Taking advantage of the specific characteristics of a transversely excited atmospheric (TEA) ${\mathrm{CO}}_2$ laser, a sophisticated technique for the analysis of chromated copper arsenate (CCA) in wood samples has been developed. In this study, a CCA-treated wood sample with a dimension of $20\mathrm{mm}\times 20\mathrm{mm}$ and a thickness of 2 mm was attached in contact to a nickel plate ($20\mathrm{mm}\times 20\mathrm{mm}\times 0.15\mathrm{mm}$), which functions as a subtarget. When the TEA ${\mathrm{CO}}_2$ laser was successively irradiated onto the wood surface, a hole with a diameter of approximately 2.5 mm was produced inside the sample and the laser beam was directly impinged onto the metal subtarget. Strong and stable gas plasma with a very large diameter of approximately 10 mm was induced once the laser beam had directly struck the metal subtarget. This gas plasma then interacted with the fine particles of the sample inside the hole and finally the particles were effectively dissociated and excited in the gas plasma region. By using this technique, high precision and sensitive analysis of CCA-treated wood sample was realized. A linear calibration curve of Cr was successfully made using the CCA-treated wood sample. The detection limits of Cr, Cu, and As were estimated to be approximately 1, 2, and $15\mathrm{mg}/\mathrm{kg}$, respectively. In the case of standard LIBS using the Nd:YAG laser, the analytical intensities fluctuate and the detection limit was much lower at approximately one-tenth that of TEA ${\mathrm{CO}}_2$ laser.