Laser diode self-mixing: Range-finding and sub-micron vibration measurement

TL;DR

Learn how to use a laser diode to make submicron measurements without the need for additional components.

Transcript

today on Applied Science I'm going to show you how to take a laser diode and without any other op tool components make submicron measurements from a few centimeters away but first nerd thunder is a collection of youtubers that are doing a little cross promotion in December including Jerry Ellsworth who actually inspired me to start making youtube v... Read More

Key Insights

• 🙂 Laser diodes have built-in monitor photodiodes that can be used for closed-loop control of light emission.
• 🙂 A retroreflector can enhance the measurement signal by reflecting the laser light back into the package.
• 👻 Laser diodes can function as self-mixing interferometers, allowing for measurements of small movements.
• 🙂 Modulating the current in the photodiode can shift the color of the emitted light, enabling distance measurements.
• 🧡 The accuracy of the measurements depends on factors such as current stability, temperature, and frequency range.
• 🧑‍🏭 External factors, such as table vibrations, can introduce noise that needs to be compensated for in the measurement.
• 🎮 Laser diodes without monitor photodiodes may not provide as precise or controlled measurements.

Questions & Answers

Q: How does the laser diode measure light emissions?

Laser diodes have monitor photodiodes inside the package that detect the emitted light and provide feedback for controlling the light output.

Q: How does adding a retroreflector improve the measurement?

A retroreflector reflects the laser light back into the package, allowing for interference with the incoming light and providing a larger signal for measurement.

Q: Can laser diodes without monitor photodiodes be used for these measurements?

Yes, laser diodes without monitor photodiodes can still be used, but they may not provide as accurate or controlled measurements.

Q: How does modulating the current in the photodiode allow for distance measurements?

Modulating the current in the photodiode causes a slight shift in the color of the emitted light. By measuring the interference pattern, it is possible to determine the distance based on the frequency of the shift.

Summary & Key Takeaways

• Laser diodes have built-in monitor photodiodes that can be used to measure light emissions and control output.

• By using a laser diode and a retroreflector, it is possible to create an interferometer and measure small movements.

• Modulating the current going into the photodiode can shift the color of the light, allowing for distance measurements.