Increasing the power, pulse energy or repetition rate, of femtosecond lasers has been a general trend in in order to comply to the needs of the market for higher throughput. One of the strategies of increasing the power has resulted in the development of a GHz femtosecond laser. When increasing the repetition rate during the process beyond several hundred kHz, the delay between the laser pulses is less than the thermal relaxation time and there is thermal accumulation in the target material. Due to thermal accumulation, which occurs over the duration of the burst, the absorption coefficient for each subsequent pulse in the burst increases and the required energy to induce ablation decreases. Thanks to a specific ablation scheme in GHz mode, the ablation efficiency is then comparable to the case of single nanosecond pulses, but with the usual quality of femtosecond processing.
- Laser technology