Diode Lasers - Q & A - Focusing, Lens, Cooling, Diodes, Safety, Parameters & others

Laser Cutting
22

That OSHA manual sure gave me a vintage fuzzy like those old instruction videos from the 60s I come across every once in a full moon but hey… At least it shed some light ( slaps thigh ) on the matter most notably:

Page 24:
Class 4 - eye hazard if direct, reflected or diffusely-reflected beam is viewed; possible skin and fire hazard
compared to the wording of:
Class 3a - eye hazard if collected or focused into eye

Pretty much confirms my suspicion towards the beam.

Page 32:
Diffuse-Reflection - Basically means unless I encapsulate the whole X-Carve in an opaque/450nm shield I will get blasted with Laser radiation no matter what - Not likely to happen.

I guess I’ll be adding the 450nm screen I’ve ordered to the poorly covered sides of the goggles and, for now, call it a day.

@JohnChamplain & @anon68752607 Asking the “wrong” question does appear to yield a more energetic discussion :wink:

2 Likes
23

The question would only have been wrong if it was left unasked :wink:

2 Likes
24

Because lasers produce a coherent and parallel beam, the biggest danger is reflections. With normal light reflected from a surface, the light reflected diffuses quickly, so it can be painful to look at, but probably isn’t harmful. Lasers are different: because there’s a chance that the reflected beam will be very coherent and mostly parallel, if it hits you in the eye, and passes through your cornea, the beam can be focused to a very fine spot on your retina, permanently damaging the spot they hit. (you can also have damage from the flash spot, like from welding)

This is why the FAA doesn’t want people shining high-power laser pointers at airplanes - you can actually cause permanent physical harm from that far away, and most people don’t understand that fundamental difference between a laser and a high powered flashlight.

The worst part about it is that because it’s focused to a tiny spot, you probably wouldn’t notice right away - your brain does a good job of masking the holes in your vision from your optic nerve, so you’d have to do a fair bit of damage before you’d realize it, but by then you’d be partially blind, and permanently so.

Short version: Not worth the risk, get proper safety gear. :slight_smile:

1 Like
25

Dear sir
i bought neje laser 20 w can you please tell me how to connect it to the xcontroller
please thank you

26

Hi Guys,

We have many questions connected with laser diodes and their power and also why we do not produce 7 or 8 single laser diode laser heads. There are a lot of different lasers on the market claimed to be 5,6,7,8, 10 15, or even 30 and 40W.

I would like to summarize it for you so you have the information from the first hand.

There are not many diodes on the market capable of outputting 6W of optical power. They have very similar specifications and all of them are rated as 5 - 6W as nominal optical power. It is possible to overdrive them and if they are well cooled they can withstand <7W.

The lifetime of the diode will be shortened by some amount depending on how much it is overdriven and how well cooled. These diodes were made to be used in projectors (mostly Casio and BenQ). Their nominal current (measured in the original device set to the full brightness) is 3,3A which results in around 5,5 - 6W of optical power. The lifetime is given as 20.000 hours BUT it means that after 20.000, half of the tested units will have a power degradation higher than 50% (including dead units). Usually, lifetime considered as good on engraving market is given as 5.000 - 10.000 hours.

The slope efficiency of this diode is a little bigger than 1W/A so to make it 7W or 8W you need to use a higher current. Changing output power by 1W is increasing the amount of heat generated by the laser diode by more than 30%!

As long as 7W may be acceptable assuming a shorter lifetime and hobby use, it is clearly powered out of spec.
8W and more is possible for a short time and will result in random failure of the laser diode. So basically 8-10W lasers may work… for a while. Short while.

If you decide to buy 5-7W laser heads from China always remember to check the current value. Of course, it is not a final confirmation but the current should be at least 3 - 3.5A.

At the same time all 15, 30, 40 W lasers are just misleadingly market to users. The value given by sellers is usually total electrical power or even a value which do not have much in common with the actual situation.

We purchased one of the 30W units to test it out. It was claimed to have a 4A working current that should correspond to around 6 - 7W of optical power depending on the lenses used. However, 4A was the maximum volume of the current (strong sawtooth) while the average current (during CW work) was around 3,7A. Assuming 5V working voltage of the laser diode and 85% efficiency of the driver Power = 3,7*5 / 0,85 = 21,7W of total electrical power. We can add 2-3W for the fan which was not the highest quality. The one we use has the power of around 6W, for example, and its cost is similar to the whole mechanical BOM of a Chinese unit.

Remember that when you are buying a 60W CO2 tube you get 60W of optical power, not 60W of total electric power needed to power the whole laser which results in 5W. People got used to this and they are not aware that companies take advantage of unaware customers. So remember about this and make good choices :wink:

1 Like
27

Very well written.

1 Like
28

Thank you for sharing this information very helpful.

1 Like