Generation of strongly-coupled plasma using Argon-based capillary discharge lasers

Argon based capillary discharge lasers operate in the extreme ultra violet (EUV) at 46.9 nm with an output of up to 0.5 mJ energy per pulse and up to a 10 Hz repetition rate. Focussed irradiances of up to 1012 W cm-2 are achievable and can be used to generate plasma in the warm dense matter regime by irradiating solid material. To model the interaction between such an EUV laser and solid material, the 2D radiative-hydrodynamic code POLLUX has been modified to include absorption via direct photo-ionisation, a super-configuration model to describe the ionisation dependant electronic configurations and a calculation of plasma refractive indices for ray tracing of the incident EUV laser radiation. A simulation study is presented, demonstrating how capillary discharge lasers of 1.2ns pulse duration can be used to generate strongly coupled plasma at close to solid density with temperatures of a few eV and energy densities up to 1×105 J cm-3. Plasmas produced by EUV laser irradiation are shown to be useful for examining the equation-of-state properties of warm dense matter. One difficulty with this technique is the reduction of the strong temperature and density gradients which are produced during the interaction. Methods to inhibit and control these gradients will be examined

The application of extreme ultra-violet lasers in plasma heating and diagnosis

Laser-plasma studies have been undertaken for 50 years using infra-red to ultra-violet lasers. We show that a new regime of laser-produced plasmas can be created with capillary discharge and free electron lasers operating in the extreme ultra-violet (EUV). For example, EUV radiation (wavelength <50 nm) has a critical electron density above electron densities formed by ionization at solid material density and so potentially can penetrate to large depth into a solid density plasma. We explore here the importance of this penetration in ablating solid targets, in creating novel warm dense matter and in the diagnosis of plasmas

Ablation of Submicrometer Holes Using an Extreme-Ultraviolet Laser

Simulations and experiments are used to study extreme-ultraviolet (EUV) laser drilling of submicrometer holes. The ablation process is studied with a 2D Eulerian hydrodynamic code that includes bound-free absorption processes relevant to the interaction of EUV lasers with a solid material. Good agreement is observed between the simulated and measured ablated depths for on-target irradiances of up to 1×1010  W cm−2. An increase in the irradiance to 1×1012  W cm−2 is predicted to ablate material to a depth of 3.8  μm from a single pulse with a hole diameter 3 to 4 times larger than the focal spot size. The model allows for the simulation of the interaction of a laser pulse with the crater created by a previous shot. Multiple-pulse lower-fluence irradiation configurations under optimized focusing conditions, i.e., approaching the diffraction limit, are shown to be advantageous for applications requiring mesoscale [(100  nm)–(1  μm)] features and a high level of control over the ablation profile