Freetrig-based pulse output apparatus for ultrafast laser, and freetrig-based pulse output control method for ultrafast laser

Abstract

The present invention relates to a FreeTrig-based pulse output apparatus for an ultrafast laser, and a FreeTrig-based pulse output control method for an ultrafast laser. An output end of an optical fiber beam splitter is connected to an optical input end of a main acousto-optic modulator, and the other output end thereof is connected to an input end of an optical fiber collimator; an optical output end of the main acousto-optic modulator is connected to an input end of an optical fiber beam combiner; a control input end of the main acousto-optic modulator is connected to an output end of a control module; an output end of the optical fiber collimator is connected to an optical input end of an on-board auxiliary acousto-optic modulator, an output end of the on-board auxiliary acousto-optic modulator is connected to the input end of the optical fiber collimator, and a control input end of the on-board auxiliary acousto-optic modulator is connected to the output end of the control module; the output end of the optical fiber collimator is connected to the other input end of the optical fiber beam combiner; an output end of the optical fiber beam combiner is connected to an input end of an optical amplifier; an output end of the optical amplifier is connected to an optical input end of a free-space acousto-optic modulator; and a control input end of the free-space acousto-optic modulator is connected to the output end of the control module.

Description

Ultrafast laser based on free trigger pulse output device and control method thereof Technical Field

[0001] The invention relates to a device for ultrafast laser based on free trigger pulse output and a control method thereof. Background Art

[0002] With the increasing application of ultrafast lasers such as picosecond and femtosecond lasers in consumer electronics, semiconductors, glass, and new energy batteries, the demand for laser pulse control in fine micro-manufacturing processes is becoming increasingly stringent. A typical application is the user's ability to freely trigger (FreeTrig) the laser's output pulses to adapt to the user's desired frequency changes. This processing feature eliminates pulse energy accumulation and provides uniform processing results, making it particularly suitable for arc processing or variable speed processing in motion systems. Despite relevant research and applications within the industry, there are still certain issues with ease of use and effectiveness.

[0003] Currently, ultrafast laser seed output is generally based on mode-locking technology. The laser's fundamental frequency is obtained by dividing the seed mode-locking frequency. However, the fundamental frequency cannot be too low, otherwise the energy of the amplified seed pulse will be too high, which may damage the optical crystal. For processing applications, the FreeTrig frequency signal input by the user to the laser is often used in the low frequency range. If the laser has frequency restrictions, the processing cannot be truly called free-trigger processing.

[0004] The ultrafast laser includes a fiber acousto-optic modulator (FAOM), an optical amplifier, a free-space acousto-optic modulator (FSAM), and a control module. The control module is connected to the fiber acousto-optic modulator (FAOM) and the free-space acousto-optic modulator (FSAM). During operation, mode-locked seed light (the mode-locking frequency is generally 25 MHz to 80 MHz) is pre-amplified to form a pre-amplified mode-locked seed light (referred to as seed light). The seed light is input into the fiber acousto-optic modulator (FAOM). Under the control of the control module, seed light of a certain frequency (called frequency-selected seed light) is selected. In practical applications, this frequency is much lower than the mode-locking frequency and is called the fundamental frequency, which is generally several hundred kHz. After being amplified by the optical amplifier, the frequency-selected seed light is input into the FSM. Under the control of the control module, the FSM outputs laser pulses of the required frequency. The optical amplifier within an ultrafast laser primarily consists of a pump source, an optical crystal, and optical lenses. During laser operation, the pump source within the optical amplifier typically operates in a constant-current, constant-current mode. Therefore, the accumulated upper-level population accumulated by the pump must be removed via frequency-selective seed light output by a fiber acousto-optic modulator (FAOM). If the fundamental frequency of the FSM is too low (e.g., less than 50k), or if the interval between pulses is too long, this can cause spontaneous transitions in the upper-level population of the pump source within the optical amplifier, resulting in spontaneous emission (ASE), which is then amplified and damaged by the optical crystal and lenses. Therefore, to obtain low-frequency pulses from the laser, the only way is to perform secondary frequency selection on the fundamental frequency pulses by controlling the FSM. However, in actual machining, the FreeTrig frequency input to the laser constantly changes during acceleration and deceleration. The laser pulses generated through secondary frequency selection cannot adapt to the frequency required for machining. This is particularly true for high-speed cutting or marking, where dotting control results in misaligned or even missed dots.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to overcome the deficiencies in the prior art and to provide an ultrafast laser device based on free trigger pulse output and a control method thereof.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The device of ultrafast laser based on free-trigger pulse output is characterized by: comprising a seed beam splitting pulse generation module, an optical amplifier, a free-space acousto-optic modulator, a control module, a photodetector and an input interface. The seed beam splitting pulse generation module comprises a fiber beam splitter, a main acousto-optic modulator, a fiber collimator, an on-board auxiliary acousto-optic modulator, a fiber collimator and a fiber combiner. The seed light is input to the fiber beam splitter input end of the seed beam splitting pulse generation module, and the fiber beam splitter is divided into two beams of light. One output end of the fiber beam splitter is connected to the optical input end of the main acousto-optic modulator, and the other output end of the fiber beam splitter is connected to the input end of the fiber collimator; the optical output end of the main acousto-optic modulator is connected to one input end of the fiber combiner; the control input end of the main acousto-optic modulator is connected to the optical input end of the fiber collimator. The input end of the optical fiber collimator is connected to an output end of the control module; the output end of the optical fiber collimator is connected to the optical input end of the on-board auxiliary acousto-optic modulator, the output end of the on-board auxiliary acousto-optic modulator is connected to the input end of the optical fiber collimator, and the control input end of the on-board auxiliary acousto-optic modulator is connected to an output end of the control module; the output end of the optical fiber collimator is connected to the other input end of the optical fiber combiner; the output end of the optical fiber combiner is connected to the input end of the optical amplifier; the output end of the optical amplifier is connected to the optical input end of the free-space acousto-optic modulator; the control input end of the free-space acousto-optic modulator is connected to the output end of the control module; the optical output end of the free-space acousto-optic modulator outputs the required light pulse; and the external trigger signal is connected to the input end of the control module through the input interface.

[0009] Furthermore, the above-mentioned ultrafast laser is based on a device with free trigger pulse output, wherein the output end of the photodetector is connected to the input end of the control module.

[0010] Furthermore, the above-mentioned ultrafast laser is based on a device with free-trigger pulse output, wherein the free-space acousto-optic modulator is a full-band 68MHz to 80MHz free-space acousto-optic modulator.

[0011] Furthermore, the above-mentioned ultrafast laser is based on a device for free-triggered pulse output, wherein the control module includes a high-speed comparator, a communication interface, an MCU and an FPGA, the photodetection signal is connected to the positive input of the high-speed comparator, the reference ground is connected to the negative input of the high-speed comparator, and the output of the high-speed comparator is connected to the global clock input of the FPGA; the external FreeTrig signal frequency is connected to the input of the FPGA; the communication interface is connected to the input of the MCU, the data bus port of the MCU is connected to the data bus port of the FPGA, and the optical signal output of the MCU is connected to the input of the FPGA; the reset output of the MCU is connected to the global reset input of the FPGA; and the three outputs of the FPGA respectively output control signals for controlling the main acousto-optic modulator, the on-board auxiliary acousto-optic modulator and the free-space acousto-optic modulator.

[0012] Furthermore, the above-mentioned ultrafast laser is based on a device with free-trigger pulse output, wherein the board-mounted auxiliary acousto-optic modulator is a surface-mount free-space acousto-optic modulator.

[0013] Furthermore, the above-mentioned ultrafast laser is based on a device with free trigger pulse output, wherein the main acousto-optic modulator is a 150-200 MHz fiber-coupled acousto-optic modulator.

[0014] The invention discloses a control method for the ultrafast laser based on free-trigger pulse output. The seed light is input into a seed beam splitting pulse generating module and is split into two beams of seed light with different powers by an optical fiber beam splitter. The main pulse beam is input into a main acousto-optic modulator, and the secondary pulse beam is input into an optical fiber collimator. The output light of the optical fiber collimator enters an onboard auxiliary acousto-optic modulator. The main acousto-optic modulator outputs a fundamental frequency seed light of a required frequency under the modulation control of the control module. The onboard auxiliary acousto-optic modulator outputs a seed light pulse cluster with a variable frequency and adjustable width under the modulation control of the control module, and inputs the seed light pulse cluster into the optical fiber collimator, and then outputs a modulated light pulse cluster. The fiber collimator and the fiber collimator form a pair of couplers to realize the process of secondary pulse light beam transmission from optical fiber to space transmission and then to optical fiber transmission; the fundamental frequency seed light and modulated light pulse are input to the fiber combiner for beam combination and output as a combined light pulse train, which is then input to the optical amplifier for amplification. After amplification, the combined light pulse train outputs an amplified light pulse train from the optical amplifier, which is then input to the free-space acousto-optic modulator and outputs the required selected pulse laser under the synchronous control of the control module. The input interface inputs the FreeTrig frequency signal to the control module to control the laser to output light pulses of the same frequency.

[0015] Furthermore, the above-mentioned ultrafast laser is based on a control method for free-trigger pulse output, wherein a photodetector is used to receive part of the mode-locked seed light, thereby outputting the seed mode-locked frequency to the control module, and the mode-locked frequency is used as the clock signal of the control module.

[0016] Furthermore, the above-mentioned ultrafast laser is based on a control method for free-trigger pulse output, wherein, when there is no input frequency signal at the input interface, the control module outputs a fixed-frequency main acousto-optic modulator gating signal to control the opening and closing of the main acousto-optic modulator. The main acousto-optic modulator can pick up one or more main pulses at the moment of opening and outputting the fundamental frequency seed light; the control module controls the gating signal of the on-board auxiliary acousto-optic modulator to be closed, the on-board auxiliary acousto-optic modulator has no secondary pulse output, the modulated light pulse cluster is empty, the fiber combiner outputs a combined light pulse train equivalent to the fundamental frequency seed light, and the combined light pulse train is amplified by the optical amplifier to form an amplified light pulse train output. If light output needs to be tested or external control is used to continuously increase light output, the control module outputs a free-space acousto-optic modulator gating signal to control the free-space acousto-optic modulator to be high, and the free-space acousto-optic modulator outputs a selected pulse laser.

[0017] Furthermore, the above-mentioned ultrafast laser is based on a control method for free-triggered pulse output, wherein the frequency signal FreeTrig frequency signal required externally during processing is input into the control module through the input interface, and the control module outputs a frequency selection control signal to control the main acousto-optic modulator to start immediately and pick up one or more main pulses, namely, the fundamental frequency seed light. The delay between the output of the fundamental frequency seed light and the input of the FreeTrig signal does not exceed 2 mode-locking frequency clock cycles, that is, less than 0.1uS; at the same time, the control module detects the FreeTrig frequency change in real time. If the input frequency is less than the fundamental frequency, the control module outputs a pulse width modulation signal, namely, the auxiliary acousto-optic modulator gating signal to control the opening and closing of the on-board auxiliary optical modulator, thereby outputting a width-modulated sub-pulse cluster to the fiber collimator and outputting a modulated light pulse cluster. The fiber combiner combines the fundamental frequency seed light and the modulated light pulse cluster and outputs a combined light pulse train, which is input into the optical amplifier. amplifier; when the FreeTrig signal frequency is lower than the minimum allowable fundamental frequency of the laser, the interval between the fundamental frequency seed lights in the combined optical pulse train is long, and the interval contains a modulated optical pulse cluster, which takes away the upper energy level particle number accumulated by the pump in the optical amplifier, protecting the optical lens and optical crystal of the optical amplifier; after the combined optical pulse train passes through the optical amplifier, it outputs an amplified optical pulse train, which contains the amplified main pulse and the amplified secondary pulse cluster. Only the amplified main pulse is required for processing, so the control module outputs the free-space acousto-optic modulator gating signal to control the synchronous start of the free-space acousto-optic modulator and pick up the main pulse, thereby outputting the selected pulse laser. The optical delay from the fundamental frequency seed light picked up by the main acousto-optic modulator to the selected pulse laser output through the free-space acousto-optic modulator is less than 0.2uS, and the total delay time from the FreeTrig pulse signal input to the optical pulse output does not exceed 0.3uS at most;

[0018] When the FreeTrig frequency is greater than or equal to the fundamental frequency, the control module turns off the onboard auxiliary acousto-optic modulator (AOM). As a result, no optical pulses are output from the modulated optical pulse cluster. The entire optical path is equivalent to amplifying only the fundamental frequency seed light through the optical amplifier and finally outputting it from the free-space AOM.

[0019] Compared with the prior art, the present invention has significant advantages and beneficial effects, which are specifically reflected in the following aspects:

[0020] ① The present invention's ultrafast laser is based on a device and control method for free-space triggered pulse output. The device splits the pre-amplified mode-locked seed light into two main and secondary seed light paths with different power ratios. The main acousto-optic modulator (AOM) is controlled to output the main pulse in accordance with the FreeTrig frequency. An onboard AOM is used to width-modulate the secondary seed light sequence to produce a secondary pulse cluster. The main and secondary modulated seed light paths are combined to achieve optical amplification. The free-space AOM synchronizes the pulse output. In FreeTrig mode, the output laser single pulse energy is stable.

[0021] ② Satisfy the free trigger pulse output. The light pulse changes with the external input frequency, with good real-time performance. The single pulse energy of the laser output pulse is consistent, ensuring the real-time requirements of processing and the stability of the single pulse energy. There is no risk of damaging the laser when working at low frequency.

[0022] ③ The laser actively adapts to the external trigger signal to control the output of the pulse, while keeping the laser single pulse energy relatively stable within a limited frequency band to meet the needs of processing applications.

[0023] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the specific embodiments of the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1: A schematic structural diagram of the device of the present invention;

[0026] Figure 2: Schematic diagram of the laser pulse output process without external Freetrig frequency;

[0027] Figure 3: Schematic diagram of the laser pulse output process in FreeTrig;

[0028] Figure 4: Schematic diagram of the control module;

[0029] Figure 5: Schematic diagram of the control flow of the control module. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein 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 claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0031] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of the present invention, directional terms and order terms are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0032] As shown in Figure 1, the device of ultrafast laser based on free-trigger pulse output includes a seed beam splitting pulse generating module 1, an optical amplifier 2, a free-space acousto-optic modulator 3, a control module 4, a photodetector 5 and an input interface 6. The seed beam splitting pulse generating module 1 includes a fiber beam splitter 101, a main acousto-optic modulator 102, a fiber collimator 103, an on-board auxiliary acousto-optic modulator 104, a fiber collimator 105 and a fiber combiner 106. The seed light is input to the input end of the fiber beam splitter 101 of the seed beam splitting pulse generating module 1, and the fiber beam splitter 101 is divided into two beams of light. One output end of the fiber beam splitter 101 is connected to the optical input end of the main acousto-optic modulator 102, and the other output end of the fiber beam splitter 101 is connected to the input end of the fiber collimator 103; the optical output end of the main acousto-optic modulator 102 is connected to one input end of the fiber combiner 106; The control input of the optical modulator 102 is connected to an output of the control module 4; the output of the fiber collimator 103 is connected to the optical input of the onboard auxiliary AOM 104, the output of the onboard auxiliary AOM 104 is connected to the input of the fiber collimator 105, and the control input of the onboard auxiliary AOM 104 is connected to an output of the control module 4; the output of the fiber collimator 105 is connected to the other input of the fiber combiner 106; the output of the fiber combiner 106 is connected to the input of the optical amplifier 2; the output of the optical amplifier 2 is connected to the optical input of the free-space AOM 3; the control input of the free-space AOM 3 is connected to the output of the control module 4; the optical output of the free-space AOM 3 outputs the required optical pulse; and the external trigger signal is connected to the input of the control module 4 through the input interface 6.

[0033] As shown in Figure 4, the control module 4 includes a high-speed comparator 401, a communication interface 402, an MCU 403, and an FPGA 404. The photodetection signal is connected to the positive input of the high-speed comparator 401, the reference ground is connected to the negative input of the high-speed comparator 401, and the output of the high-speed comparator 401 is connected to the global clock input of the FPGA 404. The external FreeTrig signal frequency is connected to the input of the FPGA 404. The communication interface 402 is connected to the input of the MCU 403, the data bus port of the MCU 403 is connected to the data bus port of the FPGA 4, and the optical signal output of the MCU 403 is connected to the input of the FPGA 404. The reset output of the MCU 3 is connected to the global reset input of the FPGA 404. The three outputs of the FPGA 404 respectively output control signals used to control the main AOM 102, the onboard auxiliary AOM 104, and the free-space AOM 3.

[0034] The high-speed comparator ADCMP553 achieves a highly stable seed mode-locking frequency as the reference clock frequency of the control module; the field programmable gate array (FPGA) implements fast sequential logic control, and the microcontroller unit (MCU) implements data interaction and settings; the FPGA404 uses Xilinx's XC6SLX4, which has a digital phase-locked loop frequency multiplication module, a frequency comparison module, an I2C interface module, and other features. It has multiple digital input and output pins and a maximum clock rate of 220MHz.

[0035] After power-up, MCU3 outputs a 1µS low-level reset signal to FPGA4, resetting all registers. The host computer sends instructions to MCU403 via communication interface 402. MCU403 receives the instructions and executes the relevant operations, setting relevant data for FPGA404 via the data bus. These settings include setting the base frequency, operating mode (GATE or FreeTrig), pulse-width modulation parameters, and controlling light output. High-speed comparator 401 compares the photodetection signal with a reference ground and then shapes the output to enable the FPGA to recognize the received frequency signal, which is consistent with the seed mode-locking frequency.

[0036] As shown in Figure 5, the control process of the control module 4, when in operation, synchronizes the mode-locked clock frequency; sets the fundamental frequency, controls the main AOM 102 to output the main pulse, and turns off the on-board auxiliary AOM 104; determines the external input frequency. If there is no input frequency, the main AOM 102 continues to control the output of the fundamental frequency pulse, and the on-board auxiliary AOM 104 is turned off; if the external input frequency is lower than the fundamental frequency, the main AOM 102 is controlled to output the main pulse with the same frequency as the external input, and the frequency and width of the secondary pulse cluster output by the on-board auxiliary AOM 104 are adjusted according to the external frequency; if the external input frequency is equal to or higher than the fundamental frequency, the main AOM 102 is controlled to output the main pulse with the same frequency as the external input, and the on-board auxiliary AOM 104 is turned off; synchronizes the gate signal of the main AOM 102 and delays it. When there is an external frequency input, test light output, or external long light output, the free-space AOM 3 is turned on to output pulses.

[0037] The optical amplifier 2 is composed of one or more pump laser diodes, optical crystals, optical isolation, optical lenses, coupling mirrors, and wave plates. Please refer to the solid femtosecond amplification device and method disclosed in patent publication number CN109936041A.

[0038] The free-space acousto-optic modulator 3 (FS AOM) is a full-band 68MHz to 80MHz free-space acousto-optic modulator.

[0039] The main acousto-optic modulator 102 is a 200 MHz fiber-coupled acousto-optic modulator (FC AOM), and the fiber beam splitter, fiber collimator, and fiber beam combiner are polarization-maintaining devices.

[0040] The onboard auxiliary AOM 104 is a surface-mount free-space AOM. The output of the photodetector 5 is connected to the input of the control module 4 .

[0041] In specific applications, the seed light (25M~80M) is input to the seed beam splitting pulse generating module 1, and is divided into two beams of seed light with different powers by the optical fiber splitter 101, generally with a power ratio of 85% and 15% (which can be adjusted appropriately in actual applications). The main pulse beam with a power ratio of 85% is input to the main acousto-optic modulator 102, and the sub-pulse beam with a power ratio of 15% is input to the optical fiber collimator 103; the output light of the optical fiber collimator 103 enters the on-board auxiliary acousto-optic modulator 104, which adopts the QUBIG company's FSi.SMD-NIR series surface-mount free-space acousto-optic modulator, which has the characteristics of small size, low power and fast response; the main acousto-optic modulator 102 outputs the fundamental frequency seed light P1 of the required frequency under the modulation control of the control module 4; the on-board auxiliary acousto-optic modulator 104 outputs a seed light pulse cluster with variable frequency and adjustable width under the modulation control of the control module 4, and inputs it into the optical fiber collimator 105 to output a modulated light pulse cluster P2. The fiber collimator 103 and the fiber collimator 105 form a pair of couplers to realize the process of secondary pulse light beam transmission from optical fiber to space transmission and then to optical fiber transmission; the fundamental frequency seed light P1 and the modulated light pulse P2 are input to the fiber combiner 106 for beam combination, and then output the combined light pulse train P3. The combined light pulse train P3 is input to the optical amplifier 2 for amplification. The optical amplifier 2 is composed of one or more pump laser diodes, optical crystals, optical isolation, optical lenses, coupling mirrors, wave plates, etc. After amplification, the combined light pulse train P3 outputs an amplified light pulse train P4 from the optical amplifier 2. The amplified light pulse train P4 is input to the free space acousto-optic modulator 3, which outputs the required selected pulse laser P5 under the synchronous control of the control module 4. The input interface 6 inputs the FreeTrig frequency signal to the control module 4 to control the laser to output light pulses of the same frequency; the photodetector 5 is used to receive part of the mode-locked seed light, thereby outputting the seed mode-locking frequency to the control module 4, and the mode-locking frequency is used to control the clock signal of the module 4.

[0042] In FIG2 , the master AOM gate signal a represents the gate signal used by the control module 4 to control the master AOM 102, the fundamental frequency seed light P1 represents the fundamental frequency seed light output by the master AOM, the modulated optical pulse cluster P2 represents the optical pulse cluster modulated from the seed light output by the fiber collimator 105, the combined optical pulse train P3 represents the optical pulse train output by the fiber combiner 106, the amplified optical pulse train P4 represents the optical pulse train output by the optical amplifier 2, the free space AOM gate signal b represents the level signal used by the control module 4 to control the free space AOM 3, and the selected pulse laser P5 represents the pulse laser (final laser output) output by the free space AOM 3. When there is no input frequency signal at the input interface 6, the control module 4 outputs the master AOM gate signal a of a fixed frequency (fundamental frequency, also called repetition frequency) to control the opening (high level) and closing (low level) of the master AOM 102. When the master AOM 102 is turned on, the master AOM 102 is turned off. One or more main pulses (depending on the processing application) can be picked up instantly, thereby outputting the fundamental frequency seed light P1; under the premise of known laser power, the fundamental frequency setting of the laser will not be less than the low frequency lower limit, so the fundamental frequency seed light P1 will not damage the optical lens and optical crystal due to the small interval between light pulses. In this case, the control module 4 controls the gating signal of the on-board auxiliary acousto-optic modulator 104 to be closed, the on-board auxiliary acousto-optic modulator 104 has no secondary pulse output, and the modulated light pulse cluster P2 is empty. At this time, the output combined light pulse train P3 of the fiber combiner 106 is equivalent to the fundamental frequency seed light P1. The combined light pulse train P3 is amplified by the optical amplifier 2 to form the amplified light pulse train P4 output. If test light output is required, or external control is continued to increase light output, the control module 4 outputs the free space acousto-optic modulator gating signal b that controls the free space acousto-optic modulator 3 to be high, and the free space acousto-optic modulator 3 outputs the selected pulse laser P5.

[0043] For processing, the single-pulse energy of the laser required for the same material under the same process conditions is constant. What differs is the processing efficiency and the cutting or marking speed, which means that the frequency of triggering the laser to generate pulse output is different. The trigger frequency will change with the speed of the processing motion system, that is, FreeTrig mode processing. If the maximum FreeTrig frequency required by the processing system is 200kHz, then 200kHz will be defined as the base frequency or the highest repetition rate when using the laser. The single-pulse energy output by the laser at the base frequency of 200kHz is the single-pulse energy required for processing. At trigger frequencies below 200kHz, the single-pulse energy output by the laser must remain unchanged. At the same time, the delay between the external frequency pulse input and the corresponding light pulse output by the laser should be very small (generally less than 1uS) to ensure dot uniformity.

[0044] Under the condition of a certain laser power, the lower the fundamental frequency, the higher the output laser single pulse energy. If the fundamental frequency is low to a certain level, such as 50kHz (the minimum fundamental frequency depends on the laser), the optical lens and optical crystal in the laser's optical amplifier 2 will be damaged by breakdown due to the influence of ASE. Combined with Figure 3, during low-frequency processing, the single pulse energy is kept stable without damaging the optical lens and optical crystal, while ensuring the real-time output of the optical pulse. In Figure 3, the FreeTrig frequency signal c represents the external frequency signal required during processing, the frequency selection control signal d represents the level signal of the control module 4 controlling the main acousto-optic modulator 102, the auxiliary acousto-optic modulator gate signal e represents the level signal of the control module 4 controlling the onboard auxiliary acousto-optic modulator 104, and the free-space acousto-optic modulator gate signal f represents the level signal output by the control module 4 to control the free-space acousto-optic modulator 3. The meanings of the fundamental frequency seed light P1 to the selected pulse laser P5 are consistent with those described in Figure 2.

[0045] When the external frequency signal FreeTrig frequency signal c required during processing is input to the control module 4 through the input interface 6, the control module 4 outputs the frequency selection control signal d to control the main acousto-optic modulator 102 to start immediately and pick up one or more (depending on the processing application) main pulses, namely the fundamental frequency seed light P1. The delay between the output of the fundamental frequency seed light P1 and the FreeTrig signal input generally does not exceed 2 clock cycles (mode-locked seed frequency cycle), that is, less than 0.1uS; at the same time, the control module 4 detects the FreeTrig frequency change in real time. If the input frequency is less than the fundamental frequency, the control module 4 outputs the pulse width modulation signal, namely the auxiliary acousto-optic modulator gating signal e, to control the opening and closing of the on-board auxiliary optical modulator 104, thereby outputting a width-modulated secondary pulse cluster to the fiber collimator 105 and outputting the modulated optical pulse cluster P2. The fiber combiner 106 combines the fundamental frequency seed light P1 and the modulated optical pulse cluster P2 and outputs the combined optical pulse train P3, which is input to the optical amplifier 2; when FreeTrig When the g signal frequency is less than the minimum allowable fundamental frequency of the laser, the interval between the fundamental frequency seed light P1 in the combined optical pulse train P3 is very long. However, this interval contains the modulated optical pulse cluster P2, which removes the upper energy level particle population accumulated by the pump in the optical amplifier 2, thereby protecting the optical lens and optical crystal. After passing through the optical amplifier 2, the combined optical pulse train P3 outputs the amplified optical pulse train P4. The amplified optical pulse train P4 contains the amplified main pulse and the amplified secondary pulse cluster. Only the amplified main pulse is required for processing. Therefore, the control module 4 outputs the free-space acousto-optic modulator gating signal f to control the synchronous opening of the free-space acousto-optic modulator 3 and pick up the main pulse to output the selected pulse laser P5. The optical delay from the fundamental frequency seed light P1 picked up by the main acousto-optic modulator 102 to the selected pulse laser P5 output by the free-space acousto-optic modulator 3 is generally less than 0.2 μs. Therefore, the total delay time from the FreeTrig pulse signal input to the optical pulse output does not exceed 0.3 μs, ensuring real-time performance.

[0046] When the FreeTrig frequency is greater than or equal to the fundamental frequency, at time T0 in Figure 3, the control module 4 turns off the onboard auxiliary AOM 104. No optical pulses are output in the modulated optical pulse cluster P2. The entire optical path is equivalent to amplifying only the fundamental frequency seed light P1 through the optical amplifier 2 and finally outputting it from the free-space AOM 3.

[0047] For the optical amplifier 2, as long as there is seed light input, it will carry away the number of pump energy level particles. The more seed light there is in the same time period, the lower the single pulse energy of the output amplified optical pulse. Therefore, to ensure that the single pulse energy of the final output pulse light at low frequency is consistent with the single pulse energy of the output light at the fundamental frequency, it is necessary to control the pulse cluster frequency and pulse cluster width of the modulated optical pulse cluster P2. The single pulse energy needs to be converted based on the power at the fundamental frequency and then calibrated. Under given different external frequencies, the PWM signal of the on-board auxiliary acousto-optic modulator 104, that is, the auxiliary acousto-optic modulator gate signal e, is adjusted to make the laser output corresponding power. Therefore, under given fundamental frequency conditions, the corresponding relationship between the external input frequency and the PWM frequency pulse width can be obtained. During operation, the control module 4 adjusts the PWM in real time according to this corresponding relationship, ultimately keeping the laser output optical pulse energy consistent.

[0048] When the FreeTrig frequency exceeds the fundamental frequency, the single-pulse energy will inevitably decrease. In this case, it is impossible to ensure the stability of the single-pulse energy by adjusting the control. During processing applications, the maximum FreeTrig frequency point is determined and used as the fundamental frequency. Therefore, the single-pulse energy can be guaranteed to be consistent below the fundamental frequency. Considering the consistency of the single-pulse energy above the fundamental frequency is meaningless.

[0049] In summary, the present invention presents an ultrafast laser device and control method based on free-space triggered pulse output. This device splits pre-amplified mode-locked seed light into two main and secondary seed light paths with different power ratios. The main acousto-optic modulator (AOM) is controlled to output a main pulse in accordance with the FreeTrig frequency. An onboard AOM is used to width-modulate the secondary seed light sequence to output a secondary pulse cluster. The main and secondary modulated seed light paths are combined to achieve optical amplification. The free-space AOM synchronizes pulse output. In FreeTrig mode, the output laser pulse energy is stable.

[0050] It meets the requirements of free trigger pulse output, and the light pulse changes with the external input frequency, with good real-time performance. The single pulse energy of the laser output pulse is consistent, ensuring the real-time requirements of processing and the stability of the single pulse energy, without the risk of damaging the laser when working at low frequency.

[0051] The laser actively adapts to the external trigger signal to control the pulse output, while keeping the laser single pulse energy relatively stable within a limited frequency band to meet the needs of processing applications.

[0052] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, improvements, and the like made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention. It should be noted that similar reference numerals and letters denote similar items in the following figures. Therefore, once an item is defined in one figure, it need not be further defined or explained in subsequent figures.

[0053] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0054] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

Claims

1. Device for output of free-triggered pulses of an ultrafast laser, Characterized in that: It includes a seed beam splitting pulse generation module (1), an optical amplifier (2), a free-space acousto-optic modulator (3), a control module (4), a photodetector (5) and an input interface (6). The seed beam splitting pulse generation module (1) includes an optical fiber splitter (101), a main acousto-optic modulator (102), an optical fiber collimator (103), an on-board auxiliary acousto-optic modulator (104), an optical fiber collimator (105) and an optical fiber combiner (106). Seed light is input to the input end of the optical fiber splitter (101) of the seed beam splitting pulse generation module (1). The optical fiber splitter (101) splits into two beams of light. One output end of the optical fiber splitter (101) is connected to the optical input end of the main acousto-optic modulator (102), and the other output end is connected to the input end of the optical fiber collimator (103). The optical output end of the main acousto-optic modulator (102) is connected to one input end of the optical fiber combiner (106). The control input end of the main acousto-optic modulator (102) is connected to one output end of the control module (4). The output end of the optical fiber collimator (103) is connected to the optical input end of the on-board auxiliary acousto-optic modulator (104). The output end of the on-board auxiliary acousto-optic modulator (104) is connected to the input end of the optical fiber collimator (105). The control input end of the on-board auxiliary acousto-optic modulator (104) is connected to one output end of the control module (4). The output end of the optical fiber collimator (105) is connected to the other input end of the optical fiber combiner (106). The output end of the optical fiber combiner (106) is connected to the input end of the optical amplifier (2). The output end of the optical amplifier (2) is connected to the optical input end of the free-space acousto-optic modulator (3). The control input end of the free-space acousto-optic modulator (3) is connected to the output end of the control module (4). The optical output end of the free-space acousto-optic modulator (3) outputs the required optical pulses. The external trigger signal is connected to the input end of the control module (4) through the input interface (6).

2. The device for output of free-triggered pulses of an ultrafast laser according to claim 1, Characterized in that: The output end of the photodetector (5) is connected to the input end of the control module (4).

3. The device for output of free-triggered pulses of an ultrafast laser according to claim 1, Characterized in that: The control module (4) includes a high-speed comparator (401), a communication interface (402), an MCU (403), and an FPGA (404). The optoelectronic detection signal is connected to the positive input terminal of the high-speed comparator (401), the reference ground is connected to the negative input terminal of the high-speed comparator (401), and the output terminal of the high-speed comparator (401) is connected to the global clock input terminal of the FPGA (404); the external FreeTrig signal frequency is connected to the input terminal of the FPGA (404); the communication interface (402) is connected to the input terminal of the MCU (403), the data bus port of the MCU (403) is connected to the data bus port of the FPGA (404), and the light output signal output terminal of the MCU (403) is connected to the input terminal of the FPGA (404); the reset output terminal of the MCU (403) is connected to the global reset input terminal of the FPGA (404); three output terminals of the FPGA (404) respectively output control signals for controlling the main acousto-optic modulator (102), the on-board auxiliary acousto-optic modulator (104), and the free-space acousto-optic modulator (3).

4. The device for output of free-triggered pulses of the ultrafast laser according to claim 1, characterized in that: The on-board auxiliary acousto-optic modulator (104) is a surface-mounted free-space acousto-optic modulator.

5. The device for output of free-triggered pulses of the ultrafast laser according to claim 1, characterized in that: The main acousto-optic modulator (102) is a fiber-coupled acousto-optic modulator with a frequency of 150 to 200 MHz.

6. The control method for realizing the output of free-triggered pulses of the ultrafast laser by the device according to claim 1, characterized in that: The seed light is input into the seed beam splitting pulse generation module (1), and is split into two seed lights with different powers by the fiber optic splitter (101). The main pulse beam is input into the main acousto-optic modulator (102), and the secondary pulse beam is input into the fiber optic collimator (103); the output light of the fiber optic collimator (103) enters the on-board auxiliary acousto-optic modulator (104). The main acousto-optic modulator (102) outputs the fundamental frequency seed light (P1) with the required frequency under the modulation control of the control module (4); the on-board auxiliary acousto-optic modulator (104) outputs a cluster of seed light pulses with variable frequency and adjustable width under the modulation control of the control module (4), and inputs it into the fiber optic collimator (105), and then outputs the modulated light pulse cluster (P2). The fiber optic collimator (103) and the fiber optic collimator (105) form a pair of couplers to realize the process of the secondary pulse beam being transmitted from fiber to space and then to fiber; the fundamental frequency seed light (P1) and the modulated light pulse (P2) are input into the fiber optic combiner (106) and combined to output the combined light pulse train (P3). The combined light pulse train (P3) is input into the optical amplifier (2) for amplification. After being amplified, the combined light pulse train (P3) outputs the amplified light pulse train (P4) from the optical amplifier (2). The amplified light pulse train (P4) is input into the free space acousto-optic modulator (3), and outputs the required selected pulsed laser (P5) under the synchronous control of the control module (4). The input interface (6) inputs the FreeTrig frequency signal into the control module (4) to control the laser to output light pulses with the same frequency.

7. The control method for the output of the ultrafast laser based on free trigger pulses according to claim 6, characterized in that: The photodetector (5) is used to receive part of the mode-locked seed light, so as to output the seed mode-locked frequency to the control module (4), and the mode-locked frequency is used as the clock signal of the control module (4).

8. The control method for the output of the ultrafast laser based on free trigger pulses according to claim 6, characterized in that: When there is no input frequency signal at the input interface (6), the control module (4) outputs the gating signal (a) of the main acousto-optic modulator with a fixed frequency to control the opening and closing of the main acousto-optic modulator (102). At the moment when the main acousto-optic modulator (102) is turned on, one or more main pulses can be picked out to output the fundamental frequency seed light (P1); the control module (4) controls the gating signal of the on-board auxiliary acousto-optic modulator (104) to be closed. The on-board auxiliary acousto-optic modulator (104) has no secondary pulse output, and the modulated light pulse cluster (P2) is empty. The combined light pulse train (P3) output by the fiber optic combiner (106) is equivalent to the fundamental frequency seed light (P1). After being amplified by the optical amplifier (2), the combined light pulse train (P3) forms the amplified light pulse train (P4) and outputs it. If it is necessary to test the output light, or the external control continuously outputs light for a long time, then the control module (4) outputs the free acousto-optic modulator gating signal (b) for controlling the free space acousto-optic modulator (3) to be high, and the free space acousto-optic modulator (3) outputs the selected pulsed laser (P5).

9. The control method for the output of free-triggered pulses of an ultrafast laser according to claim 6, characterized in that: During processing, the required external frequency signal, the FreeTrig frequency signal (c), is input into the control module (4) through the input interface (6). The control module (4) outputs a frequency selection control signal (d) to control the immediate activation of the main acousto-optic modulator (102), and picks out one or more main pulses, namely the fundamental frequency seed light (P1). The delay between the output of the fundamental frequency seed light (P1) and the input of the FreeTrig signal does not exceed 2 mode-locking frequency clock cycles, that is, less than 0.1 μs. At the same time, the control module (4) detects the change of the FreeTrig frequency in real time. If the input frequency is less than the fundamental frequency, the control module (4) outputs a pulse width modulation signal, namely the auxiliary acousto-optic modulator gating signal (e), to control the activation and deactivation of the on-board auxiliary optical modulator (104), so as to output a width-modulated secondary pulse cluster to the fiber collimator (105) and output a modulated optical pulse cluster (P2). The fiber combiner (106) combines the fundamental frequency seed light (P1) and the modulated optical pulse cluster (P2) and outputs a combined optical pulse train (P3), which is input into the optical amplifier (2). When the FreeTrig signal frequency is less than the lowest allowable fundamental frequency of the laser, the interval between the fundamental frequency seed lights (P1) in the combined optical pulse train (P3) is long, and the interval contains the modulated optical pulse cluster (P2), which takes away the upper-level particles accumulated by the pump in the optical amplifier (2), protecting the optical lenses and optical crystals of the optical amplifier (2). The combined optical pulse train (P3) outputs an amplified optical pulse train (P4) after passing through the optical amplifier (2). The amplified optical pulse train (P4) contains the amplified main pulse and the amplified secondary pulse cluster. Only the amplified main pulse is required during processing. Therefore, the control module (4) outputs a free-space acousto-optic modulator gating signal (f) to control the synchronous activation of the free-space acousto-optic modulator (3) and pick out the main pulse, thereby outputting the selected pulsed laser (P5). The optical delay from the fundamental frequency seed light (P1) picked out from the main acousto-optic modulator (102) to the selected pulsed laser (P5) output through the free-space acousto-optic modulator (3) is less than 0.2 μs. The total delay time from the input of the FreeTrig pulse signal to the output of the optical pulse does not exceed 0.3 μs at most; When the FreeTrig frequency is greater than or equal to the fundamental frequency, the control module (4) turns off the on-board auxiliary acousto-optic modulator (104), and there is no output optical pulse in the modulated optical pulse cluster (P2). The entire optical path is equivalent to only amplifying the fundamental frequency seed light (P1) by the optical amplifier (2) and finally outputting it from the free-space acousto-optic modulator (3).

Images