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When a lens is limited to 500MW/CM2 what does that mean?

Alaskan

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I'm looking at the rating of a beam expander and it's 500MW/CM2, what does that mean? 500 milliwatts per square centimeter? Dumb question to follow, how wide a spot is that in inches, if circular?
 
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diachi

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Re: When a lens is limited to 500mw / CM2 what does that mean?

Alaskan said:
I'm looking at the rating of a beam expander and it's 500mw CM2, what does that mean? 500 milliwatts per square centimeter? Dumb question to follow, how wide a spot is that in inches, if circular?
Click to expand...

That's 0.16 square inches, so about 0.23" radius or about 0.46" diameter.

Yes, it means the damage threshold for the optics is 500mW/cm^2
 
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Pi R Squared

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Re: When a lens is limited to 500mw / CM2 what does that mean?

Alaskan said:
I'm looking at the rating of a beam expander and it's 500mw CM2, what does that mean? 500 milliwatts per square centimeter? Dumb question to follow, how wide a spot is that in inches, if circular?
Click to expand...

Yes square centimeter, I can't think much about math right now but a centimeter is 0.393 inch, a square centimeter is 5/32 of a square inch, or 0.15625 of a square inch.

Alan
 
Cyparagon

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Re: When a lens is limited to 500mw / CM2 what does that mean?

That's a measure of power density. Power density goes up as the beam diameter goes down, or as the power goes up. Time to dust off your pre-algebra. To calculate:

power/area
power/(pi(diameter/2)²)
(set units: ) mW/(pi((mm/10)/2)²)
(Simplify: ) 400 * (power in mW) / (pi * (diameter in mm)²) = power density in mW/cm²

Or for a rectangular beam:
100 * (power in mW) / ((X diameter in mm) * (Y diameter in mm)) = power density in mW/cm²
 
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Alaskan

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Re: When a lens is limited to 500mw / CM2 what does that mean?

Looks like my 1000mw laser is far too powerful for the input, max at 2mm diameter beam is 15mw :(

Thank you for helping.
 
hakzaw1

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Re: When a lens is limited to 500mw / CM2 what does that mean?

I was reading about some 'pricey' BSCs( beam splitting or combining cubes)-- In a Group Buy(IIRC $35 each (so that was cheaper)) for combining high power blue lasers these were tested with 20W of power for a long period (called iirc 'baking') this was done to show the potentail buyers that the cube's coatings can take that kind of power.

2cm square is the standard for computing potential danger to the eyes & most consider (10 mW/2cm2) to be the highest safe power that is 'eyesafe' at the normal eye opening (7 mm) for the time we see the laser before the auto- blink/block or look away 'kicks in' (- as .25 seconds-)-- Search 'Laser MPE' for more info.

There are however other factors that need to be considered- example would be ...405 lasers (like a blacklight on crack) Its NOT 'seen' by our eyes as being 'bright' and thus the opening of the eye will be bigger than other colors that are seen as being as bright-

Bigger opening means bigger risk- and the "worst case'' is when a laser happens to enter the eye directly in the center of the eye- as the eye's 'lens' can magnify the power by as much as 100,000 times- sorta like a mag glass and the sun.

A 'fairly' good way to judge safety when you dont have much to work with- (Like a power meter) is this: after looking at the lasers close your eyes and look away ...when you open you will see 'after-images' just like you would after looking at the sun- IF these do not go away in a half minute or less- that indicates the light was quite bright and maybe dangerously bright. -- TO be sure - most keep laser beams horizontal and no lower than 3 meters from the highest point where people are- any beams going upwards from 3 M. are also NOT going to be a danger to the eyes.-- at NO time should most lasers ever hit people (ANYWHERE)unless they are wearing glasses for that color ( wavelength)

Of course there are many other factors- reflections from mirrors and glass are bad-
even just looking TOO long at the laser 'spot' on white or light colored surfaces.

AND.. with all the bad press lately about lasers and terrorists, most here ONLY use lasers outdoors at night if they are NOT around ANY people- and especailly 'NOT' airports.( stay 10 miles away)

Lasers (>5mW) are not totally 'legal' around unprotected people. If a complaint is made do not expect anyone to take your side on this.

check out the link in my sig below- read what happened to those arrested and read what they said about it..


hak


can you see this??
 
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Alaskan

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Re: When a lens is limited to 500mw / CM2 what does that mean?

hakzaw1

I followed your link, thanks, sobering situation. I left a remark on the page.

What do you all think about SpecialOptics use of "500 MW/cm2" - MW in caps is meant to be milliwatts, right? I thought it was supposed to be mW. I'm not sure if their use of MW doesn't mean something else, can't be megawatts for pulsed laser right? They call this a high laser power level rating.... Confused.

See: http://specialoptics.com/products/beam_exp_high_power.html
 
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hakzaw1

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Re: When a lens is limited to 500mw / CM2 what does that mean?

man that sure looks like a typo
500 MW?? does that even exist??

is this right? 500 MW = 500,000 mW

just sent them a Q about that- BBL with the reply-hak
 
Alaskan

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Re: When a lens is limited to 500mw / CM2 what does that mean?

Thanks, interested in knowing.

Here's a cut and paste from another thread ( http://laserpointerforums.com/f37/anyone-owning-pointer-larger-read-90838-8.html#post1355136 ) I didn't want to get off topic, so as to find someone who can comment, I'm pasting it as a quote here:

From what I'm finding, most IR laser diodes have a fairly wide aperture and terrible divergence, because of that I'm not really worried about harm being done to any pilots eye sight with them if they are a thousand feet away, but some of the low powered single mode diodes you won't find in a commercially marketed laser pointer, can have small diode apertures below 5um (micro, and not meaning beam width, the emitting side of the chip itself). If you let the beam expand and then collimate it at a much wider beam, the divergence can be incredibly small, much smaller than most of our laser pointers, far less than even the good ones. In that case, you might have an IR laser pointer with a divergence of .01 mRad or better with just a 100mm diameter lens. However, these single mode diodes have low output power, about 300mw at most. So, they can be very good pointers with an incredibly long "throw" without dissipating very much for a distance of a hundred or more miles. From that, I'd expect, if you targeted the ISS and they had a camera capable of detecting it, and you were skilled enough to get and keep the beam centered on them, I suspect it would be one of the brightest man made point sources of IR at specific wavelength from the earth, from their view. This is only if you expand the beam enough, I believe a six inch expansion from 5um ought to do it at 300mw. Of course, expanding 300mw of IR out to six inches would dilute it quite a bit, so much I doubt it would be very dangerous close in but don't hold me to that, I haven't done the calculations to see.

According to some graphs I've found, 1um is a good wavelength to use from the standpoint of atmospheric absorption. There are better wavelength windows than 1000nm, but for what I could find available in single mode laser diodes of that kind, that's the least expensive part of the IR band to build something which can do that at a few hundred mW of power output.

I've made some WAG assumptions here, one of them being how much IR at what bands are emitted from the earth, manmade or not. Also, I don't know how sensitive our solid state cameras are to 1um, maybe not enough to be making such statements. If anyone with some expertise in this area can comment, I'm interested in knowing. Hope I'm not full of bull with these ideas, this is something I'm trying to nail down but can't find all the info I need to do so. Maybe I will make another thread in order this one isn't taken off topic. I don't want that to happen to this laser safety thread, the info is too important.
Click to expand...
 
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Alaskan

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Re: When a lens is limited to 500mw / CM2 what does that mean?

I don't know what they mean by MW then, 500mW seems too small, 500 MW too large. Edit: I'm convinced the must be mega watt pulses of 10-20 nano seconds, why they don't give average power?

- - - - - - - - - - - - - - - - - - - - - - - - -

EDIT: This changes everything...

I found this rating for something on another web site:

500W/cm2 for CW Laser / 500MW/cm2 for pulsed laser @ 10ns
Click to expand...

OK, if the relationship between their product, and the beam expander I am interested in with the input power limit of 500MW/cm2 is the same for peak pulse to average or CW power, then I can safely input a bit over 15 and a half watts when the beam is 2mm wide. I only want to put one watt in, so I'm good to go.

Web site the above quote came from: http://www.photonik.com.sg/products..._Polarizers/Glan_Laser_Calcite_Polarizers.pdf

Power density calculator for dummies who hate using math: (that's me) http://www.ophiropt.com/laser-measu...ergy-meters/services/power-density-calculator
 
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