Old 10-01-2008, 04:10 AM #1
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Default So whats the verdict, open can or not?

i hear some people say that open can 803t is a bad idea. is it?

how many ppl run open?

and what kind of power increase did you get?


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Old 10-01-2008, 04:35 AM #2
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Default Re: So whats the verdict, open can or not?

The power increase is minimal.. I think 2mW at best. Opening the can does shorten the diode's life because of exposure to air..

The verdict so far is that it is not worth it, in the case of violet diodes anyhow..
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Old 10-01-2008, 06:19 PM #3
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Default Re: So whats the verdict, open can or not?

If the glass window is already broken, take the can off. It's already open to atmosphere anyway, and the loose glass could kill it.

It the window is still ok/intact, then just leave it in place and trust the engineers that made the thing.
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Old 10-01-2008, 06:30 PM #4
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Default Re: So whats the verdict, open can or not?

From what I understand, opening the can of the 405 subjects the crystal inside the LD to:


Hygroscopy is the ability of a substance to attract water molecules from the surrounding environment through either absorption or adsorption.

Hygroscopic substances include honey, glycerol, ethanol, methanol, concentrated sulfuric acid, methamphetamine, iodine[1], and concentrated sodium hydroxide (lye). Calcium chloride is so hygroscopic that it eventually dissolves in the water it absorbs: this property is called deliquescence (see below). Because of their affinity for atmospheric moisture, hygroscopic materials may need to be stored in sealed containers. When added to foods or other materials for the express purpose of maintaining moisture content, such substances are known as humectants.

Materials and compounds exhibit different hygroscopic properties, and this difference can lead to detrimental effects, such as stress concentration in composite materials. The amount a particular material or compound is affected by ambient moisture may be considered its coefficient of hygroscopic expansion (CHE) (also referred to as CME, coefficient of moisture expansion) or coefficient of hygroscopic contraction (CHC)—the difference between the two terms being a difference in sign convention and a difference in point of view as to whether the difference in moisture leads to contraction or expansion.

A common example where difference in this hygroscopic property can be seen is in a paperback book cover. Often, in a relatively moist environment, the book cover will curl away from the rest of the book. The unlaminated side of the cover absorbs more moisture than the laminated side and increases in area, causing a stress that curls the cover toward the laminated side. This is similar to the function of a bi-metallic strip. Inexpensive gauge-type hygrometers frequently seen domestically make use of this principle.

The similar-sounding but unrelated word hydroscopic is sometimes used in error for hygroscopic. A hydroscope is an optical device used for making observations deep under water.


And, are there any long term successes? :-/
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Old 10-01-2008, 11:40 PM #5
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Default Re: So whats the verdict, open can or not?

I don't think it's as much about hygroscopy as it is about oxidation of materials, and it's not really about the crystalline components of the LD itself, but instead about the facet coatings. *The facet coatings may oxidize and make them ineffective or lead to COD, and I suppose they may absorb some water (who knows what facet coatings a company used in making the diodes). *But the InGaN, AlGaN, and GaN are all pretty much inert. *You'd have to do some major-league reverse engineering to find out what's in the diode, what materials and structure they used in both the crystal growth and processing, and then a ton of major tests on those materials to see what effects exposure to atmosphere will generally have on them, but I'm going to guess that there's not a lot that's going to happen to the actual nitrides in the laser, but that the facet coatings MAY suffer from exposure.

But really, there's almost zero to gain, and there's a lot of risk (mess up the diode when removing the can, exposure to atmosphere, etc.). if the can is fine. *If the window is already broken, however, I think you're risking more to leave it on than to try to remove it and save the diode. *If the window is broken, it's already exposed to atmosphere, so go ahead and remove the can. *Otherwise, there's VERY little extra output power to be gained.

Anecdotally, the window broke out of a PHR diode that I have, so it has been exposed to atmosphere for about 2 months now, and I haven't noticed any degradation in performance.


ETA: Also, I doubt any companies so far have taken the time/energy/money to investigate if exposure to atmosphere will have long-term deleterious effects on the lasers, so I'd be willing to wager that them putting a pan on the diode instead of the open-can approach is from them taking the same "better safe than sorry" approach to the problem that I take, to just leave it unless it's broken anyway.
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Old 10-02-2008, 04:39 AM #6
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Default Re: So whats the verdict, open can or not?

If it aint broke, don't fix it. I've removed cans off of a LLOOOTT of diodes. The blu-rays do seem to die faster without the can -- but as a last resort to save a diode from a broken window, getting the can off is essential.

If anyone has a glass diode window that IS broken I'm sure they could convince a certain member of these forums, who happens to have the 130-dollar tool required to take the can off safely, to do it if they asked him REALLLLLY nicely. * ;D
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