Let's first take a look at what happens when material is machined with these long pulse lasers. Machining with long pulse lasers The most fundamental feature of material interaction in the long pulse regime is that the heat deposited by the laser in the material diffuses away during the pulse duration, as shown in Figure 3.1. Technically speaking, the laser pulse duration is longer than the heat diffusion time . This may be desirable if you are doing laser welding, but for most micromachining jobs, heat diffusion into the surrounding material is undesirable. There are several reasons why heat diffusion is detrimental to the quality of the machining.
Heat diffusion reduces the efficiency of the micromachining process.
Heat diffusion sucks energy away from the work spot - energy that would otherwise go into removing material. Think of it as trying to fill a bucket full of holes with water. You have to pour a lot more water into the bucket to compensate for the water that leaks away. The higher the heat conductivity of the material the bigger the size of the holes and the more water you need to be poured into the bucket to fill it. These effects are best observed in the animated version of Figure 3.1 - click on image to see animation.