Divergence over Power

Hi Guys,

I'm in the market for a nice portable high powered laser. I managed to muster up some excess cash (gotta love eBay to help get rid of junk)....enough for an RPL-425 from Optotronics.

I this power range, I'm thinking that divergence is a lot more important than power because I think anything over 350mW is plenty power to do all the fun things that people with lasers do...and with better divergence, I can do all those fun things a lot farther..... :evil:

I already have a 150+mW green pointer from Jack and it should have a divergence of about 1.2 mrad. I think the beam is nice but I would like it tighter.

My question is, is there such a thing as a production portable laser with divergence of less than 0.8 mrad? I'm willing to pay a premium to get that. Would Optotronics be able to help me out in this regard? Thanks!

WP

There are some portable lasers with divergence figures that low, but typically with higher powered portables divergence is pretty rough compared to lower powers. Optotronics may be able to help. You should contact them directly and tell them what you're looking for.

Another option is to obtain a beam expander for your portable once you get it. The main purpose of a beam expander is to improve divergence over a long distance.

I have been searching the same thing. You could buy a new lens and lens assembly from Larry, I guess since it isn't green laser specific power should be around 95% but you would get a much tighter beam

ALso as Elektrofreak mentioned, beam expanders seem to be very popular here. Some are a little pricey, but they do make the beam much longer and thinner. Better for burning!

My dream would be to have a 30x beam expander, my laser will go 30X longer, AND I can burn like crazy from far away and faster

Tighter beam narrower beam doesn't make for better divergence. In fact a lower divergence equals a beam that's wider. As for making a laser with a low divergence there are two ways of doing this a. use a diverging lens with focal length less than what is in use in the RPL. Or. b. use a longer focal length collimating lens greater than what is in use in the RPL

themandalorian
ALso as Elektrofreak mentioned, beam expanders seem to be very popular here. Some are a little pricey, but they do make the beam much longer and thinner. Better for burning!
My dream would be to have a 30x beam expander, my laser will go 30X longer, AND I can burn like crazy from far away and faster

Actually they don't make the beam thinner. Say for instance you have a handheld laser with a beam diameter at the aperture of 1mm, expanding that 30x would create a beam 30mm in diameter. That's why they are called beam expanders. Expanding the beam won't make for better burning unless you focus the beam.
A demo YouTube - Laser Igniter 300 Feet

Hello!

My name is Damian,
I'm new to this Forum, I want to ask more experienced users about one thing.

I'm also looking for a laser that has a low divergence numbers at 100 mW of green. Recently purchased DX cheap lasers regularly had 0,9 -1,1 mrad measured at 50 meters. The spot had about 50 mm of diameter, I want something better.

I've read that laser's beam divergence depends on initial beam diameter, so when I'll use a beam expander, a divergence go lower by the expander ratio. That's true. But I've also noticed that one unit has 1,5 mrad and the other 0,8 mrad of divergence. Both have a 1 mm diameter beam. In addition, I've noticed, that unfortunately, the more power it has, the worse divergence it brings... If both beams are expanded in the same ratio, why one laser has better divergence than theother one? Without any expander used... What is the reason for that? Does lens and crystal quality matter? Is this a wrong lens focus? Or maybe safety issues?

Sorry for bad language!

Cheers!

I think this is because 0.01 milimeters of difference in the distance from the diode to the lens makesthe difference.

Yours,
Albert

Go for a lab laser. Excellent divergence in a portable laser is really hard to find.

I have a coherent lab laser here that is 532nm with a .5mm beam at aperture and less than 1mrad divergence :evil:

steve001 said:

Tighter beam narrower beam doesn't make for better divergence. In fact a lower divergence equals a beam that's wider. As for making a laser with a low divergence there are two ways of doing this a. use a diverging lens with focal length less than what is in use in the RPL. Or. b. use a longer focal length collimating lens greater than what is in use in the RPL

Click to expand...

Hmmm.... I thought the whole point of better divergence is to get a tighter beam, so that the beam goes farther. So are you saying that the lower the divergence, the bigger the spot will be at large distances? Doesn't make sense to me..... :thinking:

What he's saying is that a beam expander expands the beam at the aperture, which allows the resulting thicker beam to maintain low divergence out to a very great distance. The far-field (distant) spot, while large, will be smaller than it would be without the beam expander and this is maintained to infinity.

Here's a cheesy Paint diagram that may help you understand:

You can see that the raw beam without the expander the beam starts off smaller and ends up larger than with the expander, where it starts off slightly larger at the aperture and ends up slightly smaller in the far-field when compared to the original raw beam

Ah. Got it. Thanks Elektrofreak. You're right....that is a cheesy diagram... (just kidding!) :na:

Ok...so the beam does get tighter in the "far-field", which is the important part. Out of curiousity, is there an optic out there that can reduce the divergence AND keep the beam diameter the same as the original aperture diameter?

The divergence of the raw beam depends on the cavity type and length. Most hobbyist lasers utilize very short Fabry-Perot cavities which are the simplest kind of cavity (everything's in a straight line). The shorter the cavity, the worse the divergence (in most cases).

A beam expander is the only way to get extremely low divergence numbers on these types of lasers. Often, beam-expanding optics are incorporated into the laser head itself in order to obtain decent divergence from the factory without the need for an external beam expander. This will give you relatively low divergence but for extremely low divergence (<1 mrad) a beam expander is still necessary even on these systems.

ElektroFreak, thanks for brief explanation. So in 'regular' pointers we cannot achieve premium divergence in pair with small beam diameter right? Do you think the cavity length depends on laser diode brand? Are the CNI diodes better than Samsung diodes?

Beam expander it is then, thanks!

Wave if the cni ones fit on rpl's get in our group buy

Windforce said:

ElektroFreak, thanks for brief explanation. So in 'regular' pointers we cannot achieve premium divergence in pair with small beam diameter right? Do you think the cavity length depends on laser diode brand? Are the CNI diodes better than Samsung diodes?

Click to expand...

That's correct. There are some exceptions to this, but for the most part DPSS (green) pointers will be prone to have higher divergence than a lab-style laser (which will have the necessary optics or cavity structure built in to give low divergence) or a laser with a more complex cavity (ring, z-fold, twisted-mode, etc.. for more info on these, google them)

The raw uncorrected beam from any laser diode has very high divergence due in part to the fact that the cavity is a few mm long (if that). A HeNe gas laser has very low divergence but has a cavity at least a few inches long if not more. Yet another cheesy Paint diagram:

ElektroFreak;

Nice explanation.

I have been testing lens assemblies for several months now ...

and see large differences in divergence among them.

The Blu-Rays are, of course, the best I have tested with short FL lenses.

I am getting 1/8" beam at 14 feet.

By my rough calculations, that looks to be ~1 mrad.

I have some adjustable-focus green lasers on the way to test also.

LarryDFW

I wonder if there is a relation between IR diode power and best possible laser divergence.

I remember my first DX 30 mW laser. It was crappy and underpowered but divergence was astonishing, 0.8 mrad! It had less then 9 mm diameter spot at 10 meters distance...

Now I'm going to buy first serious green laser pen with 100 mW+. I'm considering CNI or Optotronics. Both companies are at highest quality. Both claim only 1.2 mrad in opposite of my 0.8 mrad crappy DX I had earlier... So what's going on?

You see, I'm a divergence maniac More then burning, I like working with laser on longer distances.

EDIT More thougths:

Let's consider two lasers: One unit from good company X with 1.5 mm beam diameter and 1.8 mrad divergence and another one, also manufactured by good company Y with 1.5 mm beam diameter but with 0.9 mrad divergence. Now imagine using focusable 10x beam expander which can tune small errors in laser module focus. We end up with 15 mm diameter beams both, but... X will have 0.18 mrad and Y will be as you expect, 0.09 mrad. Now, consider that both companies are good quality, can we correct poor divergence of X laser by regulating focus of our expander? Or we cannot do this becouse that's the nature of the X laser?