Energy deposition of explosive materials under femtosecond-laser irradiation

The absorption of femtosecond-laser energy by energy material is influenced by the material's optical absorption coefficients. To study the energy deposition of a 810-nm near-infrared femtosecond laser in explosive materials, we calculated their reflection coefficient, linear absorption coefficient, and two- and three-photon absorption coefficients using a first-principles method. The materials studied were HMX, TATB, RDX, PETN, and TNT. We obtained the energy deposition at two intensities (10¹³ and 10¹⁴ W/cm²). The results showed that the reflection coefficients differ among the different explosives, decreasing in the order of TATB > TNT > RDX > PETN > HMX, and the linear absorption coefficient decrease in the order of TATB > TNT > RDX > HMX > PETN. Thus, the strongest laser absorption was observed for TATB. For near infrared laser with a wavelength of 810 nm, TATB and TNT have a weak two-photon absorption effect and a strong three-photon absorption effect, whereas HMX, RDX, and PETN have almost no two-photon absorption effect and only a very weak three-photon absorption effect. A higher laser power density corresponds to a stronger ability of explosives to absorb laser energy through the multiphoton effect. For a given laser energy, the ablation depth of explosives increases in the order of TATB < TNT < RDX < HMX < PETN.