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diff --git a/Source/FieldSolver/SpectralSolver/SpectralFieldData.H b/Source/FieldSolver/SpectralSolver/SpectralFieldData.H
new file mode 100644
index 000000000..8e58aa1d8
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+++ b/Source/FieldSolver/SpectralSolver/SpectralFieldData.H
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+#ifndef WARPX_SPECTRAL_FIELD_DATA_H_
+#define WARPX_SPECTRAL_FIELD_DATA_H_
+
+#include <WarpX_Complex.H>
+#include <SpectralKSpace.H>
+#include <AMReX_MultiFab.H>
+
+// Declare type for spectral fields
+using SpectralField = amrex::FabArray< amrex::BaseFab <Complex> >;
+
+/* Index for the fields that will be stored in spectral space */
+struct SpectralFieldIndex {
+  enum { Ex=0, Ey, Ez, Bx, By, Bz, Jx, Jy, Jz, rho_old, rho_new, n_fields };
+  // n_fields is automatically the total number of fields
+};
+
+/* \brief Class that stores the fields in spectral space, and performs the
+ *  Fourier transforms between real space and spectral space
+ */
+class SpectralFieldData
+{
+    friend class PsatdAlgorithm;
+
+    // Define the FFTplans type, which holds one fft plan per box
+    // (plans are only initialized for the boxes that are owned by
+    // the local MPI rank)
+#ifdef AMREX_USE_GPU
+    // Add cuFFT-specific code
+#else
+    using FFTplans = amrex::LayoutData<fftw_plan>;
+#endif
+
+    public:
+        SpectralFieldData( const amrex::BoxArray& realspace_ba,
+                      const SpectralKSpace& k_space,
+                      const amrex::DistributionMapping& dm );
+        SpectralFieldData() = default; // Default constructor
+        SpectralFieldData& operator=(SpectralFieldData&& field_data) = default;
+        ~SpectralFieldData();
+        void ForwardTransform( const amrex::MultiFab& mf,
+                               const int field_index, const int i_comp);
+        void BackwardTransform( amrex::MultiFab& mf,
+                               const int field_index, const int i_comp);
+
+    private:
+        // `fields` stores fields in spectral space, as multicomponent FabArray
+        SpectralField fields;
+        // tmpRealField and tmpSpectralField store fields
+        // right before/after the Fourier transform
+        SpectralField tmpSpectralField; // contains Complexs
+        amrex::MultiFab tmpRealField; // contains Reals
+        FFTplans forward_plan, backward_plan;
+        // Correcting "shift" factors when performing FFT from/to
+        // a cell-centered grid in real space, instead of a nodal grid
+        SpectralShiftFactor xshift_FFTfromCell, xshift_FFTtoCell,
+                            zshift_FFTfromCell, zshift_FFTtoCell;
+#if (AMREX_SPACEDIM==3)
+        SpectralShiftFactor yshift_FFTfromCell, yshift_FFTtoCell;
+#endif
+};
+
+#endif // WARPX_SPECTRAL_FIELD_DATA_H_