How to Analyze Raman Spectra: From Raw Data to Vibrational Peaks

Raman spectroscopy is a powerful non-destructive tool used to observe vibrational, rotational, and other low-frequency modes in a system. However, Raman signals are notoriously weak and often obscured by heavy fluorescence background noise. Analyzing Raman spectra requires a strict processing pipeline.

Step 1: Cosmic Ray Removal

Raman detectors (CCDs) are highly sensitive. Cosmic rays hitting the detector generate sharp, single-pixel spikes of massive intensity. These must be removed using a modified z-score threshold filter before processing, as they will corrupt baseline corrections and peak fits.

Step 2: Fluorescence Subtraction

Fluorescence can be orders of magnitude stronger than the Raman signal. We apply the Asymmetric Least Squares (ALS) algorithm or a Whittaker Smoother to isolate the smooth fluorescence background and subtract it, yielding flat, level baselines.

Step 3: Noise Filtering

Clean high-frequency CCD read-out noise by running a Savitzky-Golay Filter (typical parameters: window size ~15, polynomial degree 2). This increases the signal-to-noise ratio (SNR) without blurring or shifting narrow Raman vibrational lines.

Step 4: Deconvolution and Peak Fitting

Raman vibrational bands often overlap, especially in carbon nanomaterials (the D and G bands). To calculate peak positions, heights, and areas, fit the overlapping region with multiple Lorentzian profiles. The Lorentzian shape is the standard model for vibrational relaxations:

Where γ (gamma) is the half-width at half-maximum (HWHM), and x₀ is the Raman shift peak center.

The AltaiPlot Advantage: Streamlined Raman Processing

Stitching together cosmic ray filters, ALS baseline subtraction, SG smoothing, and multi-peak Lorentzian fits in a Python notebook requires writing over 150 lines of boilerplate code. AltaiPlot streamlines this workflow with integrated tools:

• Baseline Wizard with Live Preview: Open the interactive Baseline Correction panel to apply AsLS or AirPLS fluorescence removal with real-time sliders for λ (stiffness) and p (asymmetry). Watch the baseline overlay update instantly before committing.
• Analysis Toolbar for Sequential Processing: Chain your workflow using the toolbar: first Fix NaNs (for cosmic ray spikes), then Baseline correction, then Smooth with Savitzky-Golay — each step previews before you apply.
• Multi-Peak Fitting with Profile Selection: Anchor multiple Lorentzian or Pseudo-Voigt curves on overlapping peaks (like D & G bands) by selecting peak regions. The solver resolves overlapping areas and reports individual peak parameters.
• Export Publication-ready Charts: Once analyzed, export vector SVG/PDF figures with 18 journal presets (Nature, IEEE, ACS, etc.) and 9 publication-quality color palettes.