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Ways to know how powerful a laser really is.

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Will

Mon Sept 07 2009, 01:21PM

Registered Member #57 Joined: Thu Feb 09 2006, 05:28AM
Location: San Diego, CA
Posts: 27

First, it should be stated that I know there is such a thing as a laser power meter, but it is out of my price range at this time.

I purchased one of these â€œ450mWâ€ laser modules on eBay: Here.

I liked the layout of it and its heat-sink-ability and obviously the stated power output wouldâ€™ve been awesome.

Now, in the past Iâ€™ve bought a 200mW laser pointer, which cost me 1/3 as much. Upon testing both units side-by-side I find that my laser pointer is as bright, or even BRIGHTER then this new module. With focusing, I also find that the 200mW burns things more readily as well. The seller was quick to say that the difference in wavelength would make a difference in burning things, but given that the pointer is 650nm and this module is stated to be 658nm I find such a claim preposterous.

So obviously this is very suspicious. I canâ€™t help but think that Iâ€™ve just bought a $140 DVD burner diode in a slick package.

It should also be noted that this module has an acrylic lens, the laser pointer has a true glass lens. Now Iâ€™m no laser expert, but can an acrylic lens even *handle* 450mW??

The other questions thusly are:

What methods could be used to test the relitive power output of the laser?

Have you, or anyone you know of, purchased one of these and found it to be bogus?

Do you know of any similar modules avalible(looking for shear brightness here ['laser show' project] not so much burning things and such like that)?

Any help would be much appreciated.
-Will

Steve Conner

Mon Sept 07 2009, 02:43PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

If you have a small solar cell, you could hook it up to a current meter, shine the lasers on it one at a time and compare the currents generated.

Looks like a DVD burner diode stuffed inside the case of a Dale wirewound resistor.

Proud Mary

Mon Sept 07 2009, 02:49PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Google: "bolometer"

...

Mon Sept 07 2009, 06:10PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Those modules are definitely a diode that was destined for a dvd-r drive (and there is about a 50% chance that it was salvaged from a drive) that has been stuffed inside a resistor case, and a cheep lens added.

As to measuring power, there are a few techniques that are available. The most accurate would be to send it to someone that has a real power meter for testing (I can do such things), but that involves mailing your laser.

The next best method would be to build this

which should give you a ballpark figure (is it 100mw or 400mw), but I wouldn't trust it to +/- 50% absolute or +/-10% relative (ie comparing your pointer to the module)

The final, least useful, method would be to use a silicon solar cell (or photodetector if no cells handy), and an attenuator (smoked plexiglass or other dark plastic would work well for this) to prevent from saturating the decector. Hook it up to an ammeter and see the current generated from each laser, you won't get an absolute value but you can get a relative value for the two lasers.

plazmatron

Mon Sept 07 2009, 06:47PM

Registered Member #1134 Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351

There is no way I would consider using an acrylic lens in anything over 15mW.
8nm would make no noticeable difference, in a lasers ability to burn things.

I you haven`t got photocells or solar cells, you can always spray paint the bulb of a thermometer black. Record the temp, aim your (know output) laser pointer at it for say 30 sec, record the temp again. Allow the thermometer to cool back to ambient, and try the same with this diode module..

Les

lpfthings

Tue Sept 08 2009, 06:13AM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

Wow, that description is unbelievably misleading! I am about 99% sure the diode used in that module was salvaged from some kind of DVD burner, but there is no way you could get 450mW from one for any amount of time. Even if it was 450mW, it'd still have a very, very hard time cutting wood!

I have built numerous laser modules with DVD diodes, and pushed them to the limits and none even came close to 450mW, maybe 300mW absolute max (Even with TEC cooling!) For that price I would recommend you try and get your money back, you can build a laser like that for less than $40 in parts!

For brightness, 635nm diodes would be the best, as the human eye is much more sensitive to it, than 650-660nm (This module). 635nm is pretty good for lasershow use, I've used it, and you can get 1-2W cmount 635nm diodes pretty cheap these days!

Will

Tue Sept 08 2009, 12:29PM

Registered Member #57 Joined: Thu Feb 09 2006, 05:28AM
Location: San Diego, CA
Posts: 27

Hey thanks a lot for the help guys. I'll keep all these methodologies in mind in the future of my laser endeavors. The seller of this item has offered a full refund, possibly a good indication that this product isnâ€™t near the advertised output. Iâ€™ll be sending it back, and looking into some 635nm diodes instead.

Thanks again.

Will

Thu Sept 10 2009, 03:58PM

Registered Member #57 Joined: Thu Feb 09 2006, 05:28AM
Location: San Diego, CA
Posts: 27

Update: I had this module tested at a metrology lab through my connections at Cubic and the results came back unsurprising. This module puts out 150mW maximum, 650nm.

Don't buy these, don't even think about it.

I haven't seen such blatant fraud since I was sold an 'adiaas' jacket in San Francisco. At least those scammers never told me that it was authentic.

c4r0

Mon Sept 21 2009, 05:38PM

Registered Member #151 Joined: Sun Feb 12 2006, 02:53PM
Location: Poland
Posts: 153

This is a laser module I made some time ago. It's a diode from 20x DVD-RW @ 600mA with acrylic lens collimator. As you can see it's 230mW.

EEYORE

Mon Oct 12 2009, 04:17PM

Registered Member #99 Joined: Thu Feb 09 2006, 06:10PM
Location: florida, usa
Posts: 637

I really do hope that you leave a negative (not a neutral) feedback for the seller. This has become a new trend on ebay with lasers. People just claim whatever they feel like claiming. Its very annoying. Do not let them continue screwing people over with their junk lasers stuffed into a resistor heatsink.

Matt

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