Fig. 4: Principle of COFT based on 3D spectral holography.

a The experimental setup. The incident optical field at CP, the checking point, is pre-chirped by an SF11 glass rod (GR1) and split by beam splitter BS1. The transmitted gating pulse is focused by the lens L1 to a thin glass plate as the Kerr medium. The reflected pulse is further chirped by an SF11 glass rod (GR2) and manipulated by a Mach-Zehnder interferometer (MZI) to generate a time-delayed reference-signal pulse pair. The reference-signal pulses are imaged by lens L2 to the Kerr medium, and the signal pulse picks up phase shift induced by the gating in the Kerr medium. After the cross-polarized gating pulse is filtered out by a polarization beam splitter (PBS), the remaining reference and signal pulses interfere and generate a 3D spectral hologram, which is imaged by lens L3 to the coded aperture of a CASSI system. Raw data is shown in the inset. b CASSI reconstruction of the 3D spectral hologram \(S\left( {x,y,\omega } \right)\) due to interference between the reference and the modulated signal probe. c The \(\left| {E\left( {k_x,k_y,t} \right)} \right|^2\) and \(\left| {E\left( {x,y,\omega } \right)} \right|^2\) 3D intensity profiles of the incident optical field. The former is predominantly obtained from the phase shift \(\theta \left( {x,y,\omega } \right)\) coded in the 3D spectral hologram. \(\left| {E\left( {x,y,\omega } \right)} \right|^2\) and \(\theta \left( {x,y,\omega } \right)\) are reconstructed from the 3D spectral hologram \(S\left( {x,y,\omega } \right)\) through the standard interference fringe analysis procedure