Green laser, weird Problem..

RedForest UK · Mar 25, 2010

I recently recieved the DX True 20mw green laser. It came on originally about half as bright as my 1mw ebay laser before dimming considerably more, i wasn't happy..

But here's the weird part, i played around with it for a while, with no effect. But then having left it for a while i started to notice every succesive time i turned it on it came on quite bright for slightly longer each time e.g. 1 second the first time before dimming, then 2 seconds etc. Anyway, the longer i left it the longer it came on for before dimming when i tested it.

Now, I'm no expert on lasers, but I had the idea that it might be working while cool before my hand warmed it up, this is now verified by me testing it outside in the cold where it performs much better than before. However still only roughly as bright as my 1mw laser.

The question is, seeing as I had thought that lasers were meant to perform poorly at low temperatures, why is does mine seem to do the exact opposite, and only work when it's cold?

EDIT: The light now seems also not to work when below a certain temperature as well and so has a pretty narrow window in which it will actually work, not simply when it is cold.

Thanks for any help.

HobbyLaser · Mar 26, 2010

That's weird - normally a green laser performs best at slightly ABOVE room temperature, and poorly in the cold. :thinking:

There are several possible reasons for temperature-based performance issues in a green laser. The first is the doubling crystal, the conversion efficiency of which can vary significantly, based on minor changes in temperature. But these typically like to run warm.

The second is the 808nm infrared pump laser diode (and how it interacts with the vanadate lasing crystal). The Neodymium-doped Yttrium Orthovanadate (aka "vanadate") solid-state lasing crystal typically used in a green DPSS laser has a VERY narrow absorption band at 808nm. A 808nm Infrared Laser Diode is used to pump (excite) this crystal, causing the crystal to lase.

But not all 808nm infrared laser diodes are the same. A poor-quality one may output at a wavelength a bit above or below the desired 808nm. If the pump diode's wavelength is too far away from the tight absorption band of the vanadate crystal, it will lase less efficiently - or not at all!

But the wavelength of a laser diode also varies by temperature. So the wavelength of a slightly out-of-tune laser diode can sometimes be "shifted" closer to the desired 808nm wavelength by altering it's temperature (making it hotter or colder). That could cause what you're seeing here - a green laser that works better when it's in a certain temperature range below room temperature.

Of course, the conversion efficiency of the doubling crystal could be reduced at colder temperatures as well, so such a laser would likely perform poorly even when cold!

Another possibility is an over-driven pump diode. If the pump diode current is set too high (an easy thing to do with these DX "True series" lasers, due to the very wide current range on the driver being used), this can cause the laser diode to run "hot", with the extra heat then causing it's wavelength to shift past the optimum 808nm, and again reducing the brightness of a green laser. This could also cause the delayed reset effect you mentioned, i.e. - an over-heated diode/module having more time to cool-off?

To get a better idea of what is going on with your laser, do the following -

1) With FRESH alkaline batteries, measure how much current the laser is drawing from the batteries, and report that back here.

2) Place the laser in one of the front pockets of a pair of jeans you are wearing at the time (positioning it so the lining of your pocket is not pressing down the "on" button) and stay indoors. Your natural body heat will warm-up and stabilize the temperature of the components inside of the laser. After a couple of hours or more, take the laser from your pocket and immediately turn it on, and notice how bright it is - has it gotten brighter, dimmer, or is it the same as before?

Once you have that information, post it here. :thumbsup:

I have a LOT of experience with those DX True series lasers (as well as the green modules they are based upon). Once we have more information, I can help you identify what is going on with your laser (and if possible, maybe even how to fix it!

)

So go try that out, then let us all know what you find out!

darkzero · Mar 26, 2010

I have this same problem with a "30mw" Romison green laserfrom DX. I have two of the same model, one does it, the other does not. When first turned on it doesn't seem that bright but will gradually get brighter after a few secs. Haven't done any testing to try and figure out why but it only does this when using a primary. If I use a li-ion I don't get this issue. I mainly use rechargeables so the issue doesn't bother me.

bshanahan14rulz · Mar 26, 2010

I have a cheap-o 30mW greenie as well. It is very picky. 2 AAA cells will last about 1 or 2 minutes before they've sagged too far to power the laser properly. A single Li-ion w/ diode seems to do the trick in my case, and in fact, I will be ordering a few of the new protected AAA's. Just wish they weren't *****fire...

I will say, that I've heard a lot of stories of a li-ion burning up the driver or overdriving the diode. Only reason I tried it was because this thing was headed for the trash anyways (after I bust it open for parts) and had only cost me about $15.

RedForest UK · Mar 26, 2010

Thanks for the in depth reply hobbylaser, this is why I love CPF!

I tried what you said and it makes the laser not really work at all, very very dim then cutting off almost immediately.

The laser was drawing 0.26A on 2 alkalines according to my DMM but with a very very low light output. Does that tell you anything?

gallagho · Apr 1, 2010

I have a tip. I had loads of problems with my DX laser, I even tried lithium cells, but it still was intermittent and took ages to 'warm up'

I fixed it by shoving a 'fibre glass pencil' used for cleaning circuit boards up the battery tube and scrubbing... hard.

Loads of brown material came out(Warning this also contains fibreglass dust, don't breath!) I did this until the end of the tube looked like clean metal.

My feeling is that as shipped the end of the inside of the battery tube that's supposed to be the +ve AAA contact is covered in coatings(& oxide?) from the manufacturing process, it even looked slightly brown before cleaning.

My laser now functions 100% more reliably :twothumbs

HobbyLaser · Apr 6, 2010

The laser was drawing 0.26A on 2 alkalines according to my DMM but with a very very low light output. Does that tell you anything?

Yes, it does.

I was hoping that either -

1) it wasn't getting enough current (which could explain the weak beam), or

2) it was getting too much and over-driving the diode (which could also cause this, for reasons explained in my prior post), as either of these are typically easy to fix.

Unfortunately, neither appears to be the case here, ~260ma is in the range you would expect for a DX True series 20mw.

I tried what you said and it makes the laser not really work at all, very very dim then cutting off almost immediately.

That (combined with your prior observations about temperature) confirms the likely worse-case cause of these problems - a poor quality "out-of-tune" 808nm IR pump laser diode.

Unfortunately, there's not much you can do about that. The wavelength a laser diode outputs is a result of manufacturing - it can't be "fixed".

And it's not really practical to replace the diode on a lower-power model either, as in the <=50mw modules, the laser diode is "press-fit" into the module!

DX True Series are usually pretty good for the price, but like anything Chinese, once in a while you get a bad one. That sounds like what happened to you.

You might want to try to "RMA" it, but if they require you ship it back to China, for something this inexpensive, it might not be worth the trouble.

Otherwise, if I were you, I would just get another one f/DX, either the True 5mw, or pony-up for the True 50.

Here's the "hot tip" why -

The True 5mw - 50mw all use the same module inside!

As a result, all of the True 5's I have seen tend to be better/brighter than a typical 5mw laser.

And if you spend the extra $ for a True 50, it will likely have one of the best modules from the lot inside (as the best of these modules get sold as 50's, lesser-quality ones can't put out the full 50, so they typically get sold-off as lower power units instead).

Either way, you'd be a LOT better off than what you've got now!

RedForest UK · Apr 7, 2010

Okay, thanks for helping me clear that up. I'll just put it down to luck of the draw when ordering cheap chinese electronics. DX offered to send me another one for a $2 fee so I've done that. Thanks for the tips as well, I'll be a bit more clued up next time I order one from DX.

bshanahan14rulz · Apr 7, 2010

RF, you aren't going to throw away the other one, are you?

RedForest UK · Apr 8, 2010

I dont know, I didnt really think about it.. Its just sat on my desk atm, are you asking as there could be some use for it or because throwing it away damages the environment or something?

bshanahan14rulz · Apr 8, 2010

Well, as long as it's dead, you can learn a lot by ripping one of those apart, plus perhaps you could use it as a host if you ever find a nice laser module.

Also, as long as it's broken and "trash" anyways, you don't have to worry about breaking it while you attempt to realign the ktp and yag.

I don't think it has any sizable amount of toxic hazards in it.

I confess, though, I was kind of hinting that if you were actually going to toss it in the garbage, perhaps toss it in a mailing envelope and send it my way. But it really IS interesting to see the guts of these greens. They are actually classical solid-state lasers like ruby lasers, only instead of using a flashtube to pump the crystal, it happens to use a laser diode.

HobbyLaser · Apr 9, 2010

Okay, thanks for helping me clear that up...
Thanks for the tips as well, I'll be a bit more clued up next time I order one from DX.

No problem, glad I could be of help!

DX offered to send me another one for a $2 fee so I've done that.

That sounds fair - are they just charging you for shipping?

BTW, I wouldn't throw it out - you can use it for practicing taking one of these apart, in case you ever have the desire or need to do some maintenance on your new laser (the first DX True I took apart, I ended-up TOTALLY mangling the case - MUCH better to get that experience on a broken one instead!

)

The module inside these guys is also pretty sweet to mess with - they have several brass pieces that just screw apart, letting you actually see how they work inside - you can see the crystals and everything! (Just don't power it up that way, as the IR those things put out inside can be dangerous!

)

Speaking of which, if that pump diode is simply out-of-tune and not totally fried, if you could figure-out a way to focus the virtually invisible IR beam, you could tear the crystals off the front and make a pretty sweet IR burning laser! Even if it's not the right frequency to make the green work right, the pump diode those use is still capable of putting-out 1/4 of a watt or more of IR laser light! :devil: (That's why green lasers eat batteries so quickly - it takes a LOT of IR to make just a little bit of green)

If you want to know how to take these apart, let me know - there's a trick to doing it!

BTW bshanahan14rulz, he doesn't live in the states, and that model is illegal to import here. Overseas shipping costs aside, his envelope might not even get past customs inspection, and it would be a shame to get into a beef with the feds over a defective laser!

Better to just get yourself a True 5 f/DX, they're only about $10 including shipping, and they use the same module that his does inside, so you could tune it up and get something much better!

bshanahan14rulz · Apr 10, 2010

True, wouldn't want to get us in trouble... Yeah, just do what HobbyLaser said. It's a great learning tool!

Did you know that unlike red, infrared, and bluray lasers, green lasers are Solid State Lasers? Same concept as a ruby laser except that another laser source is used as the pump instead of a flashtube. Greenies are amazing.

vitor · Jul 9, 2016

HobbyLaser said:
That's weird - normally a green laser performs best at slightly ABOVE room temperature, and poorly in the cold. :thinking:

There are several possible reasons for temperature-based performance issues in a green laser. The first is the doubling crystal, the conversion efficiency of which can vary significantly, based on minor changes in temperature. But these typically like to run warm.

The second is the 808nm infrared pump laser diode (and how it interacts with the vanadate lasing crystal). The Neodymium-doped Yttrium Orthovanadate (aka "vanadate") solid-state lasing crystal typically used in a green DPSS laser has a VERY narrow absorption band at 808nm. A 808nm Infrared Laser Diode is used to pump (excite) this crystal, causing the crystal to lase.

But not all 808nm infrared laser diodes are the same. A poor-quality one may output at a wavelength a bit above or below the desired 808nm. If the pump diode's wavelength is too far away from the tight absorption band of the vanadate crystal, it will lase less efficiently - or not at all!

But the wavelength of a laser diode also varies by temperature. So the wavelength of a slightly out-of-tune laser diode can sometimes be "shifted" closer to the desired 808nm wavelength by altering it's temperature (making it hotter or colder). That could cause what you're seeing here - a green laser that works better when it's in a certain temperature range below room temperature.

Of course, the conversion efficiency of the doubling crystal could be reduced at colder temperatures as well, so such a laser would likely perform poorly even when cold!

Another possibility is an over-driven pump diode. If the pump diode current is set too high (an easy thing to do with these DX "True series" lasers, due to the very wide current range on the driver being used), this can cause the laser diode to run "hot", with the extra heat then causing it's wavelength to shift past the optimum 808nm, and again reducing the brightness of a green laser. This could also cause the delayed reset effect you mentioned, i.e. - an over-heated diode/module having more time to cool-off?

To get a better idea of what is going on with your laser, do the following -

1) With FRESH alkaline batteries, measure how much current the laser is drawing from the batteries, and report that back here.

2) Place the laser in one of the front pockets of a pair of jeans you are wearing at the time (positioning it so the lining of your pocket is not pressing down the "on" button) and stay indoors. Your natural body heat will warm-up and stabilize the temperature of the components inside of the laser. After a couple of hours or more, take the laser from your pocket and immediately turn it on, and notice how bright it is - has it gotten brighter, dimmer, or is it the same as before?

Once you have that information, post it here. :thumbsup:

I have a LOT of experience with those DX True series lasers (as well as the green modules they are based upon). Once we have more information, I can help you identify what is going on with your laser (and if possible, maybe even how to fix it! )

So go try that out, then let us all know what you find out!

Helllo!
So i have a green laser 532nm with a li-ion battery 18650 , i think it's that problem wiht the temperature , because after 1 or 2 sec laser power is not the same, and i can't see that green awesome line... What i can do for change that? For fix that problem and use the full power to see the line.... Sorry for the bad English !

Green laser, weird Problem..

RedForest UK

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HobbyLaser

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darkzero

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bshanahan14rulz

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RedForest UK

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RedForest UK

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