Judge a germanium lens supplier on infrared metrology capability, not on polishing capability alone. Germanium is opaque in the visible, so transmitted wavefront must be measured at infrared wavelengths. Every fringe specification is meaningless without its test wavelength stated on the drawing. Uncoated germanium reflects…
A useful custom optical window specification should define more than material and dimensions. At minimum, it should describe the operating wavelength, substrate or material grade, geometry, thickness, clear aperture, optical quality, surface imperfections, parallelism or wedge, coating performance, angle of incidence, environment, inspection conditions, and…
Surface flatness and wavefront error are related, but they are not interchangeable specifications. Surface flatness describes how much a nominally flat optical surface departs from an ideal plane. Wavefront error describes how much an optical component or system changes the shape of an optical wavefront…
Scratch-dig limits discrete local defects; surface roughness is the RMS height of fine texture across the whole surface. The MIL-PRF-13830B scratch number is a visibility grade, not a width; the dig number is diameter in 0.01 mm. Roughness-driven scatter scales with (σ/λ)², so the same…
Polarization can change the measured transmission or reflection spectrum of an optical interference filter, especially when the filter operates at a non-normal angle of incidence. At oblique incidence, s-polarized and p-polarized light no longer interact with the multilayer coating in exactly the same way. Their…
Optic diameter is the physical outside diameter of a circular optical component. Clear aperture is the region of that optic over which specified optical performance is required. The clear aperture is therefore usually smaller than the physical diameter, because part of the edge may be…
A collimated N-BK7 plano-convex lens with f = 50 mm reaches the 0.07 λ RMS diffraction limit at f/6.4 (computed, 587.6 nm). Face the curved side of a plano-convex lens toward the collimated beam; reversing it quadruples computed longitudinal spherical aberration. An asphere corrects on-axis…
A cone half angle shifts an interference filter’s spectrum toward shorter wavelengths and softens its edges; a pure tilt only shifts it. With the chief ray normal and a uniformly filled pupil, the mean shift equals half the marginal-ray shift. The same cone produces far…
Two optical components can look almost identical, use the same substrate material, and have similar dimensions—yet their coating costs may be very different. The reason is that optical coating cost is driven less by the visible amount of coating material and more by the difficulty…
The topic is suitable as a foundational definition page. GIAI already has more specific content covering 1064 nm F-theta lenses, field-size calculation, standard vs. telecentric designs, and F-theta lens selection, so this page should act as the conceptual pillar rather than duplicate those narrower articles.…
A beam expander is an afocal telescope that scales a collimated beam diameter by M. Far-field divergence scales by 1/M; the diameter-angle product stays fixed at one wavelength. Galilean layouts avoid an internal focus; Keplerian layouts allow pinhole spatial filtering. Focused spot diameter shrinks by…
A beamsplitter does not treat s- and p-polarized light the same way. At any angle other than normal incidence, the reflectance of a surface or coating is higher for s-polarization than for p-polarization, and the difference grows with the angle of incidence. At 45°, the…
