Ultrafast Single Pulse Imaging With Large Field of View for Dynamic Measurement Based on Virtually Imaged Phased Array

ABSTRACT An ultrafast two‐dimensional (2D) imaging system with large field of view is proposed by leveraging virtually imaged phased array through Galilean beam expanding. By integrating wavelength division multiplexing technology of a virtual imaging phased array with spatial spectroscopy of a grating, broadband spectra of an ultrafast laser pulse are mapped onto a 2D plane. Subsequently, Galilean structure is employed for beam expansion, thereby achieving a large field‐of‐view 2D imaging capability. A dispersion Fourier transform module is also incorporated into the system, enabling the mapping of wavelength to time, facilitating ultrafast imaging through the detection of pulse signals by high‐speed photodetector. The experimental setup employs a home‐made mode‐locked laser with a spectral bandwidth of 12 nm, capable of large‐field imaging of 6 × 20 mm 2 , representing a 20‐fold expansion compared to the unexpanded field of view, and an imaging frame rate of up to 7.75 MHz is obtained. The dynamic imaging capability of the system is demonstrated through imaging a freely falling sphere. The proposed imaging system, with its large field of view and high frame rate, is ideal for high‐speed flow diagnostics.