That's a really great question. One of the more significant differences between the two lasers is the power that they emit. Since the laser that is used at the grocery store does not burn (or even heat up) the items it scans, it may be obvious that there is a lower amount of power in the "laser beam". Here is a little analogy I like to think of. Imagine taking 2 identical pieces of garden hose. One of them is connected to your kitchen sink, and the other is connected to a fire hydrant. The hose connected to the fire hydrant will have quite a bit more water flowing through it, and thus feel more "powerful". Another difference between the lasers is the kind of light they emit. You may have noticed that when the groceries are scanned you can see a red light on the side (note: you should never look into any sort of laser, even those at the grocery store... they can cause serious and permanent damage to your eyes). The lasers that are used to cut metal can be a different color (I have seen blue, red, and a few other colors). Each 'color' of light has a different energy. There are verified theories that light comes in small particles which are called photons. Meaning, one can think of a 'beam' of light as being a bunch of really small marbles, instead of a stream of water. The photons that are blue have more energy than photons that are red.

An understanding of how lasers function is necessary to explain the last difference, which has to do with the different materials the lasers are made from. Lasers work by having some sort of source of a single color of light that is placed inside of a "resonating cavity". The simplest form of resonating cavity is two mirrors. Light that gets trapped inside the mirrors will bounce back and forth, and every time it passes through the light source it creates more light. If one of the mirrors lets a small amount of light out of it, the light that comes out the end is what is seen as the 'laser beam'. In the case of the laser at the grocery store the light source that is used is something called a 'semiconductor laser diode'. Essentially it is a material that when electricity is passed through it, light gets emitted at a certain wavelength (color). It is a solid material. In the case of a high-power laser that cuts through metal, the material that is used is a gas. When electricity is passed through the gas item there is a certain wavelength. Differences in the chemical composition of the semiconductor versus the gas lead to fundamental differences in the maximum output power of the laser.

There are two big differences. One is how big the laser is. Grocery scanner lasers (and laser pointers) are about 5 milliwatts, which is enough to make a spot of light that can be seen. A dim light bulb is about 50 watts, or 50 thousand times more energy, but it shines in all directions, not just on one spot like a laser. An industrial laser for cutting and welding can be around 1 to 10 kilowatts. A portable heater usually produces 1 kilowatt, so imagine that much heat put on the size of a laser spot. That's how the big lasers can cut through metal.

The other difference is the color of the light that the laser produces. Grocery scanners make red light, so the black and white stripes can be detected easily. Cutting and welding lasers make all sorts of colors, when a person is putting together a factory which will use lasers like this they choose one that will be absorbed well by what they want to cut. One example of this is in medicine, where lasers are used in surgery sometimes to keep people from bleeding. By using a blue laser, the blood absorbs the light and heats up so that the cut stops bleeding (the same way fried egg doesn't run). Since other parts of the patient (nerves, bones,etc.) reflect the laser, they aren't hurt.

The red lasers used to scan bar codes at the checkout counter are just a few milliwatts (1/1000 of a watt). The lasers that can burn through metal are 1000's of watts. Even a 1-watt laser, if you shine it on your hand (NEVER EVER LOOK DIRECTLY AT IT) starts to feel a bit warm.

Other lasers are also at different energies of light. The red lasers you see in markets are Helium-Neon ("HeNe" for short) lasers. Some lasers produce UV radiation, and are so powerful you must wear protective eye coverings just to work in the same room with them. I don't know off hand what lasers you are talking about, but I suspect it would be a very high-energy, high-power laser.

Here is a good place to read about lasers: here

I think the main difference is the amount of power the laser emits. You can have lasers that are different wavelengths (colors) but if the laser is powerful enough, I don't think it really matters what wavelength it operates at. It looks like there are a couple different types of lasers that are sold for cutting;

If you search on the internet for "cutting lasers" you should find lots of neat info. Here's one example: click here