NPL Interferometer

Summary

The video introduces the concept of interferometers, optical devices used for beam interference. It categorizes them into two types: wavefront division interferometers and amplitude division interferometers. Specific examples, like the Rayleigh interferometer and Michelson's interferometer, are discussed. The focus shifts to the NPL flatness interferometer, used for checking the parallelism of gauge blocks, involving a mercury vapor lamp, green filter, and collimating lens. The video explains how interference fringes indicate flatness errors or taper in gauge faces. Future sessions will cover the Peter NPL interferometer.

Takeaways

• 📚 Interferometers are optical instruments that produce beam interference, classified into wavefront division and amplitude division interferometers.
• 🔍 Wavefront division interferometers split or construct two wavefronts using selected screens, with examples including the Rayleigh interferometer and Lloyd's mirror.
• 🌟 Amplitude division interferometers divide a light beam into two beams using a beam splitter, with the Michelson interferometer as an example.
• 🔬 The NPL (National Physical Laboratory) flatness interferometer is used to check the parallelism of gauge blocks.
• 💡 The light source for the NPL flatness interferometer is a mercury vapor lamp, with light passing through a condensing lens and green filter to produce monochromatic light.
• 🌐 The monochromatic light is directed through a pinhole to create an intense point source, which is used to project a parallel beam of light onto the gauge and base plate.
• 🎯 The base plate acts as a datum, with its surface accurately finished for reflection, while the optical flat reflects part of the beam to form interference fringes.
• 🔄 The reflected light beams from the optical flat and base plate create interference fringes, visible through an eyepiece.
• 📏 The pattern of the interference fringes indicates whether the workpiece is parallel, showing flatness errors if there are variations.
• 🔍 Different fringe patterns indicate various issues, such as taper or convex/concave surfaces, which signify gauge surface errors.

Q & A

What is an interferometer?

An interferometer is an optical instrument that produces beam interference or multiple beam interference.

How are interferometers classified?

Interferometers are broadly classified into two types: wavefront division interferometers and amplitude division interferometers.

What is the difference between wavefront division and amplitude division interferometers?

Wavefront division interferometers split the wavefront into two or more parts, while amplitude division interferometers split a light beam from one source into two beams using a beam splitter.

Can you give an example of a wavefront division interferometer?

Examples of wavefront division interferometers include the Rayleigh interferometer and Lloyd's mirror.

What is an example of an amplitude division interferometer?

An example of an amplitude division interferometer is the Michelson interferometer.

What is the NPL flatness interferometer?

The NPL flatness interferometer is a device used to check the parallelism of gauge blocks, and it uses light from a mercury vapor lamp passed through a green filter to create interference fringes.

What does NPL stand for, and where is it located?

NPL stands for the National Physical Laboratory, and it is located in the UK.

How does the NPL flatness interferometer work?

It uses light from a monochromatic source that passes through a pinhole to create an intense point source of light. The light reflects off an optical flat and the workpiece or base plate, forming interference fringes which indicate surface flatness.

What do interference fringes indicate in the NPL flatness interferometer?

Interference fringes indicate the parallelism of the workpiece surface. Matching fringes suggest the workpiece is parallel, while irregular fringes suggest a flatness error.

What is the significance of the fringe patterns in the interferometer?

Fringe patterns reveal different surface qualities. For example, tapering fringes indicate that the gauge faces are not parallel, and specific patterns like convex or concave fringes indicate surface curvature.