Divergence!

[Deleted member 8382]

I would like to know how divergence is calculated, what units are used on its measurement and what divergence values are acceptable for a normal laser.

Thanks!

 

[ElektroFreak]

Divergence is measured in mrad (milliradians). I'm unsure as to the exact equation, but here's an online divergence calculator:

http://www.pseudonomen.com/lasers/calculators/mRadCalculator.html

This is what I use to calculate divergence.

Usually the lower the number the better, but most people shoot for 1.4 mrad or less. It is common to see commercial lasers set at 1.1 mrad or less.

 

[Deleted member 8382]

I just love the way I get best answers almost instantly here.

Thanks ElektroFreak!!

 

[kendon]

imo this explains it quite good:

http://en.wikipedia.org/wiki/Mrad

basically it says that 1 rad means that if your beam would leave the lens with a diameter of 3 millimeter with 1 rad, it would be 3 millimeter plus 1 meter (=radius or distance) in diameter. since we are talking about m(illi)rad here just substitute meter with millimeter. so for this example the beam at 1 meter distance would be 3 millimeter plus 1 millimeter in diameter. that's 4 ;D

sry for my grammar, never got that if-clause thing right... :

 

[realista]

.....hello.... WHY there isn't any laser at 0.00 mrad? is it too difficult? TEORICALLY....every focusable laser could be at 00000 mrad... is it true? you could tell me" yes.... but i'ts a VERY DIFFICULT thing to do.. because changing 0.01 millimeters the rotatory adjustament.. the mrad could change A LOT".

i think..... if a laser is focused when is construpted.... could be focused at 0000 mrad......

another questiondemand... oh i don't know how i must say in the english languade qhen i want to ask somewhat...QUESTION..DEMAND. or REQUEST ?
a laser focused at near 00000 mrad... could reach a quite infinite distance? for eample.. a 100mw green laser at 00 mrad.. could reaches about 100 kilometres? maybe not.. because the light is absorbed by the Particle pollution.. but a 250 or higher power... should reach more of 100 kilometres...

i want a 0 mrad laser :

 

[ElektroFreak]

.....hello.... WHY there isn't any laser at 0.00 mrad? is it too difficult? TEORICALLY....every focusable laser could be at 00000 mrad... is it true? you could tell me" yes.... but i'ts a VERY DIFFICULT thing to do.. because changing 0.01 millimeters the rotatory adjustament.. the mrad could change A LOT".

i think..... if a laser is focused  when is construpted.... could be focused at 0000 mrad......

another questiondemand... oh i don't know how i must say in the english languade qhen i want to ask somewhat...QUESTION..DEMAND. or REQUEST ?
a laser focused at near 00000 mrad... could reach a quite infinite distance? for eample.. a 100mw green laser at 00 mrad.. could reaches about 100 kilometres? maybe not.. because the light is absorbed by the  Particle pollution.. but a 250 or higher power... should reach more of 100 kilometres...

i want a 0 mrad laser  :

The reason that there are no lasers with a divergence of 0 mrad is because ALL light diverges, laser light just diverges much, much less than regular incoherent light. It would be impossible to obtain a divergence of 0 mrad.

 

[realista]

WHY is it impossible? you must imagine a focusable laser. whtn you focus the point at about 5 meters...but for example the dilda red....moving the focus point to 20 metres...then 50 meters... then there is a point in wich the mrad is o !!! this is a difficult point to find... but for an istant.. the laser has 0 mrad. why no one can understand me XD ?

 

[ElektroFreak]

While I can't give you detailed hard math to prove it, (allthough someone else here might), everything I've read and been taught states that it is impossible to obtain 0mrad divergence (or perfectly identical beam width out to infinity). When calculating divergence, to have true 0mrad you would have to have all zeroes to an infinite number of decimal places. This is impossible. No matter what, there is always some divergence.  Also, what you are saying would have to be true for normal light as well as lasers, since the act of focusing any light requires passing a parallel point. If you could focus a flashlight even close to parallel to infinity, why would we even need lasers? A mathematically parallel perfect beam is not possible with coherent or incoherent light.

 

[Deleted member 8382]

I've been trying to measure the divergence on mine and i obtained 0.6mrad for a newwish laser. Is it posible or just me who is not making the good measurementes.

How to do them properly? I tested on 10 meters and found it was going from 1.5 at first to 7.5 at end, maybe I should use a longer distance?

 

[ElektroFreak]

I've been trying to measure the divergence on mine and i obtained 0.6mrad for a newwish laser. Is it posible or just me who is not making the good measurementes.

How to do them properly? I tested on 10 meters and found it was going from 1.5 at first to 7.5 at end, maybe I should use a longer distance?

First of all, .6mrad is quite possible. Just because it is a cheap laser doesn't mean that it can't have decent divergence specs.. If you are using the divergence calculator that I posted earlier in this thread, then the measurements should be accurate as long as you have accurately measured beam width and the distance from the laser.

 

[Deleted member 8382]

The fact is that I really dont know how to measure it. The max distance I can measure across at home is 10~ meters, I have some homemade security googles that help me to distinguish the real dot from the light around it, so is that exaclty wht I need to measure right?

I can't belive my so fucking cheap laser have a 0.6mrad divergence its a treasure then? xd

 

[ElektroFreak]

That's exactly how it's done! Your measurement should be accurate..

 

[Geneticz]

Lasers just cant be focused to 0 mrad.....just....not....possible. Just the way stuff works. Personally, I haven't tested the divergence on my X-25, mainly because I dont trust anyone with my laser :

 

[Deleted member 8382]

its really hilarious im hearing wicked lasers on divergence over 1mrad while my chinese cheap laser have half divergence than those lol