Chirag Rajyaguru

Efficient soft x-ray emission source at 13.5 nm by use of a femtosecond-laser-produced Li-based microplasma

A proof-of-principle experiment was demonstrated to optimize a Li-based microjet target coupled to dual subpicosecond laser pulses as a 13.5 nm soft x-ray emission source. An optimum pulse duration of 450 fs to achieve a maximum emission at 13.5 nm was well explained by the resonant absorption process. Utilization of dual femtosecond pulses revealed that the optimum pulse separation around 500 ps was necessary to achieve a maximum soft x-ray conversion efficiency of 0.2%, where plasma hydrodynamics could not be neglected. A one-fluid two-temperature hydrodynamic simulation reproduced this optimum pulse separation behavior.

Debris characteristics of a laser-produced tin plasma for extreme ultraviolet source

We measured debris characteristics of a tin (Sn) plasma produced by a 10-ns infrared Nd:YAG laser. A maximum kinetic energy of 7keV of tin ions was observed. Such suprathermal tin ions emitted from a solid planar target consisted of singly and doubly ionized tin ions. Both suprathermal ions and neutral fragments emitted from a target showed the angular distributions of cos4θ which were narrower than the 13.5-nm extreme ultraviolet (EUV) emission distribution of cos0.5θ. These measurements would give important information on debris mitigation for efficient EUV sources in the next generation lithography.

Hot Ion Beam Generation from Rare-Gas Cryogenic Targets

Energetic ions having a maximum velocity of the order of 107 cm/s were detected in the interaction of a frequency-doubled Q-switched Nd:YAG laser with rare-gas cryogenic targets at the laser intensity of 1 ×1012 W/cm2. It was observed that the angular distribution of ions strongly peaked in the target normal direction confined to a narrow range of angle following ~cos pθ ( p=3–5). Scaling of the ion current and their velocity as a function of an incident laser energy were investigated. To analyze the effect of energetic particles from a plasma, a silicon substrate was used as a particle target. Its surface morphology revealed that micron-size solid fragments from the target dominantly affected the silicon surface.

Dynamics of the discharge-pumped vacuum ultraviolet Kr/sub 2//sup */ laser

A numerical simulation code has been developed to investigate the dynamics of the discharge-pumped vacuum ultraviolet Kr/sub 2//sup */ laser. Dynamics of spectral narrowing of the laser emission down to 0.2-nm full-width at half-maximum (FWHM) was well reproduced. Small signal gain behavior as a function of the applied voltage was predicted to have a gain coefficient of 0.08 cm/sup -1/ at the applied voltage of 32 kV, which was more than twice as large as the experimentally observed maximum gain value (0.035 cm/sup -1/). The code predicted that the laser output energy could become more than 1 mJ at the applied voltage at the Kr gas pressure of 10 atm.

Enhancement of extreme ultraviolet emission from a laser-produced-lithium plasma by use of dual laser pulses

The use of dual laser pulses, a lithium plasma source produces unambiguously defined line emission at 13.5 nm with almost no off-band components, which minimize unnecessary heating of EUV optics. A plasma hydrodynamic calculation evaluated the plasma expansion time of 80 ns, within which the plasma density decreased to the critical density of the 1064-nm laser pulse.

Vacuum ultraviolet argon excimer laser pumped by high-intensity laser-produced electrons

In this paper, we proposed a new method to demonstrate a practical Ar/sub 2/ laser by use of an ultrashort-pulse high-intensity laser. Characteristics of the initial electrons produced by an optical-field-induced ionization (OFI) process were controlled by appropriate choice of the high-intensity laser parameters. These controlled electrons then initiated the Ar/sub 2/ production kinetics. To increase a gain-length product, an Ar-filled hollow fiber was used to extend the excitation plasma length up to 30 cm, where the high-intensity laser and 126-nm VUV radiation were propagated.

Vacuum ultraviolet argon excimer laser initiated by high-intensity laser-produced electrons

The Ar2* excimer production kinetics were initiated by electrons produced in the optical-field-induced ionization (OFI) process. The use of an Ar-filled hollow fiber extended an OFI plasma length up to 30 cm. By use of a 126-nm mirror, the maximum one-pass gain coefficient at 126 nm was observed to be 0.58% cm-1 at 10 atm Ar.

Enhancement of EUV emission from a liquid microjet target by use of dual laser pulses

Extreme ultraviolet (EUV) radiation at the wavelength of around 13nm waws observed from a laser-produced plasma using continuous water-jet. Strong dependence of the conversion efficiency (CE) on the laser focal spot size and jet diameter was observed. The EUV CE at a given laser spot size and jet diameter was further enhanced using double laser pulses, where a pre-pulse was used for initial heating of the plasma.

Output energy and conversion efficiency of extreme ultraviolet radiation from rare gas cryogenic targets

Characteristics of extreme ultraviolet (EUV) light at the wavelength between 5 to 20 nm from rare gas cryogenic targets irradiated with a nano-second laser pulse are studied. Spatial distribution of the EUV light and the ion current was measured and found to vary as cos2θ and cos6θ, respectively, where θ is an angle to the target normal. Energetic ions were detected, which had a velocity of the order of 106 cm/s. According to the observed cos2θ spatial distribution, the spatially-integrated total EUV output energy for the xenon cryogenic target was evaluated to be 1.5 mJ/pulse, leading to the conversion efficiency of 0.2%/pulse.