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What is the range of a 150mw, 300mw and 600mw laser for wavelengths 808nm and 980nm?

A way to compute the outdoor and indoor range as a function of power and wavelength would be helpful.

Well in the 808 to 908 nm you are working in the range of photon emission of water. I have not heard of a H2O laser yet; but, you never know… I have seen some Noble gas lasers work near this frequency range however, most generate much higher power then the mw range you are querying about.

As to the range of a laser it really depends on the divergence of the beam. The greater the beam spreads out from the end of the laser the less likely it will go far with any appreciable energy. And example might be a Helium Neon at 6.15 um and 5 mw with a beam divergence of 1.5 radians. Though visible at the target up to 1 mile away
the amount of energy is very small and can only be observed as a distant red dot. That you have chosen a laser with a higher energy density (by a factor of about 10,000) you might be able to detect it at a distance of 100 miles as a small bluish dot regardless of the power level. All the power level at this distance will do is determine the relative intensity of the blue dot, (IE faint, barely visible, clearly visible in a dark night sky.) However, you would not be able to see the ends on the surface of the planet as the curvature of the earth limits the distance between two points at about 6 feet above the ground to around 14-15 miles.)

The other issue you have is how much interference there is between the laser and the target. Indoors you can simulate long distances using fiber optic cables; however, most are tuned for higher frequencies. Though Corning makes a 50nm single mode fiber that might be used to simulate a long distance; however as a general rule Bell Labs discovered the greatest distance they could send a high frequency signal through the fiber with a loss of less then one third the signal strength is around 160 miles. In free air emissions there are a number of variables, dust or aerosols, rain, water vapor even the nitrogen in the air can attenuate the power of the laser. Again Bell Labs did a number of experiments using laser to attempt to form a very tight communications channel between ground stations and satellites, they found it was possible; however, the interference was so great that even with 100 watts of a blue laser the signal would not allow a reliable signal.

But, I digress, if you want to calculate the db loss you have to know the signal loss of the medium the laser light will pass. There are a number of tables that will help you estimate this data; but, you have to pay attention to the test conditions. As a general rule you need to know the initial power, the attenuation of the medium and the minimum detection power required of the detector. You have the initial power in your choices above, the minimum power of the detector will generally be around 10mw at this frequency. So you only need to know the db loss of the medium. The general rule of thumb is as you double the distance you reduce the energy level by the square root of the initial power. So if you start with 100 mw at 1 meter you would be at 10 mw at 100 meters. If you start with 1 watt you would normally reach 10 mw at 1000 meters. If you start with 10 watts you would normally reach 10 mw at 10,000 meters. All providing you do not have much interference.
If the medium has a db loss of 3db that means in addition to the squares rule you would have half the power or distance capability. If you have 9db loss you would have about 1/8th the power level.

I don’t know how much this will help you; but, these are general rules of thumb that should at least help you determine for yourself the type of data you might need to either do more research or guide you in your research.

Good Luck,
Dave Cooke

Laser range finder for autonomous vehicles

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