Four Wave Mixing generated from a chirped pump pulse in a photonic crystal fiber can provide large gain bandwidth and high gain value offering great parameters for ultra-short pulse amplification. However, the time to frequency distribution of the bands is an important feature to improve the maximum amplification performance. Here, we present a method to retrieve the spectrogram from multiple shot-to-shot spectral measurement using the dispersive Fourier transform method without the need to inject a seed and any iterative complex algorithm.