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Typical Beam Divergence Rates

Gobc

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Hi Guys,

This is my first laser project and I'm going to be building a mid power blue laser. I'm looking to output 100-200mw. I've already aquired my laser diode and have tested it using a my own little test rig. I was a little surprised that lasers require focusing optics (first time remember). After poking around the internet a bit, It seems like 1.2-1.5mrad is a typical value for beam divergence. Is this true, or are the stats I found from really cheap low quality laser optics?

I calculated that 1.2mrad = 12cm/100yard. This seams extremely large. I know people have been driving leds past 1W, however even at that power output, I can't see imagine the beam being visible past a few hundred meters.


Is it possible to achieve better? Feel free to recommend projects.
 



RA_pierce

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Typical for greens is 1.2-1.5mRad. A good green will be less than 1.2mRad.

Typical for single-mode diodes (405nm and 655nm) with Aixiz focusable lens is 0.5mRad.

Typical for multi-mode diodes (445nm and 808nm) with Aixiz focusable lens is 0.5mRad x 1.6mRad.

Remember that the 445nm diodes have a large emitter that outputs a "stripe" rather than a dot, so each axis has a different divergence angle.

To calculate the beam size over a distance, you need to know:

  • Beam diameter at aperture
  • Beam divergence
  • The distance you are measuring
There is a handy calculator that will do it for you, too:
pseudonomen137's JScript Laser Calculators
 

steve001

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Hi Guys,

This is my first laser project and I'm going to be building a mid power blue laser. I'm looking to output 100-200mw. I've already aquired my laser diode and have tested it using a my own little test rig. I was a little surprised that lasers require focusing optics (first time remember). After poking around the internet a bit, It seems like 1.2-1.5mrad is a typical value for beam divergence. Is this true, or are the stats I found from really cheap low quality laser optics?

I calculated that 1.2mrad = 12cm/100yard. This seams extremely large. I know people have been driving leds past 1W, however even at that power output, I can't see imagine the beam being visible past a few hundred meters.


Is it possible to achieve better? Feel free to recommend projects.

Divergence rate has nothing to do with cheapness. It's just a number. Yes, it is possible to achieve lower divergence. The important question too ask would be is it practical while not spend much $ on beam correction optics. Optics that will circularize the beam plus optics for producing a lower divergence.

100-200mw of blue light from your laser will be significantly brighter then 1W from a blue LED because the laser is collimated and even if the LED is collimated.

To calculate using pseudonomen137's JScript Laser Calculators you'll have to run the numbers twice. Once for the fast axis and once for the slow axis. But before you use the app you'll need to measure at 10 meters what the beam diameter and length are then calcualte the angle of degrees if you want to be precise. Measuring Angles in the Sky
Or you can forget all of that and just experiment with inexpensive optics at first.
 

Gobc

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Thanks guys. I just wanted to know what a typical laser pointer is capable achieves in terms of divergence. I wouldn't mind a a tighter beam however. Can anybody recommend some optics?
 

RA_pierce

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100-200mw of blue light from your laser will be significantly brighter then 1W from a blue LED because the laser is collimated and even if the LED is collimated.

That is not true. For one, LEDs do not emit monochromatic light, so there is one difference, but assuming the wavelength(s) were the same for the blue laser and the LED, 200mW of laser light is going to be less bright than 1000mW of LED light.

The LED will be less intense since nothing can compete with lasers when it comes to squeezing lots of power in a small area, but if the wavelengths and power is the same, the brightness will be the same.

Thanks guys. I just wanted to know what a typical laser pointer is capable achieves in terms of divergence. I wouldn't mind a a tighter beam however. Can anybody recommend some optics?

There aren't many optics sets designed specifically for this (correction and collimation) that are within the average hobbyist's price range, but a beam expander might be close to what you are looking for.

If you want a lens you can simply slap in front of a laser diode and have a great beam, you're going to have a tough time searching. These blue diodes have terrible beam characteristics (although not as bad as some) and are not so easy to tame.

There was a group buy going some time ago for cylindrical correction optics. Your other choice is to collimate the beam with an aspheric lens and use anamorphic prisms to re-shape the output.
 

Gobc

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There aren't many optics sets designed specifically for this (correction and collimation) that are within the average hobbyist's price range, but a beam expander might be close to what you are looking for.

If you want a lens you can simply slap in front of a laser diode and have a great beam, you're going to have a tough time searching. These blue diodes have terrible beam characteristics (although not as bad as some) and are not so easy to tame.

There was a group buy going some time ago for cylindrical correction optics. Your other choice is to collimate the beam with an aspheric lens and use anamorphic prisms to re-shape the output.


Correct me if I'm wrong, but the collimating lens will make the beam straight, and the asperhic lens will change the shape (from rectangle to circular)?
 

RA_pierce

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Correct me if I'm wrong, but the collimating lens will make the beam straight, and the asperhic lens will change the shape (from rectangle to circular)?

No, the aspheric lens would be the "collimating" lens which would reduce the diode's "raw" divergence off the emitter to make the characteristic laser beam.
To change the beam shape to a circle (more or less), either a cylindrical lens or anamorphic prism pair could be used. Another option would be to use fiber optics.
 




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