Energy attenuation control system for narrow pulse laser

Abstract

This narrow-pulse laser energy attenuation control system relates to the field of narrow-pulse lasers. It includes an energy attenuation control board, a servo, an energy photodiode, a trigger photodiode, and a computer. The servo carries a circular progressive attenuation plate, and the energy attenuation control board connects to the servo and controls its rotation. The energy attenuation control board is externally connected to an energy photodiode to receive laser light signals, convert them into electrical signals, and then feed them to the energy attenuation control board for sampling. The energy attenuation control board is also externally connected to a light-emitting diode to receive laser light signals and convert them into TTL-level electrical signals for output to peripheral devices. The computer is connected to the energy attenuation control board for data exchange. The system is highly integrated, integrating energy attenuation control, energy measurement, and energy trigger output, enabling real-time energy measurement and control.

Description

Technical Field

[0001] The present invention relates to the field of narrow pulse laser, in particular to an energy attenuation control system of narrow pulse laser. Background Art

[0002] With the increasing application of lasers, nanosecond narrow pulse lasers have become widely used. However, due to the high laser power, direct application to optical components often causes irreparable damage to the devices. Therefore, it is necessary to attenuate the energy of nanosecond narrow pulse lasers. To enable real-time monitoring and control of the output energy of narrow pulse lasers, it is necessary to develop an energy attenuation control system that matches the laser. Summary of the Invention

[0003] The purpose of the present invention is to solve the above-mentioned problems in the prior art and provide an energy attenuation control system for narrow pulse lasers.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] The energy attenuation control system for a narrow pulse laser comprises an energy attenuation control board, a steering gear, an energy photodiode, a trigger photodiode, and a computer; the steering gear carries a circular progressive attenuation plate, the energy attenuation control board is connected to the steering gear and controls the rotation of the steering gear; the energy attenuation control board is externally connected to an energy photodiode to receive the laser light signal, convert it into an electrical signal, and supply it to the energy attenuation control board for sampling; the energy attenuation control board is externally connected to a light-emitting diode to receive the laser light signal and convert it into a TTL-level electrical signal to output to peripheral equipment; and the computer is connected to the energy attenuation control board for data exchange.

[0006] The energy attenuation control board includes an energy detection and signal conditioning module, an external trigger module, an optical shutter control module, a microprocessor and a power supply module; the energy photodiode is connected to the microprocessor through the energy detection and signal conditioning module; the external trigger module is connected to the trigger photodiode; the optical shutter control module is connected to the microprocessor, and the optical shutter control module is used to receive high and low level switching signals from the microprocessor to control the switching of the optical shutter, thereby controlling the output of the laser signal; the power supply module supplies power to the energy attenuation control board.

[0007] The energy detection and signal conditioning module includes an I / V conversion circuit, a pole-zero phase elimination circuit, a pre-stage amplifier circuit, a post-stage amplifier circuit and a dual-channel high-speed comparator connected in sequence, wherein the input end of the I / V conversion circuit is connected to the energy photodiode, and the output end of the dual-channel high-speed comparator is connected to the microprocessor.

[0008] The servo receives a pulse width modulation signal with a variable duty cycle output by a microprocessor to control the rotation angle of the servo, driving the rotation of the circular progressive attenuation plate on the servo, thereby controlling the energy of the passing laser.

[0009] The trigger photodiode adopts a PIN silicon photodiode with a response time of ns, receives an external pulse laser signal with a wavelength range of 200ns to 1100nm and an energy less than 100μj, and generates a voltage signal with an amplitude greater than 3V and a rising edge less than or equal to 2ns through an external trigger module, which is used to trigger other devices.

[0010] The energy photodiode adopts a PIN silicon photodiode with a response time of nanoseconds, receives the laser signal transmitted through the circular progressive attenuation plate, converts it into a pulse current signal, and converts it into a voltage signal through an I / V conversion circuit.

[0011] The microprocessor adopts an STM32 microprocessor.

[0012] The circular progressive attenuation plate adopts a circular gradient neutral density filter.

[0013] The energy attenuation control board is connected to the computer via a USB interface.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0015] 1. The system of the present invention has high integration, integrating energy attenuation control, energy measurement and energy trigger output into one, which can realize real-time measurement and control of energy.

[0016] 2. The present invention achieves energy attenuation by controlling the steering gear.

[0017] 3. The present invention amplifies the signal and then uses a dual-channel high-speed comparator to complete the standardized cutting of the signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention;

[0019] Figure 2 It is the overall circuit diagram of the I / V conversion circuit, the pole-zero phase elimination circuit, the pre-stage amplifier circuit, and the post-stage amplifier circuit;

[0020] Figure 3 This is the circuit diagram of a dual-channel high-speed comparator;

[0021] Figure 4 This is the circuit diagram of the external trigger module;

[0022] Figure 5 This is the USB interface circuit diagram;

[0023] Figure 6 This is the circuit diagram of the optical shutter control module;

[0024] Figure 7 This is the circuit diagram of the power module;

[0025] Figure 8 It is the program flow chart of the microprocessor. DETAILED DESCRIPTION

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0027] like Figure 1 As shown, this embodiment includes an energy attenuation control board, a servo, an energy photodiode, a trigger photodiode and a computer;

[0028] The servo is equipped with a circular progressive attenuation plate, which adopts a circular gradient neutral density filter; the energy attenuation control board is connected to the servo and controls the rotation of the servo; the energy attenuation control board is externally connected to an energy photodiode to receive the laser light signal and convert it into an electrical signal, and supply it to the energy attenuation control board for sampling; the energy attenuation control board is externally contacted with a light-emitting diode to receive the laser light signal and convert it into a TTL level electrical signal to output to the peripheral device; the computer and the energy attenuation control board are connected through a USB interface for data exchange, controlling the rotation of the servo, and at the same time obtaining the pulse width of the electrical pulse signal converted from the laser signal of different energies through the USB interface, and performing pulse width and energy conversion calibration in the computer software.

[0029] The energy attenuation control board includes an energy detection and signal conditioning module, an external trigger module, an optical shutter control module, a microprocessor and a power supply module;

[0030] The energy photodiode is connected to the microprocessor through the energy detection and signal conditioning module; the external trigger module is connected to the trigger photodiode; the optical shutter control module is connected to the microprocessor, and the optical shutter control module is used to receive the high and low level switching signals of the microprocessor to control the switching of the optical shutter, thereby controlling the output of the laser signal; the power supply module supplies power to the energy attenuation control board.

[0031] In this embodiment, the microprocessor adopts an STM32 microprocessor.

[0032] like Figures 1-2 As shown, the energy detection and signal conditioning module includes an I / V conversion circuit, a pole-zero phase elimination circuit, a pre-stage amplifier circuit, a post-stage amplifier circuit and a dual-channel high-speed comparator connected in sequence, wherein the input end of the I / V conversion circuit is connected to the energy photodiode, and the output end of the dual-channel high-speed comparator is connected to the microprocessor.

[0033] The servo receives a pulse width modulation (PWM) signal with a variable duty cycle output from the microprocessor IO port to control the rotation angle of the servo, driving the rotation of the circular progressive attenuation plate on the servo, thereby controlling the energy of the passing laser.

[0034] The trigger photodiode adopts a PIN silicon photodiode with a response time of ns, receives an external pulse laser signal with a wavelength range of 200ns to 1100nm and an energy less than 100μj, and generates a voltage signal with an amplitude greater than 3V and a rising edge less than or equal to 2ns through an external trigger module, which is used to trigger other devices.

[0035] The energy photodiode is a photoelectric conversion device for narrow pulse lasers. It uses a PIN silicon photodiode with a response time of nanoseconds to receive the laser signal transmitted through the circular progressive attenuation plate and convert it into a pulse current signal, which is then converted into a voltage signal through an I / V conversion circuit.

[0036] like Figure 2 As shown, the photodiode's photocurrent signal is proportional to the energy of the incident light signal. In the I / V conversion circuit, the energy photodiode (PD_ATT_C is the negative electrode, PD_ATT_A is the positive electrode) operates at zero bias, resulting in low noise and low dark current, enabling precise linear operation and suitable for more accurate measurement systems. The Texas Instruments OPA657 operational amplifier is used, with a high gain bandwidth of 1.6GHz. C16 is the feedback capacitor, and the T-type feedback resistor network composed of resistors R11, R12, and R13 can effectively improve the phase margin and stability of the operational amplifier.

[0037] The pole-zero phase elimination circuit is mainly used to reduce the accumulation and undershoot of the output pulse signal of the I / V circuit. Adjusting R17 to a suitable value can eliminate the undershoot generated during the formation of the output pulse signal of the I / V circuit.

[0038] The front and rear amplification circuits use the OPA2377. The OPA2377 series operational amplifier is a broadband CMOS amplifier that provides extremely low noise, low input bias current, and low offset voltage. It also operates at a low quiescent current of 0.76mA (typical). The two-stage amplification allows for flexible adjustment of the voltage amplification ratio.

[0039] Figure 3This is a dual-channel high-speed comparator circuit diagram. The front- and rear-stage amplifiers produce an amplified half-wave signal, the width of which is linearly proportional to the laser energy. The stronger the laser energy, the wider the bandwidth of the half-wave signal output through the front-end I / V and amplifier circuits. For a laser signal energy of 80µJ, the corresponding half-wave signal has a pulse width of approximately 600µs, while for a laser signal energy of 0.3µJ, the corresponding half-wave signal has a pulse width of approximately 8µs. The dual-channel high-speed push-pull comparator TLV3502 reshapes the half-wave signal into a square wave output, meeting the requirements of the subsequent STM32 microprocessor for square wave pulse width measurement. The TLV3502's out-of-band input common-mode range makes it ideal for low-voltage applications. Its rail-to-rail output can directly drive CMOS or TTL logic.

[0040] Figure 4 This is the circuit diagram of the external trigger module. The trigger photodiode operates under reverse bias. Applying a reverse bias to the trigger photodiode can achieve higher switching speeds, but at the expense of linearity. This makes it suitable for detecting high-speed optical pulses. In this invention, the reverse voltage DCIN is 12V, and J5 is the BNC output port.

[0041] Figure 5 This is the USB interface circuit diagram. The CP2104 is a highly integrated USB-to-UART bridge housed in a compact 4mm x 4mm package. The CP2104 is a USB 2.0 full-speed device with an integrated USB clock, voltage regulator, and programmable memory. PC software connects to the CP2104 via the USB interface, converting data into serial data for communication with the STM32 microprocessor. UART2_RX and UART2_TX are connected to the STM32 microprocessor's serial port pins.

[0042] Figure 6 This is the circuit diagram of the optical shutter control module. The circuit of the optical shutter control module uses a P-channel enhancement mode MOS field-effect transistor, where VCC_SHUTTEER is connected to the positive electrode of the external optical shutter, and SHUTTER_CTRL is connected to the common IO pin of the STM32 microprocessor. When SHUTTER_CTRL is high, VCC_SHUTTEER is the input DCIN voltage; when SHUTTER_CTRL is low, VCC_SHUTTEER output is zero level.

[0043] Figure 7This is the circuit diagram of the power module. The entire hardware operates at a 12V, 1A input voltage. Overvoltage protection is implemented using the 8550 transistor and the AO3401A field-effect transistor. DCIN generates a -5V voltage through the TPS5401 step-down converter, providing a negative voltage for the op amp. Simultaneously, DCIN generates a +5V voltage through the SY8120 synchronous step-down regulator, providing a positive voltage for the op amp. VCC5V then generates VCC3V3 through the MCP1703 DC-DC converter, which is then supplied to the STM32 microprocessor.

[0044] Figure 8 This is the program flow chart of the STM32 microprocessor, which mainly includes initialization, heartbeat packet sending and serial port receiving, as follows:

[0045] 1. The initialization work of each system resource is as follows:

[0046] 1) System clock initialization, default is 72MHz

[0047] 2) Print serial port initialization

[0048] 3) System timer initialization

[0049] 4) Servo PWM drive initialization

[0050] 5) Timer capture pulse width initialization

[0051] 6) Optical shutter drive initialization

[0052] 7) Initialization of host computer communication serial port

[0053] 2. Sending heartbeat packets:

[0054] When the host computer's communication serial port is idle, the system will capture and measure the pulse width every second; after obtaining the pulse width measurement data, it will send a pulse width data heartbeat packet to the host computer.

[0055] Pulse width capture calculation uses mean filter method:

[0056] First, the obtained pulses are filtered to remove waveforms with excessively long pulse widths; pulses within a normal pulse width range are obtained, and a certain number of these pulse width values ​​are averaged.

[0057] 3. Serial port reception:

[0058] 1) Because sending heartbeat packets and receiving data from the host computer are mutually exclusive processes, the main system uses serial port polling to achieve communication. At the same time, it is either sending a heartbeat packet or receiving data from the host computer. At the same time, receiving data from the host computer has a higher priority than sending a heartbeat packet. That is, when preparing to send a heartbeat packet, the serial port receiving process will interrupt the former and execute the serial port receiving and parsing process instead.

[0059] 2) A timeout mechanism is used to determine whether the serial port has received a complete set of data. As long as the serial port receives a byte of data, the counting timer will be restarted. If the next byte is not received within 10ms, it is determined that the timeout has expired, which means that all bytes sent by the host computer have been received.

[0060] 4. After receiving the data, the serial port parses the command and takes action according to the communication protocol:

[0061] 1) Set the servo angle command, the servo rotates to the corresponding angle, and responds upstream.

[0062] 2) Set the optical shutter switch. The system executes the optical shutter switch action and gives a response upstream.

[0063] The computer serial port tool communicates with the STM32 microprocessor through the serial port interface and protocol. The serial port communication baud rate is 115200, no parity check, 8 data bits, and 1 stop bit. The communication protocol is as follows:

[0064] 1. Set up the servo

[0065] After processing the user input, the computer software downloads only the servo position and angle to the STM32 microprocessor. If the setting fails, the user will be prompted on the interface to indicate that the setting failed.

[0066] 2. Report pulse width data

[0067] When the computer issues a command to set the servo, the STM32 microprocessor receives the command data and returns a response and the corresponding pulse width to the computer software. The STM32 microprocessor must report the pulse width data to the computer within 5 seconds. If it times out, the servo setting is considered a failure. Furthermore, if there is a response but the response indicates a failure, the servo setting is also considered a failure.

[0068] 3. Heartbeat packet

[0069] The STM32 microprocessor periodically sends heartbeat packets to the computer software at 1-second intervals. The heartbeat packets contain real-time pulse width data, and the computer needs to display the received pulse width time on the interface. The heartbeat packets contain only pulse width data, and other data can be expanded if required.

[0070] 4. Optical shutter switch

[0071] The computer software issues the shutter on / off command. Upon receiving the command, the hardware executes the corresponding action and returns a response. The hardware must report the pulse width data to the computer within 5 seconds. If this timeout occurs, the setting is considered a failure. Furthermore, if there is a response but the response indicates a failure, the setting is also considered a failure.

[0072] The protocol data format is shown in Table 1:

[0073] Table 1

[0074]

[0075] For example, consider the following: servo settings, as shown in Table 2. The servo angle is in hexadecimal, for example, 18 degrees, which converts to hexadecimal 0x12. The pulse width data is reported, as shown in Table 3, with a decimal precision of 2 digits (pending and subject to change). This means the data is scaled 100 times, and the computer display requires processing. For example, a pulse width of 12.30µs is reported to the computer as 1230, which displays as 12.30µs on the screen. All data is in little-endian format, with the low byte first and the high byte last. For CRC verification, refer to the crc16.c file below, which uses the CRC-CCITT (XModem) algorithm.

[0076] Table 2

[0077] 0xfe 0x01 00 00 00 0x05 00 00 00 0x01 0x19 00 00 00 0xef 0x12 (this value is ignored) 0x16 Frame header Command Type Payload field length gear Servo angle CRC check Frame tail

[0078] Table 3

[0079] 0xfe 0x02 00 00 00 0x05 00 00 00 0x00 0xA7 00 00 00 0xde 0x23 (ignore this value) 0x16 Frame header Command Type Payload field length answer Pulse width data CRC check Frame tail

[0080] In the computer software's serial port configuration, select the virtual serial port created by the currently connected USB. The monitoring information section of the software interface primarily displays debugging information regarding the interaction between the software and the STM32 microprocessor. Energy calibration primarily controls the rotation of the servo angle, thereby controlling the laser energy received by the energy photodiode. This energy is converted into a pulse signal via the energy attenuation control board. The STM32 microprocessor measures the pulse signal width and reports it to the "Pulse Width (us)" field in the computer software menu. The actual laser energy after passing through the attenuator at this angle is then measured by the energy detection instrument and recorded in the "Energy (uj)" field in the menu. This completes the calibration of one point. In actual testing, at least three points must be measured and calibrated for each gear. This calibration establishes the corresponding curve between pulse width and energy. In subsequent measurements, the pulse width alone is sufficient to determine the current laser energy.

Claims

1. Energy attenuation control system for narrow pulse laser, characterized by: The system comprises an energy attenuation control board, a steering gear, an energy photodiode, a trigger photodiode, and a computer; the steering gear carries a circular progressive attenuation plate, the energy attenuation control board is connected to the steering gear and controls the rotation of the steering gear; the energy attenuation control board is externally connected to an energy photodiode to receive laser light signals and convert them into electrical signals, which are then supplied to the energy attenuation control board for sampling; the energy attenuation control board is externally connected to a light-emitting diode to receive laser light signals and convert them into TTL-level electrical signals for output to peripheral devices; the computer is connected to the energy attenuation control board for data exchange; By controlling the rotation angle of the servo, the laser energy received by the energy photodiode is controlled, which is converted into a pulse signal through the energy attenuation control board, and the width of the pulse signal is measured. At this angle, the actual energy of the laser after passing through the attenuation plate is measured and recorded to complete the calibration of one point. At least three points are measured and calibrated for each angle position, and the corresponding curve relationship between pulse width and energy is completed through calibration. The TTL level signal output by the trigger photodiode generates a voltage signal with an amplitude greater than 3V and a rising edge less than or equal to 2ns through an external trigger module; The servo receives a pulse width modulation signal with a variable duty cycle output by a microprocessor to control the rotation angle of the servo, driving the rotation of the circular progressive attenuation plate on the servo, thereby controlling the energy of the passing laser; The energy photodiode adopts a PIN silicon photodiode with a response time of nanoseconds, receives the laser signal transmitted through the circular progressive attenuation plate, and converts it into a pulse current signal.

2. The energy attenuation control system of narrow pulse laser according to claim 1, characterized in that: The energy attenuation control board includes an energy detection and signal conditioning module, an external trigger module, an optical shutter control module, a microprocessor and a power supply module; the energy photodiode is connected to the microprocessor through the energy detection and signal conditioning module; the external trigger module is connected to the trigger photodiode; the optical shutter control module is connected to the microprocessor, and the optical shutter control module is used to receive high and low level switching signals from the microprocessor to control the switching of the optical shutter, thereby controlling the output of the laser signal; the power supply module supplies power to the energy attenuation control board.

3. The narrow pulse laser energy attenuation control system according to claim 2, characterized in that: The energy detection and signal conditioning module includes an I / V conversion circuit, a pole-zero phase elimination circuit, a pre-stage amplifier circuit, a post-stage amplifier circuit and a dual-channel high-speed comparator connected in sequence, wherein the input end of the I / V conversion circuit is connected to the energy photodiode, and the output end of the dual-channel high-speed comparator is connected to the microprocessor.

4. The energy attenuation control system of narrow pulse laser according to claim 2, characterized in that: The servo receives a pulse width modulation signal with a variable duty cycle output by a microprocessor to control the rotation angle of the servo, driving the rotation of the circular progressive attenuation plate on the servo, thereby controlling the energy of the passing laser.

5. The energy attenuation control system of narrow pulse laser according to claim 2, characterized in that: The trigger photodiode adopts a PIN silicon photodiode with a response time of ns, receives an external pulse laser signal with a wavelength range of 200ns~1100nm and an energy less than 100μj, and generates a voltage signal with an amplitude greater than 3V and a rising edge less than or equal to 2ns through an external trigger module, which is used to trigger other devices.

6. The energy attenuation control system of narrow pulse laser according to claim 2, characterized in that: The energy photodiode adopts a PIN silicon photodiode with a response time of nanoseconds, receives the laser signal transmitted through the circular progressive attenuation plate, converts it into a pulse current signal, and converts it into a voltage signal through an I / V conversion circuit.

7. The narrow pulse laser energy attenuation control system according to claim 2, characterized in that: The microprocessor is an STM32 microprocessor.

8. The narrow pulse laser energy attenuation control system according to claim 1, characterized in that: The circular progressive attenuation plate adopts a circular gradient neutral density filter.

9. The narrow pulse laser energy attenuation control system according to claim 1, characterized in that: The energy attenuation control board is connected to the computer via a USB interface.

Images