Nonlinear spectral Interferometry for NIR sources

This work presents a commercial webcam CMOS (Complemented-Metal-Oxide-Semiconductor) implemented as a spectrometer for femtosecond pulses characterization at the Near-Infrared region (NIR, 1.1 - 1.6 μm), applying spectral interferometry. The spectral interferometry setup consists of a collinear Michelson interferometer in which two femtosecond pulses replicas, generated from a home-made Optical Parametric Oscillator (fs-OPO), are relatively delayed with respect to each other. A reflecting grating disperses the pulse replicas and then, the modulated spectrum is generated in a 2-Fourier setup, using a single lens, with the CMOS sensor located at the Fourier plane. The NIR CMOS response is produced through the Two-Photon Absorption (TPA) effect, capable of generating the nonlinear spectral intensity and the corresponding modulated spectrum (spectral interferometry signal). The cost-effective TPAspectrometer is capable of measuring the interferogram, with a high resolution of 0.72nm and very high sensitivity of few 𝜇W average power or few fJ per pulse. Finally, we calculate the spectral phase difference using a phase retrieval algorithm from the nonlinear spectral interferometry signal.