Nice Etalon in a sealed box. I'm assuming it s uncoated as I have a similar thinner one for sale that is uncoated and has similar part#s See spec. sheet for details. This one says 3.175mm thick on the box and the spec. sheet has a 3.18mm  one which I'm calling the same  and has an FSR (GHz) of  32.43 @ 1014nm. See my other sales for the thinner (1mm) version.