Questions about 638nm

[Lethere Belight]

Just got a 300mw 638. (With power cert showing 290mw and I measure 275 so its putting out close).
Just wanted something reddish, inexpensive with some power.
Adding to the collection.
Any way, it is focusable but will not focus to a "dot". I get a bar/rectangle. About 1" at 10 feet.
VERY bright with dim bars on each side.
Also came with a "star burst effect" attatchment that I didn't care about. Even all the "stars" are not dots but also rectangles.(this is a separate cap that unscrews) If I shine a 200 green throught this cap it does make dots.
I also used the lens assembly from another host and get the same results.
Is this wave length like some blues that won't make a dot?
Also this has virtually ZERO heat. Won't light a match. I can hold it right up against my hand/arm and feel nothing.

 

[RA_pierce]

Do some searching and reading.

The shape of the beam is determined by the diode. It is called a "multimode" diode.
There are different ways a diode can be multimode but long story short, it's normal for this type of diode.

Also, red lasers don't produce much heat when shone on skin because most of the light is transmitted through it or reflected.
In order to produce heat the light must be absorbed.
Try a dark object like a black balloon. Coloring the match tip black with a marker may help, too. You can try making a mark on your skin as well, and then applying the laser... and tell us what happens.

Also, the laser will be much more intense when it is focused. That way all the light is concentrated on a small point. Putting a dark object in the point of convergence should produce some smoke. 275mW is a good amount of power. Not a ton these days but definitely enough to toast some stuff if done right.

 

[Lethere Belight]

Yes I'm aware it needs to be focused. Thats what I'm trying to figure out. The best I can get is the "bar" no dot so I'm guessing this is it if it is that type of diode.
I agree at 275 something should happen. It will make a bit of smoke up against black elecrtical tape. Will not light a black match.

 

[jakeGT]

Nope that is 100% completely normal. These multimode 638nm diodes have horrible dots which are actually big rectangles. Also because of the output being closer to a rectangle than a dot makes it a terrible laser for burning.

 

[astroidninja]

If you have goggles then you should be able to focus it enough to easily light matches and burn through electrical tape. If you don't have goggles... well you really shouldn't be trying to burn things in the first place.

 

[DrSid]

Also, even with multimode diodes .. you will get smaller dot if you focus closer. What can be easy from 2 inches may be impossible from 10 feet.

 

[RyanElectro]

^^ this. It's virtually impossible to burn with a 635 from 10 ft. Focus your laser so the focal point is around 2-5 inches, and it should smoke stuff instantly.

 

[Lethere Belight]

I wasn't trying to burn at 10'. That was just for spot size reference
It will get the power meter up to 275 in 20 sec but won't light a black match.
At this point I am thinking of taking it apart and maybe putting in another module.
Pretty ugly beam the way it is.

 

[Lethere Belight]

My fault. It's doing what it is supposed to. In small print under the description it says:

"Due to the fast axis divergence of 638nm laser diode. The dot of this laser will be focused as slightly line shape rather than perfect dot. A small shadow appeared next to the dot is normal phenomenon and will not affect the using"

Should have checked it out more carefully.
Still not sure what the purpose of this is.

 

[DrSid]

Purposes ? Who needs them !

 

[Lethere Belight]

I mean the purpose of a "bar shaped" beam with a shadow. I like pointy dots.
But hey, what ever turns you on go for it.

 

[Blord]

The purpose of this kind of diodes is to give intense light over a wide area like in a projector. Just like the 445nm diode.

The purpose of a round dot is to write bits on a surface of a disc. That is why 405nm (Blu-Ray) and 660nm (DVD ) diode have a better beam profile.

 

[DrSid]

Yes .. generally if you want better beam, you have to limit active area of the laser .. which means to limit power. So single mode diodes with nice dots are usually used only in data recording.

 

[Atomicrox]

I'm assuming you have that Lazerer one because of the star cap?

I have one which they measured at 415mW and it's not that weak. Focusing it I can get it to write in light wood (using goggles). For some odd reason (most likely reflection) it takes a while to sting skin.
I agree the dot is kinda ugly, though.

I also like the diffraction cap. You can make a lot of different shapes by rotating both rings (the diffraction ring and the focusing ring). It's also cool to remove it from the laser and look at a regular lamp thru it while rotating.

Edit: it also has the brightest dot of all my lasers and I can sometimes get it to reach clouds, which is insanely cool.