What Expansion Ratio?

EpicHam · Jun 27, 2013

Sup folks!

I got a little question.
I see all these beam expanders with different expansion ratios , from 2x all the way to 10x.

I know that a wider beam diameter will mean a lower divergence which in other word decreases the fanning out at long distance.

However, this also mean that the beam's illuminance intensity would also be much lower right?
Since we are spreading the same power over a larger volume of dust.

So, what I want to ask is.
How do I know what expansion ratio I want for a specific wavelength , power, divergence ,blah blah blah.

Basically , what kinda expander do I want for a CNI PGL-III-C 532nm 500mW laser.
1.5mm beam diameter at aperture
Beam divergence <1.5mrad
TEM00

PS:
Would really appreciate it if there's an explanation for the decision too

Cheers

steve001 · Jun 27, 2013

EpicHam said:
Sup folks!

I got a little question.
I see all these beam expanders with different expansion ratios , from 2x all the way to 10x.

I know that a wider beam diameter will mean a lower divergence which in other word decreases the fanning out at long distance.

However, this also mean that the beam's illuminance intensity would also be much lower right?
Since we are spreading the same power over a larger volume of dust.

So, what I want to ask is.
How do I know what expansion ratio I want for a specific wavelength , power, divergence ,blah blah blah.

Basically , what kinda expander do I want for a CNI PGL-III-C 532nm 500mW laser.
1.5mm beam diameter at aperture
Beam divergence <1.5mrad
TEM00

PS:
Would really appreciate it if there's an explanation for the decision too
Cheers

There's not an explanation other than how much you want to decrease the divergence. It's your choice.

EpicHam · Jun 27, 2013

steve001 said:
There's not an explanation other than how much you want to decrease the divergence. It's your choice.

Well.... I can't really say by how much I want to decrease when I don't know precisely how does it affect my beam.

Lets say I want my 500mW 523nm to be highly diffraction limited collimated for at least 10km outwards.
While maintaining reasonable amount of intensity.

What would be appro for such an occasion then?

steve001 · Jun 27, 2013

EpicHam said:
Well.... I can't really say by how much I want to decrease when I don't know precisely how does it affect my beam.

Lets say I want my 500mW 523nm to be highly diffraction limited collimated for at least 10km outwards.
While maintaining reasonable amount of intensity.

What would be appro for such an occasion then?

There's no real answer because this "While maintaining reasonable amount of intensity." is too vague of a parameter.
This app may help you better visualize what you want.
Divergence matters - beam behavior over distance - Laserworld AG - show laser light effects for laser display and laser entertainment

EpicHam · Jun 28, 2013

Well we have formulas and numbers to reflect our observations and predict what will be the consequence of such an action.

But when I don't even have a reference of brightness , since I have only owned 1 laser before.

How do I even interpret what does that kind of number reflect in terms of observable changes irl??

steve001 · Jun 28, 2013

EpicHam said:
Well we have formulas and numbers to reflect our observations and predict what will be the consequence of such an action.

But when I don't even have a reference of brightness , since I have only owned 1 laser before.

How do I even interpret what does that kind of number reflect in terms of observable changes irl??

You heard of experimentation haven't you? Well, that's your only option right now. Spend some money and buy a beam expander.

BShanahan14rulz · Jun 28, 2013

it makes the beam bigger.

Also, this may be useful info
http://en.wikipedia.org/wiki/Inverse-square_law

Alessandros · Jun 28, 2013

EpicHam said:
Well we have formulas and numbers to reflect our observations and predict what will be the consequence of such an action.

But when I don't even have a reference of brightness , since I have only owned 1 laser before.

How do I even interpret what does that kind of number reflect in terms of observable changes irl??

Here's a good reference on brightness.
Rohanhill's Relative Perceived Brightness Calculator

Alessandros · Jun 28, 2013

EpicHam said:
Well we have formulas and numbers to reflect our observations and predict what will be the consequence of such an action.

But when I don't even have a reference of brightness , since I have only owned 1 laser before.

How do I even interpret what does that kind of number reflect in terms of observable changes irl??

Here's a good reference on brightness.

HTML:

http://rohanhill.com/tools/relativebrightness/

EpicHam · Jun 28, 2013

BShanahan14rulz said:
it makes the beam bigger.

Also, this may be useful info
http://en.wikipedia.org/wiki/Inverse-square_law

I know , I know.
But what I don't know is HOW MUCH bigger do I want?
Visualization is tough without on-site experience ...

Thats why I am posting this thread.

Cos I lack in experience , you got plenty.
From your experience , under those circumstances.
What expansion ratio do i want?

steve001 · Jun 28, 2013

EpicHam said:
I know , I know.
But what I don't know is HOW MUCH bigger do I want?
Visualization is tough without on-site experience ...

Thats why I am posting this thread.

Cos I lack in experience , you got plenty.
From your experience , under those circumstances.
What expansion ratio do i want?

WE don't know how much bigger, bigger is either. Do you understand it's personal preference.

AJ Pierson · Jul 1, 2013

Honestly, I would suggest you take the advice offered by steve001, and just buy an expander and gain some personal experience with it because so much of what you're asking depends on your OWN personal preference.

That said: I would suggest a common 10X expander. Why?...Because they're fairly common and not hard to find, and also because the 10X factor makes for very quick calculations and intuitive use.

I also suggest that you avoid the wicked laser expander. It was reviewed here, and they seem to be JUNK.

Be sure to find one with adjustable focus. There are also ZOOM expanders available (variable ratio), but they tend to be pricey.

BShanahan14rulz · Jul 1, 2013

I understand. You have a specific power density you are trying to achieve using a known source, the 0.5W, <1.5mRad @ 1.5mm aperture diameter laser, but only know that end power density by eyeballing it?

You can try expanding the beam with a lens and seeing what power density you are looking for. When it's the right density, measure the diameter of the spot and you should have at least a starting point for what you're looking to achieve.

Bionic-Badger · Jul 1, 2013

EpicHam said:
I know , I know.
But what I don't know is HOW MUCH bigger do I want?
Visualization is tough without on-site experience ...

Thats why I am posting this thread.

Cos I lack in experience , you got plenty.
From your experience , under those circumstances.
What expansion ratio do i want?

Why do you think we can help you work backwards from some unknown parameters? There aren't just tables around with some optimal point. If you have no idea what you even want there is no help for you.

You are going to have to decide on what you want as your final parameters, as in how bright you need the spot to be at the target distance, the size, you power budget, your monetary budget, etc. Then you have to provide the conditions your laser will be operating in, etc.

If you have no experience with what you want, then you should experiment and see what you need/want. Otherwise, you're just taking the word of someone who has no idea what you're really after. Try using a focusable laser of a known power and see how it looks at whatever distance you're thinking of.

What Expansion Ratio?

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