LPF Site Supporter
- Jan 29, 2014
Compare the power density of a 450nm blue M140 1.4 watt multimode diode and a 175mw 450nm single mode diode after 1000 meters distance when using a 6mm diameter single element collimation lens (pushed hard, I don't remember the part number).My use to point the night sky and aim at the distance. 1.4W too powerful and dangerous.
I am not aware of any 200mw or higher power output rated visible spectrum single mode laser diodes, unless at about 405nm. Although I believe some SM laser diodes may be possible to be pushed that high with reduced life expectancy. There is a problem pushing some SM diodes too hard, some break out of single mode when pushed to run very far outside of their design values.
Divergence calculator: https://www.laserworld.com/en/laserworld-toolbox/divergence-calculator.html#divergence
I threw some beam diameter guesses into the equation, but at a far distance it won't make that much difference if I am off by a few mm there, for a given divergence figure.
If you can find the divergence of a specific 450nm single mode diode and plug the figures in you can get better numbers. Larger diameter beams produce different amounts of divergence for a given diode, the larger the beam diameter the lower the divergence. The above figures are assuming a 6mm diameter collimating lens which is common for most laser pointers.
This example is for a single element lens like the G2. Although the multi-element 6mm diameter lenses we are commonly using will produce a lower divergence than a single element lens, this is mostly due to their longer focal length and the resulting larger beam diameter filling more of the lens aperture (producing a wider or thicker beam out of the pointer). However, depending upon the specific multi-mode diodes beam characteristics, some having a wider angle of radiation out of the diode, the longer FL of the 3 element lenses we use allows too much of the beam to spread within the barrel of the lens holder before reaching the lens, often truncating, or cutting some of the beam off causing additional loss.