Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

[Accutronitis]

I did some measuring of the divergence of both my lasers a little while ago today and here is what I got.

At 50 feet my Thor Saber had a spot size of a 1/2 inch x 1/2 inch.

At 50 feet Thor's Hammer had a spot size of 6 inches x 1/2 inch.

Is that good or bad ?

 

[diachi]

Re: Is A Spot Size Of a 1/2 Inch At 50 Feets Good ?

Assuming an initial beam diameter of 5mm then that works out to ~0.5mRad for the Thor Saber (pretty damn good!). For the Thor's Hammer build that works out to ~9.6mRad (terrible) on the fast axis and 0.5mRad on the slow axis.

 

[Accutronitis]

Assuming an initial beam diameter of 5mm then that works out to ~0.5mRad for the Thor Saber (pretty damn good!). For the Thor's Hammer build that works out to ~9.6mRad (terrible) on the fast axis and 0.5mRad on the slow axis.

Thanks !

I don't have any fast axis correction on Thor's Hammer yet but I'm working on it.....

 

[diachi]

Re: Is A Spot Size Of a 1/2 Inch At 50 Feets Good ?

Thanks !

I don't have any fast axis correction on Thor's Hammer yet but I'm working on it.....

The ~9.6mRad fast axis divergence sort of gave that away! Post results once you have that worked out!

 

[Accutronitis]

The ~9.6mRad fast axis divergence sort of gave that away! Post results once you have that worked out!

Will do and thanks for the info !

 

[Accutronitis]

Sorry to double post but I wanted to make sure you seen this...

Originally Posted by diachi
Check out my Reddit Subreddit! >>/r/laserpointers<<

I DID ! The way you improvise while more or less using what you have available to customize a strong fix for something that would otherwise be dead reminds me of me ! lol

 

[steve001]

I did some measuring of the divergence of both my lasers a little while ago today and here is what I got.

At 50 feet my Thor Saber had a spot size of a 1/2 inch x 1/2 inch.

At 50 feet Thor's Hammer had a spot size of 6 inches x 1/2 inch.

Is that good or bad ?

Your question is equivalent to asking which flavor of plain or french vanilla ice cream is good or bad. In other words your question is entirely subjective and not simply answerable. There's plenty of information out there on divergence, Rayleigh Length and how to measure it.

 

[Accutronitis]

Re: Is A Spot Size Of a 1/2 Inch At 50 Feets Good ?

Your question is equivalent to asking which flavor of plain or french vanilla ice cream is good or bad. In other words your question is entirely subjective and not simply answerable. There's plenty of information out there on divergence, Rayleigh Length and how to measure it.

I'm sorry but what are you talking about ??? I got the exact answer I was looking for with the very first reply from diachi below, He told me everything I wanted to know in detail !

Again thank you diachi !

Assuming an initial beam diameter of 5mm then that works out to ~0.5mRad for the Thor Saber (pretty damn good!). For the Thor's Hammer build that works out to ~9.6mRad (terrible) on the fast axis and 0.5mRad on the slow axis.

 

[Alaskan]

Good = acceptable ? That my friend is entirely up to you, but I know what you meant.

Another way of approaching this is to ask what most members think an acceptable amount of divergence is, but that will vary. My own preference is that 1.2 mRad or lower full angle divergence is good, others think 1.5 mRad or less is fine. I don't like 1.5 or above mRad for my laser pointers, to me any higher than that isn't good, but when compared to the divergence produced by the NUBM44 diode when using a 6 mm diameter collimation lens, it is quite good. I guess it comes down to there is no bad or good, just preferences or suitability to application. I like using my laser pointers to deliver power at extreme distances in as tight a spot as reasonably possible, so for me 2 mRad is bad, 1.5 on the margin between good and bad, 1.2 good, 1.0 mRad excellent, less; outstanding.

Here is a link to an online divergence calculator, play around with the numbers to see what divergences produce what diameter of spot at different distances: pseudonomen137's JScript mRad Calculator

 

[Accutronitis]

pseudonomen137's JScript mRad Calculator says my Thor Saber is a outstanding 0.83mRad !

But I'm still working on the "Hammer" so i'll get back to that one later....

Thanks for the Calculator !

His other calculator is cool to, It says my Thor Saber will have a spot diameter of 2.9 inches at 300 feet and at 1 mile it will be 52.6 inches in diameter !

What is the best divergence you've ever heard of ?

Back in the day the Las Vegas Hilton used powerful lasers to project nearly horizontal beams across the Las Vegas Valley. The Hilton’s origin point was its huge, mid-century modern pylon sign, and was touted as the world’s most powerful public laser display by its creator, Laser Fantasy International. While the Hilton laser did offer a sort of pulsing “show,” it was during its rest mode when it projected low-lying static beams in four directions around the Valley. One of those directions was Lone Mountain which is very close to where I live, The distance was about 14 mile and the spot on lone mountain was really pretty dang small ! It was a green beam and that beam was very visible looking at it from any direction including directly from the side and quite a ways away and you could still see it no problem !!!

I wonder what's it's power and divergence was back then, And What kind of laser was it ?

 

[Alaskan]

The lowest divergence I've heard of in a pointer which has over 500 mw of output without a beam expander, or large diameter collimation lens is the RPL series made by Optotronics which produces .9 to 1.0 mRad. However, there are some single mode laser pointers which probably have that or better, but since they are such low power I don't have much interest in them as a single diode unit.

Your .8 mRad pointer is producing outstanding divergence, even DPSS lasers don't normally have less than 1.0 mRad full angle divergence, and that's for the expensive high quality ones. For any given laser the divergence of the collimated output depends upon the beam diameter. Low divergence while at the same time having a small beam diameter is the cats meow because the beam stands out so brightly due to a higher power density in a small area. A 1.0 mRad full angle divergence laser pointer which produces a beam which is only 1 or 2 mm wide a few inches past the output (at infinity focus) is a great pointer, if you can find one. You won't find that unless it is DPSS, or perhaps a low power single mode laser diode. OK, for the hair splitters, masking the output of a high power multimode laser diode which has had its beam expanded can produce a low divergence small diameter beam output too, I've considered doing that myself, but it just seems like an awful waste of power for what I like to use my pointers for. I'm no expert, still learning a lot every year so if someone can share another way to get a tiny diameter beam at 1 watt or higher that doesn't use a DPSS or single mode diode I'd love to hear from you.

Any multimode laser diode can have low divergence, you just need to expand the beam enough which means using a larger diameter collimation lens with a longer focal length to allow the beam to naturally expand into wider beam prior to collimation, or, just stick a two lens beam expander in the front of your already collimated laser pointer output and that will reduce the divergence, but at a cost, the added loss of using more lenses.

Here's a cut and paste snip I found online comparing 1.2 to 1.5 mRad and showing how much more power is delivered at a distance with only that amount of difference: https://www.optotronics.com/laser-divergence.php

Laser Divergence

Why a small change in this specification greatly affects laser beam intensity.

Divergence is the increase in laser beam diameter with distance from the aperture from which the beam emerges in any plane that intersect the beam axis. What this means is that the diameter of the beam expands over distance at an angle (the divergence in milliradians or mrad ). As this angle increases, (even by small amounts) the diameter of the beam increases and the area of the beam (Area of a circle = π multiplied by the square of the radius) increases at an exponential rate. Optotronics handheld laser products have a divergence spec. of 1.2mrad orless (unless otherwise noted). Most other suppliers of handheld laser products have a divergence spec. of 1.5mrad. This means that for the same beam diameter and output power, the light intensity or irradiance (Output power / area of beam spot) is up to 56% greater with a divergence of 1.2mrad vs 1.5mrad. So with an Optotronics laser your not only getting more for your money, your getting a beam that's 14.8% more intense at 0.50 meters distance to over 55% more intense at distances of greater than 60 meters.

 

[steve001]

Re: Is A Spot Size Of a 1/2 Inch At 50 Feets Good ?

I'm sorry but what are you talking about ??? I got the exact answer I was looking for with the very first reply from diachi below, He told me everything I wanted to know in detail !

Again thank you diachi !

Dachi gave you an answer that was subjective. However, the fact that you liked the answer is entirely subjective too.
Some folks like a thin highly divergent beam for burning.
Others like myself like a wide low diverging beam. Good or bad is relative to what one prefers. That's why I said your question can't simply be answered.

A few questions.
What is the beam diameter as it leaves the lens?
What is the beam diameter at 30 meters?
What is the beam diameter at >50 feet?
Have you determined the Rayleigh Length?

 

[Accutronitis]

Re: Is A Spot Size Of a 1/2 Inch At 50 Feets Good ?

The lowest divergence I've heard of in a pointer which has over 500 mw of output without a beam expander, or large diameter collimation lens is the RPL series made by Optotronics which produces .9 to 1.0 mRad. However, there are some single mode laser pointers which probably have that or better, but since they are such low power I don't have much interest in them as a single diode unit.

Your .8 mRad pointer is producing outstanding divergence, even DPSS lasers don't normally have less than 1.0 mRad full angle divergence, and that's for the expensive high quality ones. For any given laser the divergence of the collimated output depends upon the beam diameter. Low divergence while at the same time having a small beam diameter is the cats meow because the beam stands out so brightly due to a higher power density in a small area. A 1.0 mRad full angle divergence laser pointer which produces a beam which is only 1 or 2 mm wide a few inches past the output (at infinity focus) is a great pointer, if you can find one. You won't find that unless it is DPSS, or perhaps a low power single mode laser diode. OK, for the hair splitters, masking the output of a high power multimode laser diode which has had its beam expanded can produce a low divergence small diameter beam output too, I've considered doing that myself, but it just seems like an awful waste of power for what I like to use my pointers for. I'm no expert, still learning a lot every year so if someone can share another way to get a tiny diameter beam at 1 watt or higher that doesn't use a DPSS or single mode diode I'd love to hear from you.

Any multimode laser diode can have low divergence, you just need to expand the beam enough which means using a larger diameter collimation lens with a longer focal length to allow the beam to naturally expand into wider beam prior to collimation, or, just stick a two lens beam expander in the front of your already collimated laser pointer output and that will reduce the divergence, but at a cost, the added loss of using more lenses.

Here's a cut and paste snip I found online comparing 1.2 to 1.5 mRad and showing how much more power is delivered at a distance with only that amount of difference: https://www.optotronics.com/laser-divergence.php

I'm pretty sure the beam isn't being clipped or masked in anyway because the 1/2 dot at 50 feet is a 1/2 inch by 1/2 inch square, If it was focused so it was clipping or part of the beam was masked I would think it would be a more rounded off beam wouldn't it ? That laser from across the room and without refocusing it from it's tightest beam in the sky will make a pair of black denim pants start smoking after just a few seconds.

When I was measuring the beam at 50 feet just out of curiosity I let my hand sweep in front of it and felt nothing so I slowed down the sweep until I just stopped with the dot on my palm and I could keep it on my palm around 6 to 10 seconds before I had to move it, Not bad for 2.2 watts at 50 feet ?

just stick a two lens beam expander in the front of your already collimated laser pointer output and that will reduce the divergence, but at a cost, the added loss of using more lenses

But doesn't that depend to some degree on the quality of the lenses involved how much added loss they will have on the output ? If the added loss was just a small fraction of the power output I would think that it would be worth the trade off for a good reduction of divergence ?

Dachi gave you an answer that was subjective. However, the fact that you liked the answer is entirely subjective too.
Some folks like a thin highly divergent beam for burning.
Others like myself like a wide low diverging beam. Good or bad is relative to what one prefers. That's why I said your question can't simply be answered.

A few questions.
What is the beam diameter as it leaves the lens?
What is the beam diameter at 30 meters?
What is the beam diameter at >50 feet?
Have you determined the Rayleigh Length?

A few questions.
What is the beam diameter as it leaves the lens? I don't know......
What is the beam diameter at 30 meters? I don't know.......
What is the beam diameter at >50 feet? 1/2 inch by 1/2 inch.....
Have you determined the Rayleigh Length?I don't know what that is........

My OP was a question of divergence and whether or not my divergence was high or low with high being bad and low being good and diachi got that right away and gave me a answer I could understand and that made sense to me.....

but here's a question, What if the beam starts out at 25mm x 5mm and after 50 feet it's 13mm ? What "mRad" would that be ?

 

[steve001]

Re: Is A Spot Size Of a 1/2 Inch At 50 Feets Good ?

I'm pretty sure the beam isn't being clipped or masked in anyway because the 1/2 dot at 50 feet is a 1/2 inch by 1/2 inch square, If it was focused so it was clipping or part of the beam was masked I would think it would be a more rounded off beam wouldn't it ? That laser from across the room and without refocusing it from it's tightest beam in the sky will make a pair of black denim pants start smoking after just a few seconds.

When I was measuring the beam at 50 feet just out of curiosity I let my hand sweep in front of it and felt nothing so I slowed down the sweep until I just stopped with the dot on my palm and I could keep it on my palm around 6 to 10 seconds before I had to move it, Not bad for 2.2 watts at 50 feet ?

But doesn't that depend to some degree on the quality of the lenses involved how much added loss they will have on the output ? If the added loss was just a small fraction of the power output I would think that it would be worth the trade off for a good reduction of divergence ?





A few questions.
What is the beam diameter as it leaves the lens? I don't know......
What is the beam diameter at 30 meters? I don't know.......
What is the beam diameter at >50 feet? 1/2 inch by 1/2 inch.....
Have you determined the Rayleigh Length?I don't know what that is........

My OP was a question of divergence and whether or not my divergence was high or low with high being bad and low being good and diachi got that right away and gave me a answer I could understand and that made sense to me.....

but here's a question, What if the beam starts out at 25mm x 5mm and after 50 feet it's 13mm ? What "mRad" would that be ?

Higher or lower you asked? Compared to what? What standard are you measuring against? You see your terminology is qualitative not quantitative. When I think of a low diverging beam I have in mind something such as 0.5mrd compared to a typical value of 1.2-1.5mrd, but that is purely arbitrary. You see, no matter how you ask the question it still comes down what you prefer.

I have no idea what the divergence would be. But one thing I know is, that beam is converging or expanding. That beam has 2 axis. You asked the question imprecisely.
I heartedly suggest you take time to do some practical measurements. And look up the definition of Rayleigh Length to see why it's important.

 

[diachi]

Re: Is A Spot Size Of a 1/2 Inch At 50 Feets Good ?

but here's a question, What if the beam starts out at 25mm x 5mm and after 50 feet it's 13mm ? What "mRad" would that be ?

The divergence would be a negative number in that case, at least for the wider axis at aperture (your smaller 5mm axis would have a positive divergence as it gets wider). The calculation is the same, and after the focal point has been reached the divergence number would change to a positive, but with equal value.


Glad someone clicked the subreddit link in my signature! Put it there to hopefully get some more active users on. Made it because /r/lasers seemed to be rather dead and wasn't sure how active the mods were, I had to PM them to get my last post to show up, not sure if others had the same issues.

 

[Accutronitis]

Re: Is A Spot Size Of a 1/2 Inch At 50 Feets Good ?

Higher or lower you asked? Compared to what? What standard are you measuring against? You see your terminology is qualitative not quantitative. When I think of a low diverging beam I have in mind something such as 0.5mrd compared to a typical value of 1.2-1.5mrd, but that is purely arbitrary. You see, no matter how you ask the question it still comes down what you prefer.

I have no idea what the divergence would be. But one thing I know is, that beam is converging or expanding. That beam has 2 axis. You asked the question imprecisely.
I heartedly suggest you take time to do some practical measurements. And look up the definition of Rayleigh Length to see why it's important.

Higher = Wider at 50 feet
Lower = Narrower at 50 feet

You should know I have a 10x beam expander on it so I guess that changes everything (that's my bad for not stating that) But I can tell you that the beam is not coming together and then getting wider again on either axis's.

The beam exits the beam expander 25mm x 5mm and after 50 feet it's 13mm square.

So the one axis starts at 25mm and gradually gets narrower and at 50 feet it's 13mm.

and the other axis starts at more like 6mm and gradually gets wider and at 50 feet it's 13mm.

But as I said nether axis go's inwards and then back out, that's the only way I know how to explain what the beam is doing.....

But i'll try and dig into what you suggest but right now I know with the setup I have right now at 50 feet the dot is 13mm x 13mm and the beam looks like a needle in the night sky and I like it !

it seem like the farther it go's up the thinner and brighter it gets even thought I know it must be getting wider as it heads out but it just doesn't look like it does ?

The divergence would be a negative number in that case, at least for the wider axis at aperture (your smaller 5mm axis would have a positive divergence as it gets wider). The calculation is the same, and after the focal point has been reached the divergence number would change to a positive, but with equal value.

So I ran the numbers through the calculator again and got this for both axis's if I did it right ?

- 0.787401412073226
+ 0.5249343349858161

I'll try to take some pictures of the dot on the wall at different distances tonight....