Laser absorption diagnostic methods were developed for the quantitative measurement of formaldehyde (CH2O) and acetaldehyde (CH3CHO) at high temperatures in shock tube kinetic studies. Investigation of the high-temperature CH2O spectrum has shown that the optimal wavelength for CH2O detection using commercially available lasers is near 2896 cm(-1). By exploiting the structural difference between the absorption spectra of CH2O and that of broadband interfering species, a two-color (2895.92 cm(-1) and 2895.60 cm(-1)) interference-free detection scheme for CH2O sensing in a combustion environment was developed. A third color (32601.10 cm(-1)) has also been added to develop a UV/IR detection scheme for combined CH3CHO/CH2O measurements. To implement these schemes, aldehyde cross-sections at all three colors were measured behind reflected shock waves over a wide span of temperatures (600-1800 K) and pressures (0.8-3.6 atm), with an uncertainty of +/- 5%, and the diagnostic schemes were validated using two controlled experiments with well-established chemistry. Applications of these diagnostics were also demonstrated in shock tube pyrolysis experiments of 1,3,5-trioxane, CH2O and CH3CHO. The unimolecular decomposition rate of 1,3,5-trioxane was determined over 869-1037 K at an average pressure of 2.1 atm: k(1)=3.58 x 10(12) exp (-18,590 K/T) s(-1), with an overall uncertainty of less than 20%. (C) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved.