Spectral narrowing of the first stage signal wave in a cascade optical parametric oscillator (OPO) using a volume Bragg grating produced narrowband ∼0.6-mJ idler pulses at 9.245 mu m from the second stage based on CdSe at a repetition rate of 100 Hz. The CdSe crystal is pumped intracavity by the signal wave from the periodically poled KTiOPO4 based first stage, and both stages operate under noncritical phase-matching conditions. The ∼8-ns-long mid-IR output pulses have a spectral bandwidth of 8.4 cm-¹. An overall quantum conversion efficiency of 14.2% from 1.064 mu m is achieved with a simple, compact, and robust all-solid-state design.