Spreading beams and power

I was wondering if there are a formula (or more than one) to calculate the exact amount of power of a beam that is spread in circle.
For example i make a "tunnel" with a rotating mirror with a 100Mw green laser. How can i calculate the power of a single spot on the projected circle?
Or a single spot if i make a line beam?
I think know it would be very useful about safety especially in laser shows.

Mille said:

I was wondering if there are a formula (or more than one) to calculate the exact amount of power of a beam that is spread in circle.
For example i make a "tunnel" with a rotating mirror with a 100Mw green laser. How can i calculate the power of a single spot on the projected circle?
Or a single spot if i make a line beam?
I think know it would be very useful about safety especially in laser shows.

Click to expand...

When making "tunnels" or simply scanning multiple "stops," or waving the beam back and forth to create a "line", you are NOT SPLITTING the beam. You are simply moving it around. It retains the full power at any point in the shape.

Peace,
dave

Ok, if the beam is currently reflected around (in tunnel) it will stop in the same spot less time than a "single still" beam, right?
So the power in that spot gotta be less, or im wrong?

yep... the beam keeps full power unless its being modulated. which wouldnt be the case unless its in a projector

Mille said:

Ok, if the beam is currently reflected around (in tunnel) it will stop in the same spot less time than a "single still" beam, right?
So the power in that spot gotta be less, or im wrong?

Click to expand...

no the beam will have the same power through the whole tunnel..

you gotta think if you move the laser in a circle or anywhere every spot that it hits will have been at the same power as before. but since it is moving it wont have to to say burn or heat up the spot because its only getting that full power for a small amount of time.

Yes i was talking about average power, like W/s or something similar.
Is average or instant power that count in laser safety?
And coming back to first question: is there some formula to calculate the average power of a single spot in a circle or line?

Power is always energy per time, J/s, aka W.  If it's moving, you get less energy into one spot because of the shorter time, but the power (energy per time) will still be the same.  What you're looking for is energy.  

As far as safety, it's both.  It's how much energy you put into a spot on your eye.  The energy input is what damages cells.  But with higher powered lasers, the time it's on a spot on your eye may be very short, but the energy imparted could still very easily be enough to hurt your eye.

As far as average power vs. peak instantaneous power:  The peak instantaneous power will the the power of the laser.  The average power will be the fraction of the time the laser spends on that spot multiplied by the power of the laser.  Say: 100mW laser spends 1% of the time on a particular spot, average power is 1mw.  But, peak instantaneous power is still 100mW, and that is still very damaging.  For what you're asking, I think you should be more worried about the peak instantaneous than the average over time, because that peak can do damage where that average over time may not.

For example, let's say I use a 250mW laser for one minute a day.  Over the course of a day, that's .06% of the day.  That means the average laser power over the day would be .17mW.  That average power, while still low enough to look safe, doesn't imply that using the laser for only one minute a day is still safe because the average is lower, especially since a 250mW can do damage in a shorter time than the blink of an eye.  The peak instantaneous power of the laser would do damage, even though the average power is very low.

At least I think it answers the question you are asking. Every situation is different though. You're asking about short flashes of a higher-powered laser. Another situation may be about very long exposures to dim laser light, like 5mW constantly all day in a lab, and that would call for a different evaluation of what to check for. But this stuff has all been looked at, there are standards/guidelines to go by for safety glasses for what is good enough for short flashes of light, and what is good enough for all-day exposure to laser light. FrothyChimp could contribute a lot more about such things.

So, how expert people in laser show can calculate if a combination of fat beams scanning the audience can be dangerous or not?
This is my final point
There are restrictions in law about scanning audience, but how can be sure to be under the threshold?

Mille said:

So, how expert people in laser show can calculate if a combination of fat beams scanning the audience can be dangerous or not?
This is my final point
There are restrictions in law about scanning audience, but how can be sure to be under the threshold?

Click to expand...

looky here free software http://www.laservisuals.com/sglite.htm

software itself will not make you know how safe it can be.. you need a lot of practice and a lot of knowledge! audience scanning is not an easy thing to make safe... but here are a few links


http://www.pangolin.com/resguide09a.htm

http://www.pangolin.com/resguide09b.htm

Yes yes i know.
I don't really look to do scanning audience, im just curious about safety systems.
Is better to know about it that don't