Question: how can you move cells with lasers? i thought lasers normally burnt things

Andrew McKinley answered on 17 Jun 2010:

That is a very good point – we do normally see lasers burning things. The thing about lasers though is that they follow the same rules of optics as normal light – a green or red laser will still pass through a window because the window doesn’t absorb the energy from the laser. Fire the same laser at a wall though, and because the wall absorbs the energy, the spot of light will start to heat up. If that heat energy does not spread out as fast as the light energy is absobed, then the spot continues to get hotter and hotter, and eventually the laser will burn through the material absorbing it.

A cell however is transparent (colourless and see-through). If we tailor the laser to make sure that the cell cannot absorb its energy, then the cell will not heat up. On the other-hand, if we tailor the laser so that the cell *does* absorb the light energy, and we focus the laser down to a tiny point, we can burn a tiny hole in the side of the cell and actually do optical injections into a single cell!

As to how a laser can move things… That’s to do with something really amazing about light. Light can actually push things around – Japan have just unfurled a solar sail that will use the sun’s light to propell spacecraft around space (see the BBC news!). The ‘pushing’ force however is really really tiny, so we can’t experience it directly ourselves We use a laser to do a similar thing on a much smaller scale, but since the cell doesn’t absorb the energy from the laser, it isn’t harmed.