Optical Breadboard Alignment: Sub-Milliradian Laser Collimation

Before any spectral measurement can be recorded, the incident beam must be parallelized into a collimated wavefront. A diverging or converging ray cone invalidates the angle of incidence assumptions required by grating spectrometers and prism benches.

The Shear Plate Interferometer

To verify beam parallelism in the laboratory, engineers employ a shear plate interferometer: a wedge of high-quality optical flat that introduces a lateral shear between front and back surface reflections.

When a collimated beam strikes the wedge:

• If the beam is perfectly collimated, interference fringes orient exactly parallel to the fiducial wire.
• If the beam diverges or converges, fringes tilt clockwise or counter-clockwise at angle \alpha.

export interface CollimatorAlignment {
  beamDiameterMm: number;
  divergenceMrad: number;
  shearAngleDeg: number;
  residualErrorRms: number;
}