- 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. This work describes the design, construction and testing of an ultra-high resolution, wide-band spectrometer for measurement and diagnostic applications. The spectrometer is a cross-axis dispersion device utilizing both a diffraction grating and virtually imaged phased array (VIPA) to simultaneously obtain a resolution better than 0.3 GHz (< 0.01 cm-1) and a spectral range over 1 THz. The design of the instrument and trade-offs encountered in low-light applications are described. The VIPA spectrometer is applied to characterization of a broad brand Type I BBO optical parametric oscillator. Simultaneous single-shot measurements of the full OPO bandwidth and resolution of individual cavity modes are demonstrated with a spectral resolution of 240 MHz.