Fast Spectrum Measurements Using Optical Computing

Abstract

Traditional spectrometers are too slow for the continuous real-time measurement of rapidly varying spectrum. Dispersive Fourier transformation (DFT) technology replaces diffraction grating and detector array in traditional spectrometers with dispersive elements and photodiodes, and therefore reaches MHz-level spectral capture rate. In addition, frequency-resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER) are also important ultrafast spectroscopy technologies in relevant fields. However, these approaches have to use mode-locked pulses as probe light, which may cause damages to some samples due to high peak power. Therefore, the requirement for light source restricts the scope of these technologies’ applications. Here, we report a general technique using optical computing for fast spectrum measurements, to overcome the bottleneck of light source in existing ultrafast spectroscopy measurement technologies. The proposed method has no strict requirement on the probe light. It means the common light source could also be applied for fast real-time spectroscopic measurements. In experiments, CW signals with four different optical spectra have been measured at capture speed of 1MHz respectively. The proposed method can overcome the limitations of existing ultrafast spectroscopy technologies in light source, and therefore provide a powerful tool for investigating rapid transient phenomena in many applications.