GHz sub-hundred femtosecond pulse string generation method, time frequency control system and femtosecond laser

Abstract

The invention discloses a GHZ sub-hundred femtosecond pulse string generation method. The method comprises the following steps: S1, carrying out dispersion pre-compensation on a pulse string; s2, reducing the main frequency of the pulse string after dispersion pre-compensation to a kHz level or a MHz level; s3, after the sub-pulse frequency in the pulse string after the main frequency is reduced is modulated to the GHz level, GHz sub-hundred femtosecond pulses are output; the technical problem that in the prior art, third-order dispersion introduced by a short-pulse optical fiber laser system and an optical fiber is serious, and then adverse influences are generated on the time-domain characteristic of the short-pulse laser system is effectively solved, the third-order dispersion of the system can be pre-compensated, the compressibility of a GHz pulse string is guaranteed, the repetition frequency is increased from GHz to THz, and the frequency-domain characteristic of the short-pulse laser system is improved. High-power GHz and THz pulse strings smaller than 100 femtoseconds are output, generation and amplification of sub-hundred femtosecond pulses with the repetition frequency as high as GHz and THz magnitude are achieved, and amplified and compressed pulse waveforms can be optimized.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast lasers, and specifically relates to a method for generating a sub-hundred-gigahertz femtosecond pulse train, a time-frequency control system and a femtosecond laser. Background Art

[0002] In recent years, the application scope of high repetition rate pulse trains has become increasingly wider. High-energy high repetition rate pulse trains with ultra-narrow pulse widths can not only improve processing efficiency, but also greatly improve processing accuracy. Common high-energy high repetition rate pulse trains are all GHz, and the pulse width exceeds 300fs. The base is large and it is difficult to obtain less than 100 femtoseconds; while the time interval of THz pulse trains is in the order of femtoseconds. In the femtosecond time scale, phase mismatch and phase distortion effects are more significant, which also limits the generation of THz femtosecond pulses.

[0003] Then, for the short-pulse fiber laser system in the existing technology, there is a very serious problem of third-order dispersion introduced by the optical fiber, which will have an adverse effect on the time domain characteristics of the short-pulse laser system, such as pulse splitting, pulse distortion, skirt and asymmetric tailing during high-repetition-rate pulse transmission and amplification. Therefore, it is necessary to effectively control the third-order dispersion. Summary of the invention

[0004] The purpose of the present invention is to provide a method for generating a sub-100-GHz femtosecond pulse train, a time-frequency control system and a femtosecond laser, so as to solve the technical problem in the prior art that the third-order dispersion introduced by the optical fiber is serious for a short-pulse optical fiber laser system, thereby adversely affecting the time domain characteristics of the short-pulse laser system. The present invention can pre-compensate the third-order dispersion of the system, thereby effectively avoiding the phenomena of pulse splitting, pulse distortion, skirt generation and asymmetric tailing that occur during high-repetition-rate pulse transmission and amplification.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: In a first aspect, the present invention discloses a method for generating a GHZ sub-hundred-femtosecond pulse train, comprising the following steps: S1, pre-compensate the pulse train for dispersion; S2, down-converting the main frequency of the pulse train after dispersion pre-compensation to kHz level or MHz level; S3, after modulating the sub-pulse frequency in the pulse train after the main frequency is reduced to GHz level, output GHz sub-hundred-femtosecond pulses.

[0006] The present invention solves the technical problem in the prior art that the third-order dispersion introduced by the optical fiber is serious for short-pulse optical fiber laser systems, thereby adversely affecting the time domain characteristics of the short-pulse laser system. The present invention can pre-compensate the third-order dispersion of the system, thereby effectively avoiding the phenomena of pulse splitting, pulse distortion, skirt generation and asymmetric tailing that occur during high-repetition-rate pulse transmission and amplification.

[0007] Preferably, in step S1, the pulse train is emitted by a seed source, and the seed source includes one of a MHz femtosecond seed source, a MHz picosecond seed source, a GHz femtosecond seed source, and a GHz picosecond seed source.

[0008] Preferably, in step S2, the main frequency of the pulse train after dispersion compensation is down-converted to a main frequency of ≤1 MHz.

[0009] Preferably, the method for generating a sub-hundred-femtosecond pulse train in GHz further comprises: S4, amplifying the power of the pulse train after sub-pulse modulation.

[0010] In addition to solving the technical problem in the prior art that the third-order dispersion introduced by the optical fiber is serious for short-pulse fiber laser systems, which in turn has an adverse effect on the time domain characteristics of the short-pulse laser system, this preferred solution can also solve the problems of inconsistent pulse waveforms, crosstalk between pulses, and uneven energy within the pulse train caused by high-order dispersion during frequency multiplication / modulation.

[0011] Preferably, the method for generating a sub-hundred-femtosecond pulse train in GHz further comprises: S5. After compressing the power-amplified pulse string, a sub-hundred-femtosecond pulse of GHz is output.

[0012] In addition to being able to solve the technical problems in the prior art of short-pulse fiber laser systems, such as severe third-order dispersion introduced by optical fibers, which in turn has an adverse effect on the time domain characteristics of short-pulse laser systems, as well as problems such as inconsistent pulse waveforms, crosstalk between pulses, and uneven energy within a pulse train caused by high-order dispersion during frequency multiplication / modulation, this preferred solution can also solve problems such as high-repetition-rate pulses being difficult to compress, excessive base size, and poor pulse contrast.

[0013] In a second aspect, the present invention further discloses a time-frequency control system for implementing the above-mentioned GHZ sub-hundred-femtosecond pulse train generation method, comprising: A light source for emitting a pulse train; A first modulation module, the input end of which is connected to the output end of the seed light source, and is used to pre-compensate for the dispersion of the pulse train emitted by the seed light source; A second modulation module, the input end of the second modulation module is connected to the output end of the first modulation module, and is used to modulate the pulse string modulated by the first modulation module to reduce the main frequency of the pulse string; A third modulation module, the input end of the third modulation module is connected to the output end of the second modulation module, and is used to modulate the pulse string modulated by the second modulation module, so that the sub-pulse frequency of the pulse string is doubled to the GHz level, and output GHz sub-hundredth femtosecond pulses.

[0014] Preferably, the second modulation module adopts an acousto-optic modulator for reducing the main frequency of the pulse string after dispersion pre-compensation by performing acousto-optic modulation on the pulse string to reduce the frequency of the pulse string.

[0015] Preferably, the third modulation module uses a frequency multiplier to modulate the sub-pulse frequency in the down-converted pulse string to GHz.

[0016] Preferably, the time-frequency control system further comprises: A power amplification module, the input end of which is connected to the output end of the third modulation module, for amplifying the power and broadening the spectrum of the pulse train modulated by the third modulation module; A compression module, the input end of which is connected to the output end of the power amplification module, is used to compress the pulse string after power amplification and output a GHz sub-hundred femtosecond pulse string.

[0017] This preferred solution can achieve GHz and THz pulses of less than 100 femtoseconds, and can optimize the pulse waveform after amplification and compression.

[0018] In a third aspect, the present invention further discloses a femtosecond laser, including the time-frequency control system as described above, capable of implementing the method for generating a sub-hundred-GHz femtosecond pulse train as described above.

[0019] The present invention has the following beneficial effects: the present invention effectively solves the technical problem in the prior art that the third-order dispersion introduced by the optical fiber is serious for the short-pulse optical fiber laser system, thereby adversely affecting the time domain characteristics of the short-pulse laser system. The present invention can pre-compensate the third-order dispersion of the system, thereby effectively avoiding the pulse splitting, pulse distortion, skirt generation and asymmetric tailing phenomena that occur during the transmission and amplification of high-repetition-rate pulses, ensuring the compressibility of GHz pulse trains, increasing the repetition rate from GHz to THz, outputting high-power GHz and THz pulse trains of less than 100 femtoseconds, realizing the generation and amplification of sub-hundred-femtosecond pulses with repetition rates of up to the GHz and THz levels, and being able to optimize the pulse waveform after amplification and compression. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to make the purpose, technical solution and advantages of the invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings, in which: Figure 1 This is the influence of third-order dispersion in the existing technology on ultrashort pulse transmission and compression.

[0021] Figure 2 It is a schematic flow chart of the method for generating a GHZ sub-hundred-femtosecond pulse train according to the present invention.

[0022] Figure 3 FIG. 4 is a working principle diagram of a frequency multiplier in an embodiment of the present invention. DETAILED DESCRIPTION

[0023] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0024] It should be noted that similar numbers and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In the description of the present invention, it should be noted that the orientation or position relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the invention product is usually placed when used, which 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 cannot be understood as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In addition, the terms "horizontal", "vertical", etc. do not mean that the components are required to be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted. In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0025] The present invention can be applied to the fields of high-speed communication, optical spectrum analysis, laser measurement, etc., for example, in ultrafast optics, frequency comb technology and high-speed data transmission.

[0026] See also Figure 1 , Figure 1 This figure shows the influence of third-order dispersion on ultrashort pulse transmission and compression in the existing technology. As can be seen from the figure, 30000fs 3 The third-order dispersion in the process of ultrashort pulse transmission and compression will cause various effects including asymmetric pulse tailing, crosstalk between pulses, reduced pulse contrast, and uneven energy within the pulse train.

[0027] First, see Figure 2 Based on the technical problems solved above, the present invention discloses a method for generating a GHZ sub-hundred-femtosecond pulse train, comprising the following steps: S1, pre-compensate the pulse train for dispersion; S2, down-converting the main frequency of the pulse train after dispersion pre-compensation to kHz level or MHz level; S3, after modulating the sub-pulse frequency in the pulse train after the main frequency is reduced to GHz level, output GHz sub-hundred-femtosecond pulses.

[0028] The present invention solves the technical problem in the prior art that the third-order dispersion introduced by the optical fiber is serious for short-pulse optical fiber laser systems, thereby adversely affecting the time domain characteristics of the short-pulse laser system. The present invention can pre-compensate the third-order dispersion of the system, thereby effectively avoiding the phenomena of pulse splitting, pulse distortion, skirt generation and asymmetric tailing that occur during high-repetition-rate pulse transmission and amplification.

[0029] Specifically, the GHZ sub-hundred femtosecond pulse train refers to a pulse train with a pulse width of sub-hundred femtoseconds and transmitted at a high repetition frequency of GHz; wherein, "sub-hundred femtosecond" means that the pulse width is less than 100 femtoseconds, the pulse width is very short, the time duration of the light wave is very short, and it has extremely high time resolution; wherein, a large number of pulses can be generated in a very short time with a high repetition frequency of GHz, and these short pulses are arranged together at certain time intervals to form a continuous sequence or string, and the GHZ sub-hundred femtosecond pulse train is suitable for application in fields requiring high data rates or high-precision measurements.

[0030] Specifically, the method for generating a GHz sub-hundred femtosecond pulse train according to the first aspect of the embodiment of the present application can generate a sub-hundred femtosecond GHz pulse train with high signal-to-noise ratio and high peak power.

[0031] Preferably, in step S1, the pulse train is emitted by a seed source, and the seed source includes one of a MHz femtosecond seed source, a MHz picosecond seed source, a GHz femtosecond seed source, and a GHz picosecond seed source.

[0032] Specifically, when the seed source is MHz, it is necessary to first modulate the sub-pulse frequency to GHz before performing step S1, and when the seed source is GHz, there is no need to increase the frequency.

[0033] Specifically, the seed source adopts a femtosecond / picosecond laser with a repetition rate of MHz or GHz.

[0034] Preferably, in step S1, single-stage or multi-stage dispersion pre-compensation is adopted.

[0035] Preferably, in step S1, the dispersion pre-compensation is located before or after the seed source emits a pulse train.

[0036] Preferably, in step S1, the dispersion precompensation includes performing second-order and third-order dispersion precompensation on the pulse train.

[0037] In a specific implementation, the second-order and third-order dispersion of the pulse train can be pre-compensated by using one of a chirped fiber grating, a prism pair, a prism pair, a chirped mirror, a dispersion compensating fiber, a dispersion flattened fiber, and a programmable acousto-optic modulator.

[0038] During specific implementation, in step S1, the compensated second-order and third-order dispersions have opposite signs to the net second-order and third-order dispersions of the system, and the range is adjustable.

[0039] Specifically, second-order dispersion refers to the frequency-dependent phase change related to the second derivative of frequency. The goal of pre-compensating second-order dispersion is to make the phase changes experienced by light waves of different frequencies during propagation cancel each other out, thereby reducing or eliminating the second-order dispersion effect; third-order dispersion refers to the frequency-dependent phase change related to the third derivative of frequency. The goal of pre-compensating third-order dispersion is to make the phase changes experienced by light waves of different frequencies during propagation cancel each other out, thereby reducing or eliminating the waveform distortion caused by third-order dispersion.

[0040] By pre-compensating the second-order and third-order dispersion, the phase changes experienced by light waves of different frequency components during propagation can be offset each other, thereby maintaining the waveform consistency of the entire pulse train, reducing waveform distortion, splitting and other problems caused by dispersion, reducing distortion during pulse propagation, and making the pulse performance more stable and controllable; pre-compensating the second-order and third-order dispersion of the pulse train can achieve the purpose of maintaining waveform consistency, reducing pulse distortion, and improving pulse contrast.

[0041] Preferably, in step S2, the main frequency of the pulse train after dispersion compensation is down-converted to a main frequency of ≤1 MHz.

[0042] Preferably, in step S2, the main frequency of the pulse train after dispersion compensation is down-converted to a range of 10 kHz to 1 MHz.

[0043] Preferably, in step S2, the main frequency of the pulse train after dispersion pre-compensation is down-converted by performing acousto-optic modulation on the pulse train.

[0044] As one of the ways to implement acousto-optic modulation of a pulse train to reduce the frequency of the pulse train, an acousto-optic modulator is used.

[0045] Specifically, the principle of using an acousto-optic modulator to implement acousto-optic modulation of a pulse train to reduce the frequency of the pulse train is to utilize the interaction between sound waves and light waves in an optical crystal. The propagation of sound waves through the crystal causes the refractive index of light to change over time, thereby causing the phase of the incident light to be modulated. For the pulse train in this solution, the acousto-optic modulator introduces sound waves into the crystal, causing the refractive index of light in the crystal to change periodically, thereby causing the phase of the pulse train to be modulated. Since the frequency of sound waves is usually much lower than the frequency of light waves, the frequency of light waves in the pulse train is reduced. Then, by controlling the frequency and intensity of the sound waves, the degree of frequency reduction of the light waves can be adjusted, thereby accurately controlling the frequency modulation of the pulse train.

[0046] Preferably, in step S3, the sub-pulse frequency in the pulse string after the main frequency is down-converted is modulated to GHz, including using a frequency multiplier to modulate the sub-pulse frequency in the pulse string after the main frequency is down-converted to GHz, and outputting GHz sub-hundredth femtosecond pulses.

[0047] Preferably, the method for generating a sub-hundred-femtosecond pulse train in GHz further comprises: S4, amplifying the power of the pulse train after sub-pulse modulation.

[0048] In addition to solving the technical problem in the prior art that the third-order dispersion introduced by the optical fiber is serious for short-pulse fiber laser systems, which in turn has an adverse effect on the time domain characteristics of the short-pulse laser system, this preferred solution can also solve the problems of inconsistent pulse waveforms, crosstalk between pulses, and uneven energy within the pulse train caused by high-order dispersion during frequency multiplication / modulation.

[0049] Preferably, in step S4, the power of the pulse train after sub-pulse modulation is amplified by nonlinear amplification to expand the spectrum width.

[0050] Preferably, the nonlinear amplification method can adopt one of self-similar amplification, parabolic amplification, and chirped pulse amplification plus self-similar amplification.

[0051] Preferably, the method for generating a sub-hundred-femtosecond pulse train in GHz further comprises: S5. After compressing the power-amplified pulse string, a sub-hundred-femtosecond pulse of GHz is output.

[0052] In addition to being able to solve the technical problems in the prior art of short-pulse fiber laser systems, such as severe third-order dispersion introduced by optical fibers, which in turn has an adverse effect on the time domain characteristics of short-pulse laser systems, as well as problems such as inconsistent pulse waveforms, crosstalk between pulses, and uneven energy within a pulse train caused by high-order dispersion during frequency multiplication / modulation, this preferred solution can also solve problems such as high-repetition-rate pulses being difficult to compress, excessive base size, and poor pulse contrast.

[0053] Preferably, in step S5, the pulse train after power amplification can be compressed by using one of a grating pair and a chirped mirror, and finally a GHz sub-hundred-femtosecond pulse train is obtained. This preferred solution can achieve GHz and THz pulses less than 100 femtoseconds, and can optimize the pulse waveform after amplification and compression.

[0054] In a second aspect, the present invention further discloses a time-frequency control system for implementing the above-mentioned GHZ sub-hundred-femtosecond pulse train generation method, comprising: A light source for emitting a pulse train; A first modulation module, the input end of which is connected to the output end of the seed light source, and is used to pre-compensate for the dispersion of the pulse train emitted by the seed light source; A second modulation module, the input end of the second modulation module is connected to the output end of the first modulation module, and is used to modulate the pulse string modulated by the first modulation module to reduce the main frequency of the pulse string; A third modulation module, the input end of the third modulation module is connected to the output end of the second modulation module, and is used to modulate the pulse string modulated by the second modulation module, so that the sub-pulse frequency of the pulse string is doubled to the GHz level, and output GHz sub-hundredth femtosecond pulses.

[0055] Preferably, the seed source adopts a femtosecond / picosecond laser with a repetition rate of MHz or GHz, which can emit a MHz femtosecond seed source, a MHz picosecond seed source, a GHz femtosecond seed source, and a GHz picosecond seed source respectively.

[0056] Specifically, the first modulation module can pre-compensate for the second-order dispersion and third-order dispersion of the pulse train emitted by the light source, and control the evolution process of the pulse in the time domain and the frequency domain.

[0057] Preferably, the first modulation module can adopt one of a chirped fiber grating, a prism pair, a prism pair, a chirped mirror, a dispersion compensating fiber, a dispersion flattened fiber, and a programmable acousto-optic modulator.

[0058] Preferably, the first modulation module is provided with a plurality of groups for performing dispersion pre-compensation on the pulse string emitted by the seed source before or after the seed source emits the pulse string.

[0059] Preferably, the second modulation module can down-convert the main frequency of the dispersion-compensated pulse train to kHz level or MHz level.

[0060] Furthermore, the second modulation module can reduce the main frequency of the pulse train after dispersion compensation to a range of 10kHz to 1MHz.

[0061] Preferably, the second modulation module uses an acousto-optic modulator to reduce the main frequency of the pulse train after dispersion pre-compensation by acousto-optic modulation of the pulse train. Specifically, the principle of using an acousto-optic modulator to implement acousto-optic modulation of the pulse train to reduce the frequency of the pulse train is to utilize the interaction between sound waves and light waves in optical crystals. The propagation of sound waves through the crystal causes the refractive index of light to change over time, thereby causing the phase of the incident light to be modulated. For the pulse train in this scheme, the acousto-optic modulator introduces sound waves into the crystal, causing the refractive index of light in the crystal to change periodically, thereby causing the phase of the pulse train to be modulated. Since the frequency of sound waves is usually much lower than the frequency of light waves, the frequency of light waves in the pulse train is reduced. Then, by controlling the frequency and intensity of the sound waves, the degree of frequency reduction of the light waves can be adjusted, thereby accurately controlling the frequency modulation of the pulse train.

[0062] Preferably, the third modulation module uses a frequency multiplier to modulate the sub-pulse frequency in the down-converted pulse string to GHz.

[0063] Specifically, the frequency multiplier includes a fiber coupler, which includes an input end, a first output end, and a second output end. The input end is used to connect an input optical signal, the first output end is used to connect a first beam splitter input end, the second output end is used to connect a second beam splitter input end, the output end of the first beam splitter is connected to a first beam combiner, the output end of the second beam splitter is connected to a second beam combiner, and the input optical signal is output from the output ends of the first beam combiner and the second beam combiner, respectively.

[0064] Specifically, the first beam splitter and the second beam splitter are 1×N beam splitters, and the first beam combiner and the second beam combiner are N×1 beam combiners. The 1×N beam splitter is used to divide the input optical signal into N channels, and the 1×N beam splitter is provided with N output ends corresponding to the N channels; the N×1 beam combiner includes N input ends, which correspond to and are connected to the N output ends of the 1×N beam splitter respectively, and the N×1 beam combiner is used to converge the optical signals of the N channels into one output port and output them.

[0065] Specifically, the optical fiber coupler is a 50:50 optical fiber coupler, which is used to evenly divide the input optical signal into two paths, which are output from the first output end and the second output end respectively, with each path accounting for 50% of the optical power.

[0066] Specifically, the principle of the frequency multiplier is that after acousto-optic modulation, a nonlinear optical effect is induced, and then the nonlinear effect can generate a new frequency component in the optical channel of the frequency multiplier, such as a second harmonic, so that twice the original frequency is generated in the output. The new frequency component is detected at the output end, and then the combination of a fiber coupler, a beam splitter, and a beam combiner can be used to achieve frequency multiplication.

[0067] See also Figure 3 , showing the schematic diagram of the structure of one of the frequency multipliers. The principle is to use the fast and slow axes of two PBSs to achieve frequency multiplication. The fast and slow axes of the two PBSs are connected by polarization-maintaining fibers. The refractive index difference between the fast and slow axes of the polarization-maintaining fiber is 10 -4 , through the 1μm band, the corresponding delay is 1fs / 3mm (0.33fs / mm). Figure 3 In the figure, the line connecting point ACB has a fast axis length of 1m, the line connecting point ADB has a slow axis length of 1m, and the refractive index difference of the polarization-maintaining fiber is 0.0001. Then the pulse delay of the 1030nm ultrashort pulse passing through the line connecting point ACB and the line connecting point ADB is 330fs.

[0068] Preferably, the time-frequency control system further comprises: A power amplification module, the input end of which is connected to the output end of the third modulation module, for amplifying the power and broadening the spectrum of the pulse train modulated by the third modulation module; A compression module, the input end of which is connected to the output end of the power amplification module, is used to compress the pulse string after power amplification and output a GHz sub-hundred femtosecond pulse string.

[0069] This preferred solution can achieve GHz and THz pulses of less than 100 femtoseconds, and can optimize the pulse waveform after amplification and compression.

[0070] Preferably, the power amplification module adopts one of self-similar amplification, parabolic amplification, chirped pulse amplification plus self-similar amplification. Specifically, the power amplification module adopts a nonlinear amplification method to expand the spectrum width.

[0071] Among them, the principle of chirped amplification technology is to disperse the energy of laser seed pulses before amplification and then concentrate it after amplification. Although chirped pulse amplification technology can obtain higher single pulse energy, there is no spectrum broadening process in its amplification process. At the same time, the strong gain narrowing effect will also cause the output pulse width to become wider. The output pulse width is often in the order of hundreds of femtoseconds. Self-similar amplification technology controls the nonlinear effect in the amplification process to accumulate linear chirps, which can achieve pulse spectrum broadening while amplifying the pulse power, support high pulse energy, and the output result is independent of the shape of the incident pulse.

[0072] Preferably, the compression module can adopt one of a grating pair and a chirped mirror. The linear chirp generated during the pulse amplification process can be compressed by the grating pair, which provides conditions for obtaining high-power and high-energy femtosecond pulse laser output.

[0073] Preferably, when the seed source is of MHz, a fourth modulation module is further provided for modulating the sub-pulse frequency of the seed source to GHz.

[0074] In a third aspect, the present invention further discloses a femtosecond laser, including the time-frequency control system as described above, capable of implementing the method for generating a sub-hundred-GHz femtosecond pulse train as described above.

[0075] The GHz sub-hundred-femtosecond pulse train generation method, time-frequency control system and femtosecond laser disclosed in the present invention have the following technical effects: the present invention effectively solves the problems of inconsistent pulse waveforms, crosstalk between pulses, and uneven energy within the pulse train caused by high-order dispersion in the frequency multiplication / modulation process, effectively avoids the phenomena of pulse splitting, pulse distortion, skirt and asymmetric tailing in the process of high repetition rate pulse transmission and amplification, effectively solves the problems of difficult compression of high repetition rate pulses, excessive base, poor pulse contrast, etc., ensures the compressibility of GHz pulse trains, increases the repetition rate from GHz to THz, outputs high-power GHz and THz pulse trains of less than 100 femtoseconds, and realizes the generation and amplification of sub-hundred-femtosecond pulses with repetition rates of up to GHz and THz levels.

[0076] It can be understood that the present invention is described by some embodiments, and those skilled in the art are aware that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the present invention. The embodiments described in the present invention are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the invention claimed for protection, but only represents the selected embodiments of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all other embodiments obtained by ordinary technicians in the field without creative work based on the embodiments in the present invention belong to the scope of protection of the present invention.

Claims

1. A method for generating a sub-hundred-femtosecond GHz pulse train, characterized in that: The following steps are involved: S1, pre-compensate the pulse train for dispersion; S2, down-converting the main frequency of the pulse train after dispersion pre-compensation to kHz level or MHz level; S3, after modulating the sub-pulse frequency in the pulse string after the main frequency is reduced to GHz level, output GHz sub-hundred-femtosecond pulses.

2. The method for generating a GHZ sub-hundred-femtosecond pulse train according to claim 1, characterized in that: In step S1, the pulse train is emitted by a seed source, and the seed source includes one of a MHz femtosecond seed source, a MHz picosecond seed source, a GHz femtosecond seed source, and a GHz picosecond seed source.

3. The method for generating a GHZ sub-hundred-femtosecond pulse train according to claim 2, characterized in that: In step S2, the main frequency of the pulse train after dispersion compensation is reduced to a main frequency of ≤1 MHz.

4. The method for generating a GHZ sub-hundred-femtosecond pulse train according to claim 3, characterized in that: The method for generating a sub-100 GHz femtosecond pulse train further comprises: S4, amplifying the power of the pulse train after sub-pulse modulation.

5. The method for generating a GHz sub-hundred-femtosecond pulse train according to claim 4, characterized in that: The method for generating a sub-100 GHz femtosecond pulse train further comprises: S5. After compressing the power-amplified pulse string, a sub-hundred-femtosecond pulse of GHz is output.

6. A time-frequency control system for implementing the method for generating a 100-femtosecond GHz pulse train as claimed in claim 1, characterized in that: include: A light source for emitting a pulse train; A first modulation module, the input end of which is connected to the output end of the seed light source, and is used to pre-compensate for the dispersion of the pulse train emitted by the seed light source; A second modulation module, the input end of the second modulation module is connected to the output end of the first modulation module, and is used to modulate the pulse string modulated by the first modulation module to reduce the main frequency of the pulse string; A third modulation module, the input end of the third modulation module is connected to the output end of the second modulation module, and is used to modulate the pulse string modulated by the second modulation module, so that the sub-pulse frequency of the pulse string is doubled to the GHz level, and output GHz sub-hundredth femtosecond pulses.

7. The time-frequency control system according to claim 6, characterized in that: The second modulation module adopts an acousto-optic modulator, which is used to reduce the main frequency of the pulse string after dispersion pre-compensation by performing acousto-optic modulation on the pulse string to reduce the frequency of the pulse string.

8. The time-frequency control system according to claim 7, characterized in that: The third modulation module uses a frequency multiplier to modulate the sub-pulse frequency in the down-converted pulse train to GHz.

9. The time-frequency control system according to claim 8, characterized in that: The time-frequency control system also includes: A power amplification module, the input end of which is connected to the output end of the third modulation module, for amplifying the power and broadening the spectrum of the pulse train modulated by the third modulation module; A compression module, the input end of which is connected to the output end of the power amplification module, is used to compress the pulse string after power amplification and output a GHz sub-hundred femtosecond pulse string.

10. A femtosecond laser, characterized in that: Comprising the time-frequency control system as claimed in claim 1.

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