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

Numerical aperture NA Laser wavelength (nm) Refractive index of the medium n

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.

Write to us and learn more

Aleksandra Łukasiewicz

Head of International Sales

+48 512 554 952 · +1 (804) 593-0282
a.lukasiewicz@gekkophotonics.com

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