Real-time spectral characterization of THz-bandwidth waveforms by unwrapping a time-lens spectrogram

We experimentally show a spectral unwrapping algorithm to analyze ultra-broadband signals using the time-lens spectrogram. By using a spectrogram with a nominal analysis bandwidth of only 56.4 GHz, we show that the analysis bandwidth can be continuously shifted to analyze a waveform with 1.97 THz bandwidth, akin to the principle of down-conversion employed in RF spectral analyzers. This allows us to obtain time-resolved spectra extending over long durations with high resolution in a single-shot manner.