In the case of a solid-state pulsed laser pumped by a millisecond optical pump, the laser output is “relaxation oscillation†and consists of a series of small spikes with subtle magnitudes and unequal intensities. They are all generated near the threshold, and the peak power is not High, in the order of tens of kilowatts. Increasing the pump energy can only increase the number of small spikes, and cannot effectively increase the peak power. Such laser beams have not met the requirements for many centuries. The Q-switching technique was developed to suppress the above relaxation oscillations and to release all pass energy compressions within a narrow pulse time.
Q-switching technology, also known as Q-switching technology, uses a method to vary the Q of the resonator according to the required procedure. When the laser begins to work, the cavity is first placed in a state of high loss and low Q. The laser cannot oscillate, but the particles are constantly pumped to the metastable state. When the number of particles in the metastable state is high enough, the Q value of the cavity is made. Suddenly increasing, like a high-speed switch, a strong oscillation is rapidly established in the cavity and a very strong narrow pulse is output in a very short time. Q-switching techniques commonly used in laser cutting machines include electro-optic Q-switching and acousto-optic Q-switching.
1. Electrooptical Q-switching method A method of using the electro-optical effect of a crystal to realize Q mutation, that is, the effect of changing the polarization direction of incident light by using an electro-optic crystal under the action of an external electric field, and artificially adding a controllable equivalent reflection. Loss method. When the working medium is excited by a xenon lamp, polarized light polarized by the xenon lamp passes through the polarizer and becomes linearly polarized light. When an appropriate voltage is applied to the electro-optic crystal, the refractive index of the crystal changes, so that the ordinary light propagated in the crystal Unusual light produces a certain phase delay, and linearly polarized light is rotated by 90° through the direction of vibration behind the crystal, and thus cannot pass through an analyzer whose polarization axis is parallel to the polarization axis of the polarizer. At this time, the electro-optical switch is turned off, so the Q value is very low and laser oscillation cannot be formed. The optical pump is continuously excited, and the number of energy level particles on the working substance continuously accumulates to the maximum value. At this moment, the voltage on the electro-optic crystal is instantly pushed off, and then the direction of vibration of the linearly polarized light does not rotate but rapidly passes through the analyzer, which corresponds to that the electro-optical switch is rapidly opened, the Q value in the cavity is increased sharply, and the laser generates a giant pulse in an avalanche manner. Actual devices often eliminate the role of analyzers and rotation.
2. Acoustic Switching Q Mode An acousto-optic Q-switch device is inserted in a continuous Nd:YAG laser. The device is composed of an acousto-optic medium, a transducer and a driving source. A tens of megahertz of RF voltage generated by the driving source is applied to the transducer. The transducer converts the electric energy into mechanical energy, performs mechanical vibration to generate ultrasonic waves, and forms an ultrasonic grating in the ultrasonic medium. When the laser passes through the ultrasonic grating, diffraction occurs and the light beam deviates from the resonant cavity, causing the loss in the cavity to increase. The Q value is very low and laser oscillation cannot be formed. The optical pump is continuously excited, and the number of energy level particles on the working substance continuously accumulates to the maximum value. When the modulation signal output from the driving source removes the ultrasonic field in the acousto-optic medium, the diffraction effect disappears, the cavity loss decreases, and the Q value slams. In addition, the laser oscillation recovers quickly and the energy is output in the form of giant pulses. The modulation signal operates at a repetition rate of 0-20 kHz, and a high repetition rate giant pulse with a repetition frequency of 0-20 kHz and a pulse width of 100 ns can be obtained. Since the modulation voltage required for acousto-optic Q-switching is very low, generally below 200V, it is easy to achieve stable Q-switching for continuous lasers.
Q-switching technology, also known as Q-switching technology, uses a method to vary the Q of the resonator according to the required procedure. When the laser begins to work, the cavity is first placed in a state of high loss and low Q. The laser cannot oscillate, but the particles are constantly pumped to the metastable state. When the number of particles in the metastable state is high enough, the Q value of the cavity is made. Suddenly increasing, like a high-speed switch, a strong oscillation is rapidly established in the cavity and a very strong narrow pulse is output in a very short time. Q-switching techniques commonly used in laser cutting machines include electro-optic Q-switching and acousto-optic Q-switching.
1. Electrooptical Q-switching method A method of using the electro-optical effect of a crystal to realize Q mutation, that is, the effect of changing the polarization direction of incident light by using an electro-optic crystal under the action of an external electric field, and artificially adding a controllable equivalent reflection. Loss method. When the working medium is excited by a xenon lamp, polarized light polarized by the xenon lamp passes through the polarizer and becomes linearly polarized light. When an appropriate voltage is applied to the electro-optic crystal, the refractive index of the crystal changes, so that the ordinary light propagated in the crystal Unusual light produces a certain phase delay, and linearly polarized light is rotated by 90° through the direction of vibration behind the crystal, and thus cannot pass through an analyzer whose polarization axis is parallel to the polarization axis of the polarizer. At this time, the electro-optical switch is turned off, so the Q value is very low and laser oscillation cannot be formed. The optical pump is continuously excited, and the number of energy level particles on the working substance continuously accumulates to the maximum value. At this moment, the voltage on the electro-optic crystal is instantly pushed off, and then the direction of vibration of the linearly polarized light does not rotate but rapidly passes through the analyzer, which corresponds to that the electro-optical switch is rapidly opened, the Q value in the cavity is increased sharply, and the laser generates a giant pulse in an avalanche manner. Actual devices often eliminate the role of analyzers and rotation.
2. Acoustic Switching Q Mode An acousto-optic Q-switch device is inserted in a continuous Nd:YAG laser. The device is composed of an acousto-optic medium, a transducer and a driving source. A tens of megahertz of RF voltage generated by the driving source is applied to the transducer. The transducer converts the electric energy into mechanical energy, performs mechanical vibration to generate ultrasonic waves, and forms an ultrasonic grating in the ultrasonic medium. When the laser passes through the ultrasonic grating, diffraction occurs and the light beam deviates from the resonant cavity, causing the loss in the cavity to increase. The Q value is very low and laser oscillation cannot be formed. The optical pump is continuously excited, and the number of energy level particles on the working substance continuously accumulates to the maximum value. When the modulation signal output from the driving source removes the ultrasonic field in the acousto-optic medium, the diffraction effect disappears, the cavity loss decreases, and the Q value slams. In addition, the laser oscillation recovers quickly and the energy is output in the form of giant pulses. The modulation signal operates at a repetition rate of 0-20 kHz, and a high repetition rate giant pulse with a repetition frequency of 0-20 kHz and a pulse width of 100 ns can be obtained. Since the modulation voltage required for acousto-optic Q-switching is very low, generally below 200V, it is easy to achieve stable Q-switching for continuous lasers.
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