Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers



Laser Pointer Store

Do red lasers have "bad" specs in general?

ixfd64

New member
Joined
Sep 12, 2007
Messages
1,142
Likes
49
Points
0
From what I've seen, green lasers usually have small beam diameters and low divergence (such as 1.4 mm at 0.9 mrad). However, I've noticed that many high-powered red lasers have much larger diameters and higher divergence (for instance, 4 mm at 2 mrad). I do know that lasers with longer wavelengths will have higher divergence, but according to the calculator I used, the difference shouldn't be that large.

On the other hand, I've also seen companies (such as this one) that claim to sell red lasers with much better specs (1.1 mm at 1 mrad). Does anyone know if they're telling the truth or not?
 

Joined
Nov 9, 2007
Messages
1,047
Likes
2
Points
0
High powered reds are made of multimode diodes so the beam specs are bad, its bascily like 3 regular diodes put together, greens ir diodes are multimode to but since its put thru dpss it makes it able to be focused better then just focusing it right of the diodes like reds.


...lazer.... ;D ;D ;D
 
Joined
Oct 1, 2007
Messages
466
Likes
6
Points
0
i believe that because the red wavelength is longer, it cant be focused as small. thats why the violet LDs are used in blu-ray drives instead of red diodes.
 

Kenom

New member
Joined
May 4, 2007
Messages
5,629
Likes
132
Points
0
Now this is where I'll have to put in my $.02. Since Green lasers utilize more than one optic they are capable of getting the divergence down quite a bit. With all of the reds we are playing with the lenses are pretty basic and are just focusing lenses, not colimating lenses. Now this is my understanding. I however do NOT really understand optics all that well so I am probably wrong!
 

Milos

New member
Joined
Apr 22, 2007
Messages
859
Likes
62
Points
0
ixfd64 said:
From what I've seen, green lasers usually have small beam diameters and low divergence (such as 1.4 mm at 0.9 mrad). However, I've noticed that many high-powered red lasers have much larger diameters and higher divergence (for instance, 4 mm at 2 mrad). I do know that lasers with longer wavelengths will have higher divergence, but according to the calculator I used, the difference shouldn't be that large.

On the other hand, I've also seen companies (such as this one) that claim to sell red lasers with much better specs (1.1 mm at 1 mrad). Does anyone know if they're telling the truth or not?
I disagree with first paragraph.
The rule of the thumb is: the wider the beam, the easier it is to collimate. That happens to be true in single mode reds versus greens. Most red pointers are well below 1mRad of divergence, while green ones have very hard time being even 1mRad because initial beam is so narrow due to DPSS process inside cavity.

Wooooooolazer is right.
When you see red laser module with 4mm beam and divergence as bad as 2mRad it almost certainly is a multi mode diode. You get more power, but worse beam spec. Its a trade off. The best example is Laserglow Orions vs. Pulsar or Glowtorch.
Orion (multimode) is more powerful in 200mW+ but divergence is higher(worse) and projected dot is not a nice round one (kinda messy and squarish).
Pulsar is about 125-150mW max but divergence is waay better and dot is very nice and round.

All single mode reds I have seen beat green lasers in divergence by large margin. And the trick is the wider beam they have.

As for 1.1mm beam REDs with 1mRad divergence, I would love to see this, or even better ever have one.
 

Abray

New member
Joined
Nov 18, 2007
Messages
933
Likes
3
Points
0
I've heard that red light scatters less than green, so they can achieve smaller divergences, is that true?
 
Joined
Oct 24, 2006
Messages
2,032
Likes
8
Points
0
Kenom said:
Now this is where I'll have to put in my $.02.  Since Green lasers utilize more than one optic they are capable of getting the divergence down quite a bit.  With all of the reds we are playing with the lenses are pretty basic and are just focusing lenses, not colimating lenses.  Now this is my understanding.  I however do NOT really understand optics all that well so I am probably wrong!
Sorry Ken, I'm gunna have to kick you in the teeth here ;) (all in good fun of course!)

There is a theoretical perfect beam, a beam where your M^2 is 1.0. The larger your M^2, the further it is from perfect. For a green laser, M^2 of 1.0 would roughly correlate to 0.68mm*mRad - where mRad is your full-angle divergence, and mm is your spot diameter at the smallest point on the beam. Now, the proportions can be changed up. You could have a 0.68mm beam and 1.0mRad, a 0.68mRad and 1.0mm, 68mm and 0.01mRad, etc.

Now, the more coherent a source, the closer you get to an M^2 of 1. DPSS lasers are very good, usually spec'd to M^2 of <1.2, meaning <0.82mm*mRad for 532nm. Single-mode red diodes like Greg's aren't quite as good, but they're still pretty low. The reason why you always see me complaining about multi-mode diodes though? Their M^2 spec is usually in the <20 range. Basically, your beam specs will be a good 15x worse than that of a greenie - not too attractive at all.

With the AixiZ units, pulsars, etc. they all use the same lens. The lens has a somewhat long focus that distributes the mm/mRad proportion a bit differently than we're used to with a greenie. The initial diameter is often a good 3-5mm. However, as opposed to a multi-mode red which would have 3-5mRads to match, the reds have a low divergence - in the <0.5mRad range. Take a pulsar next to a CNI greenie and the CNIs beam will be MUCH smaller in the first few feet. Go out 100meters though, and the pulsar's diameter will be a small fraction of the CNI. So neither unit has really bad beam specs, but they're in different proportions.

Cavity optics can be crucial in getting good coherence, but no matter how many external optics you shove in a greenie they could only serve one function: decreasing coherence ever so slightly and actually making the beam worse. All the optics in a greenie do help is getting a good proportion of mm to mRad for us, but they don't actually improve the (minimum diameter)*mRad factor at all.

Damn physics is always getting in the way of our fun.
 

Kenom

New member
Joined
May 4, 2007
Messages
5,629
Likes
132
Points
0
See now I knew I was wrong but essentially your also saying I'm right. By utilizing the proper optics we can actully get the divergence down on a red was essentially what I was trying to say just not having the knowledge to back it up with. I know it all pans out differently over different distances and whatnot.
 
Joined
Nov 9, 2007
Messages
1,047
Likes
2
Points
0
Lol Milos actually counted how many o's are in my name :eek:

I shoulda got a better name..

....lazer... ;D ;D ;D
 

Milos

New member
Joined
Apr 22, 2007
Messages
859
Likes
62
Points
0
wooooooolazer said:
Lol Milos actually counted how many o's are in my name :eek:

I shoulda got a better name..

....lazer... ;D ;D ;D

heheh .. I was gonna just copy/paste at first, than I felt lazy and held ooooo down till I thought it was just about enough ;D ;D
I guess I'm pretty goood with my keyboard ::)
 




Top