Distributed chirped pulse dispersion regulation and control system

Abstract

The invention discloses a distributed chirped pulse dispersion regulation and control system, and the system employs the characteristic that second-order dispersion symbols of different types of dispersion regulation and control devices are different, and carries out the excessive broadening of a near Fourier transform limit pulse through second-order positive dispersion. Second-order negative dispersion is used for partially compensating the second-order dispersion of the excessively broadened seed light before pulse amplification, and then a negative dispersion compressor is used for further performing dispersion regulation and control on the amplified pulse after amplification, so that the broadening amount of the seed light can be continuously adjusted, and the requirement of accurate dispersion compensation of the system is met. According to the scheme, the broadening amount can be flexibly adjusted, meanwhile, the broadening device can be matched with the dispersion of the compressor, and a brand new technical path is provided for fully extracting medium stored energy and achieving accurate dispersion regulation and control.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular, to a distributed chirped pulse dispersion regulation system. Background Art

[0002] High-energy, high-repetition-rate picosecond lasers in the near-infrared 1-μm band are key tools for conducting frontier research such as high-energy density physics experiments and secondary radiation sources. Since the chirped pulse amplification technology was proposed by the G. Mourou research group in the United States in 1985, it has always been the main method for obtaining 1-μm high-energy pulses, and the stretching device and the compression device play key roles in it.

[0003] How to achieve precise dispersion regulation in a chirped pulse amplification system is a difficult problem that must be faced to obtain high-quality pulses. At present, stretcher with microjoule-level single-pulse energy mainly includes chirped volume Bragg gratings, Martinez stretchers, etc., which provide a single positive dispersion for the pulse to be stretched injected. However, although the chirped volume Bragg grating is small in size, it is limited by its fixed dispersion amount in practical applications; the Martinez stretcher has continuously adjustable dispersion, but its volume is relatively large. Existing dispersion regulation means are difficult to simultaneously meet the application requirements of being compact, having continuously adjustable dispersion amount, and being matched with the compressor at the same time. Summary of the Invention

[0004] In view of this, the present invention provides a distributed chirped pulse dispersion regulation system. This system broadens the near Fourier transform limited pulse through second-order positive dispersion. The provided negative dispersion compressor can be divided into two parts. One part is combined with the stretcher before pulse amplification, and the other part is used for dispersion regulation of the amplified pulse. This solution can not only flexibly adjust the broadening amount, but also meet the needs of precise dispersion compensation of the system.

[0005] A distributed chirped pulse dispersion regulation system includes a fiber laser, a beam expander and collimator, a shaping device, an isolation device, a stretcher, a chirped pulse amplifier, and a compression device that are sequentially arranged along the light propagation direction on the seed light amplification optical path;

[0006] The fiber laser is used to output a broadband pulse close to the Fourier transform limit as a broadband seed light;

[0007] The beam expander and collimator is used to expand and collimate the broadband seed light;

[0008] The shaping device is used to control the spot shape, spatial intensity distribution, and beam aperture of the expanded broadband seed light;

[0009] The isolation device is used to ensure that the broadband seed light only transmits forward to the chirped pulse amplifier and prevent the optical pulse amplified by the chirped pulse amplifier from transmitting backward;

[0010] The chirped pulse amplifier is used to amplify the broadband seed light broadened by the broadening device;

[0011] The compression device is used to compress the amplified optical pulse so that it reaches the near Fourier transform limit pulse width;

[0012] Among them, the broadening device includes a pulse broadening device and a dispersion compensation device. The pulse broadening device is used to over-broaden the broadband seed light through second-order normal dispersion, and the dispersion compensation device is used to partially compensate the second-order dispersion of the over-broadened broadband seed light through second-order negative dispersion.

[0013] Preferably, the pulse broadening device includes a first polarization beam splitter prism, a beam steering component arranged on the transmission optical path of the first polarization beam splitter prism, and a chirped Bragg grating. The beam steering component is used to make the beam passing through the first polarization beam splitter prism enter and exit the chirped Bragg grating repeatedly for over-broadening. A first half-wave plate is arranged between the first polarization beam splitter prism and the beam steering component, and a first quarter-wave plate is arranged between the beam steering component and the chirped Bragg grating. The dispersion compensation device is arranged on the reflection optical path of the first polarization beam splitter prism.

[0014] Preferably, the beam steering component includes a second polarization beam splitter prism arranged on the transmission optical path of the first polarization beam splitter prism and a first prism arranged on the reflection optical path of the second polarization beam splitter prism. The first half-wave plate is located at the lower part of the reflection surface of the first polarization beam splitter prism, and the first quarter-wave plate is arranged on the transmission optical path of the second polarization beam splitter prism.

[0015] Preferably, a high-reflection film is provided on the rear surface of the chirped Bragg grating.

[0016] Preferably, the dispersion compensation device includes a second half-wave plate, a third polarization beam splitter prism, a second quarter-wave plate, a dispersion amount fine-tuning device, and a second mirror. The broadband seed light over-broadened by the pulse broadening device sequentially passes through the second half-wave plate, the third polarization beam splitter prism, and the second quarter-wave plate and then enters the dispersion amount fine-tuning device. After the dispersion amount fine-tuning device partially compensates the second-order dispersion of the over-broadened broadband seed light, the broadband seed light is reflected by the second mirror and returns along the original path. After passing through the dispersion amount fine-tuning device and the second quarter-wave plate in sequence, it is reflected from the reflection surface of the third polarization beam splitter prism and outputs, and enters the chirped pulse amplifier.

[0017] Preferably, a first mirror is further arranged between the second half-wave plate and the third polarization beam splitter prism. The first mirror is used to reflect the beam passing through the second half-wave plate so that the beam passes through the third polarization beam splitter prism.

[0018] Preferably, the dispersion amount fine-tuning device includes a first reflective grating and a second reflective grating. The first reflective grating and the second reflective grating are parallel to each other. The first reflective grating is inclined and arranged on one side of the second quarter-wave plate, and the second mirror is vertically arranged on one side of the second reflective grating.

[0019] Preferably, the compression device includes a pair of dielectric film gratings for compressing the broadband seed light to perform residual compensation on its second-order dispersion, and a second prism for fine-tuning the longitudinal displacement of the medium film grating for the optical pulse in order to separate the compressed pulse.

[0020] Preferably, the isolation device is a Faraday isolator based on the magneto-optical rotation effect;

[0021] The output spectrum of the broadband seed light output by the fiber laser matches the emission wavelength of the gain medium in the chirped pulse amplifier, and the output pulse is time-synchronized with the laser pumping device in the chirped pulse amplifier.

[0022] Preferably, one or more beam expanding and collimating devices are provided.

[0023] The beneficial effects of the present invention are as follows:

[0024] 1. The present invention utilizes the characteristic that the second-order dispersion signs of different types of dispersion control devices are different. By using the second-order positive dispersion to over-expand the near Fourier transform limit pulse, and then using the second-order negative dispersion to compensate a part of the second-order dispersion of the over-expanded seed light before pulse amplification, and then using the negative dispersion compressor to further perform dispersion control on the amplified pulse after amplification, distributed dispersion control is performed on the near Fourier transform limit broadband seed pulse injected into the system. It can not only realize continuous adjustment of the seed light broadening amount to meet the accurate dispersion compensation requirements of the system, but also ensure the compact structure of the expander. This scheme can not only flexibly adjust the broadening amount, but also match the dispersion of the compressor, providing a new technical path for fully extracting the energy storage of the medium and realizing accurate dispersion control.

[0025] 2. The present invention can realize continuous adjustment of the second-order dispersion amounts of the expander and the compressor, which can not only ensure sufficient amplification of the broadband seed pulse in the gain medium, but also reduce the total volume of the expander and the compressor, providing a reliable technical route for the dispersion management of compact high-energy high-repetition-rate picosecond lasers. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0027] Figure 1 It is a schematic diagram of the system composition of the distributed chirped pulse dispersion control system of the present invention.

[0028] Figure 2 It is a schematic diagram of the structure of the stretching device.

[0029] Figure 3 It is a schematic diagram of the structure of the compression device.

[0030] Figure 4 It is a flowchart for calculating the total volume of the stretching device and the compression device.

[0031] The meanings of the labels in the figure are as follows:

[0032] 1 is a fiber laser,

[0033] 2 is a beam expander and collimator,

[0034] 3 is a shaping device,

[0035] 4 is an isolation device,

[0036] 5 is a stretching device, 5-1 is a first polarization beam splitter prism, 5-2 is a second polarization beam splitter prism, 5-3 is a first quarter-wave plate, 5-4 is a chirped Bragg grating, 5-5 is a first prism, 5-6 is a first half-wave plate, 5-7 is a second half-wave plate, 5-8 is a first mirror, 5-9 is a third polarization beam splitter prism, 5-10 is a second quarter-wave plate, 5-11 is a first reflection grating, 5-12 is a second reflection grating, 5-13 is a second mirror,

[0037] 6 is a chirped pulse amplifier, 6-1 is a first dielectric film grating, 6-2 is a second dielectric film grating, 6-3 is a second prism, 7 is a compression device. Specific embodiments

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be described below through specific embodiments shown in the drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0039] The terms used in this disclosure are only for the purpose of describing specific embodiments and are not intended to limit this disclosure. The singular forms "a", "the", and "said" used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0040] It should be understood that although the terms first, second, third, etc. may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be construed as indicating or implying relative importance. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this disclosure, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "when" or "while" or "in response to determining".

[0041] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms longitudinal, transverse, upper, lower, front, rear, left, right, vertical, horizontal, top, bottom, inner, outer, etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0042] In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms installation, connection, and coupling should be understood in a broad sense. For example, it may be a mechanical connection or an electrical connection, or it may be the communication inside two elements. It may be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0043] In the following description, the suffixes such as "module", "component", or "unit" used to represent elements are only for the convenience of describing the present invention, and they do not have a specific meaning in themselves. Therefore, "module" and "component" can be used interchangeably.

[0044] For a better understanding of the technical solution of the present invention, the present invention will be described in detail below with reference to the drawings.

[0045] The present invention provides a distributed chirped pulse dispersion control system, which includes a fiber laser 1, a beam expander and collimator 2, a shaping device 3, an isolation device 4, a broadening device 5, a chirped pulse amplifier 6, and a compression device 7 arranged on the seed light amplification optical path. The fiber laser 1, the beam expander and collimator 2, the shaping device 3, the isolation device 4, the broadening device 5, the chirped pulse amplifier 6, and the compression device 7 are arranged in sequence along the light propagation direction.

[0046] The fiber laser 1 is used to output broadband pulses with near Fourier transform limit as broadband seed light. The output spectrum of the laser pulses output by the fiber laser 1 matches the emission spectrum wavelength of the gain medium in the amplification device 6. The output pulses are time-synchronized with the amplifier laser pumping device, and the output pulse energy and repetition frequency can be adjusted according to the overall design requirements.

[0047] The beam expanding and collimating device 2 is used to expand and collimate the broadband seed light, and it is connected to the output end of the fiber laser 1 through a polarization-maintaining fiber. On the entire seed light amplification optical path, one or more beam expanding and collimating devices 2 can be set according to the specific requirements of beam amplification. Each beam expanding and collimating device 2 can also be set to multiple stages to achieve multi-stage amplification of the beam. The beam expanding and collimating device 2 can use a Galilean configuration or a Kepler configuration according to the requirements to achieve high-quality beam expansion.

[0048] The shaping device 3 is used to control the spot shape, spatial intensity distribution, and beam aperture of the expanded broadband seed light. The spot shape of the seed light adjusted by the shaping device 3 is preferably matched with the shape of the gain medium in the amplification device 6. For example, if the gain medium used in the amplification device 6 is square, the shaping device 3 adjusts the spot shape to square; if the gain medium is circular, the shaping device 3 adjusts the spot shape to circular. In this embodiment, the shaping device 3 adjusts the spot of the seed light to a square spot.

[0049] The isolation device 4 is used to ensure that the broadband seed light only transmits forward to the chirped pulse amplifier 6 and prevent the amplified optical pulses from the chirped pulse amplifier 6 from transmitting backward to ensure the safe use of the fiber laser 1. The isolation device 4 can use a Faraday isolator or other optical isolation elements or structures. In this embodiment, the isolation device 4 selected is a Faraday isolator based on the magneto-optical rotation effect.

[0050] The pulse broadening device 5 is used to broaden the broadband seed light pulses so that the output laser pulse width is equal to the width of the pump light pulses output by the laser pumping device used in the chirped pulse amplifier 6.

[0051] The chirped pulse amplifier 6 is used to amplify the broadband seed light broadened by the pulse broadening device 5.

[0052] The compression device 7 is used to compress the amplified optical pulses to make them reach the near Fourier transform limit pulse width.

[0053] The above-mentioned broadening device 5 includes a pulse broadening device and a dispersion compensation device. The pulse broadening device is used to excessively broaden the broadband seed light through second-order normal dispersion, while the dispersion compensation device is used to partially compensate the second-order dispersion of the excessively broadened broadband seed light through second-order negative dispersion. The chirped laser pulse width output from the dispersion compensation device should be equal to the width of the pump light pulse output by the laser pumping device used in the chirped pulse amplifier 6. After the light beam is amplified in the chirped pulse amplifier 6, it is input into the compression device 7 for compression. The compression device 7 further compensates the second-order dispersion of the light beam input into it through second-order negative dispersion, so that the pulse width of its output reaches the near Fourier transform limit pulse width.

[0054] Specifically, the pulse broadening device includes a first polarization beam splitter prism 5-1, a beam steering component disposed on the transmission optical path of the first polarization beam splitter prism 5-1, and a chirped Bragg grating 5-4. A first half-wave plate 5-6 is disposed between the first polarization beam splitter prism 5-1 and the beam steering component, and a first quarter-wave plate 5-3 is disposed between the beam steering component and the chirped Bragg grating 5-4. The dispersion compensation device is disposed on the reflection optical path of the first polarization beam splitter prism 5-1.

[0055] The first polarization beam splitter prism 5-1 is used to transmit a beam of a certain fixed polarization state and reflect a beam of another polarization state. Both the first half-wave plate 5-6 and the first quarter-wave plate 5-3 are used to change the polarization state of the light beam. The beam steering component is used to make the light beam passing through the first polarization beam splitter prism 5-1 enter and exit the chirped Bragg grating 5-4 repeatedly for excessive broadening. When the broadband seed light output by the isolation device 4 passes through the first polarization beam splitter prism 5-1, it directly enters the beam steering component. The beam steering component makes the broadband seed light enter and exit the chirped Bragg grating 5-4 repeatedly. The chirped Bragg grating 5-4 provides sufficient second-order normal dispersion to excessively broaden the broadband seed light. The "excessive" means that the pulse width of the broadband seed light realizes a magnitude change, for example, broadening a femtosecond-level optical pulse to a picosecond-level optical pulse, or broadening a picosecond-level optical pulse to a nanosecond-level optical pulse, or broadening a femtosecond-level optical pulse to a nanosecond-level optical pulse.

[0056] By setting the beam steering component, the light beam can be made to transmit one or more passes in the chirped Bragg grating 5-4 as needed to obtain sufficient second-order normal dispersion. In this embodiment, the specific parameters of the chirped Bragg grating 5-4 are: full width at half maximum 8 nm, broadening amount 500 ps.

[0057] The beam steering assembly includes a second polarization beam splitter prism 5-2 and a first prism 5-5. The second polarization beam splitter prism 5-2 is disposed on the transmitted light path of the first polarization beam splitter prism 5-1. The first half-wave plate 5-6 is disposed between the first polarization beam splitter prism 5-1 and the second polarization beam splitter prism 5-2 and is located below the reflection surface of the first polarization beam splitter prism 5-1. The first prism 5-5 is disposed on the reflected light path of the second polarization beam splitter prism 5-2. The first quarter-wave plate 5-3 is disposed on the transmitted light path of the second polarization beam splitter prism 5-2. The chirped Bragg grating 5-4 is disposed downstream of the first quarter-wave plate 5-3. In other embodiments, the beam steering device may also be configured in other structural forms.

[0058] A high-reflection film is provided on the rear surface of the chirped Bragg grating 5-4. Thus, when the light beam passing through the first polarization beam splitter prism 5-1, the second polarization beam splitter prism 5-2, and the first quarter-wave plate 5-3 enters the chirped Bragg grating 5-4, second-order normal dispersion is obtained within the chirped Bragg grating 5-4 for one-time broadening, and then it is reflected on its rear surface and returns along the original path to the beam steering assembly. After the transmission direction is adjusted by its second polarization beam splitter prism 5-2 and the first prism 5-5, it enters the chirped Bragg grating 5-4 again to further obtain second-order normal dispersion for secondary broadening. Then, after being reflected again on the rear surface of the chirped Bragg grating 5-4, it sequentially passes through the first quarter-wave plate 5-3, the second polarization beam splitter prism 5-2, and the first half-wave plate 5-6, and then is incident on the reflection surface of the first polarization beam splitter prism 5-1. After being reflected by the first polarization beam splitter prism 5-1, it enters the dispersion compensation device.

[0059] The dispersion compensation device includes a second half-wave plate 5-7, a third polarization beam splitter prism 5-9, a second quarter-wave plate 5-10, a dispersion amount fine-tuning device, and a second mirror 5-13. Both the second half-wave plate 5-7 and the second quarter-wave plate 5-10 are used to change the polarization state of the light beam. The function of the third polarization beam splitter prism 5-9 is the same as that of the first polarization beam splitter prism 5-1 and the second polarization beam splitter prism 5-2, which are all used to transmit the light beam of a certain fixed polarization state and reflect the light beam of another polarization state. The dispersion amount fine-tuning device is used to provide a small amount of second-order negative dispersion to partially compensate the second-order dispersion of the over-broadened broadband seed light. The second mirror 5-13 is used to change the propagation direction of the light beam.

[0060] The broadband seed light overbroadened by the above pulse broadening device sequentially passes through the second half-wave plate 5-7, the third polarization beam splitter prism 5-9, and the second quarter-wave plate 5-10 and then enters the dispersion amount fine-tuning device. After the dispersion amount fine-tuning device partially compensates the second-order dispersion of the overbroadened broadband seed light, the broadband seed light is reflected back along the original path by the second mirror 5-13 and sequentially passes through the dispersion amount fine-tuning device and the second quarter-wave plate 5-10, and then is incident on the reflection surface of the third polarization beam splitter prism 5-9, and is reflected and output by the third polarization beam splitter prism 5-9, and then enters the chirped pulse amplifier 6 for amplification.

[0061] Preferably, a first mirror 5-8 is further disposed between the second half-wave plate 5-7 and the third polarization beam splitter prism 5-9. The first mirror 5-8 is used to reflect the light beam passing through the second half-wave plate 5-7 so that the light beam passes through the third polarization beam splitter prism 5-9. In this embodiment, the first mirror 5-8 is a mirror inclined at 45°.

[0062] Assume that the polarization state of the laser pulse output by the fiber laser 1 is horizontal polarization. The optical pulse after beam expansion and collimation by the beam expansion and collimation device 2, adjustment by the shaping device 3, and isolation by the isolation device 4 is also horizontal polarization. The first polarization beam splitter prism 5-1, the second polarization beam splitter prism 5-2, and the third polarization beam splitter prism 5-9 are all highly transmissive to horizontal polarization and highly reflective to vertical polarization. Then, the broadband optical pulse with horizontal polarization sequentially passes through the first polarization beam splitter prism 5-1, the second polarization beam splitter prism 5-2, and the first quarter-wave plate 5-3, and enters the chirped volume Bragg grating 5-4; a high-reflection film is coated on the rear surface of the chirped volume Bragg grating 5-4, and the broadband optical pulse returns along the original path, passes through the first quarter-wave plate 5-3, and at this time the polarization becomes vertical polarization; the second polarization beam splitter prism 5-2 is highly reflective to the optical pulse and enters the first prism 5-5. The optical pulse undergoes a small lateral displacement in the first prism 5-5, and is incident on the second polarization beam splitter prism 5-2 again. After being highly reflected by the second polarization beam splitter prism 5-2, it sequentially passes through the first quarter-wave plate 5-3 and the chirped volume Bragg grating 5-4, and is reflected from the rear surface of the chirped volume Bragg grating 5-4 and returns along the original path through the first quarter-wave plate 5-3. After passing through the first quarter-wave plate 5-3, the polarization of the optical pulse becomes horizontal polarization, and then it sequentially passes through the second polarization beam splitter prism 5-2 and the first half-wave plate 5-6. After passing through the first half-wave plate 5-6, the polarization becomes vertical polarization. Then, the first polarization beam splitter prism 5-1 is highly reflective to the optical pulse, causing it to pass through the second half-wave plate 5-7. After passing through the second half-wave plate 5-7, the polarization of the optical pulse becomes horizontal polarization, and then it passes through the mirror 5-8, is transmitted through the third polarization beam splitter prism 5-9 and the second quarter-wave plate 5-10, and enters the dispersion fine-tuning device for dispersion compensation; the optical pulse emerging from the dispersion fine-tuning device is vertically incident on the second mirror 5-13, is reflected by the second mirror 5-13 and returns along the original path, passes through the dispersion fine-tuning device and the second quarter-wave plate 5-10 again, the polarization becomes vertical polarization, is highly reflected and output by the third polarization beam splitter prism 5-9, and enters the chirped pulse amplifier 6.

[0063] The chirped volume Bragg grating 5-4 provides sufficient second-order positive dispersion to over-broaden the broadband seed light; the dispersion amount fine-tuning device provides a small amount of second-order negative dispersion. The dispersion amount fine-tuning device can partially compensate for the second-order dispersion of the over-broadened broadband seed light, realizing continuous adjustable broadening amount of the broadband seed light pulse. Since the pump pulse widths of the laser pumping devices used in different chirped pulse amplifiers 6 are different, the laser pulse width output from the above-mentioned third polarization beam splitter prism 5-9 should be equal to the width of the pump light pulse output by the laser pumping device used in the chirped pulse amplifier 6. If the two are not equal, the dispersion amount fine-tuning device needs to be adjusted. Since the dispersion amount fine-tuning device only partially compensates for the second-order dispersion of the over-broadened broadband seed light, the dispersion compensation amount of the dispersion amount fine-tuning device for the over-broadened broadband seed light needs to match the dispersion compensation amount of the compression device 7 to achieve precise control of the seed light dispersion.

[0064] The dispersion amount fine-tuning device should fully consider the problem of pulse width matching between the seed source and the pump light, so that the seed source can be fully amplified. The dispersion amount supplemented by the dispersion amount fine-tuning device is equal to the difference between the dispersion amount when the seed source is broadened to the required pulse width and the existing dispersion amount. Dividing this dispersion amount difference by the dispersion amount supplemented by the unit length of the dispersion amount fine-tuning device can obtain the distance that the dispersion amount fine-tuning device needs to move (i.e., the distance that needs to be moved between the first reflective grating 5-11 and the second reflective grating 5-12).

[0065] The dispersion amount fine-tuning device includes a first reflective grating 5-11 and a second reflective grating 5-12. The first reflective grating 5-11 and the second reflective grating 5-12 are parallel to each other. The first reflective grating 5-11 and the second reflective grating 5-12 have the same grating line density. The first reflective grating 5-11 is inclined on one side of the second quarter-wave plate 5-10, and the second mirror 5-13 is vertically arranged on one side of the second reflective grating 5-12. In other embodiments, the dispersion amount fine-tuning device can also adopt other structural forms.

[0066] In this embodiment, the first reflective grating 5-11 and the second reflective grating 5-12 can use reflective gratings with a grating line density of 1740 lp / mm and coated with dielectric films, which are used to provide a small amount of continuously adjustable second-order negative dispersion to realize dispersion pre-compensation for the pulses to be injected into the chirped pulse amplifier 6. The dispersion compensation amount can be adjusted by adjusting the distance between the first reflective grating 5-11 and the second reflective grating 5-12.

[0067] The chirped pulse amplifier 6 is an arbitrarily beam-amplifiable structure composed of two symmetrically placed sheet-like gain media, a laser pumping device with an output wavelength of 940 nm, and supporting optical elements such as a cooling medium and mirrors. For example, it can be the power amplifier system described in invention patent CN116979355A.

[0068] The compression device 7 includes a pair of dielectric film gratings (the first dielectric film grating 6-1 and the second dielectric film grating 6-2) for compressing broadband seed light to perform residual compensation for its second-order dispersion, and a second prism 6-3 for finely adjusting the longitudinal displacement of the medium film grating for the centered optical pulse to separate the compressed pulses. The relatively arranged dielectric film gratings have the same line density. In actual use, a grating with an appropriate scale density is selected according to specific requirements, and at the same time, the grating size and the distance between the two pairs of grating pairs are designed according to specific requirements. In this embodiment, the dielectric film grating is a reflective dielectric film grating or a transmissive dielectric film grating, and the line density of the dielectric film grating is 1740 lp / mm.

[0069] The specific implementation manners of the present invention will be described in detail below through specific examples.

[0070] In this embodiment, the fiber laser 1 outputs chirped optical pulses with an energy of about 30 μJ, a spectral full width at half maximum of about 8 nm, a pulse width of about 200 fs, close to the Fourier transform limit, and a repetition frequency of 10 Hz. After passing through the beam expander collimator 2, the shaping device 3, the isolation device 4, and the stretching device 5, about 10 μJ of energy is used as the broadband seed light for the chirped pulse amplifier 6. The chirped pulse amplifier selects a Yb:YAG sheet-like gain medium, uses a multi-pass active mirror amplification configuration, and the pump light intensity is 15 kW / cm 2 , the small-signal gain of Yb:YAG is 0.8358 / cm, and the chirped pulse amplifier can achieve a gain of 10 6 . After amplification, a single-pulse energy output of 10 J can be achieved, and the spot size is 2 cm × 2 cm.

[0071] Assume that the optical pulses output by the broadband fiber laser 1 are horizontally polarized. The first polarization beam splitter prism 5-1, the second polarization beam splitter prism 5-2, and the third polarization beam splitter prism 5-9 are all highly transmissive to horizontally polarized light and highly reflective to vertically polarized light. The broadband optical pulses with horizontal polarization pass through the first polarization beam splitter prism 5-1, the second polarization beam splitter prism 5-2, and the first quarter-wave plate 5-3 in sequence and enter the chirped volume Bragg grating 5-4. The chirped volume Bragg grating 5-4 has a size of 5 × 5 × 50 mm, a bandwidth (full width at half maximum) of 8 nm, can be stretched to 500 ps, and the amount of second-order dispersion provided by passing through the chirped volume Bragg grating 5-4 once is 7.2×10 7 fs 2The rear surface of the chirped volume Bragg grating 5-4 is coated with a high-reflection film. The broadband optical pulse is emitted from its rear surface and returns along the original path. After passing through the first quarter-wave plate 5-3, the polarization becomes vertical polarization at this time. The second polarization beam splitter prism 5-2 highly reflects the optical pulse and enters the first prism 5-5. The optical pulse undergoes a small lateral displacement in the first prism 5-5 and is incident on the second polarization beam splitter prism 5-2 again. After being highly reflected by the second polarization beam splitter prism 5-2, it successively passes through the first quarter-wave plate 5-3 and the chirped volume Bragg grating 5-4, and is reflected from the rear surface of the chirped volume Bragg grating 5-4 and returns along the original path through the first quarter-wave plate 5-3. After passing through the first quarter-wave plate 5-3, the polarization of the optical pulse becomes horizontal polarization, and then it successively passes through the second polarization beam splitter prism 5-2 and the first half-wave plate 5-6. After passing through the first half-wave plate 5-6, it becomes vertical polarization, and then the first polarization beam splitter prism 5-1 highly reflects the optical pulse, making it exit to the second half-wave plate 5-7 after "two in and two out", and enter the grating pair part that provides a small amount of negative dispersion;

[0072] The optical pulse is incident on and exits the chirped volume Bragg grating 5-4 twice, and a total second-order dispersion amount of 1.54×10 8 fs 2 is obtained, and the pulse width is broadened from 200 fs to 1 ns;

[0073] Next, the optical pulse successively passes through the second half-wave plate 5-7 and the mirror 5-8. The optical pulse is horizontally polarized and then transmits through the third polarization beam splitter prism 5-9 and the second quarter-wave plate 5-10, and enters the dispersion compensation device composed of the first reflective grating 5-11 and the second reflective grating 5-12. The first reflective grating 5-11 and the second reflective grating 5-12 are dielectric film reflective gratings with a ruling density of 1740 lp / mm. The Littrow angle of the grating is 63.65°, and the incident angle is 68°; The optical pulse exiting from the dispersion compensation device is vertically incident on the second mirror 5-13, and after being reflected by the second mirror 5-13, it returns along the original path, passes through the dispersion compensation device and the quarter-wave plate 5-10 again, and the polarization becomes vertical polarization, and is output after being highly reflected by the third polarization beam splitter prism 5-9 and enters the chirped pulse amplifier 6.

[0074] In the chirped pulse amplifier 6, assuming that the input pulse spectrum is nearly Gaussian, according to the empirical formula of pulse amplification: where λ 1 is the bandwidth of the amplified output pulse, λ g is the emission bandwidth of the gain medium, λ 0 is the bandwidth of the input pulse, and G is the total gain of the amplification device. The spectral width (full width at half maximum) of the output pulse is 2.32 nm. Based on this, the pulse width of the output chirped pulse can be deduced according to the chirp rate.

[0075] In the compression device 7, a dielectric film reflective grating with a grating pair selection line density of 1740 lp / mm is used. The distance between the grating pair is determined by the time width of the output pulse amplified by the chirped pulse amplifier 6. Considering the actual compression efficiency of each grating is ~95% and the reflection efficiency of the mirror coated with a high-reflection film is 99.8%, the efficiency of the entire compressor is approximately 80%. The pulsed energy after compression is approximately 8 J.

[0076] To achieve a compact laser dispersion control system, it is necessary to ensure sufficient broadening, which is beneficial for the seed pulse to fully extract and store energy during the amplification process; at the same time, it is necessary to avoid excessive broadening, which would make the volume of the compression device too large. Therefore, it is necessary to consider the overall design scheme of the dispersion control system, and the key parameters determining its volume are shown in Table 1 below.

[0077] Table 1

[0078]

[0079] During the amplification process, continuous adjustment of broadening and compression is achieved according to actual needs, and the second-order dispersion of the distributed compensation system is compensated. While ensuring the output energy and the safe and stable operation of the system, the compactness of the laser dispersion control system is realized.

[0080] It should be clear that the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

Claims

1. A distributed chirped pulse dispersion control system, characterized in that: It comprises a fiber laser (1), a beam expansion and collimation device (2), a shaping device (3), an isolation device (4), a stretching device (5), a chirped pulse amplifier (6) and a compression device (7) which are arranged in sequence along the light propagation direction on the seed light amplification optical path; The fiber laser (1) is used to output broadband pulses close to the Fourier transform limit as broadband seed light; The beam expansion and collimation device (2) is used to expand and collimate the broadband seed light; The shaping device (3) is used to control the spot shape, intensity distribution and beam aperture of the broadband seed light after beam expansion; The isolation device (4) is used to ensure that the broadband seed light is transmitted to the chirped pulse amplifier (6) only in the forward direction, and to prevent the optical pulse amplified by the chirped pulse amplifier (6) from being transmitted in the reverse direction; The chirped pulse amplifier (6) is used to amplify the broadband seed light broadened by the broadening device (5); The compression device (7) is used to compress the amplified optical pulse to make it reach a pulse width close to the Fourier transform limit; The stretching device (5) comprises a pulse stretching device and a dispersion compensation device, wherein the pulse stretching device is used to excessively stretch the broadband seed light through second-order positive dispersion, and the dispersion compensation device is used to partially compensate for the second-order dispersion of the excessively stretched broadband seed light through second-order negative dispersion.

2. The distributed chirped pulse dispersion control system according to claim 1, characterized in that: The pulse broadening device comprises a first polarization beam splitter prism (5-1), a beam steering component and a chirped Bragg grating (5-4) arranged on a transmission light path of the first polarization beam splitter prism (5-1); the beam steering component is used to make a light beam penetrating the first polarization beam splitter prism (5-1) repeatedly enter and exit the chirped Bragg grating (5-4) for excessive broadening; a first half-wave plate (5-6) is arranged between the first polarization beam splitter prism (5-1) and the beam steering component; a first quarter-wave plate (5-3) is arranged between the beam steering component and the chirped Bragg grating (5-4); and the dispersion compensation device is arranged on a reflection light path of the first polarization beam splitter prism (5-1).

3. The distributed chirped pulse dispersion control system according to claim 2, characterized in that: The light beam steering component comprises a second polarization beam splitter prism (5-2) arranged on a transmission light path of a first polarization beam splitter prism (5-1), a first prism (5-5) arranged on a reflection light path of the second polarization beam splitter prism (5-2), the first half-wave plate (5-6) being located at the lower part of a reflection surface of the first polarization beam splitter prism (5-1), and the first quarter-wave plate (5-3) being arranged on the transmission light path of the second polarization beam splitter prism (5-2).

4. The distributed chirped pulse dispersion control system according to claim 2, characterized in that: The rear surface of the chirped Bragg grating (5-4) is provided with a high reflection film.

5. The distributed chirped pulse dispersion control system according to claim 1 or 2, characterized in that: The dispersion compensation device comprises a second half-wave plate (5-7), a third polarization beam splitter prism (5-9), a second quarter-wave plate (5-10), a dispersion amount fine-tuning device and a second reflector (5-13). The broadband seed light that is excessively broadened by the pulse broadening device sequentially passes through the second half-wave plate (5-7), the third polarization beam splitter prism (5-9) and the second quarter-wave plate (5-10) before entering the dispersion amount fine-tuning device. After the dispersion amount fine-tuning device partially compensates for the second-order dispersion of the excessively broadened broadband seed light, the broadband seed light is reflected by the second reflector (5-13) back to the original path, sequentially passes through the dispersion amount fine-tuning device and the second quarter-wave plate (5-10), and then is reflected and outputted from the reflection surface of the third polarization beam splitter prism (5-9) to enter the chirped pulse amplifier (6).

6. The distributed chirped pulse dispersion control system according to claim 5, characterized in that: A first reflector (5-8) is also arranged between the second half-wave plate (5-7) and the third polarization beam splitter prism (5-9), and the first reflector (5-8) is used to reflect the light beam passing through the second half-wave plate (5-7) so that the light beam passes through the third polarization beam splitter prism (5-9).

7. The distributed chirped pulse dispersion control system according to claim 6, characterized in that: The dispersion fine-tuning device comprises a first reflective grating (5-11) and a second reflective grating (5-12), the first reflective grating (5-11) and the second reflective grating (5-12) are parallel to each other, the first reflective grating (5-11) is tiltedly arranged on one side of the second quarter-wave plate (5-10), and the second reflector (5-13) is vertically arranged on one side of the second reflective grating (5-12).

8. The distributed chirped pulse dispersion control system according to claim 1, characterized in that: The compression device (7) includes a pair of dielectric film gratings for compressing broadband seed light to perform residual compensation for its second-order dispersion, and a second prism (6-3) for fine-tuning the longitudinal displacement of the light pulse in the dielectric film grating pair so as to separate the compressed pulse.

9. The distributed chirped pulse dispersion control system according to claim 1, characterized in that: The isolation device (4) is a Faraday isolator based on the magneto-optical effect; The output spectrum of the broadband seed light output by the optical fiber laser (1) matches the emission spectrum wavelength of the gain medium in the chirped pulse amplifier (6), and the output pulse is time-synchronized with the laser pumping device in the chirped pulse amplifier (6).

10. The distributed chirped pulse dispersion control system according to claim 1, characterized in that: The beam expansion and collimation device (2) is provided with one or more.

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