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We report the feasibility of using CW intracavity laser absorption spectroscopy (ICLAS)$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$ as a probe in detecting transient species generated by pulsed laser photolysis. The method of detection uses a time-generated CW laser beam and time-resolved spectra which are delayed with respect to the photolysis pulse. Variable time delays and a constant generation time have been used to detect the time dependence of the absorbing species at times as short as a few microseconds. We applied the technique to the study of the time evolution of the formation of the free radical HCO generated by photolysis of gas-phase acetaldehyde $(CH3CHO)$ at pressures down to tens of mtorr. We have also found that the ultimate sensitivity of the ICLAS technique is limited mainly by the mechanical stability of the cavity. $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}$M. Chenevier, M. A. Melieres, F. Stoeckel, to be published $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$G. H. Atkinson, A. H. Laufer and M. J. Kurylo, J. Chem. Phys. 59 (1973) 350. $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$G. H. Atkinson, T. M. Heimlich and M. W. Schuyler, J. Chem. Phys. 66 (1977 5005. $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}$ A. J. Gill and G. H. Atkinson, Chem. Phys. Letters, 64 (1979) 426. $\mathrm{<mrow\; data-mjx-texclass="ORD">5</mrow>}$R, J. Gill, W. D. Johnson and G. H. Atkinson, Chem. Phys. 58 (1981) 29.