In this process the laser is used to heat the surface of materials. Any subsurface heating is accomplished by conduction. For intensity values up to about 1x104 W/cm2, the absorbed power depends on the wavelength ( λ), the material (and its surface condition). Generally, as the material temperature increases, so does the absorption of laser light. The most relevant processing parameters are the laser power and the beam/material interaction time. In metals, local surface heating is very rapid and produces a thin hot layer on a relatively cool bulk material. This conducts heat away from the surface very quickly. Cooling rates of the order of several thousand degrees per second are possible, which can be used to advantage in producing microstructural changes, for example, in transformation hardening which uses IR lasers.
More recently, the laser has been used as a tool for the direct shaping or forming of metallic components by using the beam as a localised and highly controllable heat source. Laser thermal forming is achieved by inducing bending through the introduction of a steep thermal gradient into a sheet material, which results in local plastic deformation and subsequent shrinkage on cooling.