Optical Materials and Components
Optical Materials and Components
This domain tests material selection and component behaviour: glasses, fused silica, crystals, polymers, thin-film coatings, filters, polarizers, waveplates, prisms, gratings, and beam splitters. You need to connect bulk properties to measured performance.
Core rules
- Dispersion is described by refractive index versus wavelength and quantified by Abbe number; low Abbe number means strong dispersion.
- Transmission range, absorption, homogeneity, bubbles, and striae are material specifications, not mere catalog labels.
- Fresnel loss at normal incidence is (R=((n_1-n_2)/(n_1+n_2))^2).
- Coatings are angle-, polarization-, and wavelength-dependent; a coating specified at 0° may fail at 45°.
- Waveplates produce retardance (\Gamma=2\pi(n_e-n_o)d/\lambda); a quarter-wave plate is wavelength-specific.
Worked example
Uncoated air-to-glass at normal incidence with (n=1.5): (R=((1-1.5)/(1+1.5))^2=(0.5/2.5)^2=0.04), or 4% per surface. A single lens has two surfaces, so about 8% reflection loss before absorption. An antireflection coating reduces this, but only over its design band and angle range. If the glass were (n=1.9), (R=((1-1.9)/(1+1.9))^2\approx9.6%) per surface, showing why high-index materials need coatings.
Traps
Using (n) at 589 nm for a 1550 nm application is a common mistake. Confusing surface reflection with bulk absorption gives wrong throughput. Ignoring polarization ruins retardance and coating calculations. Also check whether a grating specification is lines/mm or line spacing in micrometres.
Exam focus
Match material to waveband, power handling, thermal expansion, and environmental durability.