Method and system for realizing independent adjustment of sub-pulse width in pulse string

Abstract

The invention belongs to the technical field of laser, and discloses a method and a system for realizing independent adjustment of sub-pulse width in a pulse string. The method comprises the following steps: a seed source generates a laser pulse, and the laser pulse is incident to a pulse stretcher; the pulse stretcher broadens the laser pulse and shears the broadened laser pulse into a pulse string formed by a plurality of pulses in a time domain; the pulse string is incident to a pulse shaper, and the pulse shaper performs amplitude modulation on the spectrum of the sub-pulse in the pulse string, so that the width of each sub-pulse in the pulse string is independently adjusted, and the pulse string with the sub-pulse width capable of being independently adjusted is obtained. According to the invention, the sub-pulse width in the pulse string can be accurately and flexibly controlled.

Description

Technical Field

[0001] The present invention belongs to the field of laser technology, and in particular relates to a method and a system for realizing independent adjustment of sub-pulse widths in a pulse train. Background Art

[0002] In recent years, ultrafast laser technology has made significant progress and has been widely used in many fields such as advanced manufacturing, ultrafast imaging, information storage, and clinical medicine. Compared with continuous laser processing or long-pulse laser processing, ultrafast laser processing has the following significant characteristics: its pulse duration is extremely short, the peak power is extremely high, and the heat-affected zone is small. The duration of the ultrashort pulse makes the laser energy mainly concentrated in the extremely small range of photon-electron interaction, significantly reducing the generation of processing defects such as recast layers and microcracks. In addition, compared with the plasma shielding effect commonly seen in long-pulse laser processing, ultrafast laser processing can effectively avoid the occurrence of this phenomenon to a certain extent.

[0003] The peak power of ultrafast lasers can be as high as 100TW, and they can process almost all materials, including metals, semiconductors, dielectrics, and biological tissues. This high peak power makes the interaction between ultrafast lasers and materials present nonlinear and non-equilibrium characteristics, and is no longer a traditional hot melting process. In addition, due to the small statistical uncertainty of the damage threshold of short-pulse lasers, their processing accuracy can break through the sub-micron level, making femtosecond laser processing show great advantages in high-precision manufacturing. In specific applications, ultrafast laser technology has shown its superiority in many fields. For example, in physics, it can be used to observe laser-induced air plasma excitation; in laser manufacturing, it can significantly improve processing efficiency and improve the surface finish of materials; in addition, through the regulation of dual-pulse sequences, ultrafast lasers can also be used to prepare sub-wavelength periodic surface structures.

[0004] Ultrashort optical pulses also have characteristics such as femtosecond duration, high peak power, and wide spectral range. These characteristics make ultrashort pulses extremely capable of shaping in the time and space domains, thereby being able to generate pulse trains with precise time intervals, pulse widths, and intensities, providing an important means for studying the basic properties and dynamic behaviors of materials. However, current research on the regulation of ultrashort laser pulse trains is still insufficient. How to achieve flexible regulation of sub-pulses within a pulse train to generate ultrashort laser pulse trains that meet specific application requirements is a key issue that needs to be urgently addressed in this field.

[0005] The pulse widths of the sub-pulses in the pulse trains currently on the market are all fixed and consistent, and the pulse width of a single pulse cannot be accurately tuned, which is not conducive to the diversified testing and optimization of laser precision machining processes. Summary of the invention

[0006] Based on this, the present invention proposes a method and system for realizing independent adjustment of the width of sub-pulses in a pulse train, which can accurately and flexibly control the width of sub-pulses in a pulse train.

[0007] The present invention provides a method for independently adjusting the width of sub-pulses in a pulse train, comprising the following steps:

[0008] The seed source generates laser pulses, which are incident on the pulse stretcher;

[0009] The pulse stretcher stretches the laser pulse and cuts the stretched laser pulse into a pulse train formed by multiple pulses in the time domain;

[0010] The pulse train is incident on a pulse shaper, and the pulse shaper performs amplitude modulation on the spectrum of the sub-pulses in the pulse train, thereby independently adjusting the width of each sub-pulse in the pulse train to obtain a pulse train with independently adjustable sub-pulse widths.

[0011] Furthermore, the pulse train is incident on a pulse shaper, and the pulse shaper performs amplitude modulation on the spectrum of the sub-pulses in the pulse train, thereby independently adjusting the width of each sub-pulse in the pulse train, specifically:

[0012] The pulse train is incident on a first diffraction grating, and the first diffraction grating expands the pulse train in a horizontal direction to form a spatial chirp;

[0013] The pulses expanded in the horizontal direction are collimated by a first lens to become parallel light;

[0014] The parallel light is incident on a half-wave plate, and the polarization direction of the light is adjusted to be parallel to the crystal optical axis of the liquid crystal spatial light modulator by the half-wave plate;

[0015] The liquid crystal spatial light modulator is placed at the focal plane of the first lens to form a Fourier transform of the input light field; the liquid crystal spatial light modulator is divided into m areas, and different areas correspond to different spectral components; based on the set pass rate of each area, the liquid crystal spatial light modulator performs amplitude modulation on the spectrum in the m areas.

[0016] Furthermore, the liquid crystal spatial light modulator performs amplitude modulation on the spectrum in the m regions, specifically:

[0017] The spectral shape of the pulse train is changed by adjusting the grayscale at different positions of the liquid crystal spatial light modulator.

[0018] Furthermore, the method further comprises:

[0019] The pulse train with independently adjustable sub-pulse widths is incident on a pulse controller, and the pulse controller controls the passage of a specific pulse in the pulse train with independently adjustable sub-pulse widths;

[0020] The optical fiber amplifier amplifies the optical signal output by the pulse controller and outputs an amplified laser pulse train.

[0021] The present invention provides a system for independently adjusting the width of sub-pulses in a pulse train, which includes the following steps in sequence along the optical path:

[0022] A seed source for generating laser pulses;

[0023] A pulse stretcher, used for stretching the laser pulse and cutting the stretched laser pulse into a pulse train formed by multiple pulses in the time domain;

[0024] The pulse shaper is used to perform amplitude modulation on the spectrum of the sub-pulses in the pulse train, thereby independently adjusting the width of each sub-pulse in the pulse train and outputting a pulse train with independently adjustable sub-pulse widths.

[0025] Furthermore, the pulse shaper includes a first diffraction grating, a first lens, a half-wave plate, a liquid crystal spatial light modulator, a polarizer, a second lens and a second diffraction grating in sequence along the optical path direction; the first diffraction grating and the second diffraction grating have the same scribed lines and are placed in parallel; the half-wave plate is used to adjust the polarization direction of the pulse to a direction parallel to the crystal optical axis of the liquid crystal spatial light modulator; the first lens and the second lens have the same focal length; the liquid crystal spatial light modulator is used to modulate the amplitude of the light beam; and the polarizer is used to change the polarization direction of the light beam.

[0026] Furthermore, the pulse stretcher includes a circulator and a chirped fiber grating, wherein a first end of the circulator is connected to the seed source, a second end of the circulator is connected to the chirped fiber grating, and a third end of the circulator is connected to the pulse shaper.

[0027] Furthermore, the chirped fiber grating is a tunable chirped fiber grating.

[0028] Furthermore, the liquid crystal spatial light modulator is a phase-type liquid crystal spatial light modulator.

[0029] Furthermore, the system also includes:

[0030] A pulse controller, used for receiving the pulse train with independently adjustable sub-pulse widths and controlling the passage of specific pulses therein;

[0031] The optical fiber amplifier is used to amplify the optical signal output by the pulse controller and output an amplified laser pulse train.

[0032] Beneficial effects of the present invention:

[0033] (1) The present invention can set the pulse width of the sub-pulse in the pulse train according to the application requirements, so that the pulse width of the sub-pulse is programmable and adjustable, thereby realizing accurate and independent control of the pulse width of the laser pulse, and overcoming the shortcoming of the prior art that it cannot be flexibly controlled.

[0034] (2) The method and system for independently adjusting the width of sub-pulses in a pulse train proposed in the present invention have a simple structure and can realize complex pulse control with only simple settings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 A schematic diagram of a system for realizing independent adjustment of sub-pulse widths within a pulse train provided by an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a pulse shaper shown in an embodiment of the present invention;

[0038] Figure 3 A schematic diagram of a system for realizing independent adjustment of sub-pulse widths within a pulse train provided by another embodiment of the present invention;

[0039] Figure 4 A flow chart of a method for realizing independent adjustment of sub-pulse widths within a pulse train provided by an embodiment of the present invention.

[0040] The meanings of the symbols in the accompanying drawings are:

[0041] 1-seed source; 2-pulse stretcher; 3-pulse shaper; 4-pulse controller; 5-fiber amplifier;

[0042] 301 - first diffraction grating; 302 - first lens; 303 - half-wave plate; 304 - liquid crystal spatial light modulator; 305 - polarizer; 306 - second lens; 307 - second diffraction grating. DETAILED DESCRIPTION

[0043] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] The present invention is applied to the fields of high-speed imaging, high-precision laser processing, etc. The pulse width of the sub-pulse in the pulse train can be set according to the application requirements, and the pulse width of the sub-pulse is programmable and adjustable, realizing the precise and independent control of the pulse width of the ultra-short optical pulse. The present invention overcomes the shortcomings of some methods in the prior art that cannot be flexibly controlled.

[0045] See also Figure 1 An embodiment of the present invention provides a system for independently adjusting the width of sub-pulses in a pulse train, which includes a seed source 1, a pulse stretcher 2 and a pulse shaper 3 in sequence along the optical path.

[0046] The seed source 1 is used to generate laser pulses. In this embodiment, the seed source is a picosecond seed source with a central wavelength of 1030 nm, a half-width of 26 nm, a pulse width of 6 ps, and an average power of 40 mW.

[0047] The pulse stretcher 2 is used to stretch the laser pulse and cut the stretched laser pulse into a pulse train formed by multiple pulses in the time domain. The pulse stretcher 2 includes a circulator and a chirped fiber grating. The first end of the circulator is connected to the seed source 1, the second end of the circulator is connected to the chirped fiber grating, and the third end of the circulator is connected to the first diffraction grating of the pulse shaper 3. In this embodiment, the chirped fiber grating adopts a tunable chirped fiber grating, whose central wavelength is 1030nm, the full width at half maximum is 30nm, and the second-order dispersion B2 that can be provided is 34.77±0.6ps 2 , the dispersion parameter D is 61.7ps / nm.

[0048] The pulse shaper 3 is used to perform amplitude modulation on the spectrum of the sub-pulses in the pulse train, thereby independently adjusting the width of each sub-pulse in the pulse train and outputting a pulse train with independently adjustable sub-pulse widths.

[0049] Figure 2The figure is a schematic diagram of a pulse shaper shown in an embodiment of the present invention. As an example, the pulse shaper includes a first diffraction grating 301, a first lens 302, a half-wave plate 303, a liquid crystal spatial light modulator 304, a polarizer 305, a second lens 306 and a second diffraction grating 307 in sequence along the optical path direction; the first diffraction grating 301 and the second diffraction grating 307 have the same scribed lines and are placed in parallel; the half-wave plate 303 is used to adjust the polarization direction of the pulse to a direction parallel to the crystal optical axis of the liquid crystal spatial light modulator 304; the first lens 302 and the second lens 306 have the same focal length; the liquid crystal spatial light modulator 304 is used to modulate the amplitude of the light beam; and the polarizer 305 is used to change the polarization direction of the light beam.

[0050] In this embodiment, the liquid crystal spatial light modulator 304 is a phase-type liquid crystal spatial light modulator with a resolution of 1920*1200 and a pixel size of 8 microns. The time interval is controllable and has an extremely short time scale. The controllable time interval is in the range of 0 to 20 ps, ​​and the accuracy is below 1 fs. In other embodiments, other models of products can also be selected.

[0051] In this embodiment, the first lens 302 and the second lens 306 both have the same focal length of 10 cm, and the first diffraction grating 301 and the second diffraction grating 307 are 1800 line / mm.

[0052] See also Figure 3 In an extended manner, the system for realizing the independent adjustment of the width of sub-pulses in a pulse train provided by the present invention may also include a pulse controller 4 and an optical fiber amplifier 5. The seed source 1, the pulse stretcher 2 and the pulse shaper 3 are necessary components for realizing the system for realizing the independent adjustment of the width of sub-pulses in a pulse train, and the pulse controller 4 and the optical fiber amplifier 5 are extended components of the system.

[0053] The pulse controller 4 is used to receive the pulse train with independently adjustable sub-pulse widths and control the passage of specific pulses therein. In this embodiment, the pulse controller adopts an acousto-optic modulator.

[0054] The optical fiber amplifier 5 is used to amplify the optical signal output by the pulse controller and output an amplified laser pulse train. In this embodiment, the optical fiber of the optical fiber amplifier can be a single-clad optical fiber or a photonic crystal optical fiber.

[0055] See also Figure 4 , a method for realizing independent adjustment of sub-pulse widths in a pulse train provided by an embodiment of the present invention comprises the following steps:

[0056] The S1 picosecond seed source generates ultrashort laser pulses and injects them into the pulse stretcher.

[0057] It should be noted that this embodiment only takes a picosecond seed source to generate ultrashort laser pulses as an example. In other embodiments, other seed sources that generate ultrashort laser pulses may also be used.

[0058] The S2 pulse stretcher stretches the ultrashort laser pulse, stretches the pulse width of the ultrashort laser pulse to the ns level, and cuts the stretched ultrashort laser pulse into a pulse train formed by multiple pulses in the time domain.

[0059] S3: The pulse train is incident on a pulse shaper, and the pulse shaper performs amplitude modulation on the spectrum of the sub-pulses in the pulse train, thereby independently adjusting the width of each sub-pulse in the pulse train to obtain a pulse train with independently adjustable sub-pulse widths.

[0060] Specifically, the pulse train is incident on a first diffraction grating, and the first diffraction grating expands the pulse train in a horizontal direction to form a spatial chirp;

[0061] The pulses expanded in the horizontal direction are collimated by a first lens to become parallel light;

[0062] The parallel light is incident on a half-wave plate, and the polarization direction of the light is adjusted to be parallel to the crystal optical axis of the liquid crystal spatial light modulator by the half-wave plate;

[0063] According to the 4f system, the liquid crystal spatial light modulator is placed at the focal plane of the first lens to form a Fourier transform of the input light field;

[0064] Dividing the liquid crystal spatial light modulator into m regions, where different regions correspond to different spectral components;

[0065] Based on the set pass rate of each area, the liquid crystal spatial light modulator performs amplitude modulation on the spectrum in the m areas; and the spectrum shape of the pulse train is changed by adjusting the grayscale at different positions of the liquid crystal spatial light modulator.

[0066] It should be noted that:

[0067] 1. When performing spectrum shaping on the signal light, the spectrum must first be expanded horizontally, and then the shaping operation is achieved with the help of a liquid crystal spatial light modulator. The basic principle is to make the grayscale corresponding to different positions of the liquid crystal spatial light modulator correspond to different positions of the spectrum.

[0068] The specific theoretical basis is as follows, based on the diffraction formula of the grating:

[0069]

[0070] Among them, θ0 is the laser diffraction angle, φ is the incident angle, m is the diffraction order, λ is the wavelength, and d is the grating constant.

[0071] 2. The position where the incident light is diffracted onto the liquid crystal spatial light modulator is the center position, denoted as x0=0, so each different position on the liquid crystal spatial light modulator corresponds to a different wavelength.

[0072]

[0073] Among them, f is the focal length of the lens, λ is the wavelength, and x is the position coordinate.

[0074] The above formula makes x and λ correspond one to one. The spectral shape of the pulse train can be changed by adjusting the grayscale at different x positions.

[0075] 3. Further, Δt=D×Δλ

[0076] Where t is the pulse width of the sub-pulse in the pulse train, D is the dispersion parameter, and Δλ is the spectrum width.

[0077] D is provided by the pulse stretcher. The sub-pulse width can be further adjusted by changing Δλ.

[0078] In this embodiment, the central wavelength of the seed source is 1030nm, the half-maximum full width is 26nm, the pulse width is 6ps, and the average power is 40mW; the central wavelength of the pulse stretcher is 1030nm, the half-maximum full width is 30nm, and the second-order dispersion B2 that can be provided is 34.77±0.6ps 2 , the dispersion parameter D is 61.7ps / nm; the first diffraction grating and the second diffraction grating are 1800line / mm; the focal lengths of the first lens and the second lens are both 10cm. These numbers are just examples; in other embodiments, different component parameter values ​​can be selected according to different requirements, and different focal lengths and grating values ​​can also be selected according to different selected values ​​of optical path components.

[0079] The scalable method for achieving independent adjustment of the width of sub-pulses within a pulse train also includes:

[0080] S4: the pulse train with independently adjustable sub-pulse widths is incident on a pulse controller, and the pulse controller controls the passage of a specific pulse in the pulse train with independently adjustable sub-pulse widths.

[0081] The S5 optical fiber amplifier amplifies the optical signal output by the pulse controller and outputs an amplified laser pulse train.

[0082] The above is a detailed introduction to a method and system for realizing independent adjustment of the width of sub-pulses within a pulse train disclosed in an embodiment of the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. At the same time, for a person skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for achieving independent adjustment of sub-pulse widths within a pulse train, characterized in that: The following steps are involved: The seed source generates laser pulses, which are incident on the pulse stretcher; The pulse stretcher stretches the laser pulse and cuts the stretched laser pulse into a pulse train formed by multiple pulses in the time domain; The pulse train is incident on a pulse shaper, and the pulse shaper performs amplitude modulation on the spectrum of the sub-pulses in the pulse train, thereby independently adjusting the width of each sub-pulse in the pulse train to obtain a pulse train with independently adjustable sub-pulse widths.

2. The method for realizing independent adjustment of sub-pulse widths in a pulse train according to claim 1, characterized in that: The pulse train is incident on a pulse shaper, and the pulse shaper performs amplitude modulation on the spectrum of the sub-pulses in the pulse train, thereby independently adjusting the width of each sub-pulse in the pulse train, specifically: The pulse train is incident on a first diffraction grating, and the first diffraction grating expands the pulse train in a horizontal direction to form a spatial chirp; The pulses expanded in the horizontal direction are collimated by a first lens to become parallel light; The parallel light is incident on a half-wave plate, and the polarization direction of the light is adjusted to be parallel to the crystal optical axis of the liquid crystal spatial light modulator by the half-wave plate; The liquid crystal spatial light modulator is placed at the focal plane of the first lens to form a Fourier transform of the input light field; the liquid crystal spatial light modulator is divided into m areas, and different areas correspond to different spectral components; based on the set pass rate of each area, the liquid crystal spatial light modulator performs amplitude modulation on the spectrum in the m areas.

3. The method for realizing independent adjustment of sub-pulse widths in a pulse train according to claim 2, characterized in that: The liquid crystal spatial light modulator performs amplitude modulation on the spectrum in the m regions, specifically: The spectral shape of the pulse train is changed by adjusting the grayscale at different positions of the liquid crystal spatial light modulator.

4. The method for realizing independent adjustment of sub-pulse widths in a pulse train according to claim 1, characterized in that: The method further comprises: The pulse train with independently adjustable sub-pulse widths is incident on a pulse controller, and the pulse controller controls the passage of a specific pulse in the pulse train with independently adjustable sub-pulse widths; The optical fiber amplifier amplifies the optical signal output by the pulse controller and outputs an amplified laser pulse train.

5. A system for realizing independent adjustment of sub-pulse widths within a pulse train, characterized in that: Along the optical path direction, it includes: A seed source for generating laser pulses; A pulse stretcher, used for stretching the laser pulse and cutting the stretched laser pulse into a pulse train formed by multiple pulses in the time domain; The pulse shaper is used to perform amplitude modulation on the spectrum of the sub-pulses in the pulse train, thereby independently adjusting the width of each sub-pulse in the pulse train and outputting a pulse train with independently adjustable sub-pulse widths.

6. The system for realizing independent adjustment of sub-pulse widths in a pulse train according to claim 5, characterized in that: The pulse shaper includes a first diffraction grating, a first lens, a half-wave plate, a liquid crystal spatial light modulator, a polarizer, a second lens and a second diffraction grating in sequence along the optical path; the first diffraction grating and the second diffraction grating have the same scribed lines and are placed in parallel; the half-wave plate is used to adjust the polarization direction of the pulse to a direction parallel to the crystal optical axis of the liquid crystal spatial light modulator; the first lens and the second lens have the same focal length; the liquid crystal spatial light modulator is used to modulate the amplitude of the light beam; and the polarizer is used to change the polarization direction of the light beam.

7. The system for realizing independent adjustment of sub-pulse widths in a pulse train according to claim 5, characterized in that: The pulse stretcher comprises a circulator and a chirped fiber grating, wherein a first end of the circulator is connected to the seed source, a second end of the circulator is connected to the chirped fiber grating, and a third end of the circulator is connected to the pulse shaper.

8. The system for realizing independent adjustment of sub-pulse widths in a pulse train according to claim 7, characterized in that: The chirped fiber grating is a tunable chirped fiber grating.

9. The system for realizing independent adjustment of sub-pulse widths in a pulse train according to claim 6, characterized in that: The liquid crystal spatial light modulator is a phase-type liquid crystal spatial light modulator.

10. The system for realizing independent adjustment of sub-pulse widths in a pulse train according to claim 5, characterized in that: The system further comprises: A pulse controller, used for receiving the pulse train with independently adjustable sub-pulse widths and controlling the passage of specific pulses therein; The optical fiber amplifier is used to amplify the optical signal output by the pulse controller and output an amplified laser pulse train.

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