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.
The KICAD design files for the electronics have been updated to the newest development version. The design is still work in progress but all functions have been successfully tested on a prototype.
[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..