Welcome to Laser Pointer Forums! If you are looking for a laser you may want to check out the Laser Company Top Sites List. The link will open in a new window for your convenience.

Colorful 2018, Colorful Laser Power Meter
 Laser Pointers Help Needed With mRad Calculations....

LPF Laser Pointer Company Database (link opens new window)

07-07-2017, 01:46 PM #1
 Banned Join Date: Dec 2016 Location: Las Vegas Posts: 1,358 Rep Power: 0
Accutronitis
Banned

Join Date: Dec 2016
Location: Las Vegas
Posts: 1,358
Rep Power: 0

I just got done measuring all the beam sizes focused to infinity at zero and out to 175 feet and here is what I got.....

Quote:
 Focused to infinity at zero feet it's 12.5mm fast axis 10mm slow axis Focused to infinity at 175 feet the fast axis was 49mm and the slow axis was 19mm Sooooo the.... Slow Axis mRad Is 0.1874765632328795 focused to infinity Fast axis mRad Is 0.6842893570104003 focused to infinity
And from what many people have told me in the past numbers that low are unbelievable, Can someone please tell me what I'm doing wrong ???

07-07-2017, 02:14 PM #2
 Class 3R Laser Join Date: Aug 2016 Location: European Union Posts: 1,305 Rep Power: 804924
Class 3R Laser

Join Date: Aug 2016
Location: European Union
Posts: 1,305
Rep Power: 804924
Re: Help Needed With mRad Calculations....

It seems to me the laser has negative divergence (might not be evident). Check it at various lower distances if the dot is bigger with distance during all beam path or it is getting smaller (sign of negative divergence) with distance in some area. It might be hard to notice unless you go through the beam. My WL Inferno has negative divergence for example, I discovered it when I was testing burning abilities and at larger distance it burned much better than close to aperture, closer look and measurements of the beam than confirmed my hypothesis.

Edit: Here for example, how to measure it - http://vlab.amrita.edu/?sub=1&brch=189&sim=342&cnt=1
__________________
"Lasers are s3xy."
"That feeling when you see colours as their wavelengths."
"Laserpainting is a drug. Do not try it."
"If you do not feel and experience the magic, you cannot become the master of wizardry."

Current collection:
405 nm | 500 mW | Wicked Lasers Lunar
445 nm | 3.5 W | Wicked Lasers Arctic
473 nm | 100 mW | Jet Lasers PL-E Pro
520 nm | 1 W | Wicked Lasers Krypton
532 nm | 100 mW | Wicked Lasers Evo
532 nm | 800 mW | Sky Lasers PL

532 nm | 1.4+ W | Optotronics RPL-II
589 nm | 50 mW | Dragon Lasers Spartan
635 nm | 750 mW | Wicked Lasers Inferno
1 W RGB projector
(+ some pointers)

Wishlisted:
Sanwu's RGB Portable

Laserpainting art:
Latest artwork: The Pandora's Black Box

The Hologram Question has just been answered! (wazup post)

LPF social media hashtag: #laserpointerforums

Last edited by Radim; 07-07-2017 at 02:24 PM.

07-07-2017, 02:49 PM #3
 Banned Join Date: Dec 2016 Location: Las Vegas Posts: 1,358 Rep Power: 0
Accutronitis
Banned

Join Date: Dec 2016
Location: Las Vegas
Posts: 1,358
Rep Power: 0
Re: Help Needed With mRad Calculations....

I walked the entire length of the beam and loked at it very carefully and it just very slowly get bigger from the laser on out........

Quote:
 The divergence of a laser beam can be calculated if the beam diameter d1 and d2 at two separate distances are known. Let z1and z2 are the distances along the laser axis, from the end of the laser to points “1” and “2”. Usually, divergence angle is taken as the full angle of opening of the beam. Then, Half of the divergence angle can be calculated as where w1 and w2 are the radii of the beam at z1 and z2. Like all electromagnetic beams, lasers are subject to divergence, which is measured in milliradians (mrad) or degrees. For many applications, a lower-divergence beam is preferable.
I don't understand what this means ?

Quote:
 Usually, divergence angle is taken as the full angle of opening of the beam
Can someone explain what the full angle of opening of the beam is ?

Last edited by Accutronitis; 07-07-2017 at 02:57 PM.

07-07-2017, 03:08 PM #4
 Class 4 Laser Join Date: Feb 2008 Location: Yellowknife, NT, Canada Posts: 9,132 Rep Power: 1258493
diachi
Class 4 Laser

Join Date: Feb 2008
Posts: 9,132
Rep Power: 1258493
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by Accutronitis I walked the entire length of the beam and loked at it very carefully and it just very slowly get bigger from the laser on out........ I checked out your link and read this..... I don't understand what this means ? Can someone explain what the full angle of opening of the beam is ?
It's just the full angle divergence, instead of the half angle divergence...?

Imagine splitting the beam in half right down the middle, then measuring the divergence of one half, that'd be the half angle divergence. The full angle is both halves added together.

You'd get the half angle by measuring the radius at different distances and the full angle my measuring the diameter.

__________________

355nm | Bruker SmartBeam | Q-Switched Nd:YAG | Awaiting Arrival
405nm | Banggood LT-850 | 50mW Metered | Review Unit | >>Review<<
445nm | Sanwu Laser Pocket Series | 400mW Metered
445nm | NDB7242E Pen Build | 60mW Metered | >>Build Thread<<
450nm | LaserPointerStore - Thor H2 | 1.6W Metered | Review Unit | >>Review<<
473nm | B&W Tek BWB-10-OEM |
488nm | Spectra Physics 163 Argon | ~30mW Metered |
495nm | Laser66 Pen Build | WIP
515nm | PL515 Pen Build | 50mW | >>Build Thread<<
520nm | Laserlands 520 5mW | 3mW Metered | Review Unit | >>Review<<
532nm | Gearbest 303 Pointer | 50mW Metered
532nm | Gearbest JD-850 Pointer | 30mW Metered |
633nm | HeNe | 6mW
633nm | Spectra Physics 155 HeNe | <1mW >>Thread<<
650nm | Sanwu Laser Pocket Series | 200mW Metered
808nm | Melles Griot 532nm Lab Unit | No Crystals >10W

B&W Tek Spectrometer
LaserBee 2.5W USB LPM

07-07-2017, 03:12 PM #5
 Class 3R Laser Join Date: Jun 2007 Posts: 1,805 Rep Power: 386771
steve001
Class 3R Laser

Join Date: Jun 2007
Posts: 1,805
Rep Power: 386771
Re: Help Needed With mRad Calculations....

Forget all that technical stuff.
Ok. Now assuming 3 things and those 3 things are you adjusted the beam until the spot size at a distance of 175 feet was as small possible or if you prefer focused to infinity (I like infinite conjugate). And you measured the beam diameter at various points along the length out to where it terminates and the results where X and X. And you calculated correctly. Then that's the correct result.

07-07-2017, 03:32 PM #6
 Banned Join Date: Dec 2016 Location: Las Vegas Posts: 1,358 Rep Power: 0
Accutronitis
Banned

Join Date: Dec 2016
Location: Las Vegas
Posts: 1,358
Rep Power: 0
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by steve001 Forget all that technical stuff. Ok. Now assuming 3 things and those 3 things are you adjusted the beam until the spot size at a distance of 175 feet was as small possible or if you prefer focused to infinity (I like infinite conjugate). And you measured the beam diameter at various points along the length out to where it terminates and the results where X and X. And you calculated correctly. Then that's the correct result.
Alaskan suggested I should be focusing to infinity so that's what I did, and then I sat it on the ground pointing at a wall at the end of my cul-de-sac which is 175 feet away from the front of my house, then I used dial calipers and measured the spot size on the wall which was 49mm on the fast axis and 19mm on the slow axis, Then I measured the spot size on the output lens of the beam expander which was 12.5 on the fast axis and 10mm on the slow axis.

After that I went to pseudonomen137's mRad Calculator for laser divergence website

and I put in the numbers I just got and I got.......

Slow Axis mRad Is 0.1874765632328795 focused to infinity.

Fast axis mRad Is 0.6842893570104003 focused to infinity.

I can't see what I'm doing wrong ???

Last edited by Accutronitis; 07-07-2017 at 03:32 PM.

07-07-2017, 04:08 PM #7
 Class 4 Laser Join Date: Feb 2008 Location: Yellowknife, NT, Canada Posts: 9,132 Rep Power: 1258493
diachi
Class 4 Laser

Join Date: Feb 2008
Posts: 9,132
Rep Power: 1258493
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by Accutronitis Alaskan suggested I should be focusing to infinity so that's what I did, and then I sat it on the ground pointing at a wall at the end of my cul-de-sac which is 175 feet away from the front of my house, then I used dial calipers and measured the spot size on the wall which was 49mm on the fast axis and 19mm on the slow axis, Then I measured the spot size on the output lens of the beam expander which was 12.5 on the fast axis and 10mm on the slow axis. After that I went to pseudonomen137's mRad Calculator for laser divergence website pseudonomen137's JScript mRad Calculator and I put in the numbers I just got and I got....... Slow Axis mRad Is 0.1874765632328795 focused to infinity. Fast axis mRad Is 0.6842893570104003 focused to infinity. I can't see what I'm doing wrong ???

So you have fast axis correction and a beam expander on there...? If so - how much expansion is the BE providing?
__________________

355nm | Bruker SmartBeam | Q-Switched Nd:YAG | Awaiting Arrival
405nm | Banggood LT-850 | 50mW Metered | Review Unit | >>Review<<
445nm | Sanwu Laser Pocket Series | 400mW Metered
445nm | NDB7242E Pen Build | 60mW Metered | >>Build Thread<<
450nm | LaserPointerStore - Thor H2 | 1.6W Metered | Review Unit | >>Review<<
473nm | B&W Tek BWB-10-OEM |
488nm | Spectra Physics 163 Argon | ~30mW Metered |
495nm | Laser66 Pen Build | WIP
515nm | PL515 Pen Build | 50mW | >>Build Thread<<
520nm | Laserlands 520 5mW | 3mW Metered | Review Unit | >>Review<<
532nm | Gearbest 303 Pointer | 50mW Metered
532nm | Gearbest JD-850 Pointer | 30mW Metered |
633nm | HeNe | 6mW
633nm | Spectra Physics 155 HeNe | <1mW >>Thread<<
650nm | Sanwu Laser Pocket Series | 200mW Metered
808nm | Melles Griot 532nm Lab Unit | No Crystals >10W

B&W Tek Spectrometer
LaserBee 2.5W USB LPM

07-07-2017, 04:38 PM #8
 Super Moderator Join Date: Jan 2014 Location: Qatar, land of the hot footed. Posts: 9,569 Rep Power: 1781829
Super Moderator

Join Date: Jan 2014
Location: Qatar, land of the hot footed.
Posts: 9,569
Rep Power: 1781829
Re: Help Needed With mRad Calculations....

A NUBM44 Laser diode using a 6 mm diameter "G2" collimating lens has under 12 mRad. From that it's easy to figure out what the divergence would be by doubling the beam diameter to get half the divergence. For example, if the beam had a divergence of 12 mRad with a 4 mm wide beam and the beam were expanded to 8 mm, the divergence would be about half or about 6 mRad, double the beam diameter again to 16 mm and about 3 mRad. At a beam diameter of 32 mm, or over an inch, about 1.5 mRad, and so on. These are very rough examples, I don't know the diameter of this diode when collimated with a G2 or similar 6 mm diameter lens at its FL.
__________________

Attention new brothers of the collimated light!

Newbie advice: Please take the time to first make an introduction in the Welcome section before posting questions: - https://laserpointerforums.com/f37

Divergence to spot size calc: - 1 mRad is about .057 degrees which expands to be very roughly ~10% the diameter of the moon or sun at their distances.

Divergence Calculator: pseudonomen137's JScript mRad Calculator - Measure your lasers beam dia. at 1 foot & then 20'.

Online calc. to determine spot intensity at different mRad's & powers: http://tinyurl.com/divergence-calculator

Laser Power Density Calculator: Laser Power Density Calculator - Ophir

Build a beam expander to reduce divergence: http://tinyurl.com/BeamExpander

University YAG Project The Professor's Homebuilt Lasers Site - YAG Lasers

YAG Power Calc. Laser Peak Power Calculator - Ophir

Angular Size Calculator; use with diode angle of radiation spec. for lens dia. at FL: Angular Size Calculator

RHD's Relative Brightness vs Wavelength Calc: https://tinyurl.com/RHD-brightness

High Current Pulse Diode Drivers: https://tinyurl.com/ya7whuk3

07-07-2017, 04:42 PM #9
 Banned Join Date: Dec 2016 Location: Las Vegas Posts: 1,358 Rep Power: 0
Accutronitis
Banned

Join Date: Dec 2016
Location: Las Vegas
Posts: 1,358
Rep Power: 0
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by diachi So you have fast axis correction and a beam expander on there...? If so - how much expansion is the BE providing?
I don't know as I'm using a input lens out of a camera lens and I'm using a jetlasers output lens from one of their 10X beam expanders.....

Quote:
I posted all the numbers I got and how I got them ???

Last edited by Accutronitis; 07-07-2017 at 04:43 PM.

07-07-2017, 04:44 PM #10
 Class 4 Laser Join Date: Feb 2008 Location: Yellowknife, NT, Canada Posts: 9,132 Rep Power: 1258493
diachi
Class 4 Laser

Join Date: Feb 2008
Posts: 9,132
Rep Power: 1258493
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by Accutronitis I don't know as I'm using a input lens out of a camera lens and I'm using a jetlasers output lens from one of their 10X beam expanders..... I posted all the numbers I got and how I got them ???

What's the diameters before and after the BE? Can easily calculate expansion factor from that. Depending on the level of expansion your numbers could well be correct.
__________________

355nm | Bruker SmartBeam | Q-Switched Nd:YAG | Awaiting Arrival
405nm | Banggood LT-850 | 50mW Metered | Review Unit | >>Review<<
445nm | Sanwu Laser Pocket Series | 400mW Metered
445nm | NDB7242E Pen Build | 60mW Metered | >>Build Thread<<
450nm | LaserPointerStore - Thor H2 | 1.6W Metered | Review Unit | >>Review<<
473nm | B&W Tek BWB-10-OEM |
488nm | Spectra Physics 163 Argon | ~30mW Metered |
495nm | Laser66 Pen Build | WIP
515nm | PL515 Pen Build | 50mW | >>Build Thread<<
520nm | Laserlands 520 5mW | 3mW Metered | Review Unit | >>Review<<
532nm | Gearbest 303 Pointer | 50mW Metered
532nm | Gearbest JD-850 Pointer | 30mW Metered |
633nm | HeNe | 6mW
633nm | Spectra Physics 155 HeNe | <1mW >>Thread<<
650nm | Sanwu Laser Pocket Series | 200mW Metered
808nm | Melles Griot 532nm Lab Unit | No Crystals >10W

B&W Tek Spectrometer
LaserBee 2.5W USB LPM

07-07-2017, 04:45 PM #11
 Class 3R Laser Join Date: Aug 2016 Location: European Union Posts: 1,305 Rep Power: 804924
Class 3R Laser

Join Date: Aug 2016
Location: European Union
Posts: 1,305
Rep Power: 804924
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by diachi It's just the full angle divergence, instead of the half angle divergence...? Imagine splitting the beam in half right down the middle, then measuring the divergence of one half, that'd be the half angle divergence. The full angle is both halves added together. You'd get the half angle by measuring the radius at different distances and the full angle my measuring the diameter.
Exactly. Now in case of positive divergence just forget the pic above and do your own slightly different: You can use geometry with goniometry and triangles found there to get formula as reasonable estimate. Just draw beam as paralel lines (distance between them is measurment of diameter close output aperture d1), draw lines of spreading beam to diameter far (d2 at distance l between place d1 and d2). Than you will see half angle triangle. Using tangens for angle found between paralel lines as tan alpha = ((d2-d1)/2)/l. The angle alpha you got is half angle - so multiply 2 is full angle. In tangens function there are diameters, to get right angle triangle you need to get radii difference - that's where 2 comes from. You can get angle in degrees or radians (divide by 1000 to get mrad). Hopefully I did not make mistake (just from head in pub ).
__________________
"Lasers are s3xy."
"That feeling when you see colours as their wavelengths."
"Laserpainting is a drug. Do not try it."
"If you do not feel and experience the magic, you cannot become the master of wizardry."

Current collection:
405 nm | 500 mW | Wicked Lasers Lunar
445 nm | 3.5 W | Wicked Lasers Arctic
473 nm | 100 mW | Jet Lasers PL-E Pro
520 nm | 1 W | Wicked Lasers Krypton
532 nm | 100 mW | Wicked Lasers Evo
532 nm | 800 mW | Sky Lasers PL

532 nm | 1.4+ W | Optotronics RPL-II
589 nm | 50 mW | Dragon Lasers Spartan
635 nm | 750 mW | Wicked Lasers Inferno
1 W RGB projector
(+ some pointers)

Wishlisted:
Sanwu's RGB Portable

Laserpainting art:
Latest artwork: The Pandora's Black Box

The Hologram Question has just been answered! (wazup post)

LPF social media hashtag: #laserpointerforums

07-07-2017, 04:51 PM #12
 Banned Join Date: Dec 2016 Location: Las Vegas Posts: 1,358 Rep Power: 0
Accutronitis
Banned

Join Date: Dec 2016
Location: Las Vegas
Posts: 1,358
Rep Power: 0
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by diachi What's the diameters before and after the BE? Can easily calculate expansion factor from that. Depending on the level of expansion your numbers could well be correct.
The beam before the beam expander size I don't know because I didn't think that needed measuring, But I do know the diameter after the BE......

Quote:
 Originally Posted by Radim Exactly. Now in case of positive divergence just forget the pic above and do your own slightly different: You can use geometry with goniometry and triangles found there to get formula as reasonable estimate. Just draw beam as paralel lines (distance between them is measurment of diameter close output aperture d1), draw lines of spreading beam to diameter far (d2 at distance l between place d1 and d2). Than you will see half angle triangle. Using tangens for angle found between paralel lines as tan alpha = ((d2-d1)/2)/l. The angle alpha you got is half angle - so multiply 2 is full angle. In tangens function there are diameters, to get right angle triangle you need to get radii difference - that's where 2 comes from. You can get angle in degrees or radians (divide by 1000 to get mrad). Hopefully I did not make mistake (just from head in pub ).
Say what, who, where ??? lol

Last edited by Accutronitis; 07-07-2017 at 04:54 PM.

07-07-2017, 04:58 PM #13
 Super Moderator Join Date: Jan 2014 Location: Qatar, land of the hot footed. Posts: 9,569 Rep Power: 1781829
Super Moderator

Join Date: Jan 2014
Location: Qatar, land of the hot footed.
Posts: 9,569
Rep Power: 1781829
Re: Help Needed With mRad Calculations....

I believe RedCowBoy did a divergence measurement using a 6 mm diameter G2 type of lens, maybe he will chime in with all his figures and we can extrapolate the expected divergence at a given beam diameter.
__________________

Attention new brothers of the collimated light!

Newbie advice: Please take the time to first make an introduction in the Welcome section before posting questions: - https://laserpointerforums.com/f37

Divergence to spot size calc: - 1 mRad is about .057 degrees which expands to be very roughly ~10% the diameter of the moon or sun at their distances.

Divergence Calculator: pseudonomen137's JScript mRad Calculator - Measure your lasers beam dia. at 1 foot & then 20'.

Online calc. to determine spot intensity at different mRad's & powers: http://tinyurl.com/divergence-calculator

Laser Power Density Calculator: Laser Power Density Calculator - Ophir

Build a beam expander to reduce divergence: http://tinyurl.com/BeamExpander

University YAG Project The Professor's Homebuilt Lasers Site - YAG Lasers

YAG Power Calc. Laser Peak Power Calculator - Ophir

Angular Size Calculator; use with diode angle of radiation spec. for lens dia. at FL: Angular Size Calculator

RHD's Relative Brightness vs Wavelength Calc: https://tinyurl.com/RHD-brightness

High Current Pulse Diode Drivers: https://tinyurl.com/ya7whuk3

07-07-2017, 05:35 PM #14
 Class 3R Laser Join Date: Jun 2007 Posts: 1,805 Rep Power: 386771
steve001
Class 3R Laser

Join Date: Jun 2007
Posts: 1,805
Rep Power: 386771
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by Accutronitis The beam before the beam expander size I don't know because I didn't think that needed measuring, But I do know the diameter after the BE...... Say what, who, where ??? lol
You only need to know that if you want to know the beam expander power. If not don't concern yourself.

You said your are using a lens from a JL expander. That implies you took one apart. I have one too. How did you ?

07-07-2017, 05:43 PM #15
 Class 3R Laser Join Date: Jun 2007 Posts: 1,805 Rep Power: 386771
steve001
Class 3R Laser

Join Date: Jun 2007
Posts: 1,805
Rep Power: 386771
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by Alaskan I believe RedCowBoy did a divergence measurement using a 6 mm diameter G2 type of lens, maybe he will chime in with all his figures and we can extrapolate the expected divergence at a given beam diameter.
For any beam expander.
If you know the focal lengths of the lenses then divide the longer focal length by the shorter focal length will give the expander power.

Last edited by steve001; 07-07-2017 at 05:46 PM.

07-07-2017, 05:45 PM #16
 Class 4 Laser Join Date: Feb 2008 Location: Yellowknife, NT, Canada Posts: 9,132 Rep Power: 1258493
diachi
Class 4 Laser

Join Date: Feb 2008
Posts: 9,132
Rep Power: 1258493
Re: Help Needed With mRad Calculations....

Quote:
 Originally Posted by Accutronitis The beam before the beam expander size I don't know because I didn't think that needed measuring, But I do know the diameter after the BE...... Say what, who, where ??? lol
It doesn't need measuring for divergence calculations, but it's good to know anyway. If it's a very large expansion that'd explain your rather low divergence.
__________________

355nm | Bruker SmartBeam | Q-Switched Nd:YAG | Awaiting Arrival
405nm | Banggood LT-850 | 50mW Metered | Review Unit | >>Review<<
445nm | Sanwu Laser Pocket Series | 400mW Metered
445nm | NDB7242E Pen Build | 60mW Metered | >>Build Thread<<
450nm | LaserPointerStore - Thor H2 | 1.6W Metered | Review Unit | >>Review<<
473nm | B&W Tek BWB-10-OEM |
488nm | Spectra Physics 163 Argon | ~30mW Metered |
495nm | Laser66 Pen Build | WIP
515nm | PL515 Pen Build | 50mW | >>Build Thread<<
520nm | Laserlands 520 5mW | 3mW Metered | Review Unit | >>Review<<
532nm | Gearbest 303 Pointer | 50mW Metered
532nm | Gearbest JD-850 Pointer | 30mW Metered |
633nm | HeNe | 6mW
633nm | Spectra Physics 155 HeNe | <1mW >>Thread<<
650nm | Sanwu Laser Pocket Series | 200mW Metered
808nm | Melles Griot 532nm Lab Unit | No Crystals >10W

B&W Tek Spectrometer
LaserBee 2.5W USB LPM

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

All times are GMT. The time now is 04:17 AM.

 -- DarkShadows V5 -- Responsive LPF -2562016 -- Default Style Contact Us - Laser Pointers - Archive - Top