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Hi all. Confused noob :)

Khorask

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Hi all.. stumbled across a few laser articles which eventually led me here in search of answers so thought Id say hi. Ive been researching lasers for a day or two but one thing still eludes me and I'm sure the answer is quite simple.

I've looked at various types of lasers and their specs and cant seem to figure out what affects the 'maximum distance' ?

Below is a kind of a 'tale' of what ive done trying to figure it all out.. and will probably make most people laugh at my lack of knowledge and or education, so if you can answer the question above no need to read the following ;) thanks.

--

A laser ive seen is the 1W S3 Krypton which has a massive max distance of around 136kms. I then compared this to the 300mw version which has a max distance of around 41km. So I figured it must be proportional or atleast related to its power. Then I compared it to another model, the S3 Artic (also 1W).

Though this is where my confusion begins, it has an equal max power than the Krypton yet only a max range of 6.8kms.

So then I thought, the wavelength must also have an influence on the max distance. So looked at other lasers, in particular the E3 Series. First I noticed the wavelengths (405 nm, 532 nm, 650 nm) = beam distance (745 meters 16474 meters 8616 meters) so as far as I could tell increasing or decreasing the wavelength didnt equate to a larger or smaller distance.

Then second, I noticed the 300mW 532 nw model had (obviously) the same wavelength and max power as the S3 Krypton. Yet the Kryptons max distance was 41kms and the e3 was 16.4kms ?

So as far as I could tell theres something other than the wavelength and max power that contribute to the max distance.. Ive looked at the other tech specs of these devices and cant figure out what makes one 1W laser shine over twice the distance of another seemingly identical one ?
 

lasersbee

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to the Forum....
Don't forget to read the FAQs...the Stickies
and the Forum Rules..

If you plan on buying anything on the Forum....
PLEASE read this first...

6 Steps To Prevent You From Getting Scammed

and this....

37 Reasons NOT to Buy From Wicked Lasers

If you do get a Laser or already have one be sure
to get appropriate Laser Safety Goggles/Glasses...

BTW... Max distance is subjective and basically useless...
It depends on the power and divergence of a Laser
and any particles in the air that reflect and or absorb
the beam...

Enjoy your stay...


Jerry
 
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Khorask

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BTW... Max distance is subjective an basically useless...
It depends on the power and divergence of a Laser
and any particles in the air that reflect and or absorb
the beam...
Jerry
Thanks.. am more interested in how they work than ever buying, making one etc (maybe in the far future).. but just had a read on beam divergence on Wikipedia and it all makes sense..

Just wish they included it in all those 'intro to laser'/'how lasers work' youtube vids I watched.

Anyway thanks
 
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Wicked lasers use marketing techniques to sell you their product and make you think you are getting the "worlds best".

Don't listen to what they tell you.

If you are interested in learning about beam distance.. Try reading Sam's FAQ.

Sam's Laser FAQ: Welcome Page
 

rhd

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"Max distance" is a garbage marketing term in my opinion. It's not a "spec" and should never be listed as one. I suspect this may be why none of the "intro to lasers" videos you watched discussed it.

The max distance a laser can go has no limit. The photons don't just "stop" and fall out of the air, land on the payment, and sit there until they eventually wash away with the rain. What stops everyone from saying "oh ya, these lasers go forever" are non-intrinsic (to the laser) factors. For example the atmosphere absorbs photons, and eventually there won't be any left. Or, the beam gets so wide that its density is low, and you can no longer discern a defined dot, so you think the beam is "gone". Some might argue that this is a real "laser characteristic", but even this factor is really just about how well your eyes/brain can discern a wide beam that is still there. Fire a laser at the moon, and sensitive equipment still registers the returning photos. Finally, if you're viewing a far-away dot, and you're located at the transmission point, then you're getting "double atmosphere tax" in the sense that the return-trip of the light will also be subject to atmospheric absorption as it travels back to your eyes.

In other words, everything that impacts "distance" is external to the laser. Different powers/beams/wavelengths will fair differently, but it's fundamentally stupid to list a "max distance" when advertising a laser because it's not a quantifiable figure. It's a meaningless number that appeals to idiots, and these laser re-sellers know it. It's sleazy marketing.
 
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Khorask

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In other words, everything that impacts "distance" is external to the laser. Different powers/beams/wavelengths will fair differently, but it's fundamentally stupid to list a "max distance" when advertising a laser because it's not a quantifiable figure. It's a meaningless number that appeals to idiots
After spending the night reading about divergence, gaussian beams and a lot of stuff I probably missed out by never doing physics in high school... I agree with ya.. but still have one or two more questions.. then I promise u ill shut up ;)

When it comes to these sleeze bags and their listings of 'max distances' I took one more look while reading about divergence earlier when trying to compare a few values and still couldnt understand the large discrepancy in 'max range' between two seemingly similar products.

product a) 1W, 532nm, divergence 1.5mRad, beam diameter 2.0 mm - 136km
product b) 1W, 445nm, divergence 1.5mRad, beam diameter 5.0 mm - 6.8km

So, they both have the same divergence
product a) at its 'advertised max distance' will have a calculated beam width of 204 Meters wide !! (expands 1.5mm per meter) yet still produce 0.25 Lux of light ??
product b) will have a beam width of 10.2890m

I know this 'spec' is somewhat of a gimmick but it must have been measured at least somewhat ? So my questions are..

1) When calculating the beam width at the advertised 'max distance', product 'b' has a much more narrow beam width. Considering both products are 1W, doesnt this indicate a more concentrated and brighter beam of light ? yet it is advertised this is the maximum distance at which the laser will produce 0.25 Lux of light?

2) Given that the divergence is the same for both products, why is product 'a' advertised as being capable of 'seeing' so much further ? (I can see why the beam width would be important over small distances, but over, eg. 136km.. an initial beam width of 2mm compared with 5mm with a divergence of 1.5mRad means nothing at this 'max distance')
 

rhd

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I know this 'spec' is somewhat of a gimmick but it must have been measured at least somewhat ? So my questions are..
You have your answer. These "specs" aren't specs. They're gimmicks.

Why are you expecting to find logical consistency in measurements that are themselves illogical to list?

You know it's BS because they're only listing one divergence figure for the 445. Either they've got some fantastic cylindrical lens or prism-based axis correction going on inside that host, or they pulled that number out of their arses ;)
 
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I agree. In most Chinese laser companies lying about their products is a standard. Very few companies give you actual data. There is no, (or non enforceable) regulation when it comes to marketing. IE They can say what ever they want, even if its a complete lie. Wicked Lasers is the king of the hill in this respect. You can buy on-spec lasers, but they usually cost much more money, because of quality control, and testing.

So dont always believe what you read in the world of lasers. You made a good move coming here, because members here have been through it all, and help others (like you) to save money, and not get ripped off.
 

Khorask

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You have your answer. These "specs" aren't specs. They're gimmicks.

Why are you expecting to find logical consistency in measurements that are themselves illogical to list?

You know it's BS because they're only listing one divergence figure for the 445. Either they've got some fantastic cylindrical lens or prism-based axis correction going on inside that host, or they pulled that number out of their arses ;)
heh ok.. ill give up :)
 

Josh K

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I'm not sure if you have read the "37 reasons not to buy from Wicked Lasers", but I do think that would clear some things up for you. They seem to have pretty bad business practices in general, so taking any of their specs seriously is hard for a lot of people around here. For instance, the S3 krypton 1w is rated at 1w right? Well I have read quite a few reviews on it here and when they put it on the LPM it's usually only coming in around 760mw (or so). Not that every one will be that same spec, but just most of them are severely underspec.

So that leads me to the distance question. I was just reading up on similar stuff yesterday. Try advanced search up top with the keyword "distance" or "divergence" as the key word in the title and it will bring up some good material. So like everyone was saying so far, the distance spec they list is pretty much useless and a marketing tactic to get people to buy it who are unfamiliar with lasers. The beam diameter at that distance is so wide that it IF they even did any tests and didn't make these numbers up randomly, that they probably used very sensitive equipment to capture a photon or two.

Also, again I have read this somewhere yesterday but to measure something like that, the earth has a curve to it, so don't quote me on this but I believe the figures were to measure 200 miles each person would have to be in a 500 foot high tower just to make up for the earths curve to get a completely straight line to each other. Not very relevant, but interesting and sounds like way more than WL is going to even attempt.

Good luck with your research and be careful with WL if you ever decide to purchase from them.
 

TomD

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-snipped-
Also, again I have read this somewhere yesterday but to measure something like that, the earth has a curve to it, so don't quote me on this but I believe the figures were to measure 200 miles each person would have to be in a 500 foot high tower just to make up for the earths curve to get a completely straight line to each other. Not very relevant, but interesting and sounds like way more than WL is going to even attempt.

-snipped-
This point also popped up while I was initially reading this thread. Maybe the MythB guys can do an experiment about this.

1) When calculating the beam width at the advertised 'max distance', product 'b' has a much more narrow beam width. Considering both products are 1W, doesnt this indicate a more concentrated and brighter beam of light ? yet it is advertised this is the maximum distance at which the laser will produce 0.25 Lux of light?

2) Given that the divergence is the same for both products, why is product 'a' advertised as being capable of 'seeing' so much further ? (I can see why the beam width would be important over small distances, but over, eg. 136km.. an initial beam width of 2mm compared with 5mm with a divergence of 1.5mRad means nothing at this 'max distance')
I assume you did your reading but assuming the specs are legit and the atmospheric conditions are perfect (smoke and cloud-free, moonless evening) XD, product "b" does not have a narrower beam width at the "max distance" because there is no longer a beam to speak of at that point--it's just no longer visible/discernible. Product "b" starts out with a wider beam diameter and fundamentally at a less visible wavelength so the difference in "max distance" is understandable. Viewing product "a" from the "max distance" of product "b" (6.8km), one should still be able to see some form of coherent green.
 
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grainde

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As TomD said green is more visible than blue ie your eyes are much more sensitive to it and blue also is scattered more by the atmosphere. These combined will help to reduce the perceived distance and visibility of the blue, wrt to the green. :beer:
 




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