Optics, lasers and measurement, explained

An afocal beam expander enlarges a collimated beam and, in doing so, reduces its divergence by the same factor. That reduced divergence

Speckle is the grainy interference pattern coherent light forms when it scatters from a rough surface. It cannot be filtered out, because

A colour glass filter absorbs unwanted light in the bulk of the glass; an interference filter reflects it from a coating. Absorption

An uncoated glass surface reflects about four per cent. A broadband antireflection coating brings that below half a per cent, but only

A metallic mirror reflects broadly at around 96 to 98 per cent and tolerates being cleaned. A dielectric stack reflects above 99,5

A polarising beamsplitter cube transmits one linear polarisation and reflects the other. Extinction ratio describes how cleanly it does so, and it

A laser damage threshold is only meaningful together with the wavelength, the pulse duration and the number of pulses it was measured

An achromat cements two glasses with different dispersions so that two wavelengths share a focus. It removes most longitudinal chromatic aberration and,

A galvanometer scanner deflects a beam through an angle, but a conventional lens places the focused spot at a distance proportional to

Silicon detectors work to about 1000 nm and are inexpensive; InGaAs covers roughly 900 to 1700 nm and costs more. The choice

A helium-neon laser oscillates on an atomic transition, so its wavelength is fixed by physics rather than by temperature and drive current.

Illumination and stray light problems are far cheaper to find in a raytrace than in a prototype. A model that imports your

Both are cage systems built around a cube with four rod faces, so an optic can be swapped without realigning the train.

A kinematic mount constrains an optic at exactly six degrees of freedom, so it returns to the same place after adjustment. Most