Modulation method of GHz pulse train envelope, laser envelope modulation system and femtosecond laser

Abstract

The present invention provides a method for modulating the envelope of a GHz pulse train, a laser envelope modulation system, and a femtosecond laser. According to a first aspect of an embodiment of the present application, a method for modulating the envelope of a GHz pulse train is proposed, comprising: downconverting the main frequency of the pulse train; modulating the sub-pulse frequencies in the pulse train after the main frequency downconversion to the GHz level; waveform-modulating the pulse train after the sub-pulse modulation; and amplifying the power of the waveform-modulated pulse train. The present invention enables an envelope independent of the rising and falling edge speeds of an acousto-optic modulator (AOM) and optimizes the amplified pulse envelope.

Description

Technical Field

[0001] The present invention relates to the field of ultrafast lasers, and in particular to a modulation method for a GHz pulse train envelope, a laser envelope modulation system and a femtosecond laser. Background Art

[0002] The ablation-cooling laser material removal mechanism is a completely new mechanism of interaction between ultrafast laser pulse trains and materials. This material processing method requires that the energy of each laser pulse train be tens to hundreds of microjoules, with an average power of about tens of watts. In addition, in the laser system, the pulse train emitted must contain sub-pulses with a GHz frequency.

[0003] Conventional GHz femtosecond lasers typically first frequency-multiply a MHz femtosecond seed source to GHz, then downconvert the main pulse to the kHz range using a fiber-coupled acousto-optic modulator (AOM). The pulse train is then amplified to increase its energy. However, directly extracting the GHz pulse train envelope using an AOM is dependent on the speed of the AOM's rising and falling edges. Furthermore, the amplified sub-pulses in the pulse train can exhibit varying degrees of energy inconsistency, often resulting in an initial pulse with excessively high energy, which can affect subsequent processing. Summary of the Invention

[0004] In response to the above-mentioned technical problems, the embodiments of the present application propose a modulation method for the envelope of a GHz pulse train, a laser envelope modulation system, and a femtosecond laser, which can achieve an envelope that is independent of the rising and falling edge speeds of the acousto-optic modulator and can optimize the amplified pulse envelope.

[0005] According to the first aspect of the embodiment of the present application, a modulation method for the envelope of a GHz pulse train is proposed, comprising: reducing the main frequency of the pulse train; modulating the sub-pulse frequency in the pulse train after the main frequency reduction to the GHz level; waveform modulating the pulse train after the sub-pulse modulation; and amplifying the power of the pulse train after the waveform modulation.

[0006] The modulation method of the GHz pulse train envelope of the first aspect of the embodiment of the present application can make the GHz pulse train envelope independent of the rising edge and falling edge time of the modulator, optimize the amplified pulse train envelope, and obtain the pulse envelope required by any process application through waveform modulation.

[0007] In some embodiments, before reducing the main frequency of the pulse train, the method further includes: generating a pulse train through a seed source.

[0008] In some embodiments, reducing the main frequency of the pulse train comprises reducing the frequency of the pulse train by performing acousto-optic modulation on the pulse train.

[0009] In some embodiments, reducing the main frequency of the pulse train includes reducing the main frequency of the pulse train to KHz level.

[0010] In some embodiments, modulating the sub-pulse frequency in the pulse train after downconversion of the main frequency to the GHz level includes: modulating the sub-pulse frequency in the pulse train after downconversion to the GHz level through a frequency multiplier.

[0011] In some embodiments, the frequency of the sub-pulses in the pulse train after the main frequency is down-converted is modulated to the GHz level, including: the frequency multiplier includes at least two 50:50 fiber couplers.

[0012] In some embodiments, the waveform modulating the pulse train after sub-pulse modulation includes: modulating the waveform of the pulse train by acousto-optic modulation.

[0013] In some embodiments, the waveform modulating the pulse train after sub-pulse modulation includes: waveform modulating the pulse train so that the sub-pulse energies of the pulse train after power amplification are consistent.

[0014] According to the second aspect of the embodiment of the present application, a laser envelope modulation system is also proposed, including: a light source, which emits a pulse train; a first modulator, which modulates the pulse train emitted by the light source to reduce the main frequency of the pulse train; a second modulator, which modulates the pulse train modulated by the first modulator to make the sub-pulse frequency of the pulse train reach the GHz level; a third modulator, which has a waveform generator, which modulates the pulse train modulated by the second modulator and modulates the amplitude of the pulse train; a power amplifier, which amplifies the power of the pulse train modulated by the third modulator; and executes any of the above-mentioned GHz pulse train envelope modulation methods.

[0015] In some embodiments, the first modulator is an acousto-optic modulator; the second modulator is a frequency multiplier composed of at least two 50:50 fiber couplers; the third modulator is an acousto-optic modulator; and the power amplifier is a fiber amplifier.

[0016] According to a third aspect of the embodiments of the present application, a femtosecond laser is also proposed, using any of the above-mentioned modulation methods for the GHz pulse train envelope.

[0017] It can be understood that the beneficial effects of the above-mentioned second and third aspects compared with the relevant technologies are the same as the beneficial effects of the above-mentioned first aspect compared with the relevant technologies. Please refer to the relevant description in the above-mentioned first aspect and will not be repeated here.

[0018] Other features and advantages of the present application will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present application. The purposes and other advantages of the present application can be achieved and obtained through the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of a modulation method for a GHz pulse train envelope according to an embodiment of the present application.

[0020] Figure 2 is based on Figure 1 Schematic diagram of an embodiment of the method.

[0021] Figure 3 is based on Figure 1 Schematic diagram of a flying laser envelope modulation system of the method.

[0022] Figure 4 This is a schematic diagram of the seed source to amplifier section in a GHz femtosecond laser of known technology.

[0023] Reference numerals:

[0024] 11: Femtosecond seed source, L1: Pulse beam, 12: First modulator, L2: Pulse beam, 13: Frequency multiplier, L3: Pulse beam, 14: Acousto-optic modulator, 15: Arbitrary waveform generator, L4: Pulse beam, 16: Fiber amplifier, 21: Light source, 22: First modulator, 23: Second modulator, 24: Third modulator, 25: Waveform generator, 26: Fiber amplifier, 31: Femtosecond seed source, 32: Frequency multiplier, 33: Acousto-optic modulator, 34: Fiber amplifier. DETAILED DESCRIPTION

[0025] In the following description, specific details such as specific system structures and techniques are provided for illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present application. However, it should be apparent to those skilled in the art that the embodiments of the present application can be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, optical paths, and methods are omitted to prevent unnecessary details from obscuring the description of the embodiments of the present application.

[0026] It should be noted that although a logical order is shown in the flowcharts, in some cases, the steps shown or described may be performed in a different order than that shown in the flowcharts. The terms "first," "second," and the like in the specification, claims, and drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0027] It should also be understood that the references to "one embodiment" or "some embodiments" described in the description of the embodiments of the present application mean that one or more embodiments of the embodiments of the present application include the specific features, structures or characteristics described in conjunction with the embodiment. Therefore, the phrases "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. that appear in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways. The terms "including", "comprising", "having" and their variations all mean "including but not limited to", unless otherwise specifically emphasized in the description of the embodiments of the present application, unless otherwise clearly defined, words such as setting, installing, connecting, etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above words in the embodiments of the present application in combination with the specific content of the technical solution.

[0028] The modulation method of the GHz pulse train envelope according to the embodiment of the first aspect of the present application is as follows: Figure 1 As shown, the modulation method of the GHz pulse train envelope includes the following steps:

[0029] S100: Down-converting the main pulse frequency of the pulse train L1 to the KHz level through modulation to obtain the pulse train L2 after the main pulse frequency is down-converted;

[0030] S200: multiplying the sub-pulse frequency in the pulse train L2 after the main pulse frequency is reduced to the GHz level to obtain the pulse train L3 after the sub-pulse frequency is doubled;

[0031] S300: waveform modulating the pulse train L3 to obtain a waveform modulated pulse train L4;

[0032] S400: Power amplifying the waveform-modulated pulse train L4.

[0033] On the one hand, since S100 reduces the main pulse frequency of the pulse string L1, S200 ensures that the sub-pulse frequency of the multiplied pulse string L3 is not affected by the rising edge, falling edge, or rising edge and falling edge of the modulator; on the other hand, since the pulse string L3 is waveform modulated in S300, the pulse string envelope of the amplified laser pulse obtained in S400 can be selected.

[0034] Figure 2 This is a schematic diagram of an embodiment of the modulation method of the GHz pulse train envelope. Figure 2 , the embodiments of the present application are described.

[0035] Before S100, the pulse train is generated by the seed source 11 and the pulse width is widened to obtain the pulse train L1. The type of the seed source 11 is not limited. Preferably, it can be a femtosecond seed source. At this time, the repetition frequency of the pulse train L1 is in the MHz level. Specifically, 20MHz to 100MHz. Figure 2 In the embodiment, the seed source 11 is a femtosecond seed source with a frequency of 50 MHz and a central wavelength of 1030 nm; the spectrum width is about 3.5 nm, and the pulse width of the pulse train L1 after being widened by the stretcher is about 200 ps.

[0036] In S100, the pulse train performs acousto-optic modulation on the pulse train L1 to reduce the frequency of the pulse train L1 and obtain the pulse train L2. Figure 2 In the embodiment of the present invention, this step is completed by using the first modulator 12. At this time, the repetition frequency of the pulse train L2 is at the KHz level. Specifically, 10kHz to 1000kHz. Figure 2 In the implementation manner, the pulse main frequency of the pulse string L2 is 500KHz.

[0037] In S200, the sub-pulse frequency in the pulse train L2 with a repetition frequency of KHz after frequency reduction is doubled to GHz. Figure 2 In the embodiment of the present invention, this step is completed using a frequency multiplier. Specifically, a frequency multiplier composed of multiple 50:50 fiber couplers is used to multiply the sub-pulse frequency to 1.6 GHz. When using this method, the main pulse frequency range does not change much and remains in the KHz level. Specifically, in Figure 2 In the implementation method, the pulse main frequency of the pulse string L3 is still 500KHz.

[0038] In S300, the pulse train L3 is waveform modulated. Figure 2 In the embodiment, this step is performed by an acousto-optic modulator 14, specifically a fiber-coupled acousto-optic modulator 14. The active output of the fiber laser is controlled by an arbitrary waveform generator 15, thereby modulating the amplitude or shape of the pulse train envelope to obtain pulse train L4. Pulse train L4 is a pulse train with GHz sub-pulses.

[0039] Furthermore, in the process of modulating the amplitude of the pulse train envelope, the main pulse train frequency remains unchanged.

[0040] Furthermore, the arbitrary waveform generator 15 outputs an analog signal to the acousto-optic modulator 14 , so the envelope of the pulse train L4 can be selected according to process requirements.

[0041] Furthermore, in conjunction with the comparative example described later, since the main frequency is downconverted beforehand, the lower frequency makes the pulse envelope interval larger. After the acousto-optic modulation, the obtained pulse train L4 is not affected by the rising and falling edges of the modulator, that is, it does not rely on the rising and falling edges of the original acousto-optic modulator.

[0042] In S400, the waveform modulated pulse train L4 is power amplified. Figure 2 In an embodiment, this step is performed by the optical fiber amplifier 16. Moreover, the sub-pulse energies of the pulse train after power amplification are consistent. In some embodiments, the energy of the pulse train after amplification can be in the order of hundreds of μJ.

[0043] Furthermore, the pulse train L4 can be modulated according to actual processing requirements to obtain desired pulse train sub-pulses, for example, by using square waves, sine waves, cosine waves, pulse waves, or other waveforms that can be generated by an arbitrary waveform generator to adjust the amplitude of the sub-pulse train.

[0044] After S400, the pulse train after amplification can also be compressed to the order of picoseconds or femtoseconds, where the sub-pulse frequency is in the order of GHz. Figure 2 In an embodiment of the present invention, the pulse width of the amplified pulse train is 300 fs.

[0045] While this embodiment describes the use of acousto-optic modulation to reduce the frequency of pulse train L1, this is not limiting. Electro-optic modulation, magneto-optic modulation, nonlinear crystals, and the like may also be used, as long as the frequency can be reduced sufficiently to avoid the rising and falling edges of the acousto-optic modulator 14. Furthermore, a chopper or the like may be used for frequency reduction.

[0046] In this embodiment, although it is mentioned that the pulse string L1 is down-converted to the KHz level, it is not limited to this. It can also continue to be MHz, or further down-converted to the Hz level. It only needs to be down-converted enough to avoid the rising edge and falling edge of the acousto-optic modulator 14.

[0047] In this embodiment, although the fiber-coupled acousto-optic modulator 14 is used to perform acousto-optic modulation on the pulse train L3, it is not limited to this. Free-space acousto-optic modulation can also be used. Furthermore, other modulation methods can also be used, as long as the envelope of the pulse train L3 can be modulated with an arbitrary waveform.

[0048] In this embodiment, although it is mentioned that the sub-pulse energies of the pulse train after power amplification are consistent, it is not limited to this. Since the envelope of the pulse train L4 can actually be modulated by an arbitrary waveform, that is, Figure 2 The arbitrary waveform generator 15 controls the acousto-optic modulator 14. Thus, the sub-pulse energies of the power-amplified pulse train can be different, specifically, selected according to process requirements.

[0049] According to the above method, the envelope of the GHz pulse train before amplification does not depend on the rising and falling edge times of the AOM 14. Through the control method of the dual-fiber coupled AOM, an analog signal can be supplied to the AOM 14 via the arbitrary waveform generator 15 to pre-modulate the envelope of the pulse train before amplification, thereby optimizing the envelope of the pulse train after amplification and obtaining the pulse envelope required for the process application.

[0050] Combine Figure 3 , Figure 3 A schematic diagram of a laser envelope modulation system using the method described in an embodiment of the present application. The laser envelope modulation system can implement any of the methods in the above embodiments to achieve GHZ pulse train envelope modulation.

[0051] Specifically, the system may include, for example: a light source 21, a first modulator 22, a second modulator 23, a third modulator 24, and an optical fiber amplifier 26. The light source 21 is used to generate a pulse train. As the light source 21, there can be listed: a seed source with a pulse width stretcher. The first modulator 22 down-converts the main frequency of the pulse train emitted by the light source 21 through modulation. In some embodiments, the light source may undergo other processing before entering the first modulator 22, such as pulse width stretching, collimation, and frequency stabilization. The second modulator 23 multiplies the frequency of the down-converted pulse train to GHz; the third modulator 24 performs waveform modulation on the pulse train after frequency multiplication in combination with the waveform generator 25, specifically, modulates the amplitude of the pulse train; the optical fiber amplifier 26 (power amplifier) ​​amplifies the power of the waveform-modulated pulse train; and finally outputs.

[0052] Furthermore, the above system can also be combined with a femtosecond laser to achieve GHz pulse train envelopes.

[0053] The method and beneficial effects of the embodiments of the present application are described below with reference to comparative examples.

[0054] [Comparative Example]

[0055] Figure 4 This is a schematic diagram of the seed source to amplifier section in a GHz femtosecond laser of known technology. Figure 4 .

[0056] The pulse train is generated by a femtosecond seed source 31, with a repetition rate in the MHz range. Without premodulation, it enters the frequency multiplier 32 directly. In the frequency multiplier 32, the sub-pulse frequency of the pulse train is multiplied to the GHz range. Then, the repetition rate of the pulse train is reduced to the kHz range by the acousto-optic modulator 33. Finally, the down-converted pulse train enters the fiber amplifier 34 for power amplification.

[0057] Combine Figure 2 and Figure 4Compared to the method in the present embodiment, when the pulse train envelope in the comparative example is down-converted, the GHz pulse train envelope directly selected by the AOM 33 depends on the rising and falling edge speeds of the AOM 33. The current AOM switching time is over 10ns, so the modulated envelope amplitude is uneven due to the rising and falling edge speeds. Furthermore, the energy of the amplified pulse train sub-pulses can also vary to varying degrees. After amplification by the fiber amplifier 34, the first pulse energy is often too high, which can affect the processing effect, lead to scrapped processed materials, and reduce the yield rate.

[0058] In summary, the modulation method for the GHz pulse train envelope and the femtosecond laser using this method proposed in the embodiments of the present application pre-modulate the pulse train envelope so that the GHz pulse train envelope is independent of the rising and falling edge times of the acousto-optic modulator, and optimizes the amplified pulse train envelope. Furthermore, the pulse envelope required for any process application can be obtained through waveform modulation.

[0059] In the description of this specification, the reference terms "one embodiment," "some embodiments," "illustrative embodiments," "example," "specific example," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiments of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any appropriate manner in any one or more embodiments or examples.

[0060] The above describes in detail the implementation methods of the embodiments of the present application in conjunction with the accompanying drawings, but the embodiments of the present application are not limited to the above implementation methods. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the technical field without departing from the purpose of the embodiments of the present application.

Claims

1. A modulation method for a GHz pulse train envelope, characterized in that: include: The main frequency of the pulse train is reduced to avoid the rising edge and the falling edge of the acousto-optic modulator; Modulating the sub-pulse frequency in the pulse train after the main frequency is reduced to the GHz level; The acousto-optic modulator performs waveform modulation on the pulse train after sub-pulse modulation; The power of the waveform-modulated pulse train is amplified.

2. The modulation method of GHz pulse train envelope according to claim 1, characterized in that: Before reducing the main frequency of the pulse train, the method further includes: The pulse train is generated by a seed source.

3. The modulation method of GHz pulse train envelope according to claim 1, characterized in that: The step of reducing the main frequency of the pulse train comprises: The pulse train is down-converted by performing acousto-optic modulation on the pulse train.

4. The method for modulating the GHz pulse train envelope according to any one of claims 1 to 3, characterized in that: The step of reducing the main frequency of the pulse train includes reducing the main frequency of the pulse train to a KHz level.

5. The modulation method of GHz pulse train envelope according to claim 4, characterized in that: Modulating the sub-pulse frequency in the pulse train after the main frequency is reduced to the GHz level includes: The frequency of the sub-pulses in the down-converted pulse train is modulated to the GHz level through a frequency multiplier.

6. The modulation method of GHz pulse train envelope according to claim 5, characterized in that: The frequency multiplier includes at least two 50:50 fiber couplers.

7. The method for modulating the GHz pulse train envelope according to claim 1, 2, 3, 5 or 6, characterized in that: The waveform modulation of the pulse train after the sub-pulse modulation comprises: The waveform of the pulse train is modulated by acousto-optic modulation.

8. The modulation method of GHz pulse train envelope according to claim 7, characterized in that: The waveform modulation of the pulse train after the sub-pulse modulation comprises: The pulse train is waveform-modulated so that the sub-pulse energies of the pulse train after power amplification are consistent.

9. Laser envelope modulation system, characterized in that, include: a light source, which emits a pulse train; a first modulator, for modulating the pulse train emitted by the light source to reduce the main frequency of the pulse train; a second modulator, modulating the pulse train modulated by the first modulator so that the sub-pulse frequency of the pulse train reaches GHz level; A third modulator, comprising a waveform generator, configured to modulate the pulse train modulated by the second modulator and modulate the amplitude of the pulse train; a power amplifier for amplifying the power of the pulse train modulated by the third modulator; wherein the first modulator reduces the main frequency of the pulse train to avoid the rising edge and the falling edge of the third modulator; Execute the method according to any one of claims 1 to 8.

10. The laser envelope modulation system according to claim 9, characterized in that: The first modulator is an acousto-optic modulator; The second modulator is a frequency multiplier composed of at least two 50:50 fiber couplers; The third modulator is an acousto-optic modulator; The power amplifier is a fiber optic amplifier.

11. A femtosecond laser, characterized in that: A modulation method for a GHz pulse train envelope according to any one of claims 1 to 8.

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