Old 04-13-2017, 04:44 PM #17
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Quote:
Originally Posted by Accutronitis View Post
Is that good or bad ?
You can only make a silk purse out a sow's ear within limits of possible optical correction. The physical beam source/diode has horrible/poor beam quality to begin with and that is not going to change no matter what you do.

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Originally Posted by steve001 View Post
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.
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Originally Posted by steve001 View Post
You see, no matter how you ask the question it still comes down what you prefer.
You are right --is that good or bad, it is subjective and almost meaningless question with relative to what not specified.
Intrinsically a NUBM44 diode laser has a poor quality beam so is never going to be really good good, as in an excellent gaussian laser beam sense.

Here are some interesting and useful calculators from Ophir:

Focal Spot Size Calculator Laser Beams: Focal Spot Size Calculator | Gaussian Laser Beams

Laser Power Density Calculator: Laser Power Density Calculator | Ophir Photonics

Laser Focusability Calculator: Laser Focusability (Gaussian Beam) | Ophir Photonics

Laser Power Through Aperture Calculator: Laser Power Through Aperture Calculator (Gaussian Beam) | Ophir Photonics

Laser Peak Power Calculator: Laser Peak Power Calculator - Ophir



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Old 04-13-2017, 05:54 PM #18
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Nice links, you are going to turn this guy into an optical techie feeding him that stuff
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Old 04-14-2017, 04:37 AM #19
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

All the Ophir Photonics links are bad.....

Also I tried to find info about "Rayleigh length" but everything I found might as well have been in a foreign languag ?

I checked out the Laser Peak Power Calculator but I don't think my beam is either Tophat or Gaussian is it ?
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Old 04-14-2017, 05:15 AM #20
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Quote:
Originally Posted by Accutronitis View Post
All the Ophir Photonics links are bad.....

Also I tried to find info about "Rayleigh length" but everything I found might as well have been in a foreign languag ?

I checked out the Laser Peak Power Calculator but I don't think my beam is either Tophat or Gaussian is it ?
RP photonics is a great source: https://www.rp-photonics.com/rayleigh_length.html?s=ak

That said ... you may need to read up on the other terms to understand that.

As for your beam, probably closer to tophat but it's going to be messy/multimode. Hard to say really without seeing it or putting on a beam profiler which can give you something like this (comparison between Gaussian and Multimode beam):



Tophat vs Guassian:

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Old 04-14-2017, 05:29 AM #21
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Quote:
Originally Posted by Accutronitis View Post
All the Ophir Photonics links are bad.....
Not true--this one is still good:
Focal Spot Size Calculator | Gaussian Laser Beams
and Laser Peak Power Calculator - Ophir
The other ones seem to be having a problem even from the Ophir site links--maybe server problem---all of them have always been good before.

EDIT: all the Ophir links are working again

also see: https://en.wikipedia.org/wiki/Laser_beam_quality

Found ths good one:
"Limitations for the Focusing of Laser Beams"
"Laser beams can be used for transmitting optical energy to rather small spots or with low beam divergence over large distances. However, there are limitations to this, which involve the optical wavelength, the beam quality and the transverse size of the used focusing or collimation optics. Some of these limitations are discussed in the following, always assuming propagation of the beam through a homogeneous medium (i.e., with no added beam distortions on the way).

If a laser beam is focused to a spot (beam waist) with beam radius w0, it exhibits a certain beam divergence angle which is inversely proportional to the waist beam radius and proportional to the optical wavelength in the M2 factor:

The used focusing optics must be able to handle that amount of beam divergence; a limitation for that results from the limited numerical aperture of the optics. Also, if the focus has to have a large distance from the focusing optics and/or the waist beam radius is small or the beam quality is low, the beam radius in the focusing optics will necessarily be quite large. A correspondingly large open aperture of the optics is required. Such factors can in practice set a lower limit to the achievable beam radius in the focus, or an upper limit to the tolerable M2 factor of the beam.

In some cases, one optimizes the beam radius in the beam focus such that the beam radius at a certain distance from the focus is as small as possible. For that purpose, one has to choose the waist beam radius such that the effective Rayleigh length of the beam equals the mentioned transmission distance. The resulting beam radius at the distant position will then be ≈1.41 times the waist beam radius.

If the sent-out beam does not have to have its focus at the focusing optics, one should place the focus in the middle between the optics and the distant point. Ideally, the effective Rayleigh length will then be half the transmission distance. The beam radius at the distance spot will be identical to that at the focusing optics, and ≈1.41 times larger than in the beam focus.

For example, if a Gaussian laser beam at 1064 nm should be sent to the moon (distance 380 000 km) in order to illuminate a small spot there, the ideal beam radius in the focus will be 8 m, such that the Rayleigh length is 190 000 km. The beam radius in the focusing optics and on the moon will then be 11.3 m. If the used sending telescope cannot be that large, the illuminated spot on the moon will be larger.

When creating a beam focus in some distance from some focusing optics with a limited open aperture, the possible waist beam radius will increase if that distance is increased. Furthermore, there is a maximum to that distance; in the extreme case, the distance equals the effective Rayleigh length of the beam, and the resulting waist beam radius will be smaller than the beam radius at the focusing optics by the square root of 2 (≈1.41). One can thus easily calculate the Rayleigh length based on the initial beam radius and thus the maximum focusing distance." ~ from middle section of: https://www.rp-photonics.com/laser_beams.html

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Old 04-14-2017, 07:00 AM #22
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Yep they are all working for me as well....

The "Limitations for the Focusing of Laser Beams" was much easier to understand more of, I think a good chunk of it actually sunk in but i'll have to read it a few more times....

Great illustrations would help a lot, I just got done watching a lot of videos on lenses, collimation, converging, diverging, expanding, virtual image vs real image, focal point, multi-lens setup, lenses vs mirrors so I'm starting to get a bit of a handle on what's going on, Thank for the nudge in the right direction......
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Old 04-15-2017, 12:48 AM #23
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

For small lasers you don't really have to do the calculus for a specific distance - relative to the optical system in a handheld 100 meters is probably about infinity for practical purposes (i.e. you cannot adjust the focus such that the beam at 100m is narrower than at say 10m from the output).

With a bigger lens you could, but given that the lenses in these things are usually under 1 cm in usable diameter, forget it.

As for the 'dot' size of these half-mutimode laser diodes: it is normal that the output looks more like a line than a dot at greater distances.

Optical systems let you trade divergence for beam diameter, and the correcting one do this in one direction but not the other. Basically you are changing the narrow but divergent part of the output to a wider but less divergent pattern. The end result will be a spot that is more square/round at a distance.
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Old 04-15-2017, 04:53 AM #24
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

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Originally Posted by Benm View Post
For small lasers you don't really have to do the calculus for a specific distance - relative to the optical system in a handheld 100 meters is probably about infinity for practical purposes (i.e. you cannot adjust the focus such that the beam at 100m is narrower than at say 10m from the output).

With a bigger lens you could, but given that the lenses in these things are usually under 1 cm in usable diameter, forget it.

As for the 'dot' size of these half-mutimode laser diodes: it is normal that the output looks more like a line than a dot at greater distances.

Optical systems let you trade divergence for beam diameter, and the correcting one do this in one direction but not the other. Basically you are changing the narrow but divergent part of the output to a wider but less divergent pattern. The end result will be a spot that is more square/round at a distance.
Yes it's def square at 50 feet, The output lens in my beam expander has a useable diameter of about 22mm so that really helps when I expander the beam as large as I can without clipping the beam on something inside the BE and then take that beam and focus it to infinity which makes the beam a thin sharp needle in the night sky !!!.....
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Old 04-16-2017, 12:52 AM #25
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Having that large a beam diameter certainly helps things.

The profile being square rather than round can't really be helped on these multimode diodes. Then again it's always a lot better than doing without: otherwise the 'dot' at say 100 meters from the laser is something like a line/rectangle with one side 10 to 20 times as large as the other at about 100 meters away.

If you want a small round dot at a distance the only way to do it is a single mode laser diode realistically.
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Old 04-16-2017, 01:30 AM #26
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Quote:
Originally Posted by Benm View Post
Having that large a beam diameter certainly helps things.

The profile being square rather than round can't really be helped on these multimode diodes. Then again it's always a lot better than doing without: otherwise the 'dot' at say 100 meters from the laser is something like a line/rectangle with one side 10 to 20 times as large as the other at about 100 meters away.

If you want a small round dot at a distance the only way to do it is a single mode laser diode realistically.
With my 44 I'm not trying for anything round as I knew before I even bought it that round was not realistically possible, With one of DTR G-2 lens at 60 paces is a very thin but wide line and if I can bring in the wide axis into a similar size as the thin axis without losing hardly any output power it could be completely square and I would be ecstatic (very happy with those results) and I would leave it just like that for as long as I own it !
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"Thor's Hammer" Americanised TLY-L201 Host Build W/Old School NASA Type Safety Switch - DTR NUBM44 6.8 Watts at 4.5 Amps 450nm Diode In 25mm Copper Module W/Driver - DTR G-2 lens - OPT Laser 6X/3X Cylindrical Three Lens Fast Axis Correction W/Focusable Convex Lens Class IV

303 Prome Star Series Green Laser 532nm 80mW DPSS Class IIIb

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Old 04-17-2017, 01:10 AM #27
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Well, with a one-directional beam expander set you can get it as close to square as you want, if you don't mind the size of the beam expander. A couple of centimeters would probably be very impractical in a handheld pointer, but perfectly fine for a lab-style enclosure.

There are roughly two ways to got about this: You can use a set of cylindrical lenses as a beam expander on on axis, or you could use a prism pair.

The latter is usually smaller in overal size but more tricky to adjust. The size makes it such that you can fit them into practical handheld lasers though, producing a much closer to square dot without having a very large diameter housing.
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Old 04-17-2017, 01:51 AM #28
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Default Re: Is A Spot Size Of a 1/2 Inch At 50 Feet Good ?

Quote:
Originally Posted by Benm View Post
Well, with a one-directional beam expander set you can get it as close to square as you want, if you don't mind the size of the beam expander. A couple of centimeters would probably be very impractical in a handheld pointer, but perfectly fine for a lab-style enclosure.

There are roughly two ways to got about this: You can use a set of cylindrical lenses as a beam expander on on axis, or you could use a prism pair.

The latter is usually smaller in overal size but more tricky to adjust. The size makes it such that you can fit them into practical handheld lasers though, producing a much closer to square dot without having a very large diameter housing.
That's what I'm doing right now and it's going to be a very small add on.....

OPT Lasers Cylindric lenses - NUBM44 beam correction tests
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My very short laser collection (for now)

Thor "Saber" Americanised Thor M II - DTR M462 2.2 Watt 462mn Diode W/Super X-Drive @ 1.8 Amps - DTR G-2 lens - JL 10X Beam Expander Class IV

"Thor's Hammer" Americanised TLY-L201 Host Build W/Old School NASA Type Safety Switch - DTR NUBM44 6.8 Watts at 4.5 Amps 450nm Diode In 25mm Copper Module W/Driver - DTR G-2 lens - OPT Laser 6X/3X Cylindrical Three Lens Fast Axis Correction W/Focusable Convex Lens Class IV

303 Prome Star Series Green Laser 532nm 80mW DPSS Class IIIb

Last edited by Accutronitis; 04-17-2017 at 01:53 AM.
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