Lasers are everywhere these days, and for very good reason. They're insanely useful. They can be used to detect chemicals, play tag, re-shape people's eyes, play music, make concerts more spectacular, play with pets, make precision cuts, and play virtual tennis inside the house. Whether lasers are used for aesthetic, utilitarian, or recreational reasons, the vast majority of lasers need one thing — a clear field between the device that emits them and whatever is supposed to receive them. Now it looks like —at least in medicine — that's about to change.
Light bulbs, windows, glasses of water; these are a few of the things that are pretty much clear, at least in the visible light spectrum. It's true that light is bent as it moves through them, but all the light that travels through is bent at the same angle. The same goes with mirrors - they might turn light completely around, but they do it in an orderly fashion, so that the 'picture' that hits them is pretty much the picture you see on the other side of them.
Other substances do not have the same kindly attitude towards light. Much of the light that hits them they absorb. The rest scatters. Each of the incoming photons is sent off in various directions. If a person is sitting on the other side of frosted sheet of glass, instead of a sharp image of a light on the other side they get a diffuse glow.
Although no one can stop such a substance from scattering light, some scientists are working on a device that will allow light to emerge on the other side as a sharp, focused beam. The problem is, the light can't start out as a sharp, focused beam. Scientists worked on the basis of trial and error, using a spatial light modulator. The SLM allowed them to adjust the phase, the speed, the intensity, and the spatial origin of laser pulses. In a test, researchers aimed the pulses at a layer of paint and recorded how much light made it to the other side, and where it did so. They then emitted an adjusted burst of light and measured how much that concentrated the light on the other side.
It was a process of trial and error, but after about ten minutes of testing, they were able to find a way to emit a bright and focused 115 femtosecond blast of laser light on the other side of the paint. With the right testing, this could not only create a laser that can blast away medical problems like cancerous cells from the other side of the skin — it could do so without damaging the skin it was shining through, since the laser light doesn't necessarily have to be intensely focused on the outside of the skin. It could just come together on the far side of healthy tissue. This may be the first step to scalpel-less surgeries.