Raman Tools
Sampling volume and depth (confocal Raman)
How much material does your Raman microscope actually „see" at a single point? From the objective's numerical aperture and wavelength, we calculate the spot diameter, depth of focus, and approximate sampling volume — critical for layers, coatings, inclusions, and thin films.
Optics
Formulas and assumptions
Lateral spot (Airy diameter): d_xy ≈ 1.22 · λ / NA
Axial depth (confocal, FWHM): d_z ≈ 1.4 · n · λ / NA²
Volume (ellipsoid): V ≈ (π/6) · d_xy² · d_z
Values for a diffraction-limited system with full aperture filling and ideal confocality. Axial resolution increases with the square of NA — this is why high NA so strongly „flattens" the volume and allows measurement of thin layers without capturing the substrate. In a real system, scattering, absorption, and the confocal pinhole size enlarge the volume.
1 µm³ = 1 femtoliter (fL). Approximate result — for precision, characterization of the specific system is required.
Have a sample you don’t want to guess about?
We conduct feasibility studies even on the most challenging samples — on your material, at your site. Leave your contact, and we will review your case and tell you directly whether Spectrally can measure it.
