01-23-2015, 05:26 AM
Quick reply before I go to bed,
The article aims to be higher than a "hobby article" by using tens of thousands of dollars of optical lab equipment to (attempt to do) a very technical analysis of a component.
No matter what the interferometer is pieced together on - it is not on an air ride table. It is not isolated from the room around it, so harmonic motion will skew any results. It is also not assembled in a screwed down fashion so there is almost certainly a great deal of "tremble" in the positioning of things. No material between the plywood and the components solves the issue - the mere presence of the plywood indicates all one needs to know about the stability of the test table.
Test flats have coatings on both sides of the component with different purposes. Antireflective coating on the back to maximize transmission, and a one-way ~5% reflective coating on the front-facing side to give the interferometer a reference beam. This second coating is much more fragile than regular AR coatings and is also far more flat. Touching it will smear it on the nanometer scale and such inaccuracies are easily measurable (they are within 10s, 100s, or 1000s of the times the measurement error of the machine) but will destroy the calibration of the machine. Of course this is not a commercial interferometer so there is no calibration to begin with, but touching the flat will induce wavefront aberrations. A photographic lens is polished to about 31nm rms roughness, a reference flat is more like 1-2nm rms roughness.
This article isn't by an optics student. Perhaps a physics one, but an optics student would have access to some space to do the test proper on an air ride table or at least a breadboard.
The charge for testing the mirror as-delivered in my lab would be less than $100. $20/hr * up to 2 hours for student's time + lab operator's commission would be all. All of our equipment was either donated or is on loan/'active donation' so we really have no right to charge for equipment use.
Our "parent organization" - CeFO - would have plenty of right to charge for equipment use in any number of labs or shops across the country.
The article aims to be higher than a "hobby article" by using tens of thousands of dollars of optical lab equipment to (attempt to do) a very technical analysis of a component.
No matter what the interferometer is pieced together on - it is not on an air ride table. It is not isolated from the room around it, so harmonic motion will skew any results. It is also not assembled in a screwed down fashion so there is almost certainly a great deal of "tremble" in the positioning of things. No material between the plywood and the components solves the issue - the mere presence of the plywood indicates all one needs to know about the stability of the test table.
Test flats have coatings on both sides of the component with different purposes. Antireflective coating on the back to maximize transmission, and a one-way ~5% reflective coating on the front-facing side to give the interferometer a reference beam. This second coating is much more fragile than regular AR coatings and is also far more flat. Touching it will smear it on the nanometer scale and such inaccuracies are easily measurable (they are within 10s, 100s, or 1000s of the times the measurement error of the machine) but will destroy the calibration of the machine. Of course this is not a commercial interferometer so there is no calibration to begin with, but touching the flat will induce wavefront aberrations. A photographic lens is polished to about 31nm rms roughness, a reference flat is more like 1-2nm rms roughness.
This article isn't by an optics student. Perhaps a physics one, but an optics student would have access to some space to do the test proper on an air ride table or at least a breadboard.
The charge for testing the mirror as-delivered in my lab would be less than $100. $20/hr * up to 2 hours for student's time + lab operator's commission would be all. All of our equipment was either donated or is on loan/'active donation' so we really have no right to charge for equipment use.
Our "parent organization" - CeFO - would have plenty of right to charge for equipment use in any number of labs or shops across the country.