Nichia 034B LED Collimation

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maccyjj

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Hello!

I am new to these forums - long time lurker, first time poster - and registered in the hope of getting some help from the many knowledgeable people here.

I work in a physics lab and we have been trying out some Nichia 034B UV LED's as a cost-effective alternative to UV lasers. However, this has required me to attempt to collimate the output from an LED (hard part) and demagnify it to a narrow beam (easy part). Unfortunately I have had some problems in the collimation process. I have read many posts about UV flashlights being made and this is pretty much what I am after - a straight enough wide beam that doesn't have to be perfectly collimated, but is quite evenly spread out. I have absolutely no prior experience in optics so I would love to hear any advice you may have on what mirrors or lenses I may need to sort-of collimate my LED. Previously I have tried an aspheric condenser lens, but I don't get a very collimated output and far down the line I get an image of the LED right in the center of my beam - something I would obviously like to avoid.

I suppose what I am asking is how you manage to make these flashlights and although I am under the impression I need some kind of parabolic reflector, I have no clue where to look for one. I hope you will be kind enough to help me out and I thank you in advance for your assistance. :)
 
A full size, glass fresnel lens, slightly defocused, may work. I used to get these lenses out of old style overhead projectors. The light loss is pretty high though. In general you need a large ratio if source to optic size to make a narrow beam.
 
How big of an aspheric did you use? A small one as used for collimating diode lasers will not collimate an LED very well.

AAS's idea I think would be worth persuing, esp. since large glass fresnels are easily harvested, whereas large diameter aspherics are a bit pricier and harder to come by.

Depending on how well collimated you require, you may just be able to get away with off-the-shelf reflectors. Again, generally speaking, a smooth, large diameter reflector will outperform a smaller diameter similar style reflector. Plastics in TIRs may be opaque to that wavelength. Probably you have a spare overhead projector rather than a shelf of random flashlight reflectors...
 
What about two aspheric condenser lenses back to back? Like so: |)(| I think that literature on thorlabs or another optics website led me to believe this produces a very small image of the die. I could be mistaken though. A call to one of these optics manufacturers would probably lead you in the right direction. Thorlabs, Edmund Optics, Melles Griot, Align Optics, Optolife, Newport.
 
Thank you everyone for the suggestions.

Regarding the Fresnel Lens, I read somewhere that the lens needs to be a distance z from the LED, where z = a^2/lambda, a being the size of the emitting area. For this LED, it's 1mm and lambda is 385nm, giving me a distance of 2.59 metres, which means essentially none of the light will get through, right?

For the aspheric lens I used one from Thorlabs (ACL4532) of focal length 32mm and diameter 45mm. I chose this one because it had the highest numerical aperture and I thought it would collect the most light.

I have inquired about some reflectors and will see if those work. I will also try to face my two identical aspheres back to back and see if that helps. Although I don't just need an image of the die, I need it to have a small divergence at large distances (~50cm). I'll try it out though.
 
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