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Invisible laser radiation in DVD drives?

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SEPEHR100

New Member
Recently, I opened up a DVD writer drive for curiosity to see its insides and mechanisms. While the drive casing was open, I plugged SATA power and signal cables to it to see it in action (opening and closing the tray while the laser/lens unit is trying to check if a valid disk is inserted or the first few seconds that the lens unit moves on the rail with the spindle spinning). Although I knew the visible laser beam is bad for the eyes if viewed directly, but I didn't know anything about "Invisible laser radiation". Sounds like they use not just on laser diode in the drives.

Now besides a little worry about if I damaged my eyes (though I never looked at the lens and laser, just viewed it from the rear), I wonder where does the invisible beam come from and what's the purpose of it? Do they come from those rounded rectangular holes that I depicted in the album below? What are they?

I looked for any IR beams with the use of my phone camera, but I couldn't find anything. o_O
 

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jpanhalt

Well-Known Member
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Probably no danger. The device is clearly labeled "Class 1". Here's Wikipedia's definition:
Wikipedia said:
CLASS 1 LASER PRODUCT

A Class 1 laser is safe under all conditions of normal use. This means the maximum permissible exposure (MPE) cannot be exceeded when viewing a laser with the naked eye or with the aid of typical magnifying optics (e.g. telescope or microscope). To verify compliance, the standard specifies the aperture and distance corresponding to the naked eye, a typical telescope viewing a collimated beam, and a typical microscope viewing a divergent beam. It is important to realize that certain lasers classified as Class 1 may still pose a hazard when viewed with a telescope or microscope of sufficiently large aperture. For example, a high-power laser with a very large collimated beam or very highly divergent beam may be classified as Class 1 if the power that passes through the apertures defined in the standard is less than the AEL for Class 1; however, an unsafe power level may be collected by a magnifying optic with larger aperture.
As for the invisible part, it could be some IR tracking diode. Apparently, 780 nm was used in the past according to several source. Now they seem to be 650 nm (red) or 405 nm (near UV).

John
 

SEPEHR100

New Member
Probably no danger. The device is clearly labeled "Class 1". Here's Wikipedia's definition:


As for the invisible part, it could be some IR tracking diode. Apparently, 780 nm was used in the past according to several source. Now they seem to be 650 nm (red) or 405 nm (near UV).

John
Yes, but on the right side, it is written "CAUTION VISIBLE AND INVISIBLE LASER RADIATION, CLASS 3B LASER RADIATION WHEN OPEN."

Where's that IR diode and what are those holes that I used two red arrows pointing to them in picture #2?
 

Externet

Active Member
All laser radiation is emitted at the bluish lens centered in picture 1. Those holes at picture 2 should be the prismatic mirrors. The radiation usually is emitted when there is a disc inserted for reading it or in higher power, for recording onto it. The laser diode is the one in picture 3 connected to pads labeled CD/GND/DVD.
If you do not know enough, stay away from tinkering with it.
 

SEPEHR100

New Member
All laser radiation is emitted at the bluish lens centered in picture 1. Those holes at picture 2 should be the prismatic mirrors. The radiation usually is emitted when there is a disc inserted for reading it or in higher power, for recording onto it. The laser diode is the one in picture 3 connected to pads labeled CD/GND/DVD.
What was the need to make holes for those mirrors?
I'm also curious to know what's the 5th picture? It belongs to the chip in picture #4. Is it some kind of heat anticipator?

If you do not know enough, stay away from tinkering with it.
Where can I find some useful information on them?
 

Externet

Active Member
Picture 5 is the belly of IC in picture 4 ; it could provide heat dissipation when certain application needs it by attaching a heat sink surface there.
 

dr pepper

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If there was a Cd in then it would have offered some protection to direct exposure.
Even then unless the Cd was recording the read laser operates at lower power, as mentioned its a class 1 device, the record laser on the other hand on some drives can and by some people is modified to burn.
Dont do that again though.
I've never had eye laser exposure however they say initially its like welding flash at first which feels like sand in your eyes.
 

jpanhalt

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I think the "welding flash" you are referring to is primarily corneal burn, hence the sand in eye feeling. Retinal burns are painless.
 

dr pepper

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Aha, I'm not medical, the sound of that is just as bad even if it doesnt hurt.
 

GromTag

Active Member
It literally feels like a grain of something is between the eye and eyelid, physically when severe. (welding mask malfunction) It does only take a moment with more powerful emitters regarding to lasers.

Been hit in the face by a 500mA green laser by a kid during a night walk, felt like I took in chlorinated water from a swimming pool in my nose and with the right eye watering, kid laughed and said something.. don't know what he said, was too busy trying to see with some discomfort to light the fuse on the firework stars that I carried then, he no laugh no more, he scream! He loss the laser tho.
 

Pommie

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I thought arc-eye (welding flash) was the eyeball getting sunburnt. I occasionally forget (getting better at remembering) to wear a glove when welding and my hand gets sunburnt after just 5 mins.
 

GromTag

Active Member
If going to be interested in lasers more than often, laser glasses would help prevent damage, color based on laser requirement by the glasses lense type, visible, invisible, and fiber optic.

welding flash is an intense emission that burns before react pertaining to our eyes, oddly many tend to focus more intently when welding causing headaches even with a good mask, I'll take my goggles any day over an electric mask that can conk out when ever even with new batteries due to the set sensor having a humidity fit malfunction and the setting being lost resulting in surprise camera flash effect.

The term is, pasting the definition as it states better,
retina, It is the second part of your eye, after the cornea, that helps to focus light and images on your retina. Because the lens is flexible and elastic, it can change its curved shape to focus on objects and people that are either nearby or at a distance.

Thus with the issues some have when intensely focused on welding work. (they let more light in)
: Edited : Thus with the focus and possible exposure to the arc flash, the results will be worse at that point, kind of a combination right hook with an upper cut.

Sun burns,
Heat emission is as of the intensity of the voltage smelting alloy, wire, steel, copper, zinc, aluminum, palladium, so on.

Hmm, the term radiation would fit more metaphorically than literal.
 
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unclejed613

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back when they had bar code scanners built-in to the checkout lane, if you stood in the wrong place while they scanned your food, you got an eyeful... fortunately the beam was in motion, but it did make you see green spots for a while...

many newer players will turn the laser off if there's no disk
 

Nigel Goodwin

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back when they had bar code scanners built-in to the checkout lane, if you stood in the wrong place while they scanned your food, you got an eyeful... fortunately the beam was in motion, but it did make you see green spots for a while...

many newer players will turn the laser off if there's no disk
As far as I'm aware ALL players have always done that, even back to the very first CD players.

The very first CD Players used some kind of 'detector' (such as an LED and photo-transistor) to detect the presence of a disc, and only then turn the laser ON.

However, it didn't take long for them to realise you could simply use the laser to detect the disc - so the disc is inserted, the laser is turned ON, and attempts to read the disc - is it can't read it, then it decides there's no disc, and displays that on the front. It also obviously turns the laser OFF again.

For servicing purposes, to see if the laser is working, you close the draw with no disc, you see the laser come ON, and the lens move up and down, trying to focus on the disc. You've got a couple of seconds before it turns OFF again.

All DVD Players, and all CD Players (except the very first) work in this way.

I'm a bit confused about "back when they had bar code scanners built-in to the checkout lane", they still do here - what else do they use there?.
 
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