A prototype cross-dispersed optical echelle spectrograph of very high resolution has been designed and built at Steward Observatory and tested at the Starfire Optical Range (SOR) 1.5 m telescope. It is the first spectrograph to take advantage of diffraction-limited images provided by adaptive optics in order to achieve a potential resolving power of $R sim 600,000$. The wavelength coverage in a single exposure is about 300 AA, which is approximately 100 times that of conventional spectrographs operating at comparable resolution. This was achieved by recording 60 cross-dispersed orders across the $18times 18$ mm$^2$ area of the CCD detector. The total efficiency of the system, including the sky and telescope transmission, spectrograph and CCD detector, is measured to be 1.3% at peak, much higher than that of other ultra-high-resolution spectrographs. Sample stellar spectra with $R sim 250,000$ are presented.
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