Amplitude-frequency modulation suppression device in a laser system

Abstract

An amplitude-frequency modulation suppression device for a laser system includes a pre-stage laser amplifier, an intracavity spectral control module, an extracavity spectral control module, and a post-stage laser amplifier placed coaxially. The intracavity spectral control module includes an additional special coating combined with a Brewster angle birefringent crystal. The extracavity spectral control module includes a polarizer, an additional coating birefringent crystal, and an analyzer. By applying additional coatings to increase transmittance, the intracavity and extracavity spectral control modules can support spectral control capabilities with different bandwidths and morphologies. This invention can effectively achieve spectral control and amplitude-frequency effect suppression in high-power laser systems. Furthermore, this spectral control method features high flexibility, high stability, and high damage resistance, making it particularly suitable for high-power, high-energy broadband laser system applications.

Description

Technical Field

[0001] This invention relates to the field of solid-state laser broadband amplification technology, and in particular to an amplitude-frequency modulation suppression device in a laser system. Background Technology

[0002] In high-power laser devices, phase modulation is used to increase the laser spectral bandwidth, reduce stimulated Brillouin scattering (SBS) of large-aperture optical components in subsequent high-power systems, ensure the safe operation of large-aperture optical components, and suppress stimulated Raman scattering (SRS) during laser target ablation, thus improving beam homogenization. However, after introducing phase modulation to broaden the spectrum, the laser pulse time waveform is modulated due to the modulation of spectral phase and amplitude after injection into the subsequent laser amplifier; this is called amplitude-frequency modulation (AFM). AFM introduces fluctuations in the time waveform, which can jeopardize the safe operation of high-power systems. Therefore, it is necessary to take measures to control the AFM effect in the device.

[0003] High-power laser devices typically consist of an all-fiber front-end coupled with a series of multi-stage solid-state laser amplifiers. Each stage of the laser amplifier achieves a different gain, ultimately reaching maximum energy output. In subsequent solid-state laser amplifiers, the laser pulse undergoes different spectral amplitude modulations, a phenomenon known as gain narrowing. The preamplifier system in the laser device handles the largest gain, enabling laser amplification from nJ to J levels and providing flexible beam control. Controlling the spectral gain narrowing in the preamplifier system and ensuring spectral control capabilities in subsequent laser amplification stages are crucial for managing the amplitude-frequency effects throughout the system. Summary of the Invention

[0004] This invention provides an amplitude-frequency modulation suppression device for laser systems, which can effectively realize spectral control and amplitude-frequency effect suppression in high-power laser systems. Moreover, the spectral control method has the characteristics of high flexibility, high stability, and high damage resistance, and is especially suitable for high-power, high-energy broadband laser system applications.

[0005] The technical solution of the present invention is as follows:

[0006] An amplitude-frequency modulation suppression device in a laser system comprises two-stage spectral control units: an intracavity spectral control module located inside the pre-stage laser amplifier, and an extracavity spectral control module located at the output of the pre-stage laser and before the subsequent laser amplification link.

[0007] The aforementioned pre-stage laser amplifier and subsequent laser amplification link are spectral control objects and need to have a certain laser gain bandwidth amplification capability;

[0008] The aforementioned pre-amplifier has a spatial structure and incorporates an intracavity spectral control module. The laser pulse can pass through the spectral control module multiple times, and the number of times it passes through the laser gain medium is consistent with the number of times it passes through the module.

[0009] The laser gain module in the laser amplifier can use common broadband gain media, such as neodymium glass and Nd:CaF2.

[0010] The intracavity spectral control module includes an additional special film layer combined with a birefringent crystal, which is placed at Brewster angle;

[0011] The membrane layer of the intracavity spectral control module provides a special spectral transmittance T. brf1_coating (λ), the single-pass spectral transmittance after passing through the intracavity spectral control module is T. total =T BRF1 (t,θ,φ,λ)T brf1_coating (λ), where t is the thickness of the birefringent crystal, θ is the crystal pitch angle, φ is the crystal rotation angle, and λ is the wavelength of the signal light;

[0012] The intracavity spectral control module and the laser gain medium are positioned on one side of the polarization analyzer, and the laser pulse passes through the same number of paths in these two modules.

[0013] The extracavity spectral control module includes a polarizer, an additional birefringent crystal with a coating, and an analyzer, wherein the birefringent crystal is incident perpendicularly; the coating provides a specific spectral transmittance T. brf2_coating (λ), the total spectral transmittance after passing through the intracavity and extracavity spectral control modules is T. total =(T BRF1 T brf1_coating (λ)G) N (λ)T BRF2 T brf2_coating (λ) enables flexible management of the laser system spectrum, where G is the single-pass gain multiple of the laser amplifier and N is the number of times the laser amplification pulse passes through the laser gain medium.

[0014] The intracavity and extracavity spectral control modules can be customized according to specific applications by designing additional coating transmittance, and can support the realization of spectral control capabilities with different bandwidths and morphologies.

[0015] The polarizing beam splitter can be replaced with a common high-damage thin-film polarizer or other device with polarization detection capabilities.

[0016] The laser beam must be a single-polarized beam, i.e., P-polarized or S-polarized, through the spectral control module.

[0017] In addition, the present invention provides a spectral management method for suppressing amplitude-frequency modulation, comprising the following steps:

[0018] Step S1: Optimize the spectral transmittance of the intracavity spectral control module to enable it to compensate for the gain spectrum of the laser gain medium;

[0019] Step S2: Add the intracavity spectral control module to the pre-amplifier, and adjust the pitch angle θ and rotation angle φ of the spectral control module to make the gain spectrum of the pre-amplifier a near-flat-top spectral output.

[0020] Step S3: Optimize the spectral transmittance of the external cavity spectral control module to enable it to compensate for the gain spectrum of the laser gain medium;

[0021] Step S4: Add an external spectral control module between the pre-stage laser amplifier and the subsequent laser amplification link, and adjust the pitch angle θ and rotation angle φ of the spectral control module so that the output gain spectrum of the subsequent laser amplifier is a near-flat-top output.

[0022] Step S5: During the output monitoring test time waveform amplitude-frequency modulation, it can be observed that the amplitude-frequency modulation is significantly suppressed;

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] This invention utilizes a multi-level spectral control module to achieve spectral management of the entire laser amplification system, significantly suppressing time waveform amplitude-frequency modulation and ensuring the safe operation of high-power laser systems. This scheme features high flexibility, high stability, and high resistance to damage, and is particularly suitable for high-power, high-beam-quality broadband laser system applications. Attached Figure Description

[0025] Figure 1 This diagram illustrates the optical path of the spectral management and amplitude-frequency modulation suppression device in a laser system, including: 1. Pre-amplifier; 2. Gain medium in the pre-amplifier; 3. Intracavity spectral control module; 4. Extracavity spectral control module; 5. Post-amplifier laser amplification link.

[0026] Figure 2 The diagram below shows the external spectral control module in the device, which includes: 401, a polarizing beam splitter; 402, a birefringent spectral filter with a special coating; and 403, a polarizing beam splitter.

[0027] Figure 3 The flowchart shows the spectral management method for suppressing amplitude-frequency modulation in the device. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments and accompanying drawings. However, this should not be construed as limiting the scope of protection of the present invention.

[0029] Please refer to Figure 1 , Figure 1The present invention provides an amplitude-frequency modulation suppression device in a laser system, comprising a pre-stage laser amplifier 1, a laser gain module 2 and an intracavity spectral control module 3 located inside the pre-stage laser amplifier, and an extracavity spectral control module 4 located between laser 1 and laser 5.

[0030] The aforementioned pre-stage laser amplifier 1 and subsequent laser amplification link 5 are spectral control objects, possessing laser gain bandwidth amplification capabilities;

[0031] The aforementioned pre-stage laser amplifier 1 has a spatial structure and incorporates an intracavity spectral control module 3, allowing the laser pulse to pass through the spectral control module multiple times.

[0032] The laser gain modules in laser amplifiers 1 and 5 can use common broadband gain media, such as neodymium glass and Nd:CaF2.

[0033] The intracavity spectral control module 3 includes an additional special film layer combined with a birefringent crystal, which is placed at Brewster angle;

[0034] The membrane layer of the intracavity spectral control module 3 provides a special spectral transmittance T. brf1_coating (λ), the single-pass spectral transmittance after passing through the intracavity spectral control module is T. total =T BRF1 (t,θ,φ,λ)T brf1_coating (λ);

[0035] The intracavity spectral control module 3 and the laser gain medium 2 are located on the same side of the polarizer, and their positions can be interchanged. The number of passes of the laser pulse through these two modules is the same.

[0036] The extracavity spectral control module 4 includes a polarizer 401, an additional birefringent crystal 402 with an additional coating, and an analyzer 403. The birefringent crystal is incident perpendicularly; the coating provides a special spectral transmittance T. brf2_coating (λ), the total spectral transmittance after passing through the intracavity spectral control module 3 and the extracavity spectral control module 4 is T. total =(T BRF1 T brf1_coating (λ)G) N (λ)T BRF2 T brf2_coating (λ) enables flexible management of the laser system spectrum;

[0037] The intracavity spectral control module 3 and the extracavity spectral control module 4 can be customized according to specific applications by designing additional coating transmittance, and can support the realization of spectral control capabilities with different bandwidths and morphologies.

[0038] The polarizing beam splitters 401 and 403 can be replaced with common high-damage thin-film polarizers or other devices that have polarization detection capabilities.

[0039] The laser beam described above must be a single-polarized beam, i.e., P-polarized or S-polarized, through the spectral control modules 3 and 4.

[0040] Laser path: Along the laser input direction, the sequence is: pre-stage laser 1, laser gain module 2, external cavity spectral control module 3, external cavity spectral control module 4, and subsequent laser amplification link 5. The laser pulse is injected into the pre-stage laser amplifier. It then passes through laser gain module 2 for energy gain, followed by spectral management through internal cavity spectral control module 3. Next, the laser pulse travels multiple times within the laser cavity through laser gain medium 2 and internal cavity spectral control module 3. After spectral management, the output laser gain spectrum of laser amplifier 1 is near-flat-top, facilitating laser amplification and spectral control in subsequent laser amplifiers. The laser pulse then undergoes spectral perforation through external cavity spectral control module 4 to pre-compensate for the gain narrowing effect introduced by subsequent laser amplification link 5. Finally, the laser pulse is injected into subsequent laser amplification link 5 for further energy enhancement.

[0041] In addition, the present invention provides a spectral management method for suppressing amplitude-frequency modulation, comprising the following steps:

[0042] Step S1: Optimize the spectral transmittance of the intracavity spectral control module to enable it to compensate for the gain spectrum of the laser gain medium;

[0043] Step S2: Add the intracavity spectral control module to the pre-amplifier, and adjust the pitch angle θ and rotation angle φ of the spectral control module to make the gain spectrum of the pre-amplifier a near-flat-top spectral output.

[0044] Step S3: Optimize the spectral transmittance of the external cavity spectral control module to enable it to compensate for the gain spectrum of the laser gain medium;

[0045] Step S4: Add an external spectral control module between the preamplifier and the subsequent amplification link, and adjust the pitch angle θ and rotation angle φ of the spectral control module so that the output gain spectrum of the subsequent laser amplifier is a near-flat-top output.

[0046] Step S5: During the output monitoring test time waveform amplitude-frequency modulation, it can be observed that the amplitude-frequency modulation is significantly suppressed;

[0047] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An amplitude-frequency modulation suppression device in a laser system, characterized in that, It includes a pre-stage laser amplifier, an extracavity spectral control module, and a post-stage laser amplifier, which are placed in sequence. The aforementioned pre-stage laser amplifier and post-stage laser amplifier serve as spectral control objects, used for laser gain bandwidth amplification; The preamplifier has a spatial structure and incorporates a laser gain medium and an intracavity spectral control module, thereby allowing the incident laser pulse to travel back and forth between the gain medium and the intracavity spectral control module multiple times. The intracavity spectral control module includes an additional special film layer that provides a special spectral transmittance and a birefringent crystal placed at Brewster's angle. The spectral transmittance of the birefringent crystal can be compensated with the gain spectrum of the laser gain medium to obtain a near-flat-top spectrum. The extracavity spectral control module includes a polarizer, an additional birefringent crystal, and an analyzer arranged sequentially along the optical axis. The spectral transmittance of the additional birefringent crystal can compensate for the gain spectrum of the gain medium in the subsequent laser amplifier. Single-pass spectral transmission via the intracavity spectral control module Where t is the thickness of the birefringent crystal. The pitch angle of the crystal. λ is the crystal rotation angle, and λ is the wavelength of the signal light. The spectral transmittance of the additional special film layer; The total spectral transmittance after passing through the intracavity spectral control module and the extracavity spectral control module Where G is the single-pass gain of the laser amplifier, and N is the number of times the laser amplification pulse passes through the laser gain medium; The spectral transmittance of the additional film layer; The laser pulses output from the pre-stage laser amplifier undergo spectral perforation via an external cavity spectral control module to pre-compensate for the gain narrowing effect introduced by the subsequent laser amplifier.

2. The amplitude-frequency modulation suppression device in a laser system according to claim 1, characterized in that, The additional birefringent crystal is a birefringent quartz crystal or a birefringent Iceland spar crystal, and the incident angle of the birefringent crystal in the external spectral control module is set to 90°. .

3. The amplitude-frequency modulation suppression device in a laser system according to claim 1, characterized in that, Adjust the pitch and rotation angles of the birefringent crystal in the intracavity spectral control module to make the output gain spectrum of the pre-stage laser amplifier a near-flat-top spectrum; Adjust the pitch and rotation angles of the birefringent crystal in the external cavity spectral control module to make the output gain spectrum of the subsequent laser amplifier near-flat-top output.

4. The amplitude-frequency modulation suppression device in a laser system according to claim 1, characterized in that, The laser gain medium is neodymium glass or Nd:CaF2.

5. A spectral management method for suppressing amplitude-frequency modulation, employing the amplitude-frequency modulation suppression device in a laser system as described in any one of claims 1-4, characterized in that, Includes the following steps: Step S1: Design the spectral transmittance of the intracavity spectral control module so that it can compensate with the gain spectrum of the laser gain medium; Step S2: Add the intracavity spectral control module to the pre-amplifier, and adjust the pitch angle θ and rotation angle φ of the birefringent crystal in the intracavity spectral control module so that the gain spectrum of the pre-amplifier is a near-flat-top spectrum output. Step S3: Design the spectral transmittance of the external cavity spectral control module so that it can compensate with the gain spectrum of the laser gain medium; Step S4: Add an external cavity spectral control module between the pre-stage laser amplifier and the post-stage laser amplifier. Adjust the pitch and rotation angles of the birefringent crystal in the external cavity spectral control module to make the output gain spectrum of the post-stage laser amplifier near-flat-top output, thereby suppressing amplitude-frequency modulation.

Images