? Drive/Disc Wear

Hey,

I was wondering about DVD (and CD) wear. I looked around and found a bunch of people talking about how lasers can wear out, but none explained how or why. Can someone explain the science of “wearing out” a laser for me? Granted, I have not built a laser of my own—yet—but I have studied them starting many years ago and know quite well how they work, but cannot figure out how it could “wear out”, at least not in any practical, detectable way.

Also, what about discs? I know they degrade with time (which really, really sucks), but does playback hurt them too? I expect that excessive heat is bad for them, but is it okay to read a disc soon/immediately after burning it (like to verify the burn was good) or should you let the disc cool down/set first?

And what about the laser? Does repeated exposure to the laser cause a disc to degrade faster? For example, is it a bad idea to buy “previously enjoyed” movies from the video store? I know that video store tapes would wear out quite a bit, but what about video store DVDs?

Thanks a lot.

A laser or lasers come in a PUH, which is a complex thing.

So, you’re saying that it’s not the actual laser that wears out, but the mechanical assembly? That makes sense to me. The gears and springs and such could rust, get clogged with dust, the lubricant can get gummed up, etc. But the laser itself wearing out doesn’t make sense. I can understand CRTs “wearing out” in that the phosphors break down and lose their emissive capabilities over time, but I don’t recall ever having heard of gems losing their atomic excitability. It’s simple quantum physics, okay maybe not so simple. :stuck_out_tongue:

[B]Synetech:[/B]

From the information I have read, playback will not cause wear or degradation to media (both organic-dye based & pressed types) as the laser power used is low. The dyes in recordable media is sensitive primarily to the UV component of light, so avoid light exposure of media :slight_smile:

Video store DVDs primary issue is most likely to be physical damage from poor handling by customers/staff (scratches, etc). If the discs are physically ok, then it should not be an issue to get these.

The laser diode in DVD writers will wear out eventually but are capable of a very high number of write cycles (20,000+), the other mechanical components in modern writers are likely to fail before the diode will.

So leaving an RW around on a table during the day (or while a black light is on) is bad for them? Can they be fixed by re-burning? What about a laser pointer? I’ve got one that’s 1mW and another that’s 5mW; is that enough to damage the disc? (What are the powers of the read and write lasers?)

What is it exactly that wears out? I guess the question is what is the laser medium that is used in optical drives? Some can wear out, but there are others that don’t. What is used in drive lasers?

It is not the laser, because that is only modulated energy… it is everything around it, which is all kinds of material that can wear out and overused. :bigsmile:
Evern a tiny mis-calibration can give terrible or really bad results.

Thanks; that’s what I figured.

[B]Synetech:[/B]

Reading power can be at a constant output level upto 10mW depending on optical medium being read AFAIK. Writing laser power in modern DVD writers is ~200-250mW+.

These 2 links may help clarify the reasons for laser diode degradation.

http://stason.org/TULARC/pc/cd-recordable/5-27-Will-the-laser-in-my-drive-wear-out.html
http://www.bostonlaserinc.com/art1.php

A link with more facts about laser diodes than you may really have wanted to know :wink: :

http://www.repairfaq.org/sam/laserdio.htm

Thanks, that’s exactly what I was looking for (a normal search brings up mostly just people telling each other things they’ve heard rather than any formal explanations.)

That’s what I figured and wanted to confirm. When I first studied lasers, they were still using rubies which is why I could not understand wear out. I’m not sure what medium they use in drives today, but considering that prices are always dropping, I wouldn’t be surprised if it was something that does indeed wear out.

So, I guess that the fans I put right under my burner are a good idea. Also, I’ve started burning at 8x even when I can do 16x, but that was for quality purposes rather than laser wear. :slight_smile:

They use semiconductor laser diodes which are similar to LEDs.
There is some good info about laser diodes on Wikipedia:

Thanks for starting this thread. It answered a few questions
for me too.

Awesome, thanks.

I guess the moral of the story is that yes, technically they won’t last forever—then again nothing does—but very few of us will have to worry about that because other parts of the burner will fail long before the laser itself will. For all intents and purposes it will last more than long enough, unless it’s defective in which case it will likely fail very soon and you’ll just use the warranty to replace the whole drive. (Even then, most people upgrade to the latest thing long before the drive fails anyway.) So we can burn with impunity—legalities aside—and will need to worry more about the disc than the drive. Finally, to paraphrase some people “what are you saving it for?” There’s no point to getting something if you’re not going to use it right? :slight_smile:

Well, that’s what I’ve taken away from this discussion.