![]() In other words, the total power from the intensity profile shown in the picture is the same for all cases. ![]() Where the aperture is partially obscured, it is assumed that the power remaining in the beam after encountering the obstruction is the same as the standard power used for full apertures. In the table, it is assumed that the same amount of power passes through each aperture shown. You will see that some aperture designs scatter some of the light far beyond the spot size. The radius, in pixels, that contains 70% of the beam power, 80% of the beam power, 90% of the beam power, and 95% of the beam power.Where not appropriate, this row is not displayed. The radius, in pixels of the image, of the spot size parameter R λ / D.The highest intensity in the diffraction pattern, relative to the maximum intensity of the first example shown.The details of near field diffraction are too complex to cover here, although you will not be too far wrong using the formulas as long as R > D.īelow, the intensity profile of a beam after leaving the death ray is shown, followed by the diffraction pattern at tight focus at the target. The above formulas are only valid when R is much larger than D. In fact, we can determine the smallest possible spot size into which you can focus the beam: if we denote the diameter of the mirror, lens, or other opening in the laser or focusing element as D, the wavelength of the light as λ, and the distance to the target as R, then the diameter of the smallest spot, S, is given byįor example, a laser that emits 5×10 -7 meter wavelength light (or 0.5 microns, this puts it in the visible green) that is focused through a 0.1 meter lens at a target 1000 meters (1 km) away will have a minimum spot size of 6×10 -3 meters (6 millimeters) and a divergence angle of 6×10 -6 radians. The amount the beam expands depends on the ratio of the initial width of the beam to the wavelength of the beam. This means that if you try to focus the beam down to a tiny point at a distant target, the beam might spread out to a much larger spot by the time it gets there. When a laser beam is propagating freely, it will naturally tend to expand. The streak is the light diffracting around the hair. You will see a streak appear on the wall through the laser dot perpendicular to the hair. This is easy to demonstrate with a laser pointer in a darkened room. ![]() It takes very narrow objects, such as hairs or thin scratches, to get noticable diffraction. Since visible light has a very small wavelength, this is why light seems to travel in straight lines. The smaller the wavelength of a wave in comparison to the size of the obstruction or opening, or the width of the beam, the less the wave diffracts. It does not even require an object in the path of the wave, any beam of waves has a tendancy to spread out to the sides due to this effect. Light is a wave in the electromagnetic field, so light undergoes diffraction. It happens with every kind of wave in nature. Similarly, a wall with a single opening will let the wave through the opening, but the edges of the wave will curve out toward the sides, causing the transmitted wave to spread out. Think of ripples on the surface of a still pond passing a post sticking out of the water. When a freely propagating wave encounters a barrier, it can curve around the barrier. To understand diffraction, you need to understand the behavior of waves. There is a fundamental physical limit on the ability of lasers to focus on their targets. How to Build a Laser Death Ray Diffraction
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