Definition Of Continuous Wave (CW) And Quasi-CW

continuous wave operation of a laser means that the laser is continuously pumped and continuously emits light. The emission can occur in a single resonator mode (→ singlefrequency operation) or on multiple modes.

In continuous-wave operation, some lasers exhibit too strong heating of the gain medium. The heating can then be reduced by quasi-continuous-wave operation, where the pump power is only switched on for limited time intervals. Quasi-continuous-wave (quasicw) operation of a laser means that its pump source is switched on only for certain time intervals, which are short enough to reduce thermal effects significantly, but still long enough that the laser process is close to its steady state, i.e. the laser is optically in the state of continuous-wave operation. The duty cycle (percentage of "on" time) may be, e.g., a few percent, thus strongly reducing the heating and all the related thermal effects, such as thermal lensing and damage through overheating. Therefore, quasi-cw operation allows the operation with higher output peak powers at the expense of a lower average power.