The goal of this project is to provide plans and techniques for building an interferometer that can accurately measure changes in distance over a range of hundreds of millimeters with sub-micrometer precision. The objective is to use low-cost, widely available components and achieve a good balance between ease of manufacturing and performance.
This repository is currently work in progress...
This project involves collimated laser beams with power levels above eye-safe limits able to cause permanent eye damage. Please use proper precautions, do your own research, and respect laser safety guidelines.
[NEW DESIGN - Version 5] FreeCAD models of the design are now online, take a look!
The Beam splitter is made from regular float glass with a thickness of about 6 mm. It does not requre any coatings and uses the inherent reflectivity of glass surfaces. It is ground to size using a diamond wetstone and a series of 3D printed jigs. The models for 3d printing can be found here:
The current recommandation is the:
For this project the laser source requires a long coherence length, which only certain laser diode models can provide.
Below is a table of laser diodes that I tested or want to test in future:
| Part Number | Nominal Current | Optimal Drive Current | Power | Wavelength | Notes | Plus on case |
|---|---|---|---|---|---|---|
| SLD3232VF | 55mA | ? | 50mW | 405nm | Not good | Yes |
| QL65E7SA | 50mA | 30mA | 7mW | 650nm | Good | Yes |
| QL65E7SB or C | 50mA | 30mA | 7mW | 650nm | Good | Yes |
| PLT520B | 225mA | ? | 110mW | 520nm | Very good (coherence length >4m) | Yes |
| PLT5 516FA | 100mA | 36mA | 30mW | 516nm | (Very) good (CURRENT CHOICE) | No |
| PLT5 520EB_Q | - | ? | 20mW | 520nm | Not tested (datasheet suggests very good) | No |
| PLT5 450(G)B | 80mA | 21mA | 100mW | 450nm | Okay | No |
| PLT5 520DB | - | ? | 10mW | 520nm | Not tested (probably not good) | No |
| PLT5 518FB_P | - | ? | 30mW | 518nm | Not tested (probably not good) | No |
For the project fast photodiodes for the visible spectral range are required. Silicon PIN Photodiodes satisfy these requirements and are readily available. To get a good signal a small active area of about 1mm² without a lens is prefereable.
The current choice is the
It is sensitive in the range of 380 nm bis 1100 nm and has a switching time of 10ns. To to reduce the footprint and remove the lense a 3D printed jig and sandpaper can be used. Mor information on this subject is coming soon..