Why did my 642nm diode die?

[steve-o]

Getting off-topic from "Why did my 642nm diode die?" .. lol .. Actually the divergence is fairly good. I'm still trying to narrow it down (pun intended) . Been talking (emailing) to a Melles-Griot optical engineer for a couple of days now to see how to try to tame the "terrible reds" .. we'll see ..

[steve-o]

Tid-bits of interesting info from Thorlabs and MG app engineers (from emails I sent/ received from them) ..

I prefer to start with focal length because that will determine the beam size.
Then narrow it down based on NA. It is best to have an NA a little higher, say 20%, for collimating light because sometimes the outside of the asphere lens (still in the CA) can “mis-collimate” the outside of the beam leaving you with a ring around the center beam. I am not saying this will happen, but there is a chance.
Then consider the AR coating. In this case –A is best but –B should work fine too.
Sometimes I like to also consider the design wavelength. However, most lenses are capable of focusing to the diffraction limit even when you work at 50% the design wavelength, so a 635nm beam can often be focused to the diffraction limit with a 1550nm DW lens. So I would say this is not as important.

I would be reluctant to say there is a better alternative lens to use. It really depends on what you want to achieve. I will say that I prefer to use Rochester lenses when I really want to push the performance of a system, instead of a Geltech/LightPath lens, when an asphere is needed. Although this is a multiple spatial mode laser diode, so I think the lens performance will be less noticeable than with a single spatial mode one.

I inquired about the 6388 emitter size..

The emitter size is 5um x 2um.
Please contact me if you have further questions.

This was about the Mitsu ML520G51 (from a different engineer):

We unfortunately do not carry a catalog product able to match the specifications given. For the laser you carry, the numerical aperture for the more divergent axis of the beam is 0.62932 (calculated by taking the sin() of 39 degrees) which is greater than any of the numerical apertures listed for the GLC line. Also, making modifications to increase the numerical aperture value (such as increasing the clear aperture and decreasing focal length) would be very expensive and difficult. I hope, however, that this gives you an idea of what to look for when finding a collimating assembly fitting for your laser.

Unfortunately, I am not aware of an online calculator able to help out with this, but the sin of the diverging angle is a good approximation when finding the numerical aperture of the beam.

[chad]

Thanks, That is interesting. Keep us updated.

chad