Barium tungsten electrodes (usually referring to barium-containing tungsten-based reserve cathodes) play a vital role in pulsed lasers, especially gas discharge-excited pulsed lasers, and are mainly used as high-performance cathodes. Its application core lies in providing an efficient, stable and long-life electron emission source to support the high current and high repetition frequency pulse discharge required by the laser.
Advantages of Barium Tungsten Electrodes in Pulsed Lasers
1. Efficient Thermal Electron Emission:
Barium tungsten cathode is a reserve diffusion cathode or impregnated cathode. Its core is to impregnate an emitting substance containing active substances (such as barium aluminate, barium calcium aluminate) in a porous tungsten matrix. When the cathode is heated to the operating temperature, the active barium atoms inside diffuse to the cathode surface through the pores of the tungsten matrix to form a monoatomic layer (or sub-monoatomic layer) of barium covering layer. This barium layer significantly reduces the work function of the tungsten surface. The reduction in work function means that at the same temperature, electrons are more easily emitted from the cathode surface, or the required emission current density can be obtained at a lower temperature. In the discharge of a pulsed laser, a strong current pulse needs to be established in a very short time. The low work function characteristics of the barium tungsten cathode enable it to provide extremely high pulse emission current density, which is necessary to trigger and maintain high-energy, high-efficiency laser pulses.
2. High Current Carrying Capacity and Stability:
The tungsten matrix itself has a high melting point, high thermal conductivity and good mechanical strength, and can withstand high temperatures and ion bombardment during the discharge process. The internal active material reserve can continuously replenish barium atoms to the surface, compensate for the loss caused by evaporation, sputtering or ion bombardment during the discharge process, and maintain the stability of the emission layer. This enables the barium tungsten cathode to withstand repeated high current shocks in the working state of the pulsed laser, maintain stable emission performance, and is not easy to be "poisoned" or rapidly decay, ensuring the stability and long life of the laser output.
3. Long Life:
Thanks to the internal active material reserve and slow consumption rate (under reasonable vacuum environment and discharge conditions), the life of barium tungsten cathodes is generally much better than other types of cathodes. In a well-maintained high/ultra-high vacuum system, the life can reach thousands or even tens of thousands of hours. For pulsed lasers (such as excimer lasers, copper vapor lasers, etc.) that need to operate stably for a long time in industrial applications and scientific research, long-life cathodes are essential, reducing maintenance downtime and operating costs.
4. Suitable for Pulsed Working Mode:
The emission response of barium tungsten cathodes is fast and can well follow the requirements of pulse discharge. During the pulse interval, the barium layer on the surface can be restored to a certain extent. It is very suitable for the needs of high repetition rate (kHz or even higher) pulsed lasers, ensuring that each pulse can obtain stable and reliable electron emission to start the discharge.
5. Relatively Low Operating Temperature:
Although the operating temperature is still high, it is significantly lower than that of pure tungsten cathodes that need to achieve the same emission current density. This is beneficial to the influence of thermal load on the overall structure of the laser and improves the thermal stability of the system.
