A full-automatic stable control passive Q-switched laser

Abstract

The application discloses a passive Q-switched laser which realizes automatic stability control of laser repetition frequency, light emission time and energy through real-time feedback. The laser is a core component of a spaceborne laser radar. The passive Q-switched laser utilizes existing photoelectric monitoring functions to form feedback. The waveform obtained by real-time monitoring of a photoelectric detector is converted into light emission time delay and energy value. After calculation, the value is compared with a set value to control parameters of a pump driving source circuit, so that the laser repetition frequency, light emission time and energy are automatically stabilized around the set value with small jitter. The application can automatically and effectively control the repetition frequency, light emission time delay and energy of the passive Q-switched laser, suppresses the jitter, improves the stability of the passive Q-switched laser, and due to the stable time delay of the external synchronization signal, the application can be used in a multi-beam condition, reduces the total time jitter, and improves the measurement precision and capability of the overall system.

Description

Technical Field

[0001] This application relates to the technical field of lasers, and in particular to a passively Q-switched laser with fully automatic stabilization control. Background Technology

[0002] Q-switching is a key technology for pulsed lasers, especially high-repetition-rate lasers operating at nanosecond levels and above. It can be divided into two types: active and passive Q-switching. Active Q-switching typically uses rotating mirrors, electro-optic Q-switching crystals, and acousto-optic Q-switching crystals for switching. This requires complex high-voltage control circuitry, and the high-voltage signal can easily interfere with other circuits, especially photoelectric detection circuits, posing safety risks. Furthermore, the added controlled electro-optic devices increase the complexity and risk of the optomechanical structure. In contrast, passive Q-switching generally utilizes the abrupt change characteristics of saturable absorber crystals to achieve Q-switching, eliminating the need for complex high-voltage control circuitry. Good passive Q-switching crystals in the currently used laser bands possess characteristics such as large absorption cross-section, short relaxation cross-section, small yield absorption cross-section, stable physicochemical properties, good thermal conductivity, damage resistance, and moisture resistance. Therefore, passive Q-switching offers advantages such as simple structure, reliable operation, high efficiency, safety, small size, and low cost, and has been widely used in military and civilian fields such as laser ranging, remote sensing, laser communication, and medical applications.

[0003] However, compared to active Q-switching, passively Q-switched pulsed lasers have poorer pulse repetition frequency, output delay, and energy stability, sometimes resulting in sub-pulses or no pulses. In the field of multi-beam lidar technology, these shortcomings make it difficult to measure accurately, difficult to mark individual pulses, and controlling multiple passively Q-switched lasers to emit light simultaneously increases the main wave gate size significantly, affecting lidar applications. Summary of the Invention

[0004] To address the above issues, this invention proposes a passively Q-switched laser that achieves fully automatic and stable control of laser repetition frequency, emission time, and energy through real-time feedback. Employing fully automatic digital control, the adjustment methods for multiple input parameters and multiple output control quantities are rationally combined and ordered, while also considering optomechanical requirements, circuit simplification, and signal optimization. This provides technical support for subsequent spaceborne lidar applications using passively Q-switched lasers.

[0005] In the first aspect, a passively Q-switched laser is provided, including a pump LD, a laser gain medium, a passively Q-switched crystal, an output mirror, a coupling lens, an optical fiber beam splitter, a photodetector, and a laser driver source.

[0006] The laser gain medium, the passively Q-switched crystal, and the output mirror are arranged in sequence to form a laser resonant cavity, which is used to absorb and amplify the energy output by the pump LD;

[0007] The coupling lens is used to couple the laser output from the output mirror to the fiber optic beam splitter;

[0008] The fiber optic beam splitter is used to split the output laser into two parts: output light and feedback light, and the feedback light is connected to the photodetector.

[0009] The photodetector is used to monitor the optical signal split by the fiber optic beam splitter in real time, convert it into an electrical signal, and feed it back to the laser driver source.

[0010] The laser driving source includes a first driving circuit, a second driving circuit, and a third driving circuit. The currents output by the first driving circuit, the second driving circuit, and the third driving circuit are superimposed to obtain a signal for driving the pump LD. The first driving circuit outputs a first driving current with a value of I1, the second driving circuit outputs a second driving current with a value of I2, and the third driving current outputs a third driving current with a value of I3. The threshold current of the pump LD is ITH. <ITH,I2<ITH,I3+I1> ITH, I3+I2>ITH, the pulse width of the first driving current is W1, the pulse width of the second driving current is W2, W1+W2=T, the start time of the third driving current is less than W1, and the end time of the third driving current is greater than W1.

[0011] The laser driver source is also used to process the signal fed back by the photodetector, convert it into laser emission delay and laser energy value, and adjust the current parameters of the first driving circuit, the second driving circuit and the third driving current according to the emission delay and laser energy value.

[0012] Compared with the prior art, the solution provided in this application has at least the following beneficial technical effects:

[0013] The laser is the core component of spaceborne lidar. This passively Q-switched laser uses existing photoelectric monitoring functions to form feedback, converting the waveforms obtained by the photoelectric detector in real time into the laser's output delay and energy value. After calculation, it is compared with the set value to control the parameters of the pump drive circuit, so that the laser repetition frequency, output time and energy are automatically stabilized near the set value with very little jitter.

[0014] This invention provides a fully automatic and effective control over the repetition frequency, emission delay, and energy of a passively Q-switched laser, while suppressing jitter. This improves the stability of the repetition frequency, emission time, and energy of the passively Q-switched laser, thereby enhancing the overall system's measurement accuracy and capability. Furthermore, due to the stable time delay with the external synchronization signal, it reduces overall time jitter in multi-beam applications. This not only satisfies the need for on-demand design of multi-beam laser parameters under different application conditions but also facilitates the accurate acquisition of the laser master wave signal, reducing the amount of data transmitted downlink. It can be applied in fields such as multi-beam lidar, laser mapping, remote sensing, and laser countermeasures using passively Q-switched lasers.

[0015] In conjunction with the first aspect, in some implementations of the first aspect, the first driving circuit and the second driving circuit are both constant current source circuits, and the third driving circuit is a narrow pulse constant current source circuit.

[0016] In conjunction with the first aspect, in some implementations of the first aspect, the timing circuit for the second drive current on / off timing control signal is connected to an inverter after the timing circuit for the first drive current on / off timing control signal, so that the second drive circuit stops working when the first drive circuit is in operation.

[0017] The inverter allows for flexible switching between the first and second drive circuits.

[0018] In conjunction with the first aspect, in some implementations of the first aspect, the constant current narrow pulse signal generated by the narrow pulse constant current source circuit is generated by a capacitor discharge circuit, wherein the switching transistor used in the capacitor discharge circuit is a MOS or IGBT, and the operational amplifier used to amplify the feedback current and the switching transistor is a high-speed dual-supply operational amplifier.

[0019] This is beneficial for producing a third drive current with a relatively good output waveform from the third drive circuit.

[0020] In conjunction with the first aspect, in some implementations of the first aspect, the laser driving source includes: a delay measurement circuit, a single pulse energy measurement circuit, a pump driving source control circuit, and a pump driving source circuit, wherein the pump driving source circuit includes the first driving circuit, the second driving circuit, and the third driving current;

[0021] The delay measurement circuit is used to compare the waveform monitored by the photodetector with the external synchronization signal, convert it into the laser output delay, and feed it back to the pump drive source control circuit.

[0022] The single-pulse energy measurement circuit is used to convert the peak value of the waveform monitored by the photodetector into a laser energy value and feed it back to the pump drive source control circuit.

[0023] The pump drive source control circuit is used to receive the laser emission delay and the laser energy value, calculate and compare them with the set value, and then control the current parameters of the pump drive source circuit.

[0024] The pump drive source circuit is used to receive the drive signal and timing signal output by the pump drive source control circuit, and generate a signal to drive the pump LD.

[0025] The laser driver source can use multiple modules to detect the output delay and pulse energy, and achieve flexible control of the driver source circuit.

[0026] In conjunction with the first aspect, in some implementations of the first aspect, the passively Q-switched laser further includes a pump temperature control device, which is used to detect the temperature change of the pump LD. The laser driving source further includes a pump temperature control circuit, which is used to receive the temperature signal output by the pump temperature control device, and output a control signal to drive the internal components of the pump temperature control device based on the pump temperature setting value, the laser output delay and the variance of the energy value, so as to achieve stable control of the pump temperature.

[0027] The pump temperature control device and pump temperature control circuit help to keep the passive Q-switched laser operating within a suitable pump temperature range.

[0028] In conjunction with the first aspect, in some implementations of the first aspect, the passively Q-switched laser further includes a crystal temperature control device, which is used to detect changes in the temperature of the passively Q-switched crystal. The laser driving source further includes a crystal temperature control circuit, which is used to receive the temperature signal output by the crystal temperature control device, and output a control signal to drive the internal components of the crystal temperature control device based on the crystal temperature setting value, the laser emission delay, and the variance of the energy value, thereby achieving stable control of the crystal temperature.

[0029] The use of crystal temperature control devices and crystal temperature control circuits helps to ensure that passively Q-switched lasers operate within a suitable crystal temperature range.

[0030] In a second aspect, a control method for a passively Q-switched laser is provided, the method being applied to a passively Q-switched laser as described in any implementation of the first aspect above, the method being executed by the laser driving source, the method comprising:

[0031] Based on the signal fed back by the photodetector, adjust the current value I3 and pulse width W3 of the third driving current until the energy peak is within the first preset energy range and the output laser has no sub-pulse or no pulse. Then adjust the time delay T3 of the third driving current relative to the external synchronization signal until the light output delay is within the first preset time delay range.

[0032] Based on the signal fed back by the photodetector, the current value I1 and pulse width W1 of the first driving current are adjusted until the light emission delay is within the second preset delay range, which is a smaller range than the first preset delay range.

[0033] Based on the signal fed back by the photodetector, the current value I2 and pulse width W2 of the second driving current are adjusted until the energy peak value is within a second preset energy range, which is a smaller range than the first preset energy range.

[0034] Due to the inherent instability of optical components, the repetition frequency of a passively Q-switched pulsed laser is unstable, and its time delay and energy also fluctuate. By first coarsely adjusting the energy while stabilizing the repetition frequency, then coarsely adjusting the time delay accuracy, followed by fine-tuning the time delay accuracy, and finally fine-tuning the energy accuracy, it is beneficial to adjust the time delay within a reasonable energy range and to avoid the impact of time delay jitter on fine energy adjustment. Adjusting the third drive current value, then the first drive current, and finally the second drive current in that order, according to the combined impact on the repetition frequency, time delay, and energy, helps improve the stability and control efficiency of the passively Q-switched laser.

[0035] In conjunction with the first aspect, in some implementations of the first aspect, the first preset energy range is within ±5% of the energy setting value, the second preset energy range is within ±1% of the energy setting value, the first preset delay range is within ±5% of the delay setting value, and the second preset delay range is within ±1% of the delay setting value.

[0036] Setting reasonable ranges for both coarse and fine control helps to quickly lock in relatively optimal current parameters.

[0037] In conjunction with the first aspect, in certain implementations of the first aspect, the method specifically includes:

[0038] The average value of the peak energy of N light pulses is compared with the set value, where the value of N is determined by the laser repetition frequency.

[0039] If the average value of the light pulse energy is within the first preset energy range, then the third driving current value I3 and the third driving current pulse width W3 are the optimal values.

[0040] If the average value of the light pulse energy is greater than the maximum value of the first preset energy range, then reduce the third driving current value I3 and the third driving current pulse width W3.

[0041] If the average energy of the optical pulse is less than the minimum value of the first preset energy range, increase the third driving current value I3 and the third driving current pulse width W3.

[0042] By adjusting the third driving current value I3 and the third driving current pulse width W3, it is beneficial to keep the average energy of the optical pulse within a relatively reasonable range.

[0043] With reference to the first aspect, in some implementations of the first aspect, the method specifically includes:

[0044] Comparing the laser output time delay with a set value to obtain Δt, wherein the adjustment amount of time delay of the third driving current relative to an external synchronization signal ΔT3=βΔt, so that the laser output time delay is stabilized within the first preset time delay range, then increasing the first driving current value I1, so that the laser output time delay is stabilized within the second preset time delay range when I1<ITH.

[0045] When the average energy of the optical pulse is within a relatively reasonable range, adjusting the time delay of the third driving current and the first driving current value I1 is beneficial to keeping the laser output time delay within a relatively reasonable range.

[0046] With reference to the first aspect, in some implementations of the first aspect, the method specifically includes:

[0047] Increasing the second driving current value I2, so that the laser output energy is stabilized within the second preset energy range when I2<ITH.

[0048] When both the average energy of the optical pulse and the laser output time delay are within relatively reasonable ranges, adjusting the second driving current value I2 is beneficial to further stabilizing the laser output energy within a reasonable range.

[0049] With reference to the first aspect, in some implementations of the first aspect, the passively Q-switched laser satisfies at least one of the following:

[0050] the time delay of the first driving current relative to an external synchronization signal T1=α(T3-W1), wherein α is within the range of [0.5, 1.5];

[0051] the time delay of the third driving current relative to an external synchronization signal T3=δ(t-W3), wherein t is a delay set value, and δ is within the range of [0.5, 1.5]. Description of Drawings

[0052] Figure 1 is a schematic structural diagram of a fully automatically stabilized passively Q-switched laser provided by the present application.

[0053] Figure 2 is a schematic structural diagram of a pump driving source circuit provided by the present application.

[0054] Figure 3 A schematic diagram of the current parameters of a pump drive source circuit provided in this application. Detailed Implementation

[0055] The present application will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0056] Figure 1 This application provides a schematic structural diagram of a passively Q-switched laser with fully automatic and stable control. The Q-switched laser may include a pump LD (laser diode) 1, a pump temperature control device 2, a laser gain medium 3, a passively Q-switched crystal 4, a crystal temperature control device 5, an output mirror 6, a coupling lens 7, an optical fiber beam splitter 8, a photodetector 9, and a laser driver source 10.

[0057] The laser gain medium 3, the passively Q-switched crystal 4, and the output mirror 6 are arranged from left to right to form a laser resonant cavity, which is used to absorb and amplify the energy output by the pump LD1, generating and outputting the optical pulses of the passively Q-switched laser. The laser resonant cavity can be a straight cavity, a folded cavity, or a ring cavity. In one embodiment, the laser resonant cavity is a straight cavity with a short cavity length.

[0058] In some embodiments, the pump LD1 can be pulse-driven, and the pump wavelength of the LD1 can be 808 nm; the laser gain medium 3 can be an Nd:YAG crystal; the passively Q-switched crystal 4 can be a Cr 4+ YAG crystal; Output mirror 6 can be a concave mirror with r=200mm. The surface of output mirror 6 can be coated with a reflective film with a reflectivity of 85% at 1064nm. The transmittance of output mirror 6 after coating is the best transmittance obtained from the test.

[0059] The pump temperature control device 2 uses a precision thermistor to detect the temperature change of the pump LD1, and works with the pump temperature control circuit 15 to stabilize the temperature of the pump LD1 at around 20°C.

[0060] The crystal temperature control device 5 uses a precision thermistor to detect the temperature change of the passively Q-switched crystal 4, and works with the crystal temperature control circuit 16 to stabilize the temperature of the passively Q-switched crystal 4 at around 20°C.

[0061] The coupling lens 7 can be positioned in the propagation direction of the laser emitted by the pump LD1 to couple the laser output from the output mirror 6 into the fiber beam splitter 8. The coupling lens 7 can be a plano-convex lens with f = 50 mm.

[0062] The fiber beam splitter 8 is used to split the output laser into two parts: output light and feedback light. The feedback light is connected to the photodetector 9.

[0063] The photodetector 9 can be used to monitor the optical signal split by the fiber optic beam splitter 8 in real time, convert it into an electrical signal, and feed it back to the laser driver 10. The photodetector 9 can be an APD or a PIN diode, converting the received optical pulse signal into an electrical pulse signal, which is then converted into laser output delay and energy values ​​by the delay measurement circuit 11 and the single-pulse energy measurement circuit 12, and fed back to the control circuit of the laser driver 10. The control circuit of the laser driver 10 can use an FPGA or DSP chip, and through programming and algorithms, achieve automatic stabilization control of the laser.

[0064] like Figure 1 As shown, the laser driver source 10 may include a delay measurement circuit 11, a single pulse energy measurement circuit 12, a pump driver source control circuit 13, a pump driver source circuit 14, a pump temperature control circuit 15, and a crystal temperature control circuit 16, which are used to generate the driving electrical signal for pumping LD1 in the passively Q-switched laser and to realize the internal temperature control of the laser.

[0065] The delay measurement circuit 11 is used to compare the waveform obtained by the photodetector 9 in real time with the external synchronization signal, convert it into the laser output delay, and feed it back to the pump drive source control circuit 13.

[0066] The single-pulse energy measurement circuit 12 is used to convert the waveform measurement peak value obtained by the photodetector 9 in real time into the laser energy value and feed it back to the pump drive source control circuit 13.

[0067] The pump drive source control circuit 13 receives the laser emission delay and energy values ​​converted by the delay measurement circuit 11 and the single pulse energy measurement circuit 12, as well as the pump LD1 temperature value and the passive Q-switched crystal 4 temperature value fed back by the pump temperature control circuit 15 and the crystal temperature control circuit 16, respectively. After calculation, it is compared with the set value to control the parameters of the pump drive source circuit 14, so that the laser repetition frequency, emission time and energy are automatically and stably controlled.

[0068] The pump drive source circuit 14 is used to receive the drive signal and timing signal output by the pump drive source control circuit 13 and generate the signal required for the stable operation of the pump LD1.

[0069] The pump temperature control circuit 15 is used to receive the temperature signal output by the pump temperature control device 2, and output a control signal to drive the internal TEC device of the pump temperature control device 2 based on the pump temperature setting value, the laser emission delay and the variance of the energy value, so as to achieve stable control of the pump temperature.

[0070] The crystal temperature control circuit 16 is configured to receive a temperature signal output by the crystal temperature control device 5, and output a control signal to drive the TEC device inside the crystal temperature control device 5 based on the set crystal temperature value, the laser output delay and the variance of energy values, so as to achieve stable control of the crystal temperature.

[0071] In some embodiments, the temperature control accuracy of the pump temperature control circuit 15 and the crystal temperature control circuit 16 is better than 0.1°C.

[0072] In some embodiments, the main part of the pump driving source control circuit 13, the pump temperature control circuit 15, and the crystal temperature control circuit 16 can be designed on the same FPGA chip, and the pump temperature control circuit 15 and the crystal temperature control circuit 16 can adopt digital PID algorithm for control. The control chip can be a single-chip microcomputer, FPGA or DSP, or a combination of two chips.

[0073] As Figure 2 shows, the pump driving source circuit 14 includes a first driving circuit 2-1, a second driving circuit 2-2, and a third driving current 2-3; wherein, the first driving current I1 output by the first driving circuit 2-1, the second driving current I2 output by the second driving circuit 2-2, and the third driving current I3 output by the third driving circuit 2-3 are superimposed to obtain a current for driving the pump LD1.

[0074] As Figure 3 shows, the first driving current I1 is a constant current source circuit, and its control parameters include: current value I1, delay T1 relative to the external synchronization signal, and pulse width W1 of the timing control signal, wherein the current value I1 < ITH, and ITH is the threshold current of the pump LD, for example, 2A. The delay T1 relative to the external synchronization signal and the pulse width W1 of the timing control signal jointly control the on-off of the first driving circuit 2-1.

[0075] As Figure 3 shows, the second driving current I2 is a constant current source circuit, and its control parameters include: current value I2 and pulse width W2 of the timing control signal, wherein: the current value I2 < ITH (threshold current of the pump LD), W2 = T (period) - W1.

[0076] In some embodiments, the timing control signal circuit of the second driving circuit can be connected with an inverter after the timing control signal circuit of the first driving circuit, so that the second driving current I2 stops working when the first driving current I1 is acting. Adopting such a control signal can not only simplify the circuit, but also shorten the switching time.

[0077] As Figure 3As shown, the third driving current I3 is a narrow pulse constant current source circuit. Its control parameters include the current value I3 (I3 is adjustable in the range of 2-10A with an adjustment accuracy of 0.1A), the relative external synchronization signal delay T3 (T3 is adjustable in the range of 10-200us), and the pulse width W3 (W3 is adjustable in the range of 50-200us).

[0078] In some embodiments, the constant current narrow pulse signal of the third drive current I3 can be generated by a capacitor discharge circuit. The switching transistor used in the discharge circuit can be a MOS or an IGBT. The operational amplifier used to amplify the feedback current and control the switching transistor is a high-speed dual-supply operational amplifier to shorten the rise and fall time of the pulse signal.

[0079] Combination Figures 1 to 3 This application also provides a control method for a passively Q-switched laser with fully automatic stabilization control, the steps of which are as follows.

[0080] a. The pump drive source control circuit 13 receives the repetition frequency f, light emission delay t, and energy setting value g sent from the outside, as well as the pump LD1 temperature value and passive Q-switched crystal 4 temperature value fed back by the pump temperature control circuit 15 and the crystal temperature control circuit 16. Based on the setting value and the current temperature, it calls the system default value, wherein the pulse width W1 of the first drive current timing control signal, the third drive current value I3, and the third drive current pulse width W3 take the default value in the corresponding range.

[0081] In one embodiment, the repetition frequency f is set to 1kHz, the period T = 1 / f = 1ms, when the first drive current value I1 = 0.5ITH = 1A, the second drive current value I2 = 0, the delay of the third drive current relative to the external synchronization signal T3 = δ(t-W3), where t is the delay setting value, δ is in the range of [0.5, 1.5], and the delay of the first drive current relative to the external synchronization signal T1 = α(T3-W1), where α is in the range of [0.5, 1.5].

[0082] b. The pump drive source control circuit 13 receives the mode control signal sent from the outside and enters the light output mode.

[0083] c. Check that the pump temperature control circuit 13 receives feedback from the pump temperature control circuit 15 and the crystal temperature control circuit 16, and that the pump LD1 and the passive Q-switched crystal 4 are stable within the range of ±0.1℃. Based on the laser energy value converted by the single pulse energy measurement circuit 12, stabilize the laser repetition frequency and determine the energy adjustment reference.

[0084] The average value of the peak energy of N emitted light pulses is calculated and compared with the set value, where N is determined by the laser repetition frequency. The average value of the peak energy of N light pulses can be calculated using a digital circuit algorithm. If the average light pulse energy is within ±5% of the set energy value, it is determined to be a no-sub-pulse or no-pulse situation. In this case, the third driving current value I3 and the third driving current pulse width W3 are optimal. If the average light pulse energy is greater than 105% of the set energy value, the third driving current value I3 and the third driving current pulse width W3 are decreased. If the average light pulse energy is less than 95% of the set energy value, the third driving current value I3 and the third driving current pulse width W3 are increased. This adjustment is repeated to ensure that only one light pulse close to the set energy value is emitted in one cycle, and that the third driving current value I3 and the third driving current pulse width W3 are optimal.

[0085] d. The pump drive source control circuit 13 receives the laser emission delay converted by the delay measurement circuit 11, compares it with the set value to obtain Δt, and adjusts the third drive current relative to the external synchronization signal delay by ΔT3 = βΔt to stabilize the laser emission delay within ±5% of the emission delay set value. Then, the first drive current value I1 is gradually increased by an initial step of 0.1A / s, and the step is weighted according to the emission delay jitter in each second thereafter. At the same time, the results of multiple measurements are fitted to calculate the optimal value of the first drive current value I1, so that the first drive current value I1 is within a suitable value less than the pump LD threshold current ITH, and the laser emission delay is stabilized within ±1% of the emission delay set value.

[0086] e. The pump drive source control circuit 13 stabilizes the laser energy based on the laser energy value converted by the single pulse energy measurement circuit 12, gradually increases the second drive current value I2 in an initial step of 0.1A / s, and weights the step according to the output energy jitter in each second thereafter. At the same time, it fits the multiple measurement results and calculates the optimal value of I2, so that I2 is a suitable value within the range of less than the pump LD threshold current ITH, and the laser output energy is stabilized within ±1% of the output energy setting value.

[0087] Due to the inherent instability of optical components, the repetition frequency of a passively Q-switched pulsed laser is unstable, and its time delay and energy also fluctuate. By first coarsely adjusting the energy while stabilizing the repetition frequency, then coarsely adjusting the time delay accuracy, followed by fine-tuning the time delay accuracy, and finally fine-tuning the energy accuracy, it is beneficial to adjust the time delay within a reasonable energy range and to avoid the impact of time delay jitter on fine energy adjustment. Adjusting the current in the order of the third driving current I3, the first driving current I1, and the second driving current I2, according to the combined impact on the repetition frequency, time delay, and energy, helps improve the stability and control efficiency of the passively Q-switched laser.

[0088] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims of the present invention.

Claims

1. A passively Q-switched laser, characterized in that, It includes a pump LD (1), a laser gain medium (3), a passive Q-switched crystal (4), an output mirror (6), a coupling lens (7), an optical fiber beam splitter (8), a photodetector (9), and a laser driver (10). The laser gain medium (3), the passive Q-switched crystal (4), and the output mirror (6) are arranged in sequence to form a laser resonant cavity, which is used to absorb and amplify the energy output by the pump LD (1); The coupling lens (7) is used to couple the laser output from the output mirror (6) into the fiber optic beam splitter (8); The fiber beam splitter (8) is used to split the output laser into two parts: output light and feedback light. The feedback light is connected to the photodetector (9). The photodetector (9) is used to monitor the optical signal split by the fiber optic beam splitter (8) in real time, convert it into an electrical signal, and feed it back to the laser driver source (10). The laser driving source (10) includes a first driving circuit (2-1), a second driving circuit (2-2), and a third driving circuit (2-3). The currents output by the first driving circuit (2-1), the second driving circuit (2-2), and the third driving circuit (2-3) are superimposed to obtain a signal for driving the pump LD (1). The first driving circuit (2-1) outputs a first driving current with a current value of I1, the second driving circuit (2-2) outputs a second driving current with a current value of I2, and the third driving circuit (2-3) outputs a third driving current with a current value of I3. The threshold current of the pump LD (1) is ITH. <ITH,I2<ITH,I3+I1> ITH, I3+I2>ITH, the pulse width of the first driving current is W1, the pulse width of the second driving current is W2, W1+W2=T, the start time of the third driving current is less than W1, and the end time of the third driving current is greater than W1. The laser driver source (10) is also used to process the signal fed back by the photodetector (9), convert it into laser output delay and laser energy value, and adjust the current parameters of the first driving circuit (2-1), the second driving circuit (2-2) and the third driving circuit (2-3) according to the output delay and laser energy value; The first driving circuit (2-1) and the second driving circuit (2-2) are both constant current source circuits, and the third driving circuit (2-3) is a narrow pulse constant current source circuit; The second drive current on / off timing control signal timing circuit is connected to an inverter after the first drive current on / off timing control signal circuit, so that the second drive circuit (2-2) stops working when the first drive circuit (2-1) is activated.

2. The passively Q-switched laser according to claim 1, characterized in that, The constant current narrow pulse signal generated by the narrow pulse constant current source circuit is generated by a capacitor discharge circuit. The switching transistor used in the capacitor discharge circuit is a MOS or IGBT. The operational amplifier used to amplify the feedback current and the switching transistor is a high-speed dual-supply operational amplifier.

3. The passively Q-switched laser according to claim 1, characterized in that, The laser driving source (10) includes: a delay measurement circuit (11), a single pulse energy measurement circuit (12), a pump driving source control circuit (13), and a pump driving source circuit (14), wherein the pump driving source circuit (14) includes the first driving circuit (2-1), the second driving circuit (2-2), and the third driving circuit (2-3). The delay measurement circuit (11) is used to compare the waveform monitored by the photodetector (9) with the external synchronization signal, convert it into the laser output delay, and feed it back to the pump drive source control circuit (13). The single-pulse energy measurement circuit (12) is used to convert the waveform measurement peak value obtained by the photodetector (9) into the laser energy value and feed it back to the pump drive source control circuit (13). The pump drive source control circuit (13) is used to receive the laser output delay and the laser energy value, calculate and compare them with the set value, and then control the current parameters of the pump drive source circuit (14). The pump drive source circuit (14) is used to receive the drive signal and timing signal output by the pump drive source control circuit (13) and generate a signal to drive the pump LD (1).

4. The passively Q-switched laser according to claim 3, characterized in that, The passively Q-switched laser also includes a pump temperature control device (2), which is used to detect the temperature change of the pump LD (1). The laser drive source (10) also includes a pump temperature control circuit (15), which is used to receive the temperature signal output by the pump temperature control device (2), and output a control signal to drive the internal components of the pump temperature control device (2) according to the pump temperature setting value, the laser output delay and the variance of the energy value, so as to achieve stable control of the pump temperature.

5. The passively Q-switched laser according to claim 4, characterized in that, The passively Q-switched laser also includes a crystal temperature control device (5), which is used to detect the temperature change of the passively Q-switched crystal (4). The laser drive source (10) also includes a crystal temperature control circuit (16), which is used to receive the temperature signal output by the crystal temperature control device (5), and output a control signal to drive the internal components of the crystal temperature control device (5) based on the crystal temperature setting value, the laser output delay and the variance of the energy value, so as to achieve stable control of the crystal temperature.

6. A control method for a passively Q-switched laser, characterized in that, The method is applied to a passively Q-switched laser as described in any one of claims 1 to 5, the method is performed by the laser driving source (10), and the method includes: According to the signal fed back by the photodetector (9), adjust the current value I3 and pulse width W3 of the third driving current until the energy peak is within the first preset energy range and the output laser has no sub-pulse or no pulse. Then adjust the time delay T3 of the third driving current relative to the external synchronization signal until the light output time delay is within the first preset time delay range. Adjust the current value I1 and pulse width W1 of the first driving current according to the signal fed back by the photodetector (9), until the light output delay falls within a second preset delay range, wherein the second preset delay range is a smaller range within the first preset delay range; Adjust the current value I2 and pulse width W2 of the second driving current according to the signal fed back by the photodetector (9), until the energy peak falls within a second preset energy range, wherein the second preset energy range is a smaller range within the first preset energy range.

7. The method according to claim 6, characterized in that, The first preset energy range is within ±5% of an energy set value, the second preset energy range is within ±1% of the energy set value, the first preset delay range is within ±5% of a delay set value, and the second preset delay range is within ±1% of the delay set value.

8. The method according to claim 6 or 7, characterized in that, The method specifically comprises: Comparing the average value of N times of optical pulse energy peaks with a set value, wherein the value of N is determined by the laser repetition rate; If the average optical pulse energy is within the first preset energy range, then the third driving current value I3 and the third driving current pulse width W3 are optimal values; If the average optical pulse energy is greater than the maximum value of the first preset energy range, then reducing the third driving current value I3 and the third driving current pulse width W3; If the average optical pulse energy is less than the minimum value of the first preset energy range, then increasing the third driving current value I3 and the third driving current pulse width W3.

9. The method according to claim 6 or 7, characterized in that, The method specifically comprises: Comparing the light output delay of the laser with a set value to obtain Δt, wherein the adjustment amount ΔT3 of the delay of the third driving current relative to an external synchronization signal is ΔT3=βΔt, so that the light output delay of the laser is stabilized within the first preset delay range, and then increasing the first driving current value I1, so that the light output delay of the laser is stabilized within the second preset delay range when I1<ITH.

10. The method according to claim 6 or 7, characterized in that, The method specifically comprises: Increasing the second driving current value I2, so that the light output energy of the laser is stabilized within the second preset energy range when I2<ITH.

11. The method according to claim 6 or 7, characterized in that, The passively Q-switched laser satisfies at least one of the following: The delay T1 of the first driving current relative to an external synchronization signal is T1=α(T3-W1), and α is in the range of [0.5, 1.5]; The delay T3 of the third driving current relative to an external synchronization signal is T3=δ(t-W3), t is a delay set value, and δ is in the range of [0.5, 1.5].

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