# Interferogram to Spectrum

Fast Fourier Transform interferograms, including zero filling, apodization and phase correction.

Inputs

- Interferogram: input interferogram

- Stored Phase: Previously calculated phase data

Outputs

- Spectra: dataset with spectra

- Phases: calulated phases

The Interferogram to Spectrum widgets calculates real or complex FFT for interferograms.

1. Info: Information about number and type of interferograms and metadata available.

2. Input Data:

   - Datapoint spacing: The pathlength step size used to calculate the output frequencies. "Auto" will use values from metadata or a default HeNe fallback.

   - Sweep direction: For datasets containing 2 full interferograms that were collected with forward and backward mirror motion.

   - ZPD Peak Search: Zero-point difference peak search algorithm. Disable search to manually enter value for entire dataset. The second entry is for double interferograms.

3. FFT Options:

   - Complex FFT: Calculate the complex FFT from Amplitude and Phase data. Data can be interleaved or amplitude on first input and phase on the second.

   - Apodization Function: Windowing function to apply before FFT

   - Zero Filling Factor: Pad dataset with zeros to 2**zff

   - Phase Correction: Calculate phase using Mertz, or use a stored phase. "None" outputs both real/imaginary values.

4. Output:

   - Limit spectral region: Cut the output to the specified range.