The application of a quasi-CW (picosecond pulse), tunable Ti:sapphire laser for absorption detection of transient species in flash photolysis kinetics experiments is presented. The spectral range of the laser, when used with a harmonic generator, covers most of the visible wavelengths allowing for the detection of a wide array of organic radical species. Paired with a temperature and pressure controlled slow flow reactor equipped with a Herriott-type optical multiple pass cell, transient absorptions of ~0.0001 can be measured, corresponding to cross section - concentration products of less than 1x10^-7 cm^-1. To determine the quality of kinetics data achievable with this apparatus, the reaction between C₂H₃ and C₂H₄ was studied at T = 400-650K. The pre-exponential factor and activation energy for C₂H₃ + C₂H₄ --> products were found to be 2.76x10^-12 cm³ molecules^-1 s^-1 and 23.1 kJ mole^-1 K^-1 respectively. The Arrhenius parameters were consistent with those found by Shestov, et al. who measured in a different temperature and pressure range using mass spectrometry. The flexibility and high sensitivity of this instrument allows direct and accurate measurement of many important transient intermediates in combustion.