Laser pulse control system and method

Abstract

The invention discloses a laser pulse control system and method, the system has a synchronous trigger control mode and an asynchronous trigger control mode, asynchronous trigger control can solve the problems of time delay scanning and accurate control in synchronous control, and the burden of an external controller is reduced, so that the cost is reduced, and the development period is shortened; the method can meet the precision requirements of different time sequence control, reduces the difficulty of algorithm development, and improves the control accuracy.

Description

Technical Field

[0001] The invention relates to the field of laser pulse control, and in particular to a laser pulse control system and method. Background Art

[0002] The control of traditional laser pulses often relies on fixed or preset parameter sets, which may be difficult to fully cover and adapt to the diversity of ranging signals in different environments. In addition, the algorithm is complex and the parameter settings are difficult to adapt to the extraction of multiple characteristic signals. It is difficult to achieve the mediation of ranging signals with different signal-to-noise ratios and different pulse shapes, thus affecting real-time control and control accuracy. Summary of the invention

[0003] The present invention provides a laser pulse control system and method, which can solve the problems pointed out in the background technology.

[0004] A laser pulse control method, comprising:

[0005] In the synchronous trigger control mode, there are the following steps:

[0006] Receive the synchronization signal sent by the pulse selector 1 and identify the rising edge of the synchronization signal, and process, generate and send a trigger signal after identifying the rising edge of the synchronization signal;

[0007] The pulse selector 2 receives the trigger signal and generates a drive signal after identifying the rising edge or falling edge of the trigger signal;

[0008] The laser outputs laser pulses;

[0009] In the asynchronous trigger control mode, the following steps are involved:

[0010] Generate a trigger signal and send it to pulse selector 1 and pulse selector 2;

[0011] Preset time delay T reset , at the delay T reset Afterwards, the counter of pulse selector 1 is reset, and pulse selector 1 selects pulses from the seed light and amplifies them through an optical amplifier, thereby changing the time interval between two pulses;

[0012] The pulse selector 2 receives the trigger signal and generates a drive signal after identifying the rising edge or falling edge of the trigger signal;

[0013] The laser outputs laser pulses.

[0014] Preferably, in the synchronous trigger control mode, the time interval from the pulse selector 1 sending the synchronization signal to the pulse selector 2 receiving the trigger signal is set to T 1 , adjust T 1So that the laser pulse is in the center of the pulse selector 2 driving signal.

[0015] Preferably, in the synchronous trigger control mode, the trigger signal includes a gate signal / tiger signal, and the width of the gate signal is smaller than the required pulse interval.

[0016] Preferably, in the asynchronous trigger control mode, the processing delay of the pulse selector 1 is set to T Aom1 , set the processing delay of pulse selector 2 to T Aom2 , T Aom1 =T Aom2 , the gate signal width of the trigger signal is (1.9~2.1)T reset .

[0017] Preferably, in the asynchronous trigger control mode, by reducing T reset The value of can be used to reduce the probability of the laser outputting multiple pulses.

[0018] Preferably, in the asynchronous trigger control mode, if the external controller uses the synchronous signal as the trigger source, by reducing T 1 The value of can be used to reduce the probability of the laser outputting multiple pulses.

[0019] A laser pulse control system comprises a laser and a controller, wherein the laser comprises a seed source, a photodetector, an amplification system and a pulse selection subsystem;

[0020] The amplification system is an optical amplifier;

[0021] The pulse selection subsystem includes a pulse selector 1 and a pulse selector 2;

[0022] The seed source is used to emit laser light;

[0023] The pulse selector 1 is used to receive and process the electrical signal converted by the photodetector from the optical pulse, and the pulse selector 1 is also used to send a trigger signal to the controller;

[0024] The optical amplifier is used for receiving and amplifying the low repetition rate pulse laser output by the pulse selector 1;

[0025] The controller is used for receiving a trigger signal and sending a trigger signal value pulse selector 2;

[0026] The pulse selector 2 receives the trigger signal and generates a corresponding driving signal, thereby releasing the regulated light pulse.

[0027] Compared with the prior art, the beneficial effects of the present invention are: the present invention proposes a laser pulse control system which can realize the control of pulse selector 1 and pulse selector 2 through an external controller, so that it has a synchronous trigger control mode and an asynchronous trigger control mode, which can adapt to different timing control accuracy requirements, reduce the difficulty of algorithm development, and increase the accuracy of control. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is the schematic diagram of the synchronous trigger control mode;

[0029] Figure 2 This is the schematic diagram of the asynchronous trigger control mode;

[0030] Figure 3 This is the laser timing diagram in synchronous trigger control mode;

[0031] Figure 4 This is the laser timing diagram in asynchronous trigger control mode;

[0032] Figure 5 This is the laser timing diagram in asynchronous trigger control mode with multiple pulse outputs. DETAILED DESCRIPTION

[0033] A specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific implementation.

[0034] Embodiment 1

[0035] like Figure 1 As shown, this embodiment proposes a laser pulse control system, such as Figure 1 As shown, the femtosecond laser system can be mainly divided into a seed source, an amplification system, a pulse selection subsystem, a photodetector and an optical path part. The optical path part is the prior art and will not be described here (the optical path part is omitted);

[0036] Wherein, the amplification system is an optical amplifier;

[0037] The pulse selection subsystem includes a pulse selector 1 and a pulse selector 2;

[0038] The pulse selector 1 is used to receive and process the electrical signal converted by the photodetector from the optical pulse, and the pulse selector 1 is also used to send a trigger signal to the controller;

[0039] The optical amplifier is used for receiving and amplifying the low repetition rate pulse laser output by the pulse selector 1;

[0040] The controller is used for receiving a trigger signal and sending a trigger signal value pulse selector 2;

[0041] The pulse selector 2 receives the trigger signal and generates a corresponding driving signal, thereby releasing the regulated light pulse;

[0042] The external controller is connected to the pulse selector 2 through a circuit, such as a coaxial cable, a shielded wire, etc. The laser emitted by the seed source is divided into two beams, one of which is incident on a photodetector (which can be an optical fiber connection or the light beam is directly incident on the detector through space transmission) to generate an electrical pulse signal, the photodetector is connected to the pulse selector 1 through a circuit, and the pulse selector is also connected to the acousto-optic modulator through a circuit;

[0043] The seed source of this embodiment is a femtosecond oscillator, which generally generates optical pulses with a repetition frequency of 40 to 50 MHz. Due to its special generation method (mode locking technology), the repetition frequency of the optical pulses generally depends only on the cavity length of the seed source laser cavity, and the repetition frequency is very stable. Although the repetition frequency of each laser cavity is stable, it is impossible to manufacture a laser cavity with exactly the same cavity length in reality, so the repetition frequency between every two laser seed sources cannot be exactly the same. Through artificial control, the difference can generally be within 0.5 MHz (the cavity length difference is about 3 cm);

[0044] The light pulses generated by the seed source will be converted into electrical signals through the photodetector to serve as the reference frequency of the laser system. Pulse selector 1 downconverts the reference frequency through high-speed electrical signal processing to obtain an electrical signal with a lower repetition rate, which is then driven by the AOM to be transmitted to AOM1. The AOM (acousto-optic modulator) is a high-speed switch that can quickly select to lose or pass the light pulse. After passing through AOM1, the laser becomes a pulse light with a lower repetition rate (2MHz is selected in this embodiment), and then passes through the optical amplification system to further increase the energy of the light pulse.

[0045] Due to the processing mode of refractive surgery, it is necessary to further reduce the frequency of the 2MHz pulse and continuously change the laser repetition frequency (i.e. change the time interval between pulses) on a time scale of 10ms. Currently, it needs to change between 100Hz and 800kHz, and it is required to output a single pulse each time it is triggered. In order to quickly control the laser repetition frequency, a pulse selector 2 is required for control.

[0046] Embodiment 2

[0047] like Figures 1 to 5 As shown, based on the first embodiment, a laser pulse control method provided by the embodiment of the present invention is specifically as follows:

[0048] In terms of the implementation of controlling the laser repetition rate, there are generally two ways to handle externally triggered pulses (or gate signals), namely gate mode and trigger mode. The so-called gate mode means that when the external input is at a high level, the laser continuously outputs 2MHz pulses. In trigger mode, the laser outputs a pulse on each rising edge. When the gate width is smaller than the pulse interval (500ns for 2MHz), the gate mode is exactly the same as the trigger mode, and only one pulse is output. In general, the sync signal of the laser is a stable 2MHz square wave signal, and the external trigger signal is generated using this 2MHZ sync signal as the trigger source. This control method is called synchronous control;

[0049] In the normal synchronous trigger control mode, as follows Figure 1 As shown, after the external controller recognizes the rising edge of the sync signal (synchronization signal), it generates a gate / trigger signal (trigger signal) after a period of processing time; the time required for signal transmission and processing can be recorded as T 1 The width of the generated gate signal is recorded as tgate. After the pulse selector 2 recognizes the rising edge (or falling edge, generally the rising edge is selected for processing) of the gate signal, it is processed and delayed by T AOM2 After that, a driving signal of AOM2 is generated. When AOM2 receives the driving signal, it generates ultrasonic waves in the acousto-optic crystal through the transducer. After a period of time (physical response), the standing wave formed by the ultrasonic waves stabilizes, forming a Bragg grating that diffracts light, thereby releasing light pulses.

[0050] Synchronous control requires precise adjustment of the delay T 1 , so that AOM2 can select a pulse at the right time; for example, in order to release only one pulse, the gate signal width needs to be smaller than the pulse interval (such as 300ns, otherwise two consecutive pulses may be released); it should be noted that when the optical pulse is at the rising edge or falling edge of AOM2 (T 3 / T 4 ), the release pulse will be affected by the unstable sound wave and distorted (such as Figure 1 As shown), we need to adjust t1 so that the pulse is exactly in the center of the AOM2 drive signal; since AOM1 also has a delay relative to the sync signal ( Figure 3 As shown by the green arrow in the figure, the pulses output by the laser may have a time delay with the pulses output by AOM1. However, in the synchronous mode, all the pulses output by AOM1 are the same, so the time delay of AOM1 relative to the sync signal is T AOM1 It doesn’t matter;

[0051] The advantage of the above synchronous control is that the output optical pulse is strictly based on 2MHz, and the pulse interval is based on 500ns, that is, no matter how the frequency of the external control is adjusted, the obtained pulse interval must be an integer multiple of 500ns;

[0052] This embodiment requires scanning T 1 To determine the optimal T 1 The output pulse is normal (in the center of the AOM2 response), the output power is observed to be maximum, or the output pulse intensity is observed to be normal through a photodetector and an oscilloscope; in addition, for mass-produced equipment, it is necessary to control various time parameters in the laser, such as T AOM2 , T 3 , T 4 etc. to avoid the need for each device to delay T 1 Scanning and testing;

[0053] In the asynchronous trigger control mode, the external controller does not need to obtain the sync signal of the laser, but directly generates a gate or trigger signal to trigger the laser to release one or a series of pulses. Through the analysis of the synchronous trigger mode, it can be seen that the delay T 1 It is very important for stable triggering and releasing pulses. When the external controller does not get the sync signal, the delay T 1 It is definitely not a stable value. Therefore, under the above timing, it is impossible to achieve the goal of releasing a pulse under each external trigger. In order to achieve a stable output of a pulse under asynchronous control, this embodiment adjusts the laser internally so that the laser releases a pulse at a fixed delay after receiving the trigger / gate signal. To achieve such a function, it is necessary to make the pulse selector 1 also controlled by the external trigger signal, as follows Figure 2 As shown;

[0054] After the laser receives the trigger signal, it is necessary not only to drive AOM2 to open, but also to reset Then turn on AOM1 (pulse selector 1) and select a pulse from the seed light for amplification (instead of continuing to amplify the pulse after 500ns), thereby artificially changing the time interval between the two pulses to achieve the above function. The timing is as follows Figure 4 As shown; in the asynchronous trigger sequence, regardless of T 1 How does it change? After the laser receives the rising edge of the gate / trigger signal, T AOM2 +T reset In order to make the output pulse exactly in the center of the AOM2 drive signal, the gate signal needs to be controlled to (1.9~2.1)T reset , as close to 2T as possiblereset , and the delay between AOM1 and sync signal is T AOM1 Need to be equal to T AOM2 , so that the pulse released by AOM2 is exactly the pulse after reset;

[0055] This embodiment realizes the above-mentioned reset function by modifying the counter inside the pulse selector 1. The pulse selector 1 will count the 40MHz pulses of the seed source and reduce the frequency to 2MHz, that is, release one pulse every 20 pulses counted. Therefore, reset only needs to clear the counter; and the pulse selector 2 only needs to identify the external trigger, and the counter (or the calculation of the time interval) is completed by the external controller.

[0056] Asynchronous trigger control can solve the problem of T in synchronous control. 1 The difficulty of scanning and precise control is reduced, which reduces the burden on external controllers, thereby reducing costs and shortening development cycles;

[0057] When T reset When the setting is unreasonable, for example, when the time is ~500ns, the reconstructed pulse is too close to another adjacent pulse. At this time, if the gate is still set to 2treset, double pulses or even triple pulses will be output. The multiple pulses at this time are different from the pulse train of the gate mode. The time interval is not fixed and their appearance is also random. 1 If T is set gate <2T reset , then zero pulse may be output;

[0058] To reduce the risk of multiple pulses being output, the orange reconstruction pulse should be placed before the purple pulse, such as Figure 4 As shown, the interval between the green and orange pulses is T 1 +T reset , while under asynchronous triggering T 1 The time is completely random, and there is no fixed timing when the asynchronous trigger is triggered, so it can be considered that 0 <T 1 <500ns, so regardless of T reset No matter how many settings are set, T 1 +T reset >500ns (i.e. the orange pulse is after the purple pulse), so the multiple pulse situation cannot be completely avoided. Therefore, this embodiment reduces T reset To reduce the probability of outputting multiple pulses, when T reset When it is very close to 0, the probability of outputting multiple pulses will be low;

[0059] In addition, this embodiment performs synchronous triggering on the hardware basis in the asynchronous trigger mode, that is, the laser hardware is set to asynchronous triggering, and the external controller still receives the sync signal as the trigger source. 1 It is stable at this time; in this case, the risk of outputting multiple pulses can be reduced or even avoided. Specifically, by changing T 1 , can adjust the interval between the clear pulse and the adjacent pulse: Figure 5 As shown, when T reset When the pulse is larger, the interval between purple and orange pulses is T reset +T 1 -500ns, then choose T 1 and T gate The output of double pulses can be avoided;

[0060] like Figure 4 As shown, when T reset When it is smaller, the interval between the green and orange pulses is T reset +T 1 , by reducing T 1 , it can completely avoid the orange pulse being after the purple pulse, thus avoiding the output of multiple pulses.

[0061] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit and essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0062] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A laser pulse control method, characterized in that: include: In the synchronous trigger control mode, there are the following steps: Receive the synchronization signal sent by the pulse selector 1 and identify the rising edge of the synchronization signal, and process, generate and send a trigger signal after identifying the rising edge of the synchronization signal; The pulse selector 2 receives the trigger signal and generates a drive signal after identifying the rising edge or falling edge of the trigger signal; The laser outputs laser pulses; In the asynchronous trigger control mode, the following steps are involved: Generate a trigger signal and send it to pulse selector 1 and pulse selector 2; Preset time delay T reset , at the delay T reset Afterwards, the counter of pulse selector 1 is reset, and pulse selector 1 selects pulses from the seed light and amplifies them through an optical amplifier, thereby changing the time interval between two pulses; The pulse selector 2 receives the trigger signal and generates a drive signal after identifying the rising edge or falling edge of the trigger signal; The laser outputs laser pulses.

2. A laser pulse control method as claimed in claim 1, characterized in that: In the synchronous trigger control mode, the time interval from pulse selector 1 sending the synchronization signal to pulse selector 2 receiving the trigger signal is set to T1, and T1 is adjusted so that the laser pulse is in the center of the pulse selector 2 driving signal.

3. A laser pulse control method as claimed in claim 2, characterized in that: In the synchronous trigger control mode, the trigger signal includes a gate signal / tiger signal, and the width of the gate signal is smaller than the required pulse interval.

4. A laser pulse control method as claimed in claim 1, characterized in that: In the asynchronous trigger control mode, the processing delay of pulse selector 1 is set to T Aom1 , set the processing delay of pulse selector 2 to T Aom2 , T Aom1 =T Aom2 , the gate signal width of the trigger signal is (1.9~2.1)T reset .

5. A laser pulse control method as claimed in claim 1, characterized in that: In asynchronous trigger control mode, by reducing T reset The value of can be used to reduce the probability of the laser outputting multiple pulses.

6. A laser pulse control method as claimed in claim 1, characterized in that: In the asynchronous trigger control mode, if the external controller uses the synchronization signal as the trigger source, the probability of the laser outputting multiple pulses can be reduced by reducing the value of T1.

7. A laser pulse control system, characterized in that: It includes a laser and a controller, wherein the laser includes a seed source, a photodetector, an amplification system and a pulse selection subsystem; The amplification system is an optical amplifier; The pulse selection subsystem includes a pulse selector 1 and a pulse selector 2; The seed source is used to emit laser light; The pulse selector 1 is used to receive and process the electrical signal converted by the photodetector from the optical pulse, and the pulse selector 1 is also used to send a trigger signal to the controller; The optical amplifier is used for receiving and amplifying the low repetition rate pulse laser output by the pulse selector 1; The controller is used for receiving a trigger signal and sending a trigger signal value pulse selector 2; The pulse selector 2 receives the trigger signal and generates a corresponding driving signal, thereby releasing the regulated light pulse.

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