In order to obtain a nanosecond-level narrow pulse width output, Q-switching technology is generally used. The megawatt-level peak power is thus obtained, which is suitable for the application of blasting target tissue with high peak power. There are two commonly used Q-switching techniques: passive Q-switching and electro-optical Q-switching. What is the difference between the two?
Passive Q-switching uses a saturable absorbing dye crystal called tetravalent chromium. This saturable absorbing dye is a non-linear absorbing substance. Put it in a resonant cavity and use its saturable absorption characteristic of light to change The absorption loss in the resonant cavity functions as a Q switch. The so-called saturable absorption characteristic means that the dye absorption rate changes with the change of light intensity. The initial absorption rate is very large. As the light intensity increases, the absorption rate decreases until the dye is saturated. Due to this characteristic and the dye’s own characteristics, it cannot be accurately controlled. Therefore, the use of passive Q-switching has poor repeatable accuracy, wide pulse width, and relatively large energy jitter.
Electro-optic Q-switching uses the electro-optic effect of the KD*P crystal to add a step voltage to the crystal to adjust the reflection loss of photons in the cavity. By adding a specific high voltage to the crystal and using the birefringence effect of the crystal on the polarized light, the incident light cannot oscillate in the resonant cavity, which is called the closed state; when the number of inverted particles in the resonant cavity reaches the maximum, suddenly Retreat the high voltage on the crystal to form the laser output. Using modern electronic circuits, the high-voltage control is very precise and controllable. Therefore, the repeatability of electro-optic Q-switching is relatively high, the energy jitter is small, and the pulse width is narrower.
Passive Q-switching has the characteristics of small size, low cost, simple and easy to use, and has been widely used in low-cost or compact solid-state laser applications.
Electro-optical Q-switching has the characteristics of high precision, low energy jitter, and narrow pulse width. It has been widely used in the field of accurate and controllable high-quality giant pulse lasers.
Further reading:Application of picoseconds