Comparison of power against other users experiences

Hi,

Now I am the proud owner of a new pair of [font=Verdana, Arial, Helvetica]Barr & Stroud goggles I was ready to test the power of my new 100mw greenie using a green led - except I cannot find my dvm - it's been a long time since I did any home electronics work.

With the goggles I was confident in trying the pointer out by burning some things to see, in a relative manner, if it's weak or near the 100mw I bought.

I failed to light a match from about 1.5 inches after maybe 15 seconds - not too good I thought. Then I tried burning holes in a black bin bag from various distances. Here's the results:

2.0 ft - a small hole in less than 2 seconds
3.0 ft - a small hole in approx 3-5 seconds

adding a few seconds makes a larger hole. Until I can reliably measure the power output within a %5-10 or so margin, can other users advise what they believe the power output might be judging by the above? As per another thread of mine the label says <50mw, but the seller says this must be an error as the sales pictures show <500mw for a 100mw greenie - and another purchaser has confirmed his label shows <500mw for the same 100mw laser as sold.

btw - mid-day in a moderately lit room but a subdued area, I can see a feint thin green beam.

Thanks for any guidance on this.
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I'm not sure how much this willl help, but I'll try.

The problem is that even a <20mW green laser produces a beam that can be faintly seen even in a lit room. So this is not really a good way of telling the output.

I find that it takes about 70-80mW to start to be successful in lighting a match if the laser has a standard 1-1.5mm diameter beam(like most pointers do) and is well colimated. The match of course has to either be red, or the tip coloured black with a marker. This is not always an easy undertaking as depending on the match's composition itself, may or may not light.

Black bin bags won't give you a ballpark estimate either, I have a <20mW laser that runs stable at ~24mW. Unfortunatley it easily makes holes in bin bags.

Ok so the above might not sound good as far as helping, but there are certain things you can do to get a rough estimate.

Try cutting electrical tape with your laser. A 20mW wonlt be able to do this and a 50mW will hav trouble with it at best. If you can do it with relative ease then you can assume it's probably higher then 50mW.

If it can cut tape but can't light a match, you might estimate it to be somewhere between 50-70mW, etc.

Much of this also depends on the initial beam diameter and the divergence of the beam, though with most portable lasers it's roughly the same from unit to unit.

Hope this might be of some help.
cheers,

Thanks for that.

As to your suggestions for cutting black tape - at what distance from the tape would you say the laser should be held? I know very close up it has a great chance, but would you say 12, 24, or more inches away to better compare to other lasers?

I tried using the laser on black gaffa tape but it seemed to melt the black top colour and leave the white backing intact - kind of expected I guess - I do not seem to have black electrical tape to hand (I know I have some somewhere - typical, when you need it it's buried away somewhere).

Thanks again. I hoped to find my meter - but I will try and perform a check at work during a quite period with no one around (I'm in an engineering dept. anyway).

I'd try this at about 7 or 8 inches, cutting through the tape usually requires the beam to not be diverged to much. You will need to apply a bit of tension to the tape, as the clear glue can sometimes be a problem if it's thick enough.

Hi,

I used the green led method to test the power of the laser. I got a higher reading with the laser pointing at an angle to the led (with extraneous light blocked out). The reading ranged from 40-50ua at best - hence around a <20mw laser

I will try black tape next but from this I doubt it will do much. It was from laser-corp off ebay, and it the typical black body with gold clasp and ends (looks like the wicked and other pen lasers). Dissapointing results.

Don't be to disheartened! The LED test is not very accurate unless it's calibrated with a known output laser. The divisional factor of 2.8 is different with each LED you use(no two are the same, even if they are the same model number).

Hi,

I emailed the seller and he was nice about it - said he would replace or give my money back. As a last resort I tried a 4th set of new batteries - what a difference

With the other sets of supposedly new batteries (1.5x volts but possibly faulty with little current capability) I measured about 30-40ua max with the led and 1 minute held on black tape from 1 inch got nowhere.

A 4th set of different make 'aaa' batteries (all alkalines btw) and the laser sprang into life. Got few ua on the led close up but approx 140ua+ at an angle to the led and about 4 inches away. Two foot from the black tape and 2 seconds in the tape starts smoking and within 20 seconds going across the tape it's in two pieces

Things have suddenly perked up. Thanks for the help given above.

Common black plastic bin bags (garbage bags) are just 17.7µM (17,700nm) thick, so it wouldn't necessarily take a whole lot of laser power to cut through them. Just ~25mW ought to do the trick here if the beam has a Gaussian (TEM00) profile and exits the laser aperture at a reasonable size (1.0 to 1.5mm); which most lasers in pointer format easily accomplish. You really do need a laser power meter (specifically designed for measuring laser radiation) to obtain an accurate measurement.

At the time, plastic bin bags was the only thing I could affect Strange that black tape is easily burnt through if the roll is under more pressure than it's own weight - which is understandable, but it seems it's not really going to happen any time soon under it's own weight (small 3/4inch roll).

This time I tried a match again - something I had attempted on this same match with the poor performing batteries - then, nothing happened, ever - this time from 11 inches away albeit with a little wavering around on my part, the match started to smoke and caught fire within 8 seconds. So, 70mw+ it seems.

It was advertised as having a Sony DPSS 100 532nm diode with cooling cct (?) - which seems to me to say the ir part is 100mw itself - not much after conversion? Possibly this is in error (ebay). It looks like a WL extreme i.e black pen with gold - exactly the samelook but not from them. I wonder if it can be modded

Thanks again.

It has to be an error, a 100mW IR diode would never give 10mW of output let alone 70+mW If it is indeed 70mW or more, it probably has a 350-500mW diode inside.