Finally, we divide the power output of the laser by the area of the final lit spot and voila! - that's how intense the laser is at the destination. From that we can use straightforward geometry to derive the diameter of the beam when it hits its target. Partly inspired by a talk at a recent astronomy meeting that explored whether we could detect photons from potential exoplanet-dwelling aliens, Inside Science performed some of our own calculations to see if a hypothetical alien Galileo could observe photons coming from Earth.Īll we need is an equation for calculating how quickly a laser beam spreads out as it travels through space. The math needed to calculate the answer is surprisingly simple. By the time the light finally reached Mars, the glint would be a million times dimmer than the faintest light visible to the human eye.īut you don’t need to take our word for it. In this article, we will be using these numbers as references. Finally, the midday sun is at a whopping 1,000 watts per square meter, about half a million times brighter than the moon.
LASER BEEM FULL
For comparison, the full moon is almost a million times brighter at one-thousandth of a watt per square meter. However, with the presence of urban light pollution, one usually can’t see stars much dimmer than the North Star, which has an intensity of around four-billionths of a watt per square meter. The dimmest light visible to the naked eye in perfect darkness is around one ten-billionth of a watt per square meter. If you didn’t make a mistake in your calculations and kept everything in radians, watts and meters, the final number should be in watts per square meter.
Π × (Beam divergence in radians × Distance) 2įinally, the brightness at the destination is given by dividing the output power of the laser over the area of the spot. Then a little bit of geometry will give us the size of the final lit spot at the destination. (The laser's wavelength)/(π × The laser's aperture) First, if we assume the laser is optimized so that its spreading angle is at its theoretical minimum, then we can calculate its beam divergence (in radians) using this equation. One only needs three rather simple equations for all the calculations done in this article.
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