The key parameters of a pulsed laser—pulse width, repetition rate, and pulse energy—each affect material processing quality in different ways. Their various combinations directly influence the precision, efficiency, and thermal effects on the material surface. Below is a detailed explanation of how these three parameters impact material processing quality and some typical application examples.
- Pulse Width
Definition: Pulse width refers to the duration of a single laser pulse, typically measured in femtoseconds (fs), picoseconds(ps),nanoseconds (ns), or microseconds (μs).
Impact:
- – Short pulse width (e.g., femtosecond, picoseconds, nanosecond): Energy is released over a very short period, minimizing heat conduction to the material’s surface, resulting in a smaller heat-affected zone (HAZ). Short pulses primarily interact with the material through optical absorption, shock waves, and vaporization, avoiding surface melting. This is ideal for precision processing, micro-machining, and processing heat-sensitive materials.
- – Long pulse width (e.g., microseconds and above): The energy release is more prolonged, often causing material melting and creating a larger heat-affected zone. Long pulse widths are suitable for cutting or welding where higher heat input is required.
Typical Applications:
- – Femtosecond lasers for precision micro-machining: For example, in medical device manufacturing, femtosecond lasers are used for minimally invasive cuts on biological materials without significant thermal effects.
- – Nanosecond lasers for solar cell micro-processing: Used for fine surface scribing without excessive thermal damage.
- Repetition Rate
Definition: Repetition rate is the number of laser pulses emitted per unit of time, typically measured in Hertz (Hz) or kilohertz (kHz).
Impact:
- – Low repetition rate: There is more time between pulses, allowing the material to cool, thus reducing heat accumulation. This is suitable for deep cutting or drilling where high single-pulse energy and minimal heat buildup are needed.
- – High repetition rate: The intervals between pulses are shorter, leading to more heat accumulation, which is beneficial for shallow processing or marking, where high efficiency and material removal rates are desired. However, excessive heat accumulation can reduce processing precision.
Typical Applications:
- – Low-frequency laser processing for deep hole drilling: For example, in aerospace, low-frequency, high-energy lasers are used to drill deep holes in engine combustion chambers, allowing sufficient cooling time between pulses and reducing thermal deformation.
- – High-frequency laser processing for rapid marking: In electronics manufacturing, high-frequency lasers are used for fast, fine marking on metal or plastic surfaces, such as engraving QR codes or text.
- Pulse Energy
Definition: Pulse energy is the energy contained in a single laser pulse, typically measured in microjoules (μJ) or millijoules (mJ).
Impact:
- – High pulse energy: Suitable for applications that require high material removal rates, such as deep cutting, welding, or processing thick materials. However, excessive pulse energy can cause surface ablation, melting, or splashing.
- – Low pulse energy: Ideal for precision processing, micro-machining, or applications where the heat-affected zone must be minimized. Lower energy pulses allow precise material removal layer by layer, avoiding excessive heat buildup or material deformation.
Typical Applications:
- – High-energy pulses for metal deep cutting: For instance, in cutting thick steel plates, high-energy pulses quickly penetrate the material for efficient cutting, but heat-affected zones must be controlled.
- – Low-energy pulses for precision engraving: In semiconductor manufacturing, low-energy pulses are used to precisely machine silicon wafers without causing thermal damage to surrounding areas.
