Ultrafast Three-Dimensional Surface Imaging Based on Short-Time Fourier Transform

A novel approach to achieving ultrafast three-dimensional (3-D) imaging based on space-to-wavelength-to-time mapping and short-time Fourier transform (STFT) is proposed and experimentally demonstrated. The fundamental concept to achieve 3-D imaging is to encode the depth information of a sample by interfering two delayed pulses that are reflected from the surface of the sample and an additional reference plane on the top of the sample. The interference pattern that contains the depth information in the frequency domain is converted into the time domain based on dispersive Fourier transform and then analyzed based on STFT. Thus, ultrafast 3-D imaging is achieved. The proposed approach is experimentally evaluated. The imaging of a sample with a depth of 1.5 mm using an ultrafast pulse laser source with a beam width of $\sim 2$ mm at a repetition rate of 48.8 MHz is demonstrated.