Laser plasma interactions in a relativistic parameter regime have been intensively investigated for studying the possibility of fast ignition in inertial confinement fusion ͑ICF͒. Using ultra-intense laser systems and particle-in-cell ͑PIC͒ simulation codes, relativistic laser light self-focusing, super hot electrons, ions, and neutron production, are studied. The experiments are performed with ultra-intense laser with 50 J energy, 0.5-1 ps pulse at 1053 nm laser wavelength at a laser intensity of 10 19 W/cm 2. Most of the laser shots are studied under preformed plasma conditions with a 100 m plasma scale length condition. In the study of laser pulse behavior in the preformed plasmas, a special mode has been observed which penetrated the preformed plasma all the way very close to the original planar target surface. On these shots, super hot electrons have been observed with its energy peak exceeding 1 MeV. The energy transport of the hot electrons has been studied with making use of K␣ emissions from a seeded metal layer in planar targets. The details of ion acceleration followed by beam fusion reaction have been studied with neutron spectrometers. Laser ponderomotive force self-focusing and hot electron generation have been applied to a compressed core to see the effect of heating by injecting 12 beams of 100 ps, 1 TW pulses.

We investigated the plasma conditions for obtaining highly efficient extreme ultraviolet light from laserproduced tin plasmas for lithography of next generation semiconductors. Based on accurate atomic data tables calculated using the detailed configuration accounting code, we conducted 1-D radiation hydrodynamic simulations to calculate the dynamics of tin plasma and its emission of extreme ultraviolet light. We included the photo-excitation effect in the radiation transport. Our simulation reproduced experimental observations successfully. Using our verified code, we found that a CO 2 laser can be useful in obtaining higher conversion efficiencies up to 4%.

Laser-produced Sn plasma is an efficient extreme ultraviolet (EUV) light source, however the highest risk in the Sn-based EUV light source is contamination of the first EUV collection mirror caused by debris emitted from the Sn plasma. Minimum mass target is a key term associated with relaxation of the mirror contamination problem. For design of the optimum minimum mass Sn target, opacity effects on the EUV emission from the laser-produced Sn plasma should be considered. Optically thinner plasma produced by shorter laser pulse emits 13.5 nm light more efficiently; 2.0% of conversion efficiency was experimentally attained with drive laser of 2.2 ns in pulse duration, 1.0 × 10 11 W/cm 2 in intensity, and 1.064 µm in wavelength. Under the optimum laser conditions, the minimum mass required for sufficient EUV emission, which is also affected by the opacity, is equal to the product of the ablation thickness and the required laser spot size. Emission properties of ionized and neutral debris from laser-produced minimum mass Sn plasmas have been measured with particle diagnostics and spectroscopic method. The higher energy ions have higher charge states, and those are emitted from outer region of expanding plasmas. Feasibility of the minimum mass target has been demonstrated to reduce neutral particle generation for the first time. In the proof-of-principle experiments, EUV emission from a punch-out target is found to be comparable to that from a static target, and expansion energy of ion debris was drastically reduced with the use of the punch-out target.

Plasma dynamics are governed by electron density (ne), electron temperature (Te), and radiative energy transfer as well as by macroscopic flows. However, plasma flow-velocity fields (vflow) inside laser-produced plasmas (LPPs) have rarely been measured, owing to their small sizes (< 1 mm) and short lifetimes (< 100 ns). Herein, we report, for the first time, two-dimensional (2D) vflow measurements of Sn-LPPs (“double-pulse” scheme with a CO2 laser) for extreme-ultraviolet (EUV) light sources for semiconductor lithography using the collective Thomson scattering technique, which is typically used to measure ne, Te, and averaged ionic charge (Z) of plasmas. Inside the EUV source, we observed plasma inflow speed exceeding 104 m/s magnitudes toward a plasma central axis from its peripheral regions. The time-resolved 2D profiles of ne, Te, Z, and vflow indicate that the plasma inflows maintain the EUV source at a temperature suitable (25 eV < Te < 40 eV) for EUV light emission at a high density (ne > 3 × 1024 m−3) and for a relatively long time (> 10 ns), resulting increment of total EUV light emission. These results indicate that controlling the plasma flow can improve EUV light output and that there is potential to increase the EUV output further.