What is the difference between continuous laser cleaning and pulsed laser cleaning?

Laser cleaning technology, as an efficient and environmentally friendly method for surface cleaning, is mainly divided into continuous laser cleaning and pulsed laser cleaning based on the different output methods of the laser. There are significant differences between the two in terms of their action mechanisms, process parameters, cleaning effects, and application fields. 
I. Mechanism of Action 
Continuous laser cleaning uses a laser beam with a constant output power to continuously irradiate the surface of the workpiece. Its cleaning mechanism mainly relies on the thermal effect. When contaminants or coatings absorb the laser energy, their temperature keeps rising, and eventually they are removed through processes such as melting, vaporization or thermal expansion. The thermal impact on the substrate is relatively continuous and profound. 
Pulsed laser cleaning employs periodic output of high peak-power laser pulses, with each pulse having an extremely short duration (typically in nanoseconds, picoseconds, or even femtoseconds). The cleaning mechanism combines thermal effects and mechanical effects. The contaminants are rapidly heated, vaporized, or ionized within an extremely short period of time, generating intense shock waves. These shock waves utilize their force to "vibrate" the contaminants away from the substrate surface. Due to the short duration of the action, the heat has no time to be widely conducted to the substrate, so the heat affected zone is relatively small. 
II. Key Process Parameters 
The core parameters of continuous laser cleaning are laser power (watts, W) and scanning speed. By matching the power and speed, the energy input per unit area (energy density) can be controlled. 
The core parameters of pulsed laser cleaning are much more complex and mainly include: 
Pulse energy (joule, J): The energy contained in a single pulse. 
Pulse Width (seconds, s): The duration of a single pulse, which determines the power density. 
Repetition frequency (Hertz, Hz): The number of pulses output per second, which affects the cleaning efficiency. 
Power density (watts per square centimeter, W/cm²): It is determined by both pulse energy and pulse width, and is the key factor in generating mechanical effects. 
III. Cleaning Effect and Characteristics 
Cleaning efficiency: Under the same average power, continuous laser, due to its uninterrupted energy output, usually has a higher material removal rate and thus a higher cleaning efficiency. The cleaning efficiency of pulsed laser is limited by the repetition frequency. 
Heat Impact: The continuous laser provides a large and continuous heat input to the substrate, which is prone to causing thermal damage to the substrate, such as melting, deformation, and changes in microstructure. This risk is particularly high for materials that are sensitive to heat. The thermal impact area of pulsed laser is small, enabling "cold processing" and making it more suitable for cleaning of precision and heat-sensitive components. 
Cleaning accuracy and controllability: By controlling the energy and quantity of individual pulses, pulsed laser can achieve layer-by-layer removal of the contamination layer, with higher control accuracy and easier realization of selective cleaning without damaging the substrate. The control accuracy of continuous laser is relatively lower. 
Cleaning mechanism application scope: Continuous laser is more suitable for removing contaminants with relatively weak bonding force to the substrate or those that can be effectively removed through thermal effects, such as oil stains, paint, rubber, etc. The mechanical impact effect of pulsed laser is more effective for removing firmly attached particles (such as dust, metal particles), oxide layers, and tiny particles. 
Equipment cost and complexity: Pulse lasers, especially ultra-short pulse lasers, generally have higher technical complexity and manufacturing costs than continuous lasers with the same average power. 
IV. Application Scenarios 
Continuous laser cleaning: This method is commonly used in large-scale, high-efficiency macroscopic cleaning scenarios, such as ship body paint removal, pre-treatment of large steel structure surfaces, and tire mold cleaning, etc. It is applicable to fields where there are no strict requirements for thermal damage to the substrate. 
Pulsed laser cleaning: Widely applied in the fields of high-precision and low-damage micro-processing and cleaning, such as cleaning of electronic components, restoration of cultural relics, decontamination of precision molds, removal of particles from the surface of semiconductor wafers, and maintenance of key components in aerospace. 

Continuous laser cleaning and pulsed laser cleaning are two technical routes based on different physical mechanisms. Continuous laser mainly relies on thermal effects, with advantages including high efficiency and large-area cleaning; pulsed laser combines thermal and mechanical effects, with the core advantage being high precision and low thermal damage. In practical applications, factors such as the material characteristics of the cleaning object, the type of contaminants, the precision requirements, and the tolerance to thermal effects need to be comprehensively considered and the appropriate technology selected.