Optical tables for measurements: Any experiences? - Page 1
Forum section: electronics / testgear

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: January 27, 2020, 03:08:33 pm
content: So I realize the focus of this forum is mostly hobby electronics, and most people will often roll their eyes when I talk about equipment because of pricerange, but here goes anyways.At work, where I am semi-lab-manager, I'm starting to use optical table style things to make measurement setups. Since right now I have a 'new lab' discount code from Thor Labs, I am stocking up on basic equipment.Anyone have experience using optical tables to make your measurement setups? Any tips/tricks/ideas (unconventional ways of using things? I am using lens-holders for holding cables straight, similarly, using V-blocks for holding on to VNA cables and reducing the forces on our connectors, etc).I seem to remember seeing a wafer-probe setup on an optical table at some point, but have to date failed to find any examples of this from the bigger sellers (Newport, Thorlabs, Edmund...)

author: JohnG
author_rank: Frequent Contributor
timestamp: January 27, 2020, 03:24:38 pm
content: I think this is a good idea. I am slowly learning about optical measurements due to my job, but have found some of the optical breadboarding concepts to be helpful.I have found two things that may be of use:1. You can use mechanical fixture plates in place of optical breadboard plates. Same spacing, same threading (at least for imperial units), relatively low cost on ebay.2. There are a lot of optical fixtures on Thingiverse if you have a 3D printer, which can lower the cost barrier.Cheers,John

author: ebastler
author_rank: Super Contributor
timestamp: January 27, 2020, 03:52:22 pm
content: You didn't really statewhyyou intend to use optical tables. Do you want to do actual optical experiments, i.e. are you interested in flat surfaces, stiffness, vibration isolation from the environment? Or do you just like the threads to hold stuff down, and maybe the steel surface so you can use magnetic holders?If you need stiffness (for vibration isolation), the thicker tables are better than the thin breadboards. They do need a dedicated support frame and at least passive vibration isolation in that case. If you just want a convenient mounting surface, the thinner breadboards are much easier to move and can sit on a regular desk/bench.In general, don't get carried away regarding the size of a table, and do keep an eye on the weight. Ideally, you still want to be able to lift them with two people, and to move them through doorframes (on a cart) while they sit horizontally and are loaded with stuff.Regarding mounting hardware: If you actually need stability/precision, the classic 1/2" post mounts suck, in my opinion. When you build an optical path high above the table, mounted on these relatively thin posts, you lose a lot of the stability awarded by the base plate. The 1" posts and 1.5" posts, pioneered by New Focus but now available from various sources, are much better. Clamping forks allow these to be positioned anywhere, away from the thread grid.If, on the other hand, you just want to hold some cables and probes in place, the thin posts should be fine. While magnetic bases may look convenient at first glance, I still prefer the clamping forks: Repositioning a post is a two-handed operation (using an Allen key and moving the post), but you have good control. And the forks take up real estate only towards one side of the post (which you can chose), and hence get in the way less than the chunky magnetic bases.

author: TimFox
author_rank: Super Contributor
timestamp: January 27, 2020, 03:53:19 pm
content: I used large optical tables at work. They were usually available with M6 holes on 25 mm centers, or 1/4-20 UNC holes on 1 inch centers. Obviously, you need to choose for consistency with your fixtures. Note that they have some vibration isolation, and high strength in compression, but little shear strength, due to the honeycomb between top and bottom plates.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: January 27, 2020, 04:24:09 pm
content: We are new to the entire optical table thing - with respect to the why: we had a few guys using our single optical breadboard for actual optics over the last years, but now with a lot of effort into millimeter-wave and THz we are seeing the use there too, as we really are entering the quasi-optical regime. Not only for the reason of things being quasi-optical, but also since it gives a rigid and repeatable framework to attach things, build measurements with PCBs and lots of connectors, etc...We have the metric type (M6 holes on 25mm grid). The mechanical department here is machining us some plates to attach VNA, spectrum analyzer and signal generator frequency extenders to the tables.One of the main things I like is that you can get rigid setups that are repeatable in placement. Also, using the xy-stages we can more accurately (and again in a repeatable way) mount devices with respect to each other.Interesting to hear that the 1/2 inch posts are not very rigid. We have a number of them, but for the extenders I'm using a system based on a 1.5 inch post. These are a lot heavier though.I might think about getting us a true table, and not just breadboards we put on tables - esp if we can build a wafer-probe system on that - but again, I have yet to find a system that does that (ofcourse I guess I can build one out of standard stages and some precision local-manufactured stuff, but owuld be cool to have a complete system...)