Noob question re. Laser Diodes and Required Optics - Page 1
Forum section: electronics / beginners

author: gavbro
author_rank: Newbie
timestamp: May 17, 2024, 02:42:25 pm
content: Hello All,I'm an IT Nerd that dabbles in electronics as a hobby, so please pardon the potentially 'stoopid' question!I'm working on a project that requires the use of a low-power ~650nM laser in the 5-10mW range, and I've hit a surprising wall in the quest to source a discrete component that I can drop onto a PCB that will work with minimal fuss. In fact, for the purposes of this post,assume I’m simply trying to build a low-cost laser pointer using discrete componentsfrom a quality/reliable source. Also, I’m not trying to do anything hyper critical (like measure distances, read/write data, cut material, etc.) – I merely want a bright red spot to be projected against a surface up to 25 yards away (unnecessarily expensive LD’s & optics will be an overkill for my application).I use Mouser and Digikey for my component needs (I'm in the US) and there don't seem to be very many options for what I'm looking for (my first surprise). From what I can gather, this is what is available from Mouser, tho Digikey is pretty much the same:https://www.mouser.com/c/optoelectronics/lasers/laser-diodes/?output%20power=7%20mW~~10%20mW&rp=optoelectronics%2Flasers%2Flaser-diodes%7C~Output%20PowerI purchased a small batch of the cheapest options available (https://www.mouser.com/ProductDetail/755-RLD65NZN5-00A) to test, and was disappointed to see that the light output is very much dispersed into a dim approximately 2-3" circle from about the same distance away from the emitter. From what I have been able to glean online, it would appear I need to additionally figure out and acquire collimation and/or focusing lenses plus some kind of mechanical assembly to hold everything together.Is my understanding above correct? Is a turnkey pre-focused PCB mountable laser diode component simply not a 'thing'? (I really just want to drop a component onto a PCB that can project a bright red spot when driven)Assuming the above is correct, where can I get more information on the specifics of what I would need and where to acquire such hardware (in bulk)? It looks like the ROHM brand LD’s are the most popular/available on Mouser and Digikey, and I have scoured the ROHM website for some kind of guides/application notes on this subject, but couldn’t find anything of substance (they have great info on high-end applications like LIDAR & driver circuits, but nothing for my simple use case)? This makes me think I’m missing a fundamental piece of this puzzle – I would assume if a component needed supporting peripherals to be useful, the manufacturer would provide some kind of guidance in their datasheets or supplemental documentation? Also, wouldn’t the likes of Mouser also sell the peripherals needed?The final point making me think I’m missing a fundamental piece of this puzzle is the fact that there appears (to me) to be a huge chasm between the cheap Amazon/Ali LD's and the 'high-end' Mouser/Digikey components - no middle ground? I can buy 20 (pre-focused) Laser Diode’s from Amazon for around $8.00 (https://www.amazon.com/gp/product/B088PQQ9XV/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1). These work great for what I need, but I would never consider this as a serious production option (obvious concerns with quality and long-term supply). Were I to try creating one of these devices using parts I can reliably source I’m looking at costs of up to $30 ea. even using 'cheap' lenses and mechanical assemblies (the ROHM website does offer lenses, but these are approaching $100 ea.) I understand the Amazon components would easily classify as ‘cheap garbage’, but the price difference between $0.40c and $30.00+ ea. seems excessive?Any pointers you could give this noob would be greatly appreciated.Thanks!

author: jmelson
author_rank: Super Contributor
timestamp: May 17, 2024, 03:25:49 pm
content: I built a laser photoplotter and needed to deliver a spot size of 0.001" onto photographic film. I glued a 3mm sphere lens into a hole in a disc and put it almost touching the front of the laser module. I then glued a piece of aluminum foil in front of the sphere lens to prevent light from coming from the edge of the sphere. I poked a pinhole in the foil. I then fitted a piece of plastic water pipe over this and mounted a microfiche lens about 6" away. The sphere collects the light from the laser and nearly collimates it, and then the other lens focuses it to the film. You can get sphere lenses from Edmund Optics, but might be able to find a cheaper source online.Jon

author: gavbro
author_rank: Newbie
timestamp: May 17, 2024, 06:59:38 pm
content: Thanks Jon, I appreciate the feedback!I got on the phone with someone from Edmund Optics (what a great experience that was - thanks for the pointerIt looks like my (naive) hope of a single turnkey PCB mountable component is just not a thing, so I've resigned myself to exploring this rabbit hole. The lady from EO was crazy helpful and I've landed on a lens (for around $30) that looks like it will do what I need. I think their optics are high-end and great quality, but ultimately a complete overkill for what I need. I ordered one to experiment with in any case. I figure I'll learn on quality components to eliminate some of the variables - I'll figure out cheaper/bulk options later when I better know exactly what to look for!Let the games beginCheers and thanks again!

author: Kleinstein
author_rank: Super Contributor
timestamp: May 17, 2024, 08:27:15 pm
content: There is quite some way to go from a bare laser diode to an approximately parallel beam. Usually the lasers have a rather asymmetric beam pattern. This is not per se bad a cylindical lense can still work. The tricky part is that most LDs have additional astigmatism and thus a different disdance for the point where the light seems to come from. So one would need a mix with a cyclidrical lense to focus the light in both directions. The "simpler" optics will provide an eliptic beam, narrow in one direction and much wider in the other. Getting a near circular beam needs extra optics matched to the beam pattern.Especially for more smaller quateties it's usually easier to get ready made lasers modules that include the optics. Getting the optics separate may well cost way more than a ready made laser with optics.

author: SteveThackery
author_rank: Super Contributor
timestamp: May 17, 2024, 09:24:11 pm
content: I was wondering the same thing - would it be feasible to redesign your product so it could use the innards from a cheap laser pointer?

author: gavbro
author_rank: Newbie
timestamp: May 18, 2024, 05:10:14 pm
content: Thank you Kleinstein! I appreciate the insights!I've come to realize that what I thought 'should' be a simple solution, does have a few additional layers of complexity I was hoping to avoid. I'm 'low-key' happy that I didn't miss anything obvious, and I just need to knuckle down and learn about all these moving parts. After absorbing a few hours of youtube videos on the principle of operation of laser diodes, right down to the quantum level of photons, electrons, and energy states, the terms coherence and collimation are no longer four letter words to meThe reason I'm trying to understand and reliably source individual components is because the concept I'm playing around with is a device that will attach to the end of a CO2 powered BB gun to have the laser momentarily activated by the CO2 gas every time the BB is fired (minus the pellet of course). This is part of a larger gaming system I'm writing software for (the 'easy' part). I need to keep size to an absolute minimum as I'm hoping to get the resultant muzzle device down to the 10-15mm depth size range (much bigger and it becomes an awkward stick out appendage). I'd like to ID reliable sources for all the parts I need in the tiny 0.023% chance I can get this all working for a decent price-point and have an opportunity to produce at quantity in the future.I was playing around with a quality brand laser diode I purchased to test with (https://www.mouser.com/ProductDetail/755-RLD65NZN5-00A) and was able to achieve a good focussed spot with a lens I liberated from one of these (https://www.amazon.com/gp/product/B088PQQ9XV/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&p&sc=1). I now feel less concerned about finding a manufacturer/supplier for lenses (at volume) knowing I can make a reliably sourced brand name LD work as needed. For prototyping/testing I'll just buy as many of these cheap Amazon LD's as I need to scavenge the lens from in the interimThanks again!

author: xvr
author_rank: Frequent Contributor
timestamp: May 18, 2024, 08:15:45 pm
content: You can use ready made laser modules:https://www.digikey.ie/en/products/filter/laser-diodes-modules/95?s=N4IgjCBcpgbFoDGUBmBDANgZwKYBoQB7KAbRAFYAGAJmoBYB2EAgZhdljAlfc%2BuZBsOYFgKGc6Y3mHJTh8HsKYE61WAA4GykA3UBOanvUC6sOusraGemXVmLOxggw11zc2NUofaP0SrVNBUFeeh97EI41HyYAXQIABwAXKBAAZSSAJwBLADsAcxAAXyKCfkgyDDRcTIACAFtCABMAVwwcEFiioA

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 20, 2024, 12:23:17 pm
content: collimator lens and you're good to go