With regard to the laser processing of brittle materials, let us introduce the basic knowledge of laser and the principle of laser processing.
What is a laser?
Laser stands for Light Amplification by Stimulated Emission of Radiation. Its significant characteristics are as follows:
- Directivity (progress in a straight line)
- Coherence (interfering)
- Monochromaticity (narrow spectrum width)
By utilizing characteristic 2, “coherence”, the laser beam can be converged into a small area (energy density becomes high).
A laser oscillator consists of an optical amplifier and an optical resonator. Its output is obtained through light oscillation by the optical resonator. The main oscillation operations are continuous wave oscillation (CW) and pulse oscillation.
Pulse oscillation has the following features:
- Output is oscillated in a pulse state.
- Heat effect can be reduced.
- The processing conditions can be modified in relation to the repetition frequency and pulse width.
In general, processing with less heat effect (lower process cost) can be realized with a shorter pulse width (time width per pulse).
Classification of laser
Lasers are classified according to multiple criteria.
- Laser oscillation medium (solid, liquid, gas, semi-conductor)
- Oscillation characteristic (continuous/CW, pulse)
- Oscillation wavelength (between ultraviolet ray and infrared ray)
- Degree of hazard (classes 1 to 4)
These are the 4 main categories.
In many cases, the oscillation wavelength is determined by the laser medium used. Processing using infrared laser, which has a long wavelength, involves thermal processing elements, and processing using ultraviolet laser, which has a short wavelength, involves non-thermal processing elements; this is also called abrasion processing.
Principle of laser processing
Natural light does not consist of a single wavelength but multiple wavelengths, however, a laser consists of one single wavelength, which is a constant and continuous wave. When the laser beam is condensed through a lens, the energy density at the focal point becomes extremely high. This optical source with a high energy density can be used for processes such as drilling and cutting.
The principle of laser processing can be divided into three parts, namely energy absorption, oscillation/dispersion, and diffusion. Laser processing is a method that utilizes oscillation at the atomic level by laser beam absorption, followed by abrupt thermal conduction by resonance vibration. Thermal processing is a method that utilizes the thermal energy generated by the absorption of the laser beam on the workpiece surface. Processing is carried out while fusing the workpiece by using the thermal energy, for which the infrared laser is often used. Abrasion processing, which is a typical non-thermal method, is used for removal by instantaneous fusion of the part where the laser beam is absorbed, followed by evaporation and diffusion.
Laser processing can provide fine processing of various materials at high speed.