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Question about Lens Outputs

IsaacT

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So I was :thinking: about the different lens options and something occurred to me.

Okay, so if a normal Aixiz lens allows a laser to do 600mW, and the 405-G-1 lens gives a 31% power boost on average, then with the better lens you are going to see roughly 786mW(131% of 600mW). Now, to me it seems that that would indicate that the 786mW of power is already there, but is being absorbed or blocked by the inferior lens....

Which brings me to my question(s):

(1) If there is already that much power being emitted from the diode, in what way is that energy lost?
(2) If it is being blocked or reflected could using an inferior lens actually lead to a loss in diode life?
(3) Would using a better lens lead to longer run times due to less heat being absorbed by the unit and more being transferred away from the unit to the "dot" or beam?

Just to reiterate why I think this: If you had an 800mW laser, and it was only outputting 600mW, would you not wonder how the power was lost, and if so, how detrimental it could be to the overall health of your laser?

I very much look forward to hearing from all of you who have much more knowledge about this field than I do. Perhaps someone can point out a fatal flaw in this logic.

Thanks for looking,
Isaac
 





Blord

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The loss is in the blocking by the lens barrel. A major part of the beam goes though the lens and a small part is blocked. A high focal lens like the G1/G2 lens will captured all the light. That is why it gives the power boost.
Also the multiple lenses will absorbed more light. All these losses will heat up the unit more. Energy isn't wasted.

I did an output test of all common lenses with a blue diode. It is interesting to see the differences between the lenses, http://laserpointerforums.com/f52/lens-comparison-445nm-h1600-diode-75324.html
 
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Hm... I don't think that optical losses necessarily result in shorter diode "life."

If you are trying to get X mW out, then using a lens that blocks a lot of the light means you have to run it at higher current which might result in more rapid degradation...
But laser diodes don't really mind heat all that much. As long as they are within normal operating temps I don't see why optical losses would make much of a difference.
 
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Optical loss no. Additional heat buildup, and back reflection should though.

Then the question becomes, even if the diode lifespan is shortened, considering the diodes are already usually not being cooled as well, and are overdriven in our handhelds... is the loss in lifetime relevant? Especially since most handhelds see just minutes of use at a time.
 
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Optical loss no. Additional heat buildup, and back reflection should though.

Then the question becomes, even if the diode lifespan is shortened, considering the diodes are already usually not being cooled as well, and are overdriven in our handhelds... is the loss in lifetime relevant? Especially since most handhelds see just minutes of use at a time.

I don't think back reflection is significant either.
Usually the lenses we use are coated for a specific wavelength range to minimize reflection. Also, the convex surface of the lens won't focus the reflected portion of the beam onto the emitter; the light is spread over a larger area.

If the diode is overdriven, then the over-current is going to make the diode run hotter than usual whether or not there is extra heat from optical losses.
 
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Some of the lenses have a flat side facing the diode, and only the front is convex, so you may actually have direct reflection back into the diode. Still, I think most of the problems people were seeing with shortened lifespans were with already sensitive diodes, such as those 405nm laser diodes. The 445nm and 638nm laser diodes seem a bit more robust.

I do wish that lens reflectance/transmission were quoted in negative dB as compared to open-air transmission, instead of a comparison increase vs. Aixiz lenses, which gives the impression that these lenses magically create power (yes, I know it's relative). For a while I wasn't even sure what Aixiz lens was being cited, and the baseline lens also changes depending on what wavelength we're using.
 
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