Time evolution of the Infrared Laser Induced Breakdown Spectroscopy of DNA bases Guanine and Adenine

Abstract

Laser-Induced Breakdown Spectroscopy (LIBS) of DNA bases Guanine and Adenine was studied using a high-power CO₂ pulsed laser (λ=10.591 μm, τ _FWHM=64 ns and fluences ranging from 25 to 70 J/cm²). The strong emission of the adenine and guanine plasma, collected using a high-resolution spectrometer, at medium-vacuum conditions (4 Pa) and at 1 mm from the target, exhibits excited molecular bands of CN (B² Σ ⁺–X² Σ ⁺) and excited neutral H and ionized N⁺ and C⁺. The medium-weak emission is due to excited species C²⁺, C³⁺, N, O, O⁺, O²⁺ and molecular band systems of $\mathrm{C}_{2}(\mathrm{d}^{3}\varPi_{\mathrm{g}}\mbox{--}\mathrm{a}^{3}\varPi_{\mathrm{u}};\ \mathrm{D}^{1}\varSigma_{\mathrm{u}}^{+}\mbox{--}\mathrm{X}^{1}\varSigma_{\mathrm{g}}^{+})$, OH(A² Σ ⁺–X² Π), NH(A³ Π–X³ Σ ⁻), CH(A² Π–X² Π), $\mathrm{N}_{2}^{+}(\mathrm{B}^{2}\varSigma_{\mathrm{u}}^{+}\mbox{--} \mathrm{X}^{2}\varSigma_{\mathrm{g}}^{+})$ and N₂(C³ Π _u–B³ Π _g). We focus our attention on the temporal evolution of different atomic/ionic and molecular species. The velocity distributions for various (different) species were obtained from time-of-flight (TOF) measurements. Intensities of some lines from C⁺ were used for determining electron temperature and their Stark-broadened profiles were employed to estimate the temporal evolution of electron density.