The development and application of two laser-absorption-spectroscopy diagnostics capable of performing high-bandwidth measurements of (1) temperature, pressure, and CO, and (2) temperature and HO in the annular combustion chamber of a rotating detonation rocket engine (RDRE) are presented. The mid-infrared (MIR) diagnostic utilized a quantum-cascade laser (QCL) to measure absorbance spectra of three CO absorption transitions near 2008.5 cm at 750 kHz using scanned-wavelength direct absorption. Measurements of gas temperature, pressure, and CO partial pressure were obtained from the QCL diagnostic using a nonlinear fitting routine to fit simulated CO absorbance spectra to measured absorbance spectra. The near-infrared (NIR) diagnostic utilized two tunable diode lasers (TDLs) emitting near 7185.6 and 6806.0 cm which were modulated at 35 and 45.5 MHz, respectively, and scanned over the linecenters of their respective HO absorption transitions to obtain measurements of WMS-4f/2f and WMS-2f/1f signals. WMS-4f/2f measurements were used to infer the collisional-broadening full-width at half-maximum (FWHM) of the HO transitions, and the WMS-2f/1f signals were then used to infer the gas temperature and HO partial pressure at up to 1 MHz. The diagnostics were packaged in single-ended sensor assemblies to enable measurements in the annulus of a methane–oxygen RDRE, and results are presented for a test case with the RDRE operating at an equivalence ratio of 1.15 and a total propellant mass flow rate of 0.6 lb/s.