the gain medium is cooled by water cooling.

[0014] In some embodiments, an etalon is further disposed between the pump laser and the collimating mirror, and the etalon is used to tune the laser wavelength emitted by the pump laser.

[0015] The present invention includes but is not limited to the following beneficial effects: (1) By combining an anti-saturable absorption material and a suitable gain medium, this solution realizes the generation of high-energy pulses; (2) The target coating design on the input mirror ensures that the focused laser enters the gain medium with a target transmittance, further improving the efficiency of laser amplification; (3) The specific coating design on the input mirror enables the focused laser to be effectively transmitted to the gain medium, and at the same time, the amplified laser beam can also be efficiently reflected. Such a design helps to improve the energy conversion efficiency and reduce energy loss; (4) Using a crystal doped with Cr 3+ ions as the gain medium, Cr ions have good laser working characteristics and can achieve efficient laser amplification in a variety of wavelength ranges; (5) The bandgap between the ground state and the excited state of the anti-saturable absorption material is zero, while there is a bandgap with a target energy between the excited state and the higher state. This design helps to achieve oversaturation of the ground state energy level and saturation of the excited state energy level, achieving the effect of secondary saturation and increasing the saturation intensity of the absorber; (6) This solution generates a pulsed laser with a target energy based on the passive Q-switching method of the anti-saturable absorption material. Since the generation of the passive Q-switched pulsed laser does not depend on an external modulator, the entire system can be more stable, reducing fluctuations caused by external factors. At the same time, by changing the characteristics of the gain medium or the anti-saturable absorption material, the parameters of the pulsed laser can be adjusted, improving the flexibility of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art.

[0017] Figure 1 is the schematic diagram of the anti-saturable absorption of the anti-saturable absorption material in the embodiment of the present invention;

[0018] Figure 2 is the structural schematic diagram of the mJ-level pulsed laser generating device in the embodiment of the present invention;

[0019] Figure 3is the energy band structure and electron density of states diagram of the HfTe material in the embodiments of the present invention 2 ;

[0020] Figure 4 is a schematic diagram of the pulse sequence and pulse shape of the mJ-level pulsed laser output in the embodiments of the present invention

[0021] In the figure, 1 is a pump laser, 2 is a collimating mirror, 3 is a focusing mirror, 4 is an input mirror, 5 is a gain medium, and 6 is an output mirror Specific Embodiments

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention

[0023] Specifically, as shown in Figure 2 , a device for generating an mJ-level pulsed laser is disclosed. The device includes a pump laser 1, a collimating mirror 2, a focusing mirror 3, an input mirror 4, a gain medium 5, and an output mirror 6 arranged in sequence. The pump laser is used to output divergent pump laser with divergent characteristics. The collimating mirror 2 is used to convert the divergent pump laser into collimated laser. The focusing mirror 3 is used to convert the collimated laser into focused laser. The focused laser is transmitted to the gain medium 5 through the input mirror 4. The gain medium 5 is used to amplify the focused laser to obtain an amplified laser beam. Among them, the two opposite sides of the input mirror 4 have target coatings. The target coating opposite to the focusing mirror 3 has a transmittance of greater than 99% for the focused laser, and the target coating opposite to the gain medium 5 has a transmittance of greater than 99% for the target laser beam. The gain medium 5 is a crystal doped with Cr 3+ ions; an anti-saturation absorption material is drop-coated on the side of the output mirror 6 facing the gain medium 5. The anti-saturation absorption material includes a ground state energy level, an excited state energy level, and higher state energy levels. The band gap between the ground state energy level and the excited state energy level is zero, and there is a band gap less than the target energy between the excited state energy level and the higher state energy levels, showing a second-order saturation characteristic. The output mirror 6 is used to output a target energy higher than 10 mJ generated by the passive Q-switching method based on the anti-saturation absorption material

[0024] It should be noted that the ground state refers to the state in which an atom is in the lowest energy level under normal conditions, and at this time, the electrons move in the orbit closest to the nucleus. The ground state and the excited state are two important concepts describing the electronic state of an atom or molecule. The ground state refers to the stable state of an atom or molecule with the lowest energy under normal conditions, and at this time, the arrangement of electrons follows the Fermi-Dirac distribution and the Pauli exclusion principle. The excited state refers to the state in which an atom or molecule absorbs a certain amount of energy and the electrons are excited to a higher energy level but not ionized

[0025] Electrons in an atom are arranged in such a way that they always occupy energy levels with lower energy as much as possible, and only a certain number of electrons can be accommodated in each energy level. This arrangement makes the atom in the most stable state. Specifically, electrons fill the energy levels in ascending order of the principal quantum number. Under each principal quantum number, electrons first fill the energy levels with smaller angular quantum numbers, such as the s energy level, and then fill the energy levels with larger angular quantum numbers, such as p, d, f, etc. When the number of electrons in a certain energy level reaches its maximum capacity, electrons will start to fill the next energy level. From the perspective of energy states, the main difference between the ground state and the excited state lies in their energy levels. The ground state is the stable state of an atom or molecule with the lowest energy, while the excited state is the state where an atom or molecule absorbs energy and transitions to a higher energy state. This change in energy can be calculated through quantum mechanics. If the energy of a molecule or atom is higher than the ground state energy, then it is in the excited state.

[0026] Further, the dropping step of dropping the reverse saturable absorption material on the side of the output mirror 6 facing the gain medium 5 can be as follows: Take 5 mg of HfTe 2 two-dimensional material powder and place it in a 10 mL centrifuge tube, and fill the centrifuge tube with alcohol. The centrifuge tube containing the HfTe 2 powder and alcohol is placed in an ultrasonic cleaner and ultrasonically treated for 12 hours. The ultrasonic vibration is used to separate out the monolayer HfTe 2 mixed solution. The ultrasonically treated mixed solution is placed in a centrifuge for centrifugation to remove large particles in the solution, and the supernatant is removed and placed in a new centrifuge tube for centrifugation again. The solution after the second centrifugation is dropped on the output mirror 6 and dried at room temperature for 12 hours to obtain the output mirror 6 coated with HfTe 2 two-dimensional material.

[0027] Specifically, the energy level relationships of the reverse saturable absorption material are as Figure 1 shown. In one example, the saturable absorption material can be HfTe 2 two-dimensional material, as Figure 3 shown. Figure 3 is a schematic diagram of the energy band structure (left) and electron density of states (right) of HfTe 2 two-dimensional material. Among them, the gap between the excited state and the ground state is 0 eV, so it is easier for ground state electrons to transition to the excited state. And there is a 1 eV band gap between the excited state and the higher state, so the process of electrons in the higher state spontaneously transitioning to the excited state is blocked and the process is slower. Specifically, the saturable process of the reverse saturable absorption material includes: When a laser is incident on HfTe 2On the surface of two-dimensional materials, if the photon energy of the laser is greater than the bandgap between the ground state and the excited state, electrons in the ground state can be excited to the excited state, and the laser is absorbed. According to the Pauli exclusion principle, each position in the excited state can only accommodate one excited electron. Therefore, when enough electrons occupy the positions in the excited state, the excited state cannot accommodate more electrons. At this time, HfTe 2 two-dimensional materials no longer absorb the laser, that is, the absorber reaches saturation. At this time, the laser can pass through HfTe more 2 two-dimensional materials, that is, under the excitation of high-energy laser, HfTe 2 The phenomenon that the absorption rate of two-dimensional materials gradually increases is called saturated absorption. During this process, the particles in the excited state will also spontaneously transition from the excited state to the ground state, but the speed of this process is slower than the excitation speed. The reverse saturated absorption process is as follows: when enough particles are accumulated in the excited state, if the energy of the pump laser is greater than the energy between the excited state and the higher state, the electrons in the excited state can be excited to transition to a higher energy level again, that is, HfTe 2 two-dimensional materials' secondary absorption of the laser. At this time, HfTe 2 the absorption rate of two-dimensional materials to the laser increases again, so this process is called reverse saturated absorption, also known as secondary absorption. Since the electrons in the excited state are depleted during the secondary absorption process, a certain amount of energy is still needed to maintain the saturation of the excited state. Therefore, the secondary absorption requires higher energy to reach saturation, and the material has a higher saturation flux. Thus, based on the reverse saturated absorption material of this solution, after the laser starts to work, the reverse saturated absorption material absorbs the laser energy to reach secondary saturation, and the energy in the laser cavity will accumulate more. The instant release of the accumulated energy will be greater, thus generating a high-energy laser pulse with a high peak value. Exemplarily, the pulse sequence and pulse shape of the obtained high-energy laser pulse are as Figure 4 shown. Among them, the pulse repetition frequency is 262 Hz, the pulse width is 454 ns. The corresponding high-energy laser pulse is 5.8 mJ.

[0028] It can be understood that this solution realizes the generation of high-energy pulses by combining a reverse saturated absorption material and a suitable gain medium; moreover, the target coating design on the input mirror ensures that the focused laser enters the gain medium with a target transmittance, improving the efficiency of laser amplification; in addition, the specific coating design on the input mirror enables the focused laser to be effectively transmitted to the gain medium, and at the same time, the amplified laser beam can also be efficiently reflected. Such a design helps to improve the energy conversion efficiency and reduce energy loss; further, using a crystal doped with Cr 3+ ions as the gain medium, Cr 3+Ions have good laser operating characteristics and can achieve efficient laser amplification within a variety of wavelength ranges; further, the bandgap between the ground state and the excited state of the reverse saturable absorption material is zero, while there is a bandgap less than the target energy between the excited state and higher states. This design helps to achieve supersaturation of the ground state energy level and saturation of the excited state energy level, reaching the effect of secondary saturation and increasing the saturation intensity of the absorber; further, this solution generates pulsed laser with the target energy based on the passive Q-switching method of the reverse saturable absorption material. Since the generation of the passive Q-switched pulsed laser does not depend on an external modulator, the entire system can be more stable, reducing fluctuations caused by external factors. At the same time, by changing the characteristics of the gain medium or the reverse saturable absorption material, the parameters of the pulsed laser can be adjusted, improving the flexibility of the system.

[0029] In some embodiments, the collimating mirror 2 is a plano-convex lens, including a collimating mirror plane and a collimating mirror convex surface, the focusing mirror 3 is a plano-convex lens, including a focusing mirror plane and a focusing mirror convex surface, and the collimating mirror convex surface faces the focusing mirror convex surface.

[0030] In some embodiments, the input mirror 4 is configured as a plano-plano lens with two flat surfaces or the input mirror 4 is configured as a plano-concave lens with one flat surface and one concave surface, and the concave surface of the plano-concave lens faces the gain medium 5, and the output mirror 6 is configured as a plano-plano lens.

[0031] It can be understood that the gain medium 5 matched with materials such as reverse saturable absorption material HfTe 2 Two-dimensional materials and other materials is also very important. Since high-energy pulsed lasers require the gain medium 5 to store more energy, the gain medium 5 requires a wider laser upper energy level, and the gain medium 5 needs to emit photons of a suitable wavelength (wavelength corresponds to energy, and suitable energy is required), so that the transition position satisfies the bandgap from the ground state to the excited state and higher states. And the gain medium 5 also needs to have strong enough gain to emit enough photons to saturate the two-dimensional material. To reduce the thermal effect in the gain medium 5 and increase the pump power, it is required that the pump laser and the emitted laser have similar wavelengths. To sum up, the gain medium 5 in this solution can be a laser crystal doped with Cr 3+ Ions, wherein the laser crystal with Cr composition emits wavelengths from visible light to below 800 nm. Exemplarily, the gain medium 5 can be chrysoberyl or titanium sapphire. In one example, the gain medium 5 can also be a laser crystal with Yb composition, such as Yb:YAG or Yb:YAP.

[0032] In some embodiments, the pump laser 1 selects a semiconductor laser emitting at a wavelength of 638 nm, and the gain medium 5 selects a target Cr 3+The chrysoberyl crystal with an ion doping concentration, the wavelength of the target energy pulsed laser output by the output mirror 6 is 755 nm, and the pulse energy is greater than 10 mJ. Preferably, the concentration of Cr can be 0.2-2 at.%, and both the pump laser and the gain medium 5 are cooled by water cooling.

[0033] In some embodiments, the pump laser 1 can emit a semiconductor laser with a wavelength of 976 nm, the gain medium 5 can be a Yb:YAG crystal (ytterbium-doped yttrium aluminum garnet), the wavelength of the target energy pulsed laser output by the output mirror 6 is 1064 nm, the pulse energy is greater than 10 mJ, the pump laser is cooled by air cooling, and the gain medium 5 is cooled by water cooling.

[0034] In some embodiments, an etalon is further provided between the pump laser 1 and the collimating mirror 2, and the etalon is used to tune the laser wavelength emitted by the pump laser 1.

[0035] Furthermore, in another example, a large-energy vortex pulsed laser or a high-order mode pulsed laser can also be generated by methods such as ring optical pumping, oblique pumping, and cavity mirror etching. The reverse saturable absorption material is not limited to HfTe 2 Two-dimensional materials, and two-dimensional materials with other similar energy levels can also be used to generate large-energy pulsed lasers.

[0036] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A mJ-level pulse laser generating device, characterized in that: The device comprises a pump laser (1), a collimator (2), a focusing mirror (3), an input mirror (4), a gain medium (5) and an output mirror (6) which are arranged in sequence. The pump laser is used to output a divergent pump laser with divergent characteristics. The collimator (2) is used to convert the divergent pump laser into a collimated laser. The focusing mirror (3) is used to convert the collimated laser into a focused laser. The focused laser is transmitted to the gain medium (5) through the input mirror (4). The gain medium (5) is used to amplify the focused laser to obtain an amplified laser beam. The input mirror (4) has target coatings on two opposite sides. The target coating opposite to the focusing mirror (3) has a target transmittance for the focused laser. The target coating opposite to the gain medium (5) has a target reflectance for the amplified laser beam. The gain medium (5) is Cr-doped. 3+ ion crystal; the output mirror (6) is drop-coated with an anti-saturation absorption material on one side facing the gain medium (5); the anti-saturation absorption material has a ground state energy level, an excited state energy level and a higher state energy level; the band gap between the ground state energy level and the excited state energy level is zero; there is a band gap between the excited state energy level and the higher state energy level that is smaller than the target energy, showing a secondary saturation characteristic; the output mirror (6) is used to output a target energy pulse laser generated by a passive Q-switching method based on the anti-saturation absorption material.

2. The pulse laser generating device according to claim 1, characterized in that: There is a band gap of 1 eV target energy between the excited state energy level and the higher state energy level.

3. The mJ-level pulse laser generator according to claim 1, characterized in that: The anti-saturation absorption material is HfTe2 two-dimensional material.

4. The mJ-level pulse laser generator according to claim 1, characterized in that: The collimating lens (2) is a plano-convex lens, comprising a collimating lens plane and a collimating lens convex surface; the focusing lens (3) is a plano-convex lens, comprising a focusing lens plane and a focusing lens convex surface; the collimating lens convex surface is opposite to the focusing lens convex surface.

5. The mJ-level pulse laser generator according to claim 1, characterized in that: The input mirror (4) is constructed as a double-sided plano-planar lens or a plano-concave lens with one side being planar and the other side being concave, the concave surface of the plano-concave lens facing the gain medium (5), and the output mirror (6) is constructed as a plano-planar lens.

6. The mJ-level pulse laser generator according to claim 1, characterized in that: The pump laser (1) is a semiconductor laser with an emission wavelength of 638 nm, and the gain medium (5) has a target Cr 3+ The output mirror (6) outputs a target energy pulse laser with a wavelength of 755 nm and a pulse energy greater than 10 mJ.

7. The mJ-level pulse laser generator according to claim 6, characterized in that: The pump laser and the gain medium (5) both dissipate heat through water cooling.

8. The mJ-level pulse laser generator according to claim 1, characterized in that: The pump laser (1) is a semiconductor laser with an emission wavelength of 976 nm, the gain medium (5) is a Yb:YAG crystal, and the wavelength of the target energy pulse laser output by the output mirror (6) is 1064 nm, and the pulse energy is greater than 10 mJ.

9. The mJ-level pulse laser generator according to claim 8, characterized in that: The pump laser is cooled by air, and the gain medium (5) is cooled by water.

10. The mJ-level pulse laser generator according to claim 6 or 8, characterized in that: An etalon is also provided between the pump laser (1) and the collimating mirror (2), and the etalon is used to tune the wavelength of the laser emitted by the pump laser (1).

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