Divergence compared: DX30 / Kai50 / DIY Red

[Benm]

I've set up a little experiment to test the divergence of these three lasers. The green ones are these models:

DX True 30 mW, $27, http://www.dealextreme.com/details.dx/sku.469
Kaidomain 50 mW CR2, $26, http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3304

The red one is DIY, GB diode housed in a MXDL flashlight and using a module like this one: http://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3201 . Total parts cost around $40. Driven at ~220 mA, output should be 125 mW or so.

As you can see, the divergence varies quite a bit between these lasers, with the red doing very well at 0.6 mrad (i adjusted it for optimal focus on the 10m target). The DX does a reasonable 1.2 mrad, and the kai is a bit worse with an oval dot, 1.7 mrad in the widest direction, 1.2 mrad in the other.

The target is 1 cm grid laserprinted on a A4 piece of ordinary paper, taped to the wall to take the picture (1/50th s exposure, f4.0).

 

[Benm]

This is how it looks with the camera pointing towards the lasers, laying on a table 10 metres away from the wall/target.

 

[eggsy]

didnt u say in your review of the Kai50 that u could focus the beam?
how is the divergence after focusing it?

 

[Benm]

This is -after- focusing it to some extent, but i'm not sure it's the optimal setting at all.

The problem is that to turn the lens, you kinda have to insert a little screwdriver/pin/whatever sideways into the aperture, blocking the beam. So there is not way for me to adjust the lens while actually looking at the output at the same time.

 

[Rhith]

Also for the divergence don't forget to account for the beam diameter, also with the DIY if it's -mRad that has to be taken into consideration. Other then that it looks great!

 

[Benm]

You're right about the initial diameter.. for the greens, this is very small (1mm or so) and won't affect the numbers much.

For the red one it's a bit of a different story since the beam comes out of the aixiz module already about 4 mm in size. On the other hand, i'm not sure i got it as paralel as can be there, since i optimized focus for the measured distace.

In any case, the red does much better, but that's probably due to the bigger initial diameter to a great degree.

 

[Rhith]

Well the thing is, I can get my red focused to be a <0.5mm dot ten meters away and say the mRad is 0.05mm, but that just wouldn't be accurate. I'm not trying to put you down I just want to make sure that we're all getting correct readings.

 

[DoughDTD]

i agree with Rhith, the whole point of divergence is to measure how much the beam deviates from its initial diameter, so it is in fact very important to know the initial diameter of the beam at aperature. For example, the DX true 30mw has been known to have a VERY small initial diameter, so it doesnt suprise me that it had the smallest dot in your distance test.
Try and figure out a way to get the initial diameters of them, then caluclate the divergence as a change in diameter, not as a function of just the final spot diameter.

Other than that nice set-up, keep up the good work and pictures, and I appreciate the review!

-Dough

 

[knimrod]

Interesting comparison..  My Kai 50mW (identical to your laser) has excellent divergence.  I'm not all that impressed with the power but the divergence is tight.  I'm still running it on the crappy CR2 battery (2.8V) it came with but I have some CR2 3.6V rechargeables on the way.

 

[Benm]

Well the thing is, I can get my red focused to be a <0.5mm dot ten meters away and say the mRad is 0.05mm, but that just wouldn't be accurate. I'm not trying to put you down I just want to make sure that we're all getting correct readings.  

You're actually correct, though it's not possible to create pinpoint spot like that 10 metres away.. at least not in practice That said, i'll try to measure the initial diameter of the dots accurately and give some adjusted figures.

My Kai 50mW (identical to your laser) has excellent divergence. I'm not all that impressed with the power but the divergence is tight. I'm still running it on the crappy CR2 battery (2.8V) it came with but I have some CR2 3.6V rechargeables on the way.

You might be in luck then! The difference between the soddy battery that comes with it and a rechargeable is quite big, at least on mine. I'd estimate is does double the output power on the rechargeable. I might be able to get the divergence better on the kai too, but it's just a pain to adjust focus.