In order to detect explosive chemicals, without getting in range, scientists have developed a testing laser. The difference is, this laser doesn't need to be shot out of a device. It's shot out of the air.
The problem with potential explosives is you generally have to get close to see if they're actually explosive or not. Whether the process involves taking a gander, swabbing the object with chemical testing agents, or just poking it with a long stick, it requires one to be far, far too close for comfort. It would be helpful to have some device that can check for explosives from a good long distance away.
To this end, scientists have created a laser. It's a normal-looking device, a tube that sends out focused beams of ultraviolet light. The ultraviolet light is focused in a cone extending from the front of the laser. The light excites the atoms of air inside the cone, bumping the electrons in those atoms up a level or two. When the electrons fall back down towards the atoms, they emit photons. Those photons excite other atoms, causing other electrons to jump and fall, and other photons to be emitted.
Inside a traditional laser device, those photons would be reflected back and forth off the walls of the laser. Since the cone has walls of air, its users rely on luck and volume. At least some of the photons will travel down the length of the cone. Repeated pulses of the laser amplify the energy inside the cone, and eventually it fires another laser back towards the end of the device. A new laser comes out of thin air, and shoots back at the original device.
Lasers come in all different colors and intensities. What changes these colors and these intensities is the material whose electrons are being excited. One kind of gas, or solid, will emit a red laser. Another will emit a violet light. The material inside the 'cone' of laser light is being excited. If it's regular old air, it will give back one color of light. If some sinister vapors are drifting off an explosive and mixing with the atmosphere, the laser will come back a different wavelength and intensity.