How far are we from the handheld laser gun? Will it replace traditional ammunition? Changing the *high power laser pointer* weapon carried by a typical rifle man is incredibly far from our current level of technology and any reasonably foreseeable past. We are not talking about just needing better batteries and better laser transmitters, but about the absolute revolutionary development of these two technologies, which have improved performance by several orders of magnitude.

Let’s put it this way: battery-powered orbital rockets are about the same difficulty. Why can laser travel over long distances? The laser beam does travel a long distance and obeys the inverse square law. By focusing the beam at a certain distance from the laser output, the inverse square law in short distances can be avoided. If done correctly, within a short distance, the beam appears to be perfectly collimated.

The beam can only be collimated on one plane, which is called the beam waist **green laser**. But why is this? Why can’t the alignment be maintained? What makes the light beam propagate? There are two ways to solve this problem. The first is based on the particle properties of light. Let us assume that the beam is facing the z direction. The Heisenberg uncertainty principle states that the smaller the uncertainty of the position of the photon in the x direction, the more uncertain the photon component of the x-direction velocity.

This means that if the beam diameter is only 2 mm, it will spread more than a 10 mm wide beam. The second method recognizes the volatility of light. The wave diffracts at the edge of the aperture or beam. The diffraction half angle is given by [Mathematics] \theta = \dfrac{\lambda}{D} [/math]. That is, the smaller the diameter of the beam (D), the larger the diffraction angle. [Mathematics]\lambda[/Mathematics] is the wavelength of the laser.

This is a function of the laser beam diameter and distance of a typical **blue laser pointer**. As you can see, the beam looks roughly collimated for about one or two meters, but after a few meters, the beam expands at a constant angle, so the beam diameter increases in proportion to the distance.