The roles of pulse width and frequency in lasers

In a laser processing system, frequency and pulse width are the key parameters that affect the energy distribution of the beam, the intensity of heat input, and the quality of the processing. Both determine the energy release mode of the pulsed laser, the peak power level, and the heating behavior of the material, and are the core indicators in the design and process setting of laser applications. 
I. The Role of Frequency in Lasers 
Affecting the way energy is output within a unit of time
The laser frequency indicates the number of laser pulses that repeat within one second. The higher the frequency, the more pulses there are, and the more continuous the heat input within a unit of time. At the same average power, increasing the frequency will reduce the energy of a single pulse. 
Affects processing speed and heat-affected zone
At higher frequencies, the laser action points are heated more uniformly, which can increase the processing speed, but it also leads to an increase in heat accumulation in the material. Low frequencies are used for applications requiring high single-pulse energy, such as deep etching or high-reflection material penetration. 
Affecting surface quality
A reasonable frequency setting can reduce slag, minimize thermal damage and stabilize the cutting or marking trajectory. An excessively high frequency may result in uneven surface erosion of the material or blurred textures. 
II. The Role of Pulse Width in Lasers 
Determine the peak power and pulse width of the pulse.
The pulse width refers to the duration of a single laser pulse. Under the same pulse energy, the shorter the pulse width, the higher the peak power. Short pulse widths are used for processing materials that are sensitive to thermal effects. 
Influencing the absorption and vaporization mechanisms of materials
Short pulse width lasers often enter a non-thermal processing mode, which is closer to "cold processing", and can reduce thermal diffusion and melting phenomena. Long pulse width mainly exhibits thermal effects and is suitable for melting, cladding or thermal deposition type processing of materials. 
Affecting processing accuracy and edge quality
Nanosecond, picosecond and femtosecond pulse widths result in different thermal influence areas during processing. The shorter the pulse width, the smaller the thermal influence area, which is suitable for precision processing or micro-structure processing. 
III. The Synergistic Effect of Frequency and Pulse Width 
Determine the balance between average power and peak power.
Average power = single pulse energy × frequency.
At a fixed average power, increasing the frequency will reduce the single pulse energy, thereby changing the peak power. The pulse width further affects the energy density profile of each pulse. 
Influence on processing efficiency and thermal control
By adjusting the frequency and pulse width, the ratio between processing efficiency and thermal influence can be controlled, enabling different process modes such as high-speed marking, deep engraving, or precise removal. 
Affecting the adaptability of different materials
Different materials have different sensitivities to the laser energy deposition mode. The combination of frequency and pulse width determines the reaction of the materials, such as melting, vaporization, plasma formation, etc.