Laser pulse control system

Abstract

The utility model discloses a pulse control system of a laser, which can control a pulse selector I and a pulse selector II through an external controller, so that the pulse selector I and the pulse selector II have a synchronous trigger control mode and an asynchronous trigger control mode. In the asynchronous trigger control mode, the problems of time delay scanning and accurate control in synchronous control can be solved, 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 utility model relates to the field of laser pulse control, especially relates to a laser pulse control system. BACKGROUND

[0002] The control of the conventional laser pulse often depends on the fixed or preset parameter set, these parameters can be difficult to comprehensively cover and adapt to the diversity of ranging signals under different environments, and there are the defects that the algorithm is complex, the parameter setting is difficult to adapt to the extraction of multiple characteristic signals, it is difficult to realize the mediation of ranging signals with different signal-to-noise ratios and different pulse shapes, thereby affecting real-time control and control precision. SUMMARY

[0003] The utility model provides a laser pulse control system can solve the problem pointed out in the background art.

[0004] A laser pulse control system, comprising a laser and an external controller, wherein the laser comprises a seed source, a photodetector, an amplification system and a pulse selector subsystem;

[0005] The pulse selector subsystem comprises a pulse selector one and a pulse selector two;

[0006] The seed source is connected with the photodetector through an optical fiber;

[0007] The external controller is connected with the pulse selector two and the pulse selector two through a circuit;

[0008] The photodetector is connected with the pulse selector one through a circuit;

[0009] The amplification system is used to receive and amplify the low-frequency pulse laser output by the pulse selector one, the pulse selector one is used to receive and process the electrical signal converted by the photodetector, and the pulse selector one is also used to send a trigger signal to the external controller;

[0010] The external controller is used to receive the trigger signal and send a trigger signal value to the pulse selector two;

[0011] The pulse selector two receives the trigger signal and generates a corresponding driving signal, thereby releasing the adjusted optical pulse.

[0012] Preferably, the amplification system is an optical amplifier.

[0013] Preferably, the seed source is a femtosecond oscillator.

[0014] Preferably, the optical pulse repetition frequency of the seed source output is 40-50 MHZ.

[0015] Preferably, the laser pulse control system has two control modes, synchronous triggering and asynchronous triggering.

[0016] In the synchronous triggering control mode, the following steps are taken:

[0017] The pulse selector one sends a synchronization signal and identifies the rising edge of the synchronization signal, and after identifying the rising edge of the synchronization signal, a trigger signal is processed, generated and sent;

[0018] The pulse selector two receives the trigger signal, and after identifying the rising edge or falling edge of the trigger signal, a driving signal is generated;

[0019] The laser outputs a laser pulse;

[0020] In the asynchronous triggering control mode, the following steps are taken:

[0021] A trigger signal is generated and sent to the pulse selector one and the pulse selector two;

[0022] A time delay T is preset reset After the time delay T reset The counter of the pulse selector one is reset, the pulse selector one selects a pulse from the seed light and amplifies it through an optical amplifier, and the time interval between the two pulses is changed;

[0023] The pulse selector two receives the trigger signal, and after identifying the rising edge or falling edge of the trigger signal, a driving signal is generated;

[0024] The laser outputs a laser pulse.

[0025] Compared with the prior art, the laser pulse control system of the utility model has the beneficial effects that: the laser pulse control system of the utility model is controlled by an external controller to control the pulse selector one and the pulse selector two, so that it has a synchronous triggering control mode and an asynchronous triggering control mode, can adapt to different timing control precision requirements, reduces the difficulty of algorithm development, and increases the control accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a schematic diagram of the laser pulse control system in the synchronous triggering control mode;

[0027] Figure 2 It is a schematic diagram of the laser pulse control system in the asynchronous triggering control mode;

[0028] Figure 3 It is a laser timing diagram in the synchronous triggering control mode;

[0029] Figure 4 It is a laser timing diagram in the asynchronous triggering control mode;

[0030] Figure 5 Laser timing diagram in the asynchronous trigger control mode for multi-pulse output.

[0031] Reference signs:

[0032] 1-seed source, 2-optical detector, 3-optical amplifier, 4-pulse selector one, 5-pulse selector two, 6-external controller. DETAILED DESCRIPTION

[0033] One specific embodiment of the present application will be described in detail below with reference to the accompanying drawings, but it should be understood that the scope of protection of the present application is not limited by the specific embodiment.

[0034] As Figure 1 shown, the present embodiment proposes a laser pulse control system, which comprises a laser and an external controller 6, as Figure 1 shown, the laser can mainly be divided into a seed source 1, an amplification system, a pulse selection subsystem, an optical detector 2 and an optical path part, the optical path part is prior art and will not be described here (the optical path part is omitted) ;

[0035] Among them, the amplification system is an optical amplifier 3;

[0036] The pulse selection subsystem comprises a pulse selector one 4 and a pulse selector two 5;

[0037] The pulse selector one 4 is used for receiving and processing the electrical signal converted by the optical detector 2 after converting the optical pulse, and the pulse selector one 4 is also used for sending a trigger signal to the external controller 6;

[0038] The optical amplifier 3 is used for receiving and amplifying the low-repetition-rate pulse laser output by the pulse selector one 4;

[0039] The external controller 6 is used for receiving the trigger signal and sending the trigger signal value pulse selector two 5;

[0040] The pulse selector two 5 receives the trigger signal and generates a corresponding driving signal, thereby releasing the adjusted optical pulse;

[0041] The external controller 6 is connected with the pulse selector two 5 through a circuit, such as a coaxial cable, a shielded wire, etc. The laser emitted by the seed source 1 is divided into two beams, one of which is incident on the optical detector 2 (which can be fiber connected or directly incident on the detector through spatial transmission of the beam) to generate an electrical pulse signal, the optical detector 2 is connected with the pulse selector one 4 through a circuit, and the pulse selector and the acousto-optic modulator are also connected through a circuit;

[0042] The seed source 1 of the embodiment is a femtosecond oscillator, which generally generates optical pulses with a repetition frequency of 40-50 MHz. Due to its special generation mode (mode locking technology), the repetition frequency of the optical pulses generally only depends on the cavity length of the seed source 1 laser cavity, and the repetition frequency is very stable. Although the repetition frequency of each laser cavity is stable, it is impossible to manufacture laser cavities with exactly the same cavity length in reality, so the repetition frequencies of the seed sources 1 of two laser devices cannot be exactly the same. Generally, the difference can be controlled within 0.5 MHz (the difference in cavity length is about 3 cm) through artificial control.

[0043] The optical pulses generated by the seed source 1 are converted into electrical signals by the photodetector 2 to serve as the reference frequency of the laser system. The pulse selector one 4 reduces the frequency of the reference frequency through high-speed electrical signal processing to obtain an electrical signal with a lower repetition frequency, and then transmits it to the AOM1 through AOM driving. The AOM (acousto-optic modulator) is a high-speed switch that can quickly select loss or pass through optical pulses. After passing through the AOM1, the laser becomes a pulsed light with a lower repetition frequency (2 MHz is selected in the embodiment), and then passes through the optical amplification system to further improve the energy of the optical pulses.

[0044] Due to the processing mode of refractive surgery, the 2 MHz pulses need to be further reduced in frequency, and the laser repetition frequency needs to be continuously changed (i.e., the time interval between pulses is changed) on a time scale of 10 ms. Currently, it needs to be changed between 100 Hz and 800 kHz, and a single pulse needs to be output each time. In order to quickly control the laser repetition frequency, the pulse selector two 5 is used for control.

[0045] The control method of the laser pulse control system of the embodiment is as follows:

[0046] In the implementation of controlling the laser repetition frequency, there are generally two ways to process the externally triggered pulses (or gate signals), which are gate mode and trigger mode. In the gate mode, the laser continuously outputs 2 MHz pulses when the external input is high. In the trigger mode, the laser outputs a pulse at each rising edge. When the gate width is less than the pulse interval (500 ns for 2 MHz), the gate mode is the same as the trigger mode, and only one pulse is output. Generally, the sync signal of the laser is a stable 2 MHz square wave signal, and the external trigger signal is generated based on the 2 MHz sync signal as the trigger source. This control method is called synchronous control.

[0047] In the ordinary synchronous trigger control mode, the following Figure 1As shown, the external controller generates the gate / trigger signal after a processing time after recognizing the rising edge of the sync signal; the time needed for signal transmission and processing can be recorded as T1, and the width of the generated gate signal is recorded as tgate. The pulse selector 2 generates the gate signal after a processing and delay time T AOM2 , and then generates the driving signal of the AOM 2. The AOM 2 generates ultrasonic waves in the acousto-optic crystal through the transducer when receiving the driving signal. After a period of time (physical response), the standing wave formed by the ultrasonic waves stabilizes, forms a Bragg grating, diffracts light, and releases a light pulse.

[0048] The delay T1 needs to be accurately adjusted under the synchronization control so that the AOM 2 can select a pulse at the right time. For example, in order to release only one pulse, the width of the gate signal needs to be less than the pulse interval (for example, 300 ns, otherwise two consecutive pulses may be released). It should be noted that when the light pulse is at the rising edge or the falling edge of the AOM 2 (T3 / T4), the released pulse will be distorted by the unstable sound wave (for example, Figure 1 As shown), so t1 needs to be adjusted so that the pulse is exactly in the center of the AOM 2 driving signal. Since the AOM 1 also has a time delay (T Figure 3 , as shown by the middle green arrow) relative to the sync signal, the pulses of the laser output may have a time delay relative to the pulses of the AOM 1 output. However, in the synchronization mode, all the pulses of the AOM 1 output are indistinguishable, so the time delay T AOM1 of the AOM 1 relative to the sync signal is not important;

[0049] The advantage of the above synchronization control is that the output light 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;

[0050] This embodiment needs to scan T1 to determine the optimal T1 value so that the output pulse is normal (in the center of the AOM 2 response), and the output power is observed to be the largest or the output pulse intensity is observed to be normal through the photodetector and the oscilloscope. In addition, for mass-produced equipment, it is necessary to strictly control various time parameters in the laser such as T AOM2 , T3, T4, etc. to avoid the need for scanning and testing of the delay T1 for each device;

[0051] 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 a pulse or a series of pulses. Through the analysis of the synchronous trigger mode, it is known that the time delay T1 is very important for the stable trigger release pulse, and when the external controller does not obtain the sync signal, the time delay T1 is not a stable value, so under the above timing, it is impossible to achieve the goal of releasing a pulse under each external trigger; in order to realize the stable output of a pulse under asynchronous control, the embodiment adjusts the laser internally, so that the laser releases a pulse at a fixed time delay after receiving the trigger / gate signal; to realize this function, the pulse selector one also needs to be controlled by the external trigger signal, as shown in the following Figure 2

[0052] After the laser receives the trigger signal, not only does it need to drive the AOM2 to open, but also needs to open the AOM1 (pulse selector one) at a specific time delay T reset After the laser receives the trigger signal, not only does it need to drive the AOM2 to open, but also needs to open the AOM1 (pulse selector one) at a specific time delay T Figure 4 As shown in the following timing diagram; in the timing of the asynchronous trigger, no matter how T1 changes, after the laser receives the rising edge of the gate / trigger signal, it can output a pulse at the time of T AOM2 +T reset In order to make the output pulse exactly in the center of the driving signal of the AOM2, the gate signal needs to be controlled to (1.9~2.1)T reset , as close as possible to 2T reset , and the time delay T AOM1 between the AOM1 and the sync signal needs to be equal to T AOM2 , so that the pulse released by the AOM2 is exactly the reset pulse.

[0053] The embodiment realizes the above-mentioned zero reset function by modifying the counter in the pulse selector one. The pulse selector one will count the 40MHz pulses of the seed source, and the frequency will be reduced to 2MHz, that is, a pulse is released every 20 counts, so the reset only needs to clear the counter; the pulse selector two only needs to identify the external trigger, and the counter (or time interval calculation) is completed by the external controller.

[0054] The asynchronous trigger control can solve the problem of scanning and accurate control of T1 in the synchronous control, reduce the burden of the external controller, thereby reducing the cost and development cycle;

[0055] When T reset ​When the setting is unreasonable, for example, ~500ns, the reconstructed pulse is too close to another adjacent pulse, and if the gate is still set to 2treset, double pulses or even three pulses will be output, which are different from the pulse train in the gate mode, and the time interval is not fixed, and the occurrence is also changed with T1 (i.e. random); and if T gate <2T reset , zero pulse can be output;

[0056] In order to reduce the risk of outputting multiple pulses, the orange reconstructed pulse should be located before the purple pulse, as shown in Figure 4 , and the interval between the green and orange pulses is T1+T reset , and the time of T1 is completely random under asynchronous triggering, and there is no fixed timing under asynchronous triggering, so it can be considered that 0<T1<500ns, and therefore no matter what T reset is set to, there is a case of T1+T reset >500ns (i.e. the orange pulse is located after the purple pulse), so the multiple pulse case cannot be completely avoided, and therefore the embodiment reduces the probability of outputting multiple pulses by reducing T reset , and when T reset is very close to 0, the probability of outputting multiple pulses will be low;

[0057] In addition, the embodiment synchronizes the hardware basis under asynchronous triggering mode, i.e. the hardware of the laser is set to asynchronous triggering, and the external controller still receives the sync signal as the trigger source, and T1 is stable at this time; in this case, the risk of outputting multiple pulses can be reduced or even avoided, and specifically, by changing T1, the interval between the clear pulse and the adjacent pulse can be adjusted: as shown in Figure 5 , when T reset is large, the interval between the purple and orange pulses is T reset +T1-500ns, and by reasonably selecting T1 and T gate , the output of double pulses can be avoided;

[0058] As shown in Figure 4 , when T reset is small, the interval between the green and orange pulses is T reset +T1, and by reducing T1, the orange pulse located after the purple pulse can be completely avoided, so that the output of multiple pulses is avoided.

[0059] It is apparent for a person skilled in the art that the present application is not limited to the details of the above-described exemplary embodiments, but that it can be implemented in other concrete forms without departing from the spirit and the essential characteristics of the present application. Therefore, the embodiments should be considered as exemplary and non-limiting, the scope of the present application being defined by the claims appended hereto rather than by the above description, and all the changes which fall within the meaning and the scope of the equivalent elements of the claims are intended to be embraced therein. Any reference signs in the claims should not be construed as limiting the claims to the figures in which the reference signs are used.

[0060] Furthermore, it should be understood that although the present specification is described in terms of embodiments, not every embodiment according to the present specification needs to exhibit each and every characteristic specified in the present specification. The specification can also be described in terms of a single independent technical solution, but this does not mean that each embodiment only contains one independent technical solution. The specification is described in this way only for the sake of clarity, and a person skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by a person skilled in the art.

Claims

1. A laser pulse control system, characterized by, The laser comprises a seed source, a photodetector, an amplification system and a pulse selector subsystem, and the external controller is connected with the pulse selector two and the pulse selector two through an electric circuit. The pulse selector subsystem comprises a pulse selector one and a pulse selector two. The seed source is connected with the photodetector through an optical fiber. The external controller is connected with the pulse selector two and the pulse selector two through an electric circuit. The photodetector is connected with the pulse selector one through an electric circuit. The amplification system is used for receiving and amplifying the low repetition frequency pulse laser output by the pulse selector one. The pulse selector one is used for receiving and processing the electric signal converted by the photodetector from the optical pulse, and sending a trigger signal to the external controller. The external controller is used for receiving the trigger signal and sending a trigger signal value to the pulse selector two.

2. A laser pulse control system as claimed in claim 1, characterized in that The pulse selector two receives the trigger signal and generates a corresponding driving signal, so as to release the adjusted optical pulse.

3. A laser pulse control system as claimed in claim 1, characterized in that The amplification system is an optical amplifier.

4. A laser pulse control system as claimed in claim 3, wherein, The seed source is a femtosecond oscillator. The optical pulse repetition frequency output by the seed source is 40-50 MHZ.

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