TW202239088A - Gigahertz pulse train femtosecond laser source capable of simultaneously increasing the inter-train frequency and the high-energy femtosecond laser source - Google Patents

Abstract

The invention is a gigahertz pulse train femtosecond laser source, comprising a femtosecond-pulse seed light source, a femtosecond laser pulse stretcher, a gigahertz train generation module, a femtosecond laser amplifier, and a femtosecond laser compressor. Wherein, the gigahertz train generation module includes a first acousto-optic modulator, fiber-coupled optical splitter, gain fiber, wavelength division multiplexer, optical isolator, passive fiber, pump diode laser, and a second acousto-optic modulator, which are used to receive the stretched pulse light from the femtosecond laser pulse stretcher and converts the stretched pulse light into low repetition rate pulse light and output it to the femtosecond laser amplifier. Therefore, the present invention utilizes the gigahertz train generation module to realize a reliable and effective solution, which can simultaneously increase the inter-train frequency and the high-energy femtosecond laser source to meet the requirements in practical application fields.

Description

Gigahertz pulse train femtosecond laser source

The invention relates to a gigahertz pulse train femtosecond laser source, in particular, it utilizes a first acousto-optic modulator, a fiber-coupled optical splitter, a gain fiber, a wavelength division multiplexer, an optical isolator, a passive fiber, a pump Pu diode laser, gigahertz series generation module of the second acousto-optic modulator, with femtosecond pulse seed light source, femtosecond laser pulse stretcher, femtosecond laser amplifier, femtosecond laser compressor, It is used to receive the stretched pulse light from the femtosecond laser pulse stretcher, convert the stretched pulse light into low repetition rate pulse light and output it to the femtosecond laser amplifier, so as to realize a reliable and effective solution, which can simultaneously improve the serial Inter-column frequency and high-energy femtosecond laser sources to meet the needs of practical applications.

Femtosecond laser sources have extremely high application value for industrial micromachining (down to the micron level). The main reason is that femtosecond laser sources can achieve "cold" processing effects, and there is almost no thermal effect. Lasers have thermal effects, resulting in poor processing results.

Please refer to the first picture, the schematic diagram of the femtosecond laser source pulse. In general, the pulse length of the femtosecond laser source pulse itself is 100-1000 femtoseconds. Femtosecond laser source pulses have two repetitive periods, wherein the pulse interval Tpulse between pulses is usually 10-50 nanoseconds.

In addition, for a burst consisting of multiple pulses, the burst interval Tburst between bursts is usually 1 microsecond to 1000 microseconds (us), and the burst interval Tburst The reciprocal of is defined as the inter-burst frequency (inter-burst frequency). Generally, the inter-burst frequency of the femtosecond laser seed source is 20-100MHz.

Referring to the second figure, a schematic diagram of a conventional femtosecond laser source, a conventional femtosecond laser source is generally composed of five parts, including a femtosecond pulse seed light source 10, a femtosecond laser pulse stretcher 20, A pulse selector 30 , a femtosecond laser amplifier 40 , and a femtosecond laser compressor 50 .

Specifically, the femtosecond pulsed seed light source 10 produces low-energy original pulsed light L10, wherein the pulse repetition rate of the original pulsed light L10 is 20-100 MHz, and the pulse length of the original pulsed light L10 is about 100-1000 femtoseconds. After that, The femtosecond laser pulse stretcher 20 extends the extended pulse light L20 of 100-1000 picoseconds, and then selects the pulse selector 30 to generate a low repetition rate pulse light L30 with a repetition rate reduced to 1-1000 kHz. The high-energy pulsed light L40 is generated by the amplification process of the second laser amplifier 40 , and finally, the required femtosecond pulsed light L50 is generated by performing appropriate femtosecond compression processing by the femtosecond laser compressor 50 .

The above technique is generally called chirped pulse amplification (CPA), which is a fairly common femtosecond laser technique in the prior art.

It is known that increasing the inter-tandem frequency from 20-100MHz to 1-10GHz can be more effectively applied to microfabrication, and the so-called more effective means that the material removal amount per pulse per unit time can be increased, and at the same time It can also maintain the characteristics of cold working. Therefore, how to make a 1-10 gigahertz (GHz) tandem high-energy femtosecond laser source is an important subject in the two technical fields of femtosecond laser source and industrial microprocessing.

However, in the conventional technology, one is to directly select and amplify the pulses by a femtosecond laser seed source with a gigahertz pulse repetition rate, but this method requires multi-stage amplifiers and the pulse train interval is determined by the seed source, which is not easy to reproduce. Make engineering adjustments. Another method is to use a 20-100MHz femtosecond laser seed source to generate pulse trains in the form of an interleaver, but this method also requires multi-stage interleavers and amplifiers, and the system is more complicated. In other words, there is currently a lack of reliable and effective solutions to meet the needs of simultaneously increasing the inter-tandem frequency and high-energy femtosecond laser sources in practical applications. Therefore, there is a great need for an innovative gigahertz pulse train femtosecond laser source to solve the above-mentioned problems of the prior art.

The main purpose of the present invention is to provide a gigahertz pulse train femtosecond laser source, including a femtosecond pulse seed light source, a femtosecond laser pulse stretcher, a gigahertz train generator module, a femtosecond laser amplifier, a femtosecond A laser compressor is used to generate femtosecond pulsed light as a gigahertz pulse train femtosecond pulsed light.

Specifically, the femtosecond pulse seed light source is used to generate the original pulse light, and the original pulse light has a pulse repetition rate of 20-100MHz and a pulse length of 100-1000 femtoseconds, and the femtosecond laser pulse stretcher is used to After receiving the original pulsed light, it is extended to generate extended pulsed light.

In addition, the gigahertz tandem generation module is used to receive the extended pulse light, and then reduce the repetition rate to generate low repetition rate pulse light. The femtosecond laser amplifier is used to receive the low repetition rate pulse light and amplify it. High-energy pulsed light is generated after processing. Furthermore, the femtosecond laser compressor is used to receive high-energy pulsed light, and generate and output femtosecond pulsed light through compression processing, which is regarded as the required gigahertz pulse train femtosecond pulsed light.

Therefore, the present invention utilizes and utilizes the first acousto-optic modulator, fiber-coupled optical splitter, gain fiber, wavelength division multiplexer, optical isolator, passive optical fiber, pumping diode laser, the second acousto-optic modulator The gigahertz serial generation module is equipped with a femtosecond pulse seed source, a femtosecond laser pulse stretcher, a femtosecond laser amplifier, and a femtosecond laser compressor to receive the stretched pulse from the femtosecond laser pulse stretcher Light, and convert the extended pulse light into low repetition rate pulse light and output to the femtosecond laser amplifier, so as to realize a reliable and effective solution, which can simultaneously increase the inter-tandem frequency and high-energy femtosecond laser source, so as to meet requirements in practical applications.

The implementation of the present invention will be described in more detail below in conjunction with the diagrams and component symbols, so that those skilled in the art can implement it after studying this specification.

Please refer to the third figure and the fourth figure, which are schematic diagrams of a gigahertz (GHz) pulse train femtosecond laser source and a schematic diagram of a gigahertz train generating module, respectively, according to an embodiment of the present invention. As shown in the third and fourth figures, the gigahertz pulse train femtosecond laser source of the embodiment of the present invention includes a femtosecond pulse seed light source 10, a femtosecond laser pulse stretcher 20, and a gigahertz train generator module 31. Femtosecond laser amplifier 40, femtosecond laser compressor 50, wherein in addition to the gigahertz serial generation module 31, femtosecond pulse seed light source 10, femtosecond laser pulse stretcher 20, femtosecond laser amplifier 40. The femtosecond laser compressor 50 belongs to the conventional technology, that is, the present invention replaces the traditional pulse picker 30 with the gigahertz serial generation module 31 .

Since the technical content of the femtosecond pulse seed light source 10, the femtosecond laser pulse stretcher 20, the femtosecond laser amplifier 40, and the femtosecond laser compressor 50 have been described in detail, they will not be described in detail below, but only focus on the description The technology and characteristics of the gigahertz serial generation module 31.

In general, the feature of the present invention is that the gigahertz pulse train is generated by the femtosecond pulse seed light source by using the gigahertz train generating module 31 . Wherein the femtosecond pulse seed light source 10 produces the original pulsed light SA with a pulse repetition rate of 20-100 MHz and a pulse length of about 100-1000 femtoseconds, and the femtosecond laser pulse stretcher 20 extends the original pulsed light SA to generate a stretched pulse After the light S1 is processed by the gigahertz serial generation module 31 of the present invention, the low repetition rate pulsed light S4 is generated, and further processed by the subsequent femtosecond laser amplifier 40 and femtosecond laser compressor 50 to generate Femtosecond pulse light SC with gigahertz serial femtosecond pulses, wherein the femtosecond laser amplifier 40 and femtosecond laser compressor 50 only amplify the gigahertz serial pulse from a low energy of about 1-100nJ to about High energy grade for industrial use from 1-100uJ.

Further refer to the fourth figure, which is a schematic diagram of the gigahertz train generating module in the gigahertz pulse train femtosecond laser source of the present invention. As shown in the fourth figure, the GHz-burst generator 31 of the present invention mainly includes a first acousto-optic modulator (AOM) 32, a fiber coupling splitter (Fiber coupler) ) 33. Gain fiber (Gain fiber) 34. Wavelength Division Multiplexer (Wavelength Division Multiplexer, WDM) 35. Optical isolator (Faraday isolator) 36. Passive fiber (Passive fiber) 37. Pump diode laser ( Pumping diode laser) 38, the second acousto-optic modulator 39, in order to receive the extended pulsed light S1 from the femtosecond laser pulse stretcher 20, and convert the extended pulsed light S1 into low repetition rate pulsed light S4 and output to the femtosecond s laser amplifier 40.

More specifically, the first acousto-optic modulator 32 and the fiber-coupled optical splitter 33 are sequentially connected via the optical fiber F, and the first acousto-optic modulator 32 and the second acousto-optic modulator 39 are used as optical switches, It is used to select the required pulse in the time domain, and the fiber-coupled optical splitter 33 provides the optical splitting function, especially, the first acousto-optic modulator 32 receives the extended pulse light S1 input by the previous stage and has a fixed pulse repetition rate, After being modulated, the first modulated pulsed light S2 is produced, and the fiber-coupled optical splitter 33 receives the first modulated pulsed light S2 and the isolated pulsed light S36 and generates and outputs the split pulsed light S3 and Coupled pulsed light S33, the second acousto-optic modulator 39 receives the coupled pulsed light S33 and generates low repetition rate pulsed light S4 after modulation.

Further, the fiber-coupled optical splitter 33 is a fiber-optic 50/50 optical splitter, which is a common component in the prior art, and is used to divide any input light of the first modulated pulsed light S2 and the polarization-maintaining pulsed light S37 into split pulsed light For the two output lights of S3 and coupled pulsed light S33, the light splitting ratio can be preferably selected as about 50%:50%, but it can also be selected as 60/40, 70/30, 80/20 etc. according to actual needs. It should be noted that the above light splitting ratio is not a key parameter for the present invention, but is just an exemplary example for conveniently illustrating the features of the present invention.

In addition, the gain fiber 34 can be Ytterbium doped single mode polarization maintaining fiber (Ytterbium doped single mode polarization maintaining fiber), used as optical amplification, and connected to the fiber-coupled optical splitter 33, in order to receive the output of the fiber-coupled optical splitter 33 The pulsed light S33 is coupled to generate and output the gain pulsed light S34.

Furthermore, the wavelength division multiplexer 35 is connected to the gain fiber 34 and the pump diode laser 38, for receiving the gain pulsed light S34 output by the gain fiber 34 and the continuous light S38 from the pump diode laser 38 , and generate and output demultiplexed pulsed light S35 through wavelength division multiplexing processing, wherein the wavelength division multiplexer 35 is to provide the pumping function of the gain fiber 34, and the pumping diode laser 38 is a single-mode laser with a wavelength of 976nm The diode laser can generate continuous light S38 with an energy of about 300-600mW and a wavelength of 976nm, so as to provide energy to the gain fiber 34 for optical amplification.

In addition, the optical isolator 36 is connected to the wavelength division multiplexer 35 for receiving the demultiplexed pulsed light S35, and generating and outputting the isolated pulsed light S36 after isolation processing. The optical isolator 36 can be a fiber-optic polarization-maintaining optical isolator, and its function is to allow the demultiplexed pulsed light S35 to pass through only one direction, while the other direction has a great loss, that is, from the optical isolator 36 to the passive optical fiber. The direction of 37, wherein the passive optical fiber 37 can choose the polarization maintaining fiber PM980, which is used to provide the polarization maintaining function in the 1030nm band, and receive the isolated pulse light S36, and generate and output the polarization maintaining pulse light S37 after polarization maintaining to the fiber coupling splitter Device 33.

In particular, pay attention to the traveling direction of the light in the fourth picture, and refer to the time-domain pulse changes in the fifth picture and the sixth picture as a comparison, where the sixth picture is the part of the partial enlarged area A in the fifth picture The enlarged signal diagram is used to illustrate the working principle of the gigahertz serial generation module 31 in the present invention.

First, you can refer to the third figure at the same time. The extended pulse light S1 is input from the input end of the gigahertz serial generation module 31. The extended pulse light S1 is generated by the femtosecond pulse seed light source 10 and has a fixed pulse repetition frequency. , and the pulse interval Tpulse between pulses is fixed, and the pulse repetition frequency fpulse is calculated by the formula fpulse= 1/Tpulse.

For example, the pulse interval Tpulse is generally in the range of 10-100 ns, therefore, the pulse repetition frequency fpulse can be calculated as about 10-100 MHz. Generally speaking, the energy of the pulse at this time is only from the seed light source, which is usually not high, about in the range of 0.1-10nJ, which is not enough for any material processing application, so it still needs to go through the subsequent femtosecond laser amplifier After the magnification of 40, it has enough strength to achieve the processing effect of destroying materials.

After passing through the first AOM 32 of the gigahertz serial generation module 31, the first modulated pulsed light S2 is output, and since the first AOM 32 is a photoelectric switch, the first control signal CT1 is in a low potential state , or when it is generally known as the switch-off state), the extended pulsed light S1 cannot pass through the first AOM 32, so a loss of about 30-60 dB will be generated. Therefore, when the first control signal CT1 is at a low potential, the first modulated pulsed light S2 does not appear, and the extended pulsed light S1 can pass through the first acousto-optic modulation until the first control signal CT1 turns to a high potential state. The device 32 outputs the first modulated pulsed light S2. It should be noted that the passed first modulated pulsed light S2 still has a certain loss, usually ranging from 3-6 dB.

In addition, the first modulated pulsed light S2 defines the zero point at which the pulse starts to be injected into the subsequent element in time.

Referring to the fourth figure again, after the first modulated pulsed light S2 reaches the coupled pulsed light S33, it will be divided into two beams, and the light splitting ratio is determined by the coupled pulsed light S33. For example, the coupled pulsed light S33 with a split ratio of 50/50 can be used. Therefore, half of the pulse energy will be sent to the second AOM 39, and the other half of the pulse energy will be sent into the optical fiber loop, that is, The position of the gain fiber 34 is amplified.

The gain fiber 34 controls the gain required for amplification by controlling the doping concentration, the length of the fiber, and matching the wavelength or power of the pump diode laser 38. Since the technology of the gain fiber 34 belongs to the known field, therefore It will not be described in detail below. In addition, the isolated pulsed light S36 mainly allows the forward pulsed light to pass through with a loss much lower than that of the reversed light, thereby achieving the effect of avoiding the generation of reversed light in this loop.

Furthermore, the length of the passive optical fiber 37 can be used to conveniently adjust the total length of the optical fiber loop, that is, the time t required for the pulse to pass through the optical fiber loop, wherein the time t can be determined by the formula t=L/vgroup , and L is the total length of the fiber, and vgroup is the traveling group velocity of the pulse in this fiber.

In order to understand the key factors of the fiber loop length, please refer to the split pulsed light S3 in Figure 5. Here, because the pulse interval Tpulse of the femtosecond laser seed source itself is different from the time Tloop of the pulse traveling in the optical fiber loop, there will be a time difference |Tpulse – Tloop|. It should be noted that this time difference can be adjusted conveniently by adjusting the length of the passive optical fiber 37, and this time difference allows us to generate a series of pulses (burst), as shown in the sixth figure.

In the sixth figure, it can be found that the time difference is equal to the pulse train interval Tburst of the pulse train to be generated, and the time difference can be positive or negative, especially both are within the scope of this embodiment. In addition, the state shown in the fifth figure and the sixth figure is that the time difference is negative, that is, the pulse generated by the optical fiber circuit will lag slightly behind the femtosecond pulse seed light source 10 to send into the optical fiber coupling splitter every time. 33 pulses.

As a further example, the length of the passive optical fiber 37 can be controlled by using an optical fiber fusion splicer in the prior art, and then the split pulsed light S3 can be measured by a photodetector and observed with an oscilloscope, so that the split pulsed light S3 can be known. The burst interval Tburst is adjusted again.

It should be noted that the fifth diagram only shows a series of pulses of up to three, but it can be easily deduced from the fifth diagram on a more delayed axis of the time axis to generate four, five, six,,,, etc. , and so on for the burst train.

The upper limit Nmax of this pulse train is limited by the pulse interval Tpulse of the laser seed source, and is determined by the formula Nmax=Tpulse/Tburst-1. The shorter the pulse train interval Tburst, the higher the upper limit of the pulse number of the pulse train. high. For example, if the pulse repetition rate of the femtosecond laser seed source is 20 MHz, the pulse interval Tpulse is 50 ns. And the pulse train interval Tburst is 1ns if we set the final output of the burst train as 1GHz (gigahertz). Therefore, max=Tpulse/Tburst-1=50ns/1ns-1=49 can be calculated.

Next, please refer to the fourth and fifth figures, where the pulse is originally the split pulse light S3, after passing through the second acousto-optic modulator 39, the second control signal CT2 is in a low potential state (or generally recognized as When the switch is closed), the pulse cannot pass through the second AOM 39 at this time, and the loss is usually 30-60dB. Therefore, when the second control signal CT2 is at a low potential, the low repetition rate pulsed light S4 does not appear. When the second control signal CT2 turns to a high potential state, the split pulsed light S3 can pass through the second acousto-optic modulator 39 to output the low repetition rate pulsed light S4. It should be noted that the passing pulse still has a certain loss, usually ranging from 3-6dB. Through this control, a single train can be selected with the required number of pulse trains N to be sent to the next stage for pulse energy amplification.

In addition, it is also very easy to adjust the number of pulse trains. The variable number of pulses is undoubtedly very important in laser microfabrication. Programmable parameters are available for users to respond to different materials, processing speeds, and removal rates. Optimization and other adjustments. The adjustment method is to adjust the second control signal CT2 of the second acousto-optic modulator 39 so that it is synchronized with the other pulses and the second control signal CT2, and can be adjusted in time. This is, can be designed by conventional technology of general digital circuit.

In addition, the second control signal CT2 of the second AOM 39 can be used to determine the required final pulse repetition rate fpulse, where the fpulse will be lower than the initial fpulse, and this fpulse has an upper limit, wherein the upper limit is determined by The number N of pulse trains required is determined. For example, if the required number of pulse trains is N=3, as shown in the fifth figure, it can be deduced that fpulse must be less than or equal to fpulse/3, because the optical fiber loop needs to be accumulated 3 times to produce a series number of N=3 Tandem. Finally, the low repetition rate pulsed light S4 will be sent out, and can be amplified and subjected to final compression processing, and then sent out of the laser body for use by users.

In summary, the feature of the present invention is that the traditional pulse selector is replaced by a gigahertz serial generation module, and it is equipped with a femtosecond pulse seed light source, a femtosecond laser pulse stretcher, a femtosecond laser amplifier, and a femtosecond laser The laser compressor is used to receive the stretched pulse light from the femtosecond laser pulse stretcher, and convert the stretched pulse light into low repetition rate pulse light and output it to the femtosecond laser amplifier, so as to generate and output high-quality gigahertz The efficacy of pulse train femtoseconds.

In particular, the gigahertz serial generation module includes a first acousto-optic modulator, a fiber-coupled optical splitter, a gain fiber, a wavelength division multiplexer, an optical isolator, a passive fiber, a pump diode laser, and a second acousto-optic The modulator, in order to realize a reliable and effective solution, can simultaneously increase the inter-tandem frequency and the high-energy femtosecond laser source, thereby meeting the needs in practical application fields.

The above are only preferred embodiments for explaining the present invention, and are not intended to limit the present invention in any form. Therefore, any modification or change of the present invention made under the same spirit of the invention , should still be included in the scope of protection intended by the present invention.

10: Femtosecond pulsed seed light source 20: Femtosecond laser pulse stretcher 30: Pulse selector 31: Gigahertz serial generator module 32: The first acousto-optic modulator 33: Fiber-coupled optical splitter 34: Gain fiber 35: wavelength division multiplexer 36: Optical isolator 37:Passive optical fiber 38:Pump diode laser 39: The second acousto-optic modulator 40: femtosecond laser amplifier 50: femtosecond laser compressor A: Partial zoom area CT1: The first control signal CT2: Second control signal F: optical fiber L10: Original pulsed light L20: Extended Pulse Light L30: Low repetition rate pulsed light L40: High energy pulsed light L50: femtosecond pulsed light S1: Extended Pulse Light S2: the first modulated pulsed light S3: split pulsed light S33: Coupled pulsed light S34: Gain pulsed light S35: Split-wave pulsed light S36: Isolated pulsed light S37: Polarization maintaining pulsed light S38: Continuous light S4: Low repetition rate pulsed light SA: original pulsed light SB: high energy pulsed light SC: femtosecond pulsed light Tpulse: pulse interval Tburst: Burst train interval

The first figure shows the waveform diagram of the femtosecond laser source pulse in the prior art. The second figure shows a schematic diagram of a conventional femtosecond laser source. The third figure shows a schematic diagram of a gigahertz pulse train femtosecond laser source according to an embodiment of the present invention. Figure 4 shows a schematic diagram of a gigahertz train generating module in a gigahertz pulse train femtosecond laser source according to the present invention. FIG. 5 shows waveforms generated by a gigahertz pulse train femtosecond laser source according to an embodiment of the present invention. The sixth figure shows a partial enlarged schematic diagram of the fifth figure.

31: Gigahertz serial generator module

32: The first acousto-optic modulator

33: Fiber-coupled optical splitter

34: Gain fiber

35: wavelength division multiplexer

36: Optical isolator

37:Passive optical fiber

38:Pump diode laser

39: The second acousto-optic modulator

F: optical fiber

S1: Extended Pulse Light

S2: the first modulated pulsed light

S3: split pulsed light

S33: Coupled pulsed light

S34: Gain pulsed light

S35: Split-wave pulsed light

S36: Isolated pulsed light

S37: Polarization maintaining pulsed light

S38: Continuous light

S4: Low repetition rate pulsed light

Claims (5)

A gigahertz (GHz) pulse train femtosecond laser source, comprising: A femtosecond pulsed seed light source is used to generate an original pulsed light having a pulse repetition rate and a pulse length; A femtosecond laser pulse stretcher is used to receive the original pulse light and stretch it to generate an extended pulse light; A gigahertz serial generation module is used to generate a low repetition rate pulse light after receiving the extended pulse light and reducing the repetition rate; A femtosecond laser amplifier is used to receive the low repetition rate pulsed light and generate a high energy pulsed light after an amplification process; and A femtosecond laser compressor is used to receive the high-energy pulsed light, and generate and output femtosecond pulsed light through compression processing, which is regarded as a GHz pulse train femtosecond pulsed light, The gigahertz serial generation module includes: A first acousto-optic modulator, which is used as an optical switch, is used to receive the extended pulsed light and generate a first modulated pulsed light after modulation processing; A fiber-coupled optical splitter is used to receive the received first modulated pulsed light and an isolated pulsed light and generate and output a split pulsed light and a coupled pulsed light after processing; A gain fiber is used for optical amplification and is connected to the optical fiber coupling splitter to receive the coupled pulsed light, and then generate and output a gain pulsed light; a pumped diode laser for generating a continuous beam; A wavelength division multiplexer, which is connected to the gain fiber and the pump diode laser, is used to receive the gain pulse light and the continuous light, and generate and output a division pulse light through wavelength division multiplexing ; An optical isolator, which is a fiber-optic polarization-maintaining optical isolator, is connected to the wavelength division multiplexer to receive the demultiplexed pulsed light, and generate and output an isolated pulsed light after isolation processing; A passive optical fiber is connected to the optical isolator for receiving the isolated pulsed light, generating and outputting the polarization-maintaining pulsed light to the fiber-coupled optical splitter after polarization-maintaining; and A second acousto-optic modulator, which is used as an optical switch, is connected to the fiber-coupled optical splitter to receive the coupled pulsed light and generate the low repetition rate pulsed light after modulation. The first acousto-optic modulator , the fiber-coupled optical splitter and the second acousto-optic modulator are sequentially connected via an optical fiber. The gigahertz pulse train femtosecond laser source as claimed in Claim 1, wherein the pulse repetition rate is 20-100 MHz, and the pulse length is 100-1000 femtoseconds. The gigahertz pulse train femtosecond laser source as described in Claim 1, wherein the pump diode laser is a single-mode diode laser with a wavelength of 976nm, the energy of the continuous light is 300-600mW and The wavelength is 976nm. The gigahertz pulse train femtosecond laser source as claimed in item 1, wherein the passive fiber includes a polarization maintaining fiber for providing the polarization maintaining function in the 1030nm band. The gigahertz pulse train femtosecond laser source as described in Claim 1, wherein the gain fiber includes a Ytterbium doped single mode polarization maintaining fiber (Ytterbium doped single mode polarization maintaining fiber) for optical amplification.

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