When laser irradiates metal, metal atoms absorb photon energy, which intensifies the vibration of atoms, that is, the amplitude increases and the vibration energy increases. When the vibration energy increases to a certain extent, the atom has obvious fluidity, not just vibrating back and forth near a certain position (for example, when an atom has a large amplitude and is collided by other atoms during the vibration process, for example, when it is far away from the original equilibrium position, the atom may lose some energy, so that the atom can only vibrate slightly near the new position, which shows that the atom flows from one position to another). When a considerable number of metal atoms have fluidity, macroscopically, the metal is liquid, that is, the metal in the irradiated part melts and breaks. This process may be accompanied by chemical reactions, and it may also break the metal bonds between metal atoms, causing the metal to break. The melting process of metal is a process of rising internal energy (the average increase of vibration kinetic energy, vibration potential energy and translation kinetic energy of atoms, that is, the intensification of thermal motion).
If the above is difficult to understand, it can also be simply said that under the action of laser, the metal melts at the irradiated place, and the melting process is a process of increasing internal energy. The source of internal energy increase can only be external laser. So light energy is converted into internal energy.
It can also be understood that the ultimate destination of external light energy is whether there are other forms besides internal energy. If there are no other forms, it can only be internal energy. Obviously, mechanical energy is constant (strictly speaking, there is a slight change, but it can be ignored), not to mention electromagnetic energy (but when considering the change of electromagnetic energy caused by the luminescence of metals due to temperature rise, this change exists, but some of the absorbed light energy is re-released in the form of light, and the energy form has not changed, so it does not need to be considered). So it can only be the change from light energy to internal energy.
Some people may wonder whether the chemical energy of the above process has changed. When there are non-inert gases around, chemical changes will occur at high temperature, which will inevitably lead to changes in chemical energy. But the chemical reaction here is generally exothermic, and when considering the chemical reaction, it is accompanied by the change of chemical energy to internal energy.