What is the optimum diameter of a laser with a further range?

[naruto]

I would like to ask a question, does the diameter of the laser spot determine the range? Or, what are the factors that determine the range of the laser? I think the laser range should be with the power, wavelength, but I do not know what the specific reasons, but also do not know whether the diameter with the spot, hoping to get everyone's help, to solve my doubts, thank you :friend:

 

[Radim]

Many factors do... I assume you want to have visible dot at some range. Here wavelength, power and beam specs are key factors. Depending on atmospheric conditions there might be various ranges as well. For visible dot of laser from your position also albedo of targeted object is influencing visibility (on white wall you get more visible dot than on dark green forest as it reflects better on white wall). For specifically beam specs divergence is crucial (how the laser dot enlarges with distance), beam expanders are used to improve it. In general you do not care that much about output beam diameter on long range, more about divergence as you can assume that somewhere in near range the diameter of thinner beam due to divergence will become bigger than diameter of beam after beam expander was used.

More about beam expanders:
https://www.edmundoptics.com/resources/application-notes/lasers/beam-expanders/

Regarding wavelength - shorter wavelength scatter more on air molecules as well as various dust and other particles in air. Also human eye is sensitive differently to various wavelengths (violet and red ends of spectre do not seem as bright as blue-green part). That's why there are yellow street lamps used - good visibility and long enough wavelength to pass through fog.

And power - it is obvious I guess. More power -> more energy density on same spot area -> more bright.

So here you have a few examples how to approach the problem.

 

[Accutronitis]

Dang those Edmund optics beam expanders are expensive, But they are research grade !

 

[Radim]

Yes, of course. Still for hobbyist purposes you can get expanders around 100 bucks. Jet Lasers (unfortunatelly very small input lens - might crop wide beam, but adapter is very smart - position can be quite easily adjusted as well as with custom part of it you can fit more lasers), Dragon Lasers (just 2X currently, but awesome design - focussable and can be used as beam expander as well as beam reducer, with universal adapter you can use almost any laser with it), Sanwu (I've no experience with Sanwu so far)... just to name a few. Or you can made your own, if you can get some tube to fit it in, AR coated lenses and some calculations of optics positions and parameters.

I posted it mainly to show how they work as it is a really nice article explaining them.

 

[steve001]

Dang those Edmund optics beam expanders are expensive, But they are research grade !

They also sell low cost expanders.

 

[naruto]

Many factors do... I assume you want to have visible dot at some range. Here wavelength, power and beam specs are key factors. Depending on atmospheric conditions there might be various ranges as well. For visible dot of laser from your position also albedo of targeted object is influencing visibility (on white wall you get more visible dot than on dark green forest as it reflects better on white wall). For specifically beam specs divergence is crucial (how the laser dot enlarges with distance), beam expanders are used to improve it. In general you do not care that much about output beam diameter on long range, more about divergence as you can assume that somewhere in near range the diameter of thinner beam due to divergence will become bigger than diameter of beam after beam expander was used.

More about beam expanders:
https://www.edmundoptics.com/resources/application-notes/lasers/beam-expanders/

Regarding wavelength - shorter wavelength scatter more on air molecules as well as various dust and other particles in air. Also human eye is sensitive differently to various wavelengths (violet and red ends of spectre do not seem as bright as blue-green part). That's why there are yellow street lamps used - good visibility and long enough wavelength to pass through fog.

And power - it is obvious I guess. More power -> more energy density on same spot area -> more bright.

So here you have a few examples how to approach the problem.

So, as you said wavelength, power and beam specs are key factors, simultaneously, atmospheric conditions might be an important reason for the impact of the range. I noticed that you said a beam specs of beam divergence, and I also have read the article you sharing, to be honest, the article is a little difficult for me to understand, but I read it carefully, but also get some information. A beam expander will increase the input laser beam by a specific expansion power, it will also decrease the divergence by the same expansion power, resulting in a smaller collimated beam at a large distance. So increase the concentration, the higher the concentration of the less scattering, the farther the range.

Now I have a another question, is some laser pen focus function similar to beam expander? :thanks:

 

[Radim]

Basically some colimators work as beam expander we have discussed it here: http://laserpointerforums.com/f49/question-about-collimated-light-collimator-100899.html

But I guess you mean changing a dot size by "focus" - like beam expander power. That corresponds to zoom function known from camera lens - these beam expanders are much more complicated and I'm not aware of any cheap one. Also there exist focussable beam expanders, but the focus here is to change collimated (close to parallel) beam to be smaller at some point and converging to that point and diverging from that point (so it is not collimated anymore), but it won't change expansion - expander power or zoom if you like. So zoom is not focus. You might play with zoomable camera lens to get idea how it works - usually there are two rings - one for zoom and one for focus (there might be also aperture adjusting ring, but it is not relevant here).

 

[steve001]

So, as you said wavelength, power and beam specs are key factors, simultaneously, atmospheric conditions might be an important reason for the impact of the range. I noticed that you said a beam specs of beam divergence, and I also have read the article you sharing, to be honest, the article is a little difficult for me to understand, but I read it carefully, but also get some information. A beam expander will increase the input laser beam by a specific expansion power, it will also decrease the divergence by the same expansion power, resulting in a smaller collimated beam at a large distance. So increase the concentration, the higher the concentration of the less scattering, the farther the range.

Now I have a another question, is some laser pen focus function similar to beam expander? :thanks:

Beam expanders are refractive telescopes.

 

[Radim]

Beam expanders are refractive telescopes.

...used from oposite side. Where there is light coming out from telescope to your eye or to some imaging device, the laser enters it.

BTW cool stuff here done with beam expander or is it telescope? Whatever, you can see it as telescope to get an idea how it is used. Note that the beam is focussed to that target spot, not collimated.

 

[Benm]

With larger lenses you get get focal points far away, but not a narrow beam at infinite distance.

 

[naruto]

Basically some colimators work as beam expander we have discussed it here: http://laserpointerforums.com/f49/question-about-collimated-light-collimator-100899.html

But I guess you mean changing a dot size by "focus" - like beam expander power. That corresponds to zoom function known from camera lens - these beam expanders are much more complicated and I'm not aware of any cheap one. Also there exist focussable beam expanders, but the focus here is to change collimated (close to parallel) beam to be smaller at some point and converging to that point and diverging from that point (so it is not collimated anymore), but it won't change expansion - expander power or zoom if you like. So zoom is not focus. You might play with zoomable camera lens to get idea how it works - usually there are two rings - one for zoom and one for focus (there might be also aperture adjusting ring, but it is not relevant here).

Okay, I will seriously understand what you said and then study it. Thank you again for sharing! :beer: